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Dry Dock / Shipyard: Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: Martin [Admin] on August 19, 2014, 07:13:23 PM

Title: Donald Campbell's Bluebird K7
Post by: Martin [Admin] on August 19, 2014, 07:13:23 PM
 Via email to Mayhem...


This is an article about the design and build of a model of Donald Campbell's Bluebird K7. The project is still very much a work in progress, but if I don't submit the 'story so far', it will never happen!
Let me begin by saying that what I know about model boats could be written on the back of a postage stamp, in block capitals, and still leave room for your shopping list so I'm receptive to comments, suggestions and criticism where I deserve it.
As a child of the fifties, I had a fascination with Campbell's Bluebird boat, K7. It never really left me and I eventually set about building a semi-scale model in 2001. I acquired the Nexus 'plan' (notoriously inaccurate I'm told, but the general shape is reasonably right) and converted that into a 3D CAD model. The model was designed as a solid lump and then sliced up to create the lateral frames.  A bit more modelling and jiggery pokery and I came up with a reasonably efficient structure; two box sections running the length of the boat with structural links between the three planing surfaces.
 


(http://u.cubeupload.com/Mayhem1/MoxYKz.jpg)
As a solid lump

(http://u.cubeupload.com/Mayhem1/GmVeMb.jpg) 
Sliced up and turned into a structure
I got the parts printed out full size and traced them onto lite ply. The main structure turned out quite light and very stiff. Topsides was planked in balsa and the access hatch cut afterwards to keep the curves smooth. I dread to think how many hours I spent sandpapering!
 (http://u.cubeupload.com/Mayhem1/d7JLdX.jpg)

(http://u.cubeupload.com/Mayhem1/AOlYjX.jpg)
 
Converted from CAD to Wood.

(http://u.cubeupload.com/Mayhem1/5BJAH0.jpg)
 
 
About half sanded

(http://u.cubeupload.com/Mayhem1/Zkb8sr.jpg) 
If only the top coat had gone as well.........
 
To make the hull waterproof and stronger I applied Ronseal wood hardener inside and out before final sanding and then applied a two-part epoxy finish to the outside before painting. I learned quickly that the two finishes interact and it made life a bit tricky - the epoxy sets too fast.
I had already bought a motor, speed controller, driveshaft and propeller. What I hadn't bought was a battery. I kept looking at the boat, looking at the prop and having serious doubts as to whether the thing would actually move, let alone 'fly'. And so there it sat, on its own shelf, gathering dust and dings for more than ten years while other things took priority over batteries in the wallet department.
Finally, the price of LiPo batteries and chargers dropped to a point where I was prepared to take the plunge, just to satisfy my curiosity. 12th August 2014, the glorious 12th, I set off to the local boating lake at 8 am, dodging the showers (and the parking fees). I had already mentally written my 'hull for sale' advert as I dropped her into the water. One click on the throttle and she's away in a remarkably convincing taxi. Another couple of clicks and to my amazement, she's climbing up onto the sponsons. This has potential. With a big grin I opened the throttle a little more and it was clear that the mighty vessel is capable of planing.  Ah, but all is not well. The steering, sluggish in taxi, is non-existent as she starts to climb. By this time, the boat is on the other side of the lake. For some reason that I really don't understand, I could just about manage a left turn (only) and brought the boat back.
 

(http://u.cubeupload.com/Mayhem1/3llBCp.jpg)Ready for the first trial

(http://u.cubeupload.com/Mayhem1/Qdtgzd.jpg) 
Original rudder arrangement
So, the first modification was to put the rudder in line with the prop. Didn't take long as I cannibalised a model car that someone had given me. One of the swing arms was perfect for the job! (I had been given me the car with an assurance that it was a petrol engine. I intended to fit the engine to Bluebird but it turned out to be a glow engine. Glow fuel is unobtainable on the Isle of Wight. You can't get it by post and, strictly, you can't transport it on the ferries. Back to the drawing board on that one. I didn't worry too much about stealing the suspension. One thing I will never do is run model cars!)

(http://u.cubeupload.com/Mayhem1/DFwu2m.jpg) 
Second rudder arrangement
Second trial. Now that's more like it. The steering has plenty of authority at low speed. As she climbs, the steering starts to lose its grip a bit. OK, head to open water and see what happens. A touch more power, lifting nicely. Crikey! The back end visibly lifts and she's away - in a right hand circle and there's nothing I can do about it. OK, that one I do understand. Surface piercing prop, no fixed fin yet and a rudder that is probably completely out of the water by now. I have to say, I never planned for the boat to be that fast and I am somewhat taken aback at how quick it is once it gets up on its toes. It also sounds awesome!

(http://u.cubeupload.com/Mayhem1/8n15Ss.jpg) 
Looking cool in taxi

(http://u.cubeupload.com/Mayhem1/wsC5wZ.jpg) 
Far from full speed but planing (the photographer couldn't keep up when she took off!)
So, we really need to do something about the steering. As I write this, Bluebird is on the operating table waiting for glue to dry. I have repositioned the prop shaft about 15mm to the right and slightly lower. I will be lowering the rudder and fitting fixed fins to the sponsons and the rear planing wedge. With anything like luck she will be back on the water for another trial at the weekend.
Vital statistics
The model is just over 1m long. I wanted a big model; if there is one thing I do know about model boats, it's that they shrink remarkably on contact with water. I scaled the design so that I could cut the main frames from a 1m sheet of ply.
The motor is a Feigao 5408407XL (Hacker clone) with a Barracuda 80 amp speed controller. The battery is a 3S 5000mAh LiPo and that set up should be spinning the Octura 442 at around 25 000 rpm.
Construction is 3mm lite ply and balsa, reinforced with polyester resin ('wood hardener') and the empty spaces are filled with polystyrene blocks. Somewhere along the line I got careless and although the bare main frame structure weighed in at around 400 grams initially, the final running weight is just over 3 kg. Far too heavy, really, but it does make the model look very realistic in the water. The canopy, by the way, was vacuum formed on the wooden plug you can see in the photos.
 
Design philosophy
I wanted a large, imposing that would look convincing on the water, not hop about all over the place. I wasn't too concerned about speed just as long as it got up on the plane. I went pretty much as big as I dared. I gave some thought to the scaling process. Hydrodynamics is a complex science and I'm not inclined to do maths unless I'm getting paid for it. Feel free to correct me if I have got this all wrong! In (very) rough terms, the speed should scale linearly (that is to say 300 mph = 30 mph for a 1/10th scale model) but the weight is a whole new ball game. For a displacement model, the weight needs to be reduced by the cube of the scale. For a planing model, things are a bit different. The lift forces generated by the water depend (roughly) on the square of the speed. And there's a sting in the tail too. The area of the surfaces that the lift force acts on decreases as the square of the scale. So, for a 1/10th scale model, we have 100th of the lift force and 100th of the lift area. The weight should be 1/10 000th of the real thing!
Bluebird was 8m long and weighed 2 1/2 tons. My model is 1m long so that's 1/8 scale. It should run at 37.5 mph and weigh - oh - 3kg! So I'm not a million miles out of that. Thinking about it, the model does sit well when static, albeit a bit on the shallow side, but I still think it could be lighter (less wear and tear on the power train). My feeling is that I got carried away with the waterproofing, filler and paint. It all adds up!
I cheated a bit by setting the sponson planing surfaces slightly deeper than scale on the basis that ripples on the lake would be like huge waves on the real thing and the flat bottomed hull would never run clear. I also made all the planing surfaces a little wider to help with the scale lift forces.
The motor mount is perhaps unusual. I wanted the thrust to be applied at the prop, not the motor, for two reasons. First, I didn't want to load the motor bearings and, second, I wanted to keep the thrust on the waterline to prevent forcing the bow down. I had read somewhere that flexible prop shafts wind up and get shorter under load (makes sense to me) so I came up with a sliding motor mount. It's constructed from brass tubes and un-etched printed circuit board material, which made it possible to solder the whole thing together before reinforcing it with fibreglass. It works jolly well! There is no lateral play but the motor is free to slide forwards and backwards to find its own position with no end thrust. I would be interested to hear how others tackle this aspect of design.

(http://u.cubeupload.com/Mayhem1/tXlE9S.jpg) 
And for those who would like to complain about the colour, yes, I know it's too dark. However, I remember the real Bluebird from the days of black and white TV and photographs. Blue always came out darker in black and white. I'll put it right in the end!
Where next?
The current model lacks a lot when it comes to finish. I was fairly confident that it would never get up to speed and I lost heart a little in the final stages. Now that I've seen that the power train is more than capable of driving a model this size I have got the bug again.  I shall carry on developing the model until it runs nicely. At that point, I will either re-finish it and add some detail or build a new hull from scratch. I'm learning a lot as I go and I reckon I could design a lighter structure, improve the performance and get a better appearance easier that way. After all, I have all the expensive bits to hand now!
Roll on the weekend!
I'll update this article as things progress.
 
Title: Re: Donald Campbell's Bluebird K7
Post by: Footski on August 20, 2014, 08:03:06 AM
Not one for fast electrics, but that I like. Beautifully built. :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: U-33 on August 20, 2014, 10:18:56 AM
An old friend of mine, Alf Blake, has built a superb model of K7, complete with a scratch built, fully operational turbine. The paint is exactly the same shade as the original, everything is perfectly to scale...only thing missing is Mr Woppit, although by now I guess Alf has found one.


The thing is absolutely frightening when he fires it up, he bolted it to his bench for the initial test, and as the revs increased, the bench moved across the workshop....gawd knows what the rev ceiling is.


I've got some photos of it somewhere, I'll get them posted up here.


Rich
Title: Re: Donald Campbell's Bluebird K7
Post by: Arrow5 on August 20, 2014, 11:08:36 AM
I believe they idle at about 80,000 rpm and are governed to 120,000 :o .  The most frightening K7  I`ve read  about was pulse jet powered, South African I think.   The more elegant K4 was my favourite Bluebird.
Title: Re: Donald Campbell's Bluebird K7
Post by: Perkasaman2 on August 20, 2014, 03:08:49 PM
Well done! Your model is superb.  :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Vintage on August 20, 2014, 03:29:14 PM
Can only echo the above, your model looks superb and it's fantastic to see someone who's so new to model boats taking on such a challenging project.

I imagine you've read "The Bluebird Years" - if you haven't then it's a fascinating insight into the Campbell story...

Keep us updated  :-))

Mark

Title: Re: Donald Campbell's Bluebird K7
Post by: sparkey on August 20, 2014, 04:14:00 PM
When I was a kid I made up a kit of bluebird all balsa and powered by a jetex motor, went well but only lasted for about  30 seconds, love to see you model on the water as I have seen another one for years,    Ray.
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on August 22, 2014, 02:31:24 PM
Can only echo the above, your model looks superb and it's fantastic to see someone who's so new to model boats taking on such a challenging project.


I can only echo the above sentiment too. Excellent approach and a very well written informative post to boot.


Good luck with the next phase(s)  :-))


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 22, 2014, 09:07:32 PM

  Via email to Mayhem...

Hi
Some time ago I posted a thread on the build and running of a ( TOUCHWOOD   K7 )  Bluebird,  http://www.modelboatmayhem.co.uk/forum/index.php/topic,26255.0.html (http://www.modelboatmayhem.co.uk/forum/index.php/topic,26255.0.html) at 1/12th scale

Originally powered with 2 xNimh batteries in parallel with a brushless motor and eventually changed to 2 x 3S Lipo's in parallel and it is a flyer  40 mph +.
A short video on you-tube    https://www.youtube.com/watch?v=fGPMBKTA1Wo (https://www.youtube.com/watch?v=fGPMBKTA1Wo) shows it at top speed.

If I can suggest that you do not try to turn K7 at speed as it will flip over and if you could remove the rear planing wedge it will allow a greater flow of water to the prop.
As you have discovered you need a lot of water to get the full benefit of it's speed.
I originally wanted to build at 1/6 scale and install a KJ66 jet engine that I had built but gave up the idea as my club lake was too small.

Good to see a scratch built hull, well done, nice job.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: tugs62 on August 22, 2014, 09:22:59 PM
I want one now just have to find some plans :-)) :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Neil on August 22, 2014, 10:10:52 PM
well...for someone proclaiming to know zilch about model boat building..................you coyuld certainly teach me a thing ot two............it sure is beautiful.
superb and well done. neil.
Title: Re: Donald Campbell's Bluebird K7
Post by: Neil on August 22, 2014, 10:12:15 PM
I want one now just have to find some plans :-)) :-))

no good you building one Tugs.........you'd only be able to sail it on Fleetwood lake once every five years or so...............it's never calm enough %% %% %% %% %%
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 26, 2014, 08:32:01 PM
First and foremost, thank you gents for your encouraging compliments. My model is not quite as beautiful as the photos suggest, but I'll keep practicing.

There's more to this model boat malarkey than meets the eye!
Run 3 was a bit of a damp squib after run 2 but a great learning experience. Please indulge me while I share what I saw and what I concluded. Where I'm wrong, put me right! Just don't laugh too loud. {-)

I had moved the prop about 10 mm starboard and lowered it about 5mm, thinking that it was too far clear of the water and causing excessive 'prop walk'. I had also fitted fins to the sponsons and one on the port side of the rear planing wedge. I lowered the rudder about 5mm.

One click of throttle and taxiing is fine. Good steering. A bit more power and the nose comes up. Not planing yet, just forcing her way through the water (displacement mode); the water is 'back filling' after the steps on the sponsons. From the off, she looks stern heavy, sluggish, though I haven't moved the CG. More power and the sponsons just about start to plane - the water is coming off the back of the steps cleanly. She's struggling and still pulling hard to starboard. Now, that has me completely confused. I decided that the rear fin might be affecting the flow into the prop and removed it. Sure enough, the performance improves, but not much. I head for open water and pile on the power. Full port rudder and she is still turning to starboard. Then suddenly the stern lifts and she starts jumping around like crazy, up and down and side to side and throwing up a huge 'rooster tail'. I did this a couple of times but I really couldn't see much through the spray. Time to head home and have a think before I do some serious damage. The sponson fins had fallen off, by the way. Wrong glue!

What I think I learned.
1) The difference in performance when a surface piercing is running right and when it's fully submerged is not subtle. It's HUGE!
2) I realised that lowering the prop was about the worst thing I could have done. I was never going to get the prop up the speed and was probably about to inflict severe pain on the motor and ESC.
3) Having realised the prop was fully submerged, I was totally at a loss to explain the starboard turn. After all, the sideways forces on the top and bottom of the prop should cancel out. I was pondering (like you do...) and thinking I should check the alignment; maybe I had built in a twist. Then it came to me. Torque roll. The torque of the prop (considerable when submerged!) was forcing the starboard sponson down. A quick trawl round the net and I think I've got that right.

So, where next? I have moved the prop up and further starboard, about 20mm off centre now. I will need to fit some fins but this time I shall keep the rear one well away from the prop.

Here are the problems. What I'm aiming for is realism:
Speed about 35 mph - I think I have ample power available for this.
Controlled acceleration
Good straight line (only) stability. The lake has a quite narrow corridor. Long ago it was great but some bright spark put a ruddy great island in the middle as a bird sanctuary - and a fountain in the middle of one of the open areas to boot. Now the water is full of feathers and the whole area is encrusted with bird droppings and infested with rats. Don't get me wrong. I like ducks. Paxo, anybody?  Anyway, I can't afford to have the model go off in a great curve before I gain control.

These requirements are not the ones normally applied to hydros (massive acceleration off the line, maximum speed and turning on a sixpence) as far as I can gather.

Somehow I need to tame that torque roll and get the prop up out of the water quicker. That's got me stumped. The prop centre line has to be about 30 - 40 mm below the static waterline to get the stern clear of the surface when she's planing. The design is  a bit reluctant to get up onto the rear wedge. The real boat was too. Campbell's method was to momentarily apply full left rudder and the water brake, slamming on the brakes as it were, causing the boat to pitch and lift the stern. But that was a completely different beast.

At the moment I am running with a planing wedge at the stern. Of course, the real thing had to have that because there was no prop but I'm wondering if the wedge and the prop are getting into an argument as to who's going to take control. Maybe I would be better setting her up as a prop rider? (I plan to try that at some stage anyway).

More than enough from me. I told you I knew nothing about model boats and now I've proved it! Any and all help gratefully received!!
Title: Calling all 3 point hydro experts - help needed!
Post by: Tim_M on August 26, 2014, 08:40:30 PM
Gents,
Could you spare the time to run through my post about Bluebird K7 (stared by Martin last week)?
It's a long thread but I could use all the advice I can get on setting up my model!
Thanks!
Title: Re: Calling all 3 point hydro experts - help needed!
Post by: ooyah/2 on August 27, 2014, 08:50:11 PM
Gents,
Could you spare the time to run through my post about Bluebird K7 (stared by Martin last week)?
It's a long thread but I could use all the advice I can get on setting up my model!
Thanks!
Tim,
If I can try and explain how I built my 1/12 scale K7 and had it running with no problems, mine is a fibre glass hull and sponsons which I bought the parts only from Touchwood models and after reading Ernie Lazenby's article in Astec models where( https://astecmodels.co.uk/ernies-set-ups-3.php (https://astecmodels.co.uk/ernies-set-ups-3.php)) he describes his build of the 1/24 th scale K7. I scaled up the main dimensions in mine.
K7 is powered with a 2850 kv brushless motor with 2 x 3S lipo's in parallel and the all up weight is 1.80 kg.

PicNo 1
The sponsons are 8" apart inside and each are 1" wide getting larger to 1.25" at the rear, the tail of the sponsons are 3/4" from the underside of the hull and the prop hub is at 3/4" inline with the sponson with no rear wedge to effect the flow to the prop.so these 3 points make the contact points of the hydro, C.G. is approx 2" from the rear heal of the sponson towards the stern.O/A length of K7 is 26"

Pic No2
The motor is offset 6 mm from the center line towards starboard and the shaft is 3/16" dia stainless in a brass tube and set at a slight downward angle and the rudder is on the port side of the prop and the blade in line with the hub of the prop, prop hub is 2" from stern as is the center line of the rudder.

Pic No 3
You can see the 1.25" width at the sponson tail

Pic No4
The 3/16" dia Stainless steel shaft with a 26mm carbon fibre surface prop from Cornwall models.
 
I think that your turning to starboard is caused  by your sponsons not being wide enough and the prop is too far out from the rudder which doesn't give the prop wash anything to bite on, and the center lines must all be as my first pic.
I am no expert on fast electric models but after following Ernies build mine will run straight at 40 mph with hands off the transmitter but I dare not try to turn it at speed as it just flips over.
 
I do hope that this is of help, I know of at least another2 K7's at 1/12  scale that run just as well as mine after the builders followed my guide.

Also the you-tube link to my K 7 at speed.  (https://www.youtube.com/watch?v=fGPMBKTA1Wo (https://www.youtube.com/watch?v=fGPMBKTA1Wo) )

George.
 
 
 
 
 
 
 
 
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 28, 2014, 12:19:45 PM
Thanks for the advice George! That's a lovely looking model you have there. I'm starting to realise that a prop-driven model is quite different to a jet driven prototype.

I'm pretty sure that my CG is way too far back. I also see the planing shoes on the sponsons that are not there in the Nexus plan I used. I was wondering about those as they do seem to show up in photos. I shall add your mods to the list of experiments. I know I'll get the boat up and running soon. The main thing is I'm enjoying discovering how!

Rgds,
Title: Re: Donald Campbell's Bluebird K7
Post by: derekwarner on August 28, 2014, 07:06:37 PM
That is brilliant acceleration and aero lift of your K7 George.......but too fast for me........Derek

https://www.youtube.com/watch?v=fGPMBKTA1Wo
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 28, 2014, 08:03:40 PM
Hi George,
I've just been out to the workshop. My model is about 1 1/2 times the size of yours so using your suggestions, the sponson steps should be about 1 7/8" wide. Mine are currently about 1 1/2" (still wider than shown in the Nexus plan). They are growing right now with a target of 2". The CG should be 3" back. Mine is 6" back. That could be something I have to live with as I can't get the battery any further forward. As a last resort, I have some sheet  lead {-). My prop is completely horizontal. I spent ages getting it that way! There's enough flex shaft after the tube to get a little bit of adjustment. I shouldn't really change so many things at once but I've seen the proof of your set up.

BTW I'm going to do another couple of runs with the wedge in place as I have an experiment I want to run on the prop. (Not so much to make the boat go fast, just something I'm curious about). Then, it will be wedge off. Follow the experts (for once).

Rgds,
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 28, 2014, 09:10:31 PM
Hi George,
I've just been out to the workshop. My model is about 1 1/2 times the size of yours so using your suggestions, the sponson steps should be about 1 7/8" wide. Mine are currently about 1 1/2" (still wider than shown in the Nexus plan). They are growing right now with a target of 2". The CG should be 3" back. Mine is 6" back. That could be something I have to live with as I can't get the battery any further forward. As a last resort, I have some sheet  lead {-) . My prop is completely horizontal. I spent ages getting it that way! There's enough flex shaft after the tube to get a little bit of adjustment. I shouldn't really change so many things at once but I've seen the proof of your set up.

BTW I'm going to do another couple of runs with the wedge in place as I have an experiment I want to run on the prop. (Not so much to make the boat go fast, just something I'm curious about). Then, it will be wedge off. Follow the experts (for once).

Rgds,

Tim,
I have a drawing from Nexus which is to a very peculiar scale but makes a model about a meter long which as you say is 1.5  x the size of mine.

Drg No 1462 x Andrew McCoy.
I intended to build this and install a jet engine into it that I made but on discussions with somebody down south who had one I decided that my lake just was not large enough for a jet powered K7. plus the fact that I didn't understand the electronics required to control a 120,000 rpm.  jet engine.

Now assuming that the drawing that I have is the one that you have all dimensions should be 1/2 size again.

On the drawing from the underside of the flat hull it's 1/2" to the bottom edge of the sponsons.
On mine it's 3/4" so on the  +1/2 again yours should be 1.125" but at least 1"

On the drawing the sponson width is 1.25" and mine is 1.25", so yours should be 1.875"

I have already suggested the removal of the rear planing wedge and the prop to be angled slightly down and the C.G.  on mine is approx 2" from the sponson heal, not the wedge rear so yours should be about 3", C.G. is very important and can be found by experiment in moving a small weight.

I would suggest that in your experiments you keep a diary and move or alter one thing at a time, it all will be worth while in the end when  K7 pops onto the plane and away she goes in a straight line..

Now I know these are a lot of suggestions but I have never known anybody to build one to your size , so it's all conjecture on my part but the drawing is very good and you have made an excellent job on building your K7.

I don't see why it wont work on the principle that I scaled up mine from a very small 1/24 K7 built by Ernie Lazenby, one of the finest exponents of fast electric scale models in the U.K..

Here is the link to Ernies Jet powered K7, it's worth a look. https://www.youtube.com/watch?v=JNBRa3oKit8

Keep experimenting and keep us all posted and if I can be of help just give a yell, just wait until you open the throttle and K7 takes off then all of your work will be worth it.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 28, 2014, 09:23:13 PM
That is brilliant acceleration and aero lift of your K7 George.......but too fast for me........Derek

https://www.youtube.com/watch?v=fGPMBKTA1Wo (https://www.youtube.com/watch?v=fGPMBKTA1Wo)



 It needs a lot of water and acts just like the full size.
 I live about 25 mls from Loch Lomond and on one occasion when the loch was flat calm I set it out about 100 yds from me and opened it up , it just accelerated faster and faster and eventualy took off, fortunately I ws able to snap shut the throttle and it dropped down onto the Starboard sponson which saved me a swim in very cold February day.

On my club lake I can only get about  6-7 sec power run, which is quite frightening for an old guy like me.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 29, 2014, 08:15:36 AM
Thanks George. I value the input from someone with practical experience of this boat. We agree on the measurements! I think you have realised that my interest lies in design and development more than running. I didn't expect this model to run at all and that's why it sat on the shelf so long. It turns out that I'm very close to having a working model now and I shall keep going, stage by stage. I can't believe the amount of power these brushless motors pump out! Eventually, I'm going to design a new (lighter) model incorporating everything I've learned and that should be a thing of beauty O0. My local lake gives me a straight run of 200m. If everything dies, I can just wait for the boat to drift in. There is a much larger natural lake a couple of miles away but I'm not sure how to get to the water's edge. I will have to be very confident in the model before I set it loose there! Busy weekend coming up but there should still be time to get a few bits sorted.

Rgds,
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 29, 2014, 09:59:30 PM
Thanks George. I value the input from someone with practical experience of this boat. We agree on the measurements! I think you have realised that my interest lies in design and development more than running. I didn't expect this model to run at all and that's why it sat on the shelf so long. It turns out that I'm very close to having a working model now and I shall keep going, stage by stage. I can't believe the amount of power these brushless motors pump out! Eventually, I'm going to design a new (lighter) model incorporating everything I've learned and that should be a thing of beauty O0 . My local lake gives me a straight run of 200m. If everything dies, I can just wait for the boat to drift in. There is a much larger natural lake a couple of miles away but I'm not sure how to get to the water's edge. I will have to be very confident in the model before I set it loose there! Busy weekend coming up but there should still be time to get a few bits sorted.

Rgds,

Tim ,
I can understand your interest in the development side of K7, I had the same when I was building my Flashsteamer
( OOYAH ) which was a 4 year journey.

I would point out that although you wish to build to scale there are some points that have to be made out of scale especially for a prop driven K7, which is basically the sponsons being wider apart and the planing wedges wider and the rear wedge dispensed with to allow free flow of water to the prop.

So jot these points in your diary, it's very important to keep a build and performance diary,  to keep you in mind if you ever design and build another K7 and keep it as light as possible.

I think you have made a great job of the K7 build and you will get there in the end, frustrating tho' it may be.

George.

Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 31, 2014, 08:22:26 PM
Hi George,
Not much progress this weekend but Bluebird is sporting a pair of nice new running shoes at the front - very sharp! Not so much luck with the CG. I trimmed out a couple of bulkheads under the cockpit and now have a space for the battery as far forward as I can get it. I've also removed the 'engine' (a spray can lid with an old hairdryer fan inside). It looked nice but surprisingly weighed 85 g - right where I didn't want it! However, the CG is still way back. I had to add 350 g to the nose to get the boat to balance at 3". That's over 10% weight increase so a non-starter. The solution is to move the motor forward and that's going to need a new prop shaft. Not a problem; the hardware will all be transferred into MkII eventually. (My thinking when I designed the boat was to put the CG at the centre of lift- i.e. 2/3 of the distance between the forward and aft shoes, assuming each gave the same lift. Twit! I forgot that, just like an aircraft, the CG has to be in front of the centre of lift otherwise the craft is inherently unstable. That one slipped under the wire %))

I have some questions for you:
1) I assume you used a rigid shaft since you mentioned stainless steel. Logically, I need to have the inner end of the shaft tube above the static waterline or provide some sort of low-resistance seal (such as a grease filled stuffing box). What was your configuration? What are your thoughts on flexible shafts? By the way, any seal I use could be 'disposable'. I have to take the shaft out after every run anyway and oil it as I'm running in salt water.

2) Can you remember what paint you used? When I built my model initially, I went to a friend who ran an automotive paint supply shop. It turned out that 'Monza Blue' covered a whole multitude of sins, depending on the car manufacturer. I settled for a blue I could get at the local hardware shop. Sadly, they still have it in stock and the only other choice is 'Sky Blue'.

I'm sure I will come up with more questions to keep you occupied. {-) Thanks for the help!
Title: Re: Donald Campbell's Bluebird K7
Post by: Flundle (Speedline Models) on August 31, 2014, 10:53:06 PM
Original colour was Himmelblau, a 1954 Mercedes car colour. Still available as a mix from car paint suppliers.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 01, 2014, 07:36:29 PM
Thanks for that Mr Speedline. Sky blue it is, then!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 01, 2014, 07:49:22 PM
Hi George,
Sorry to keep bombarding you with questions but there is something I need to check before I get the knife out!

You describe the CG on your model as being 2" behind the sponson heal, not the wedge rear. Do I take it you mean 2" from the rounded end of the sponson? I think I misunderstood you and I have been trying to get the CG on mine 3" from the edge of the sponson planning shoe - the step, if you like. The only way I can do that is to put the motor under the cockpit. It's do-able BUT I would need a 27" long prop shaft >>:-( Ouch, they're expensive!

If you mean the measurement to be from the rearmost point of the sponson body then I'm pretty much there with my current set-up. (The rounded part of the sponson extends about 3" from the step at my scale) You can understand why I want to check :}

Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 01, 2014, 09:04:21 PM
Hi George,
Not much progress this weekend but Bluebird is sporting a pair of nice new running shoes at the front - very sharp! Not so much luck with the CG. I trimmed out a couple of bulkheads under the cockpit and now have a space for the battery as far forward as I can get it. I've also removed the 'engine' (a spray can lid with an old hairdryer fan inside). It looked nice but surprisingly weighed 85 g - right where I didn't want it! However, the CG is still way back. I had to add 350 g to the nose to get the boat to balance at 3". That's over 10% weight increase so a non-starter. The solution is to move the motor forward and that's going to need a new prop shaft. Not a problem; the hardware will all be transferred into MkII eventually. (My thinking when I designed the boat was to put the CG at the centre of lift- i.e. 2/3 of the distance between the forward and aft shoes, assuming each gave the same lift. Twit! I forgot that, just like an aircraft, the CG has to be in front of the centre of lift otherwise the craft is inherently unstable. That one slipped under the wire %) )

I have some questions for you:
1) I assume you used a rigid shaft since you mentioned stainless steel. Logically, I need to have the inner end of the shaft tube above the static waterline or provide some sort of low-resistance seal (such as a grease filled stuffing box). What was your configuration? What are your thoughts on flexible shafts? By the way, any seal I use could be 'disposable'. I have to take the shaft out after every run anyway and oil it as I'm running in salt water.

2) Can you remember what paint you used? When I built my model initially, I went to a friend who ran an automotive paint supply shop. It turned out that 'Monza Blue' covered a whole multitude of sins, depending on the car manufacturer. I settled for a blue I could get at the local hardware shop. Sadly, they still have it in stock and the only other choice is 'Sky Blue'.

I'm sure I will come up with more questions to keep you occupied. {-) Thanks for the help!



Duplicate pictures removed ...............  ken





 
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 01, 2014, 09:52:49 PM
Hi George,
Sorry to keep bombarding you with questions but there is something I need to check before I get the knife out!

You describe the CG on your model as being 2" behind the sponson heal, not the wedge rear. Do I take it you mean 2" from the rounded end of the sponson? I think I misunderstood you and I have been trying to get the CG on mine 3" from the edge of the sponson planning shoe - the step, if you like. The only way I can do that is to put the motor under the cockpit. It's do-able BUT I would need a 27" long prop shaft >>:-( Ouch, they're expensive!

If you mean the measurement to be from the rearmost point of the sponson body then I'm pretty much there with my current set-up. (The rounded part of the sponson extends about 3" from the step at my scale) You can understand why I want to check :}


Tim,

I am getting completely confused,
To post pics on the forum I have to send them to my lap top from my MAC and then on to the forum It would appear that I have duplicated the pics so here is the right up that should have gone with the pics.
I hope that it ll makes sense.

George.


 Hi Tim,
 
 I don't know what happened as I was about to post some answers I must have clicked a wrong key and everything  disappeared so here goes again
 
 I have never used a flexi shaft but can see some advantage in being able to adjust the prop up and down to suit the ride.
 I used the ridged shaft as I had a spare prop tube in my spares box, made new bearing ends and bored them out to 3/16" dia.There is a lock nut behind the prop and a brass collar grub screwed to the shaft at the motor end with minimal clearance allowed about .0005"
 I use Lithium grease bought some years ago from Halfords which is a water proof grease and I use it on all of my steam boats and this K7.
 I bought a small syringe from the Pharmacy and use this to pump in grease with the shaft removed.
 Never had any problems with the ingress of water and see no reason not to use this with salt sea water.
 
 The C.G. in my K7 is measured from the rounded heal of the sponson
 
 Pic
 
 No1 Shows the motor coupling and the grub screwed brass collar and a previous pic shows the lock nut behind the prop.
 
 No 2  Position of motor and Lipos.
 
 No3  K7 flat out with the rear tip of the sponson just touching the water and the hull running parallel to the water that's what you should be trying to acheive.
 
 Please don't be bothered about asking questions,I am only to pleased to help if I have the answers.
 
 My pics seam to have been duplicated.
 
 George.
 
 
 
 
Title: Re: Donald Campbell's Bluebird K7
Post by: Flundle (Speedline Models) on September 01, 2014, 11:23:32 PM
The trick is to balance the boat on the sponsons planing wedges and the prop. There's no 'right way' to do it but the flexible shaft will enable you to adjust the angle of the shaft if necessary. This will lift the back end quickly and get her up out of the water quicker.
I don't know if a surface drive prop needs to have a lift angle, the motor power would decide that I guess.
Just looking down in the engine bay would lead me to think the C of G won't be far off. The sponsons will be relatively heavy and most of them is in front of the C of G.
It all looks fun, I have played around with model K7s for years and they have all worked reasonably well so there is a wide envelope to explore.
Your inspiring me to do the 1/8 Ducted Fan version that's been sitting around my workshop for ages.

Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 02, 2014, 08:08:51 AM
Hi Guys,
I really appreciate your input to this project. All the 'theory' and CAD work isn't worth a jot compared to the knowledge of those who've actually built the boat! Thank goodness I checked with you George before hacking out another hole in the hull! The motor will go back in and the battery will be moved about as ballast. I notice your motor is the same colour as mine :-)) I weighed mine last night - 640 g. It's a monster! Also, you have a proper cooling jacket. The cooling coil arrangement is a very poor way to cool a motor, of course. I was thinking of making a jacket until I saw how cheap they are. MkII will definitely have one of those!

I love the picture of your model at speed. Just the effect I want to see (one day).

I did try to make a ducted fan model about 30 years ago using a 6" extractor fan and a 540 stock motor. Like that was ever going to work. I think it was producing about 100 g of thrust (on a good day). Mind you, the intakes were beautiful! I've looked at some of the electric duct fans on the market now. Tempting (but I'll wait until you've made it work  {-))

More test runs soon, I hope.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 02, 2014, 08:22:36 PM
The wedge is gone! Next time Bluebird hits the water it will be with a naked bottom. Skinny dipping  {-)

I was of a mind to try another run before I removed the wedge but then I realised I was just making more work fixing up what was going to come off later. (I guess) I could have made it plane using a different drive  - fully submerged - but that concept was superseded years ago by the prop rider. The clue's in the name. More to the point (or 3 points?) your models work!

Tell you what though; I never intended that wedge to come adrift when I built the model. It took a hammer and chisel to get it off! (Mallet, actually. I may be a bodger but I know what to hit with what :-)))

Glue's drying. Sandpaper tomorrow!
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 02, 2014, 11:31:52 PM
Tim,

I would definitely have the prop at a downward angle to create lift of the stern.

I have knowledge of several K7's built, some with solid shafts like mine and some with flexi-shafts and every one has the surface prop set with the hub level with the sponson edges and at a slight angle.

The beauty of a flexi is that you can alter the angle to suit by experiment.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 02, 2014, 11:34:47 PM
The trick is to balance the boat on the sponsons planing wedges and the prop. There's no 'right way' to do it but the flexible shaft will enable you to adjust the angle of the shaft if necessary. This will lift the back end quickly and get her up out of the water quicker.
I don't know if a surface drive prop needs to have a lift angle, the motor power would decide that I guess.
Just looking down in the engine bay would lead me to think the C of G won't be far off. The sponsons will be relatively heavy and most of them is in front of the C of G.
It all looks fun, I have played around with model K7s for years and they have all worked reasonably well so there is a wide envelope to explore.
Your inspiring me to do the 1/8 Ducted Fan version that's been sitting around my workshop for ages.

Speedline,

 On the 1/24 scale model built by Dave Abbot , Dave built the small K7 with a solid shaft at an angle and the prop sticking out about 3" to the stern which I must say looks rather odd on a 13" long model but then it has to be so to get the solid shaft in and connected to the motor and the prop hub level with the sponson edges.
 
 Regarding putting a Ducted fan into a K7 on all my discussions with K7 builders and on line comments it is generally stated that the air  intakes are not large enough  to let a fan work properly, the only one that I ever saw was a 1/24" scale K7 and the builder had to drill a series of holes in the engine bay cover to get the fan to work, it's on you-tube somewhere.
 
 It may be a bit different with a larger scale model and as far as I am aware Ernie Lazenby tried it and it didn't work on  1/6th scale K7.
 If it is developed enough and somebody prepared to get it going I would be one of the first to have a try, so best wishes .
 
 George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Flundle (Speedline Models) on September 03, 2014, 08:11:19 PM
Hi George.
Yes the little one is a different ball game.
Ernie L had one and like all his models, it went FAST!
The most fun I have had with one was when a party of us took all our K7's to Coniston and stayed in Pier cottage. That day I had a pocket full of Estes rocket motors! I still have the remains of the model.
 
I was talking about larger scale versions really,1/6th or 1/8.
Interestingly I have a 90mm ducted fan unit which, on 18.5 volts (a 5 cell turnigy Lipo) will deliver 11 lbs of thrust. The actual air intake area of the engine is smaller than the cross sectional area of the two air intakes on a 1/8th K7 so there should be no problem (?????). I have run it (the DF unit)  and its amazing! Its louder than the Wren MW44.
The unity is a cheapo from Hobby King so I don't stand too close......
Title: Re: Donald Campbell's Bluebird K7
Post by: Flundle (Speedline Models) on September 03, 2014, 08:16:19 PM
If somebody with a real interest wants to try a ducted fan and do a build on this site so we can all see AND Martin is happy about it, Ill donate a 1/8th K7 kit to the project.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 03, 2014, 11:35:20 PM
If somebody with a real interest wants to try a ducted fan and do a build on this site so we can all see AND Martin is happy about it, Ill donate a 1/8th K7 kit to the project.

P.M. sent

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 04, 2014, 12:47:29 PM
Here's something I prepared offline......
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 04, 2014, 11:58:20 PM
Here's something I prepared offline......

Tim,
Thanks for the input on E.D.Fs.

On your 3 - points
1. Getting the air flow into the fan right
2.Getting enough low speed thrust to lift the boat onto the plane
3.Water ingress.

It has always been my thought on No 1 that the air delivery into the fan and exiting would need to be ducted with very light Ali, something in the region of the old Printers Litho plate in a bellmouth shape behind the pilot seat into the fan which also sort of coincides with No2.
No 3. is a great concern as in my 1/12 scale when I apply full power K7 buries itself under the water before popping up on the plane.
I don't know if this is common to the 1/12 scale as when you look at Ernie Lazenby's K7 which is 1/6 scale it sits higher on the water at rest and when power is applied there doesn't appear to be any wash going over the bow of the boat and into the Turbine.
I would therefor suggest to any builder of an E.D.F. powered K7 to keep it as light as possible to get that high ride and prevent water ingress to the fan
My K7 from Touchwood had many cast resin parts which I dispensed with and made from Balsa and 1/32marine ply  to keep the weight down
 ( 1.85 kg )

I must say that D.C's  Bluebird K7 provokes a lot of interest not only at the lake but as a conversation piece on how to get it to plane.

I must have been lucky to get it correct first time and would dearly love to take up Speedline's offer of a 1/8 K7 but I just don't have the space to build it or store it when made.

Wow!!!! 11lbs thrust you would really need to be careful that it didn't take off !!!!!!! and have plenty of water to sail it.

George.


P.S.  best of luck over the weekend, keep in touch as to how K7 went.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 13, 2014, 11:57:57 AM
I'm gonna need a bigger lake.

Oh, and a new speed controller  {-)

A lot has happened in the last two weeks. I followed George's guidance: made the front running shoes about 30% wider, got rid of the rear wedge, moved the prop to the right and moved the CG forward. Apart from the shoes, the rest turned out to be a pretty complex, slow process, partly because I only have 'slow' glue. The wedge was very difficult to remove. Once it was off, I set about re-setting the prop. As things stood, I would have needed a severe S bend in the tube (already in bad shape) so it was off to the local hardware shop for a new length of brass tube. Looks like gold (and cost about the same!). I rebuilt the entire drive line, which involved hacking out a fair bit of structure and re-making the motor mount. I set up the drive with the prop at the recommended height the motor as low as possible and the shaft dead straight. This gave me the 'bit of down' on the prop that looked about right so I set everything in place, leaving a couple of inches of flex shaft free to give me some adjustment should I need it. I've kept the flex shaft and strut for the moment, because that is what I have. I've left the rudder behind the prop because that seems to work rather well (even though the transom does look a bit like a construction site - hardly 'scale!). I removed some structure under the cockpit and made a new home for the battery way up in the nose (I have to push it in with a (soft) stick that also locks it in place). I also removed the dummy engine as this was rather heavy and right on the stern. Net result is that the CG is a little further forward than suggested but now easy to adjust by moving the battery. Finally I added little fins to the front shoes and fitted the stabiliser fin as per the plan - I found it in a drawer. (But you may notice it's on the wrong side!!)

Friday afternoon was spent preparing for an evening run and the boat was behaving very badly, as if it were reluctant to go back in the water. Every nut, bolt and washer fought back. Glued bits fell off, wouldn't quite fit.... Last straw was when the Tx battery gave up as I was trimming the rudder but we got there in the end. In the water. Cameraman ready? 'Battery's dead, Dad'.  {-)

So, in words. One click and some low speed taxiing to encourage the local wildlife to move on (except for three signets, who decided this was all jolly interesting and they would stay to watch, thank you very much). Another click and she's moving well - in a straight line! Up to 1/4 throttle and she rises gently onto the plane. Now that's what I was hoping to see; not a sudden lurch but a controlled transition - a silly idea, I know, and the cause of many problems. Getting bolder, I push the stick forward and she's away, fully planing, just kissing the surface as she goes and straight as an arrow. And travelling at one helluva rate of knots! A few seconds later and it's time to pull back - she's almost out of sight. Turn around and off we go again. Steering is good. Of course, I wouldn't try to turn corners at this speed but 'course corrections' are easy and precise. If anything, she looks a little light on the stern and there is a hint of hopping up and down. That can be fixed.

A few speed runs and I'm getting the hang of it (almost). At this point, I realised I'm at half throttle. What? It's already too fast! I couldn't resist the urge to give her the gun so up went the stick. Oh my Lord! She took off like a rocket on steroids! I have no idea how fast she was moving but she was covering about fifty yards in a very few seconds. Shut down quick before she ended up in the Solent. Clearly, full throttle runs are not going to be marathons.

I did a few more runs at 'sensible' speeds (interspersed with the odd sprint) and then suddenly the motor stopped. I had already found out from the maker of the ESC what should happen, so I shut the throttle and waited for the ESC to reset so I could bring her in under taxi. And waited, and waited. Nothing, zilch, nada, though I could still wiggle the rudder. Oops. Something's wrong. There she sat, about twenty feet from the shore - and the wind had dropped to nothing. Not a breath. Not even an irate swan to come over and chase the intruder off its patch. 

I left nipper on guard duty and popped home (half a mile) to find a rope or something. No luck there, so it was plan B. On with the shorts. By the time I got back, Bluebird had drifted reasonably close to the opposite bank but was still out of reach. After a little more waiting, there was only one thing for it. Into the lake. The water was below waist deep, not a problem - but cool. However, although it's an artificial lake, there is a thick layer of mud on the bottom. After a few steps, that layer was getting seriously thick and I decided that calling the Fire Brigade to pull me out would take some explanation so I retreated.

Plan C. We started throwing stones over the boat so that the ripples pushed her to the side. That worked - but.... How difficult is it to hit a small model boat with a hefty stone at twenty feet? Not that difficult, it turns out. I read that Bluebird had suffered a bird strike on the rear boom before her final run. Am I taking realism too far? :embarrassed:

Eventually the boat was recovered. I looked inside and there were signs that the ESC had got pretty hot. Then I noticed that two of the motor wires had come unsoldered and the two capacitors on the feed end had come off. Serious heat!

Saturday morning I was resigned to buying a new ESC but took a careful look at the old one first. There were no signs of damage to any of the chips. Maybe... The capacitors had me going for a while as I wasn't sure which way round to fit them. I applied a bit of logic (positive to positive lead etc.) and looked closely at the pads they had come away from. Under an eyeglass, I could match up the legs to the right pads from the shape left behind. What's to lose? Soldering iron out, eyeglass in. You need a lot of heat to get those big wires back on and there's a real risk of burning you nose when you are that close. Connect up, waiting for the bang. Bleep bleep... We're back in business!

I see what they've done with the speed controller. It's a marvel of miniaturisation but at the expense of robustness. I worked for many years on 'electronic packaging' and I have to say, if someone passed me that design for approval, I would give them a slap! Hopefully, it will hold up long enough to get some video (if I lay off the throttle!).

And so, plan for the day. Pack is charged, Tx on charge, camera on charge. Brain still running on empty. If the weather hold out, it'll be off to the lake this evening, armed with a 'rescue boat' (nipper has a 'toy' speedboat that he's not that impressed with but it will do to nudge Bluebird in if we get another disaster) and a 50m ball of string to make a drag line if all else fails. Oh, need to charge the 'rescue' boat's pack!

With luck I'll be able to post some pictures and video tomorrow  :}

(I need to find out how to reduce the file size of my pictures first as they are far too big to upload)
Title: Re: Donald Campbell's Bluebird K7
Post by: w3bby on September 13, 2014, 01:44:39 PM
Sounds like you have the set up almost done.. Look forward to a video  :-))

Tip for retrieval, a fishing rod with a tennis ball attached to the line...
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 13, 2014, 01:58:00 PM
Ha, yes! The stupid thing is, I live on an island, half a mile from the sea and I don't fish! Might have to invest in a rod. My wife keeps saying she wants to go fishing; she can borrow it. {-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 13, 2014, 02:27:07 PM
Battle scars (as befits a development model) :}
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 14, 2014, 11:00:28 AM
In the spirit of sharing I have posted a couple of 'warts and all' videos on UTube.

At the risk of sounding like a fisherman's story of the one that got away, this is NOT the same boat I saw on Friday evening! In the shorter video you can see that she is unbalanced, dragging her tail, which is why I brought her in and shoved the battery forward. In the second video she's getting up some speed but nothing like I saw on Friday. Still seems to be dragging her tail and working very hard. I saw this type of performance at less than half throttle on Friday. She is also visibly listing to port. That needs investigation - maybe the sponson has water in it - she did sit dead in the water for about an hour.

At the end of the run, the motor cut again. This time the controller recovered but I only got about half a second of power and lost the rudder too. Today's preliminary post-mortem suggests it may be an Rx problem. Who would be stupid enough to put a Rx in a boat and rush off without bothering to go back indoors to get a plastic bag as a minimum? {:-{

'Rescue 1' was brought into service to retrieve the model. I wish we'd video'd that bit; it was far more entertaining. I have suddenly developed a deep respect for all the tug modellers out there.  :}

http://youtu.be/3PNkNYx1EXs
http://youtu.be/8NouIM3qSlo
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 14, 2014, 08:45:18 PM
In the spirit of sharing I have posted a couple of 'warts and all' videos on UTube.

At the risk of sounding like a fisherman's story of the one that got away, this is NOT the same boat I saw on Friday evening! In the shorter video you can see that she is unbalanced, dragging her tail, which is why I brought her in and shoved the battery forward. In the second video she's getting up some speed but nothing like I saw on Friday. Still seems to be dragging her tail and working very hard. I saw this type of performance at less than half throttle on Friday. She is also visibly listing to port. That needs investigation - maybe the sponson has water in it - she did sit dead in the water for about an hour.

At the end of the run, the motor cut again. This time the controller recovered but I only got about half a second of power and lost the rudder too. Today's preliminary post-mortem suggests it may be an Rx problem. Who would be stupid enough to put a Rx in a boat and rush off without bothering to go back indoors to get a plastic bag as a minimum? {:-{

'Rescue 1' was brought into service to retrieve the model. I wish we'd video'd that bit; it was far more entertaining. I have suddenly developed a deep respect for all the tug modellers out there.  :}

http://youtu.be/3PNkNYx1EXs (http://youtu.be/3PNkNYx1EXs)
http://youtu.be/8NouIM3qSlo (http://youtu.be/8NouIM3qSlo)

Hi Tim,
If I may comment on the 2- videos that you have shown.

No 1,

K7 is quite definitely tail dragging which can be caused by not enough power to lift the tail or the angle that the prop is at is too shallow  have a look at a you-tube video  ( Brushless Bluebird K7 )----http://www.youtube.com/watch?v=mjckMFo6TUE
In it my K7 is powered by Nimh  7 x Sub C cells on 4.300 amps and it runs very flat as does the other video previously shown on 3S lipo's but very much faster, the point being that my K7 is much lighter than yours at 1.85kg but the same power input.
Try altering the angle to see if that helps.
As your E.S.C. is overheating is the prop too big ? and as it's not water cooled this could be another reason for overheating.

All of the E.S.C's that I use are water cooled, one which wasn't when I received it but I made a water cooling plate the same as the ones that I already had.

If you wish I can make a water cooler for you which you then Silicone it to the underside of your E.S.C. and then put it into a piece  of heat shrink tube, simple but effective.

When K7 is running it would appear that the sponson tops are not parallel to water line , is this the case ? or is it just the tail down attitude that makes them appear so.
In fact on the full size K7 the tops had a slight downward slope to the bow and the forward angle of attach was 3.75 deg and the rear attack was 2.5 deg.

On my K7 they are parallel to the water  and as near as doesn't matter to the above angles.
At the time that I built mine I was not aware of all of these angles so I must have been lucky to get it correct first time.

On videos 1 & 2  you have too much rudder throw which makes the lining up of K7 before applying power very difficult, I would cut the throw by 50% as a starting point and you will find it much easier to control.

It's hard to make comments from this distance but I would say that you are not far off from getting it to run true and fast baring in mind that your K7 is larger than mine and heavier so don't despair keep at it until you get it right.

Lastly D.C's K7 hit the duck on the forward spar on the port side, so fill in your dent and have another go at hitting the port sponson.
Best wishes
George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 15, 2014, 08:14:55 AM
Thanks for your comments George - constructive and accurate as always!
On Friday, she was not 'tail dragging' and there was a huge step up from the performance in the videos. I didn't have the battery fully located forward in the videos and it makes a big difference. I'm pretty much at the limit of how far forward I can get the CG without added unwanted weight but I have seen this model run properly (much flatter). I think the sponsons may be angled down a bit in my build (to get a higher ride height). Not the right solution, in hindsight, but it will be fixed in the next build. I think the prop is OK for size; when she gets up level the motor is running much faster and sounds 'free'. More experiments on the angle wouldn't go amiss, I agree.

I found on Sunday that the port sponson had a split and it had water in it (along with the polystyrene blocks, fortunately). That would not be helping at all. I need to take a breath this week and sort a few things out. I have to confess I was in a rush to get a video on line after my marathon narrative on Friday's runs and I got careless. You can't rush a lady.

Oh yes, the breakdown at the end. Rx dried out, lesson learned, wrist slapped. :}

I may take you up on your offer of a cooling plate! Let me see what I have in the garage (my 'cave' as my wife calls it) before I trouble you.

I may not, however, follow your suggestion of hurling more rocks at Bluebird.  {-) Did you notice I nearly got myself a duck for dinner??

Onward and upward!!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 15, 2014, 07:38:26 PM
George, I think you've done this before!
I was giving your comments some thought today (OK, I should have been thinking about work but nobody can see inside my head).

I'm not sure why the boat changed so much in 24 hours but I think the CG shifted - poor battery location and maybe there's a bit of waterlogging around the stern. There have been so many changes and not all the internals are perfectly sealed now. A small weight gain that far back has a big effect.

Having seen what happens when the prop truly breaks the surface (all hell breaks loose but the boat is flat) I think there's enough power there and enough lift from the prop. I think it's a case of too much lift at the front rather than not enough at the back. Not quite as daft as it sounds! When the boat is building speed, the front rises too soon, which pushes the prop deep in the water so it's not working well. Once the boat gets a bit of speed up the prop starts to surface drive and the revs and speed go up dramatically. I think if I can get the stern to rise at a lower speed so the prop's working well, that will do the trick rather than adding more down thrust for the moment (which would work but could be too much when she's up and running). Keep the bow down while building speed - I remember you said your model sometimes took a dip before planing. Just my theory. I may be completely wrong.

I went out and took some measurements on the sponsons. I can still do trigonometry. :-))
With the bottom of the hull set horizontal, the tops of the sponsons are, indeed, sloping down at about 3 degrees. I think I planned that to raise the ride height so the bottom was clear of the non-scale waves.

The planing shoes are quite a different story. They are sloping at 9 1/2 degrees. That's a tad different to your set up  O0 and I bet it goes a long way to explaining why she's bludgeoning her way through the water and rising too soon. I checked the Nexus plan and the slope on that is 6 degrees. Still too much for scale. Unsurprisingly, 6 degrees from the plan plus my 3 degree 'adjustment' adds up to 9 degrees!

I have to repair the split sponson anyway and I will change the angle of attack at the same time. Of course, I can't just take material off the back of the shoe; that would lower the ride. I need to add about 20mm to the front. That will move the 'break' point backwards but I think that should be OK because that is well clear of the water when running. I might even bite the bullet and get the tops horizontal. We'll see.

Between us, we'll get this beauty flying :}
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 15, 2014, 09:07:40 PM
Tim,
Yes my K7 plows under the water before coming up on the plane, you can see that on the y-tube vid but as the whole hull is sealed I just whack open the throttle and away it goes water and all.
Your boat being that bit larger will not do this, in my early discussions with Ernie Lazenby his K7 with the jet engine being to 1/6 th scale sat well above the level that mine did and it didn't plow under on start up but was up on the plane very quickly.
D.C,s K7 on start up pushed so much water over the bow that he could not see where he was going before he had it planing, I have often thought that if the step at the bow was not there the boat would not displace so much water but never thought on that when I built it, I am not suggesting that you cut it out.

Regarding the angles that I quoted were for the full size K7 but I don't have a clue as to what they are on mine but I will have a check and let you know so don't start hacking bits out just yet.

If it was me, I would make a weight the same as the 3s Lipo and fix it in the position that you have the LIpo at present as it will not effect the weight very much and then position the Lipo on the C.G.to allow very minor adjustments to get the balance correct and as you have now sealed the hull and it's water tight it can't be far off from flying.
I must say that you are not very far off of getting it correct even though on the last Video K7 was a bit tail down and the water over the boat is not excessive, also cut the rudder movement as suggested

If you care to P.M. me with your e-mail address I can send pics far quicker and easier than I can on the forum,
if  you do this I can send some sketches of my sponson angles.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: klz on September 15, 2014, 10:12:21 PM
Hi guys I understand emailing pictures is easier than posting them on the forum but could you keep the topic going I have been following this with great interest.

klz
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on September 15, 2014, 10:35:14 PM
Hi guys I understand emailing pictures is easier than posting them on the forum but could you keep the topic going I have been following this with great interest.
klz


Yep - me too George and Tim. Not said anything so far but following it all with great interest. Don't keep us in the dark guys  ok2


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 15, 2014, 11:51:53 PM

Yep - me too George and Tim. Not said anything so far but following it all with great interest. Don't keep us in the dark guys  ok2


Ramon

Kiz & Ramon
 
 My problem is that to post pics on the forum my MAC needs Windows and I have to mail them to my Lap top and then to the forum which is rather a long method.
 However as a test I am trying to post a resized pic  of K7 showing the lift dimensions so I hope it works and if so I can then post pics of the Sponson angle of attack.
 
 Test didn't work I shall try again via Laptop tomorrow.
 
 George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 16, 2014, 08:04:44 AM
Nice to know we're keeping people entertained! Thanks for your interest.

George, pm sent
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 16, 2014, 06:32:24 PM
Kiz & Ramon
 
 My problem is that to post pics on the forum my MAC needs Windows and I have to mail them to my Lap top and then to the forum which is rather a long method.
 However as a test I am trying to post a resized pic  of K7 showing the lift dimensions so I hope it works and if so I can then post pics of the Sponson angle of attack.
 
 Test didn't work I shall try again via Laptop tomorro

 
 George.

Just to let you see that this old Clydeside hammer and chisle engineer is trying to catch up on I.T.
No1
Here is the pic of the sponson angles on my 1/12 th scale K7 which are not the same as D.C's full size K7 but they work and certainly lift the boat off of thwater and onto the plane.
No2
 
Wishfull thinking.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 16, 2014, 07:04:47 PM
Now, that's cool picture! :}
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 16, 2014, 08:15:48 PM
Dunnit.

The stbd sponson has been dropped 20mm at the front. The boom is now sticking out of the top so I'll need a power bulge; I can just pretend I modelled an earlier version.  :} (I decided not to go into the hull to drop the boom as the structure inside there is pretty complex and there was a good chance of wrecking something). The mod is not pretty but it is strong (large blocks going right onto the original sponson internal structure).

I won't post a picture of the present state of repair. Let's just say, like all surgery, it will look OK when the swelling goes down %)

Title: Re: Donald Campbell's Bluebird K7
Post by: klz on September 16, 2014, 08:26:17 PM
I agree that is a cool picture  :-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on September 16, 2014, 11:24:27 PM
George if that's a problem please don't struggle with it - it was just that I have been enjoying following every post twixt you and Tim and didn't want to miss something  ok2


I agree too - a novel picture indeed  :-))


Ramon

Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 16, 2014, 11:35:04 PM
George if that's a problem please don't struggle with it - it was just that I have been enjoying following every post twixt you and Tim and didn't want to miss something  ok2


I agree too - a novel picture indeed  :-))


Ramon

Ramon & Kiz,
It's not really a problem, just a round about way to post pics so I shall keep you all informed but remember it's Tim's thread and he will be posting pics on his progress as it develops.
Thanks for looking on.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 18, 2014, 08:37:49 PM
I was just having a thought on some of the problems encountered while running my K7.
 
Some cracks began to appear on the top of the hull which I have deduced are caused by the constant buffeting of the sponsons on the water at high speeds.
These are attached via a 3/8" dia Ali tube passing thro' the hull and the Sponsons attached at ether end and I assume that it's the deflection of the Ali tube causing the hull to crack on top. The pics only show the cracks on the Port side but since these pics were taken the cracks are now the same on the starboard side.
 
Pics No 1-2-3 show the cracks and No 4 shows the inside of the hull.

On reflection if I was to build another K7 I would re enforce the inside , Port & Starboard with a piece of 1/4" ply bonded into the sides to give some support and to stop the flexing.
At this late stage it's impossible to get inside to do anty re enforcing, the yellow object up front is the E.S.C. and it's wedged in to prevent any movement.
If anybody is considering using a Touchwood K7 I would recommend this strengthening to be done, you must remember this kit is for display purposes and the Fibre glassing is quite poor.
I hope that the pics come thro'
George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 18, 2014, 08:51:23 PM
George, did the decals come with the kit? I have some paper for making decals but haven't yet found the right artwork. Do my eye's deceive me or is one of those union flags upside down?  :D (They are different but I wouldn't know which one is right, by the way  {-))

Hey, Those cracks are just a sign that you've enjoyed your model!!
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 18, 2014, 09:02:35 PM
George, did the decals come with the kit? I have some paper for making decals but haven't yet found the right artwork. Do my eye's deceive me or is one of those union flags upside down?  :D (They are different but I wouldn't know which one is right, by the way  {-) )

Hey, Those cracks are just a sign that you've enjoyed your model!!

Hi Tim,
Yes they come with the kit but as I only purchased the hull and the sponsons I had to buy them as well, think the cost of transfers were a ridiculous £8.

I never gave the flag a thought so I have just Googled images  and it looks very similar to the transfer so I suppose Google has it correct.

I sure have had some fun with this K7, much more heart stopping than a Steam boat !!!!!!!!

Mind you when I sail my flash steamer I have to go and have I lie down to recover after running it.
George.


Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 19, 2014, 05:00:32 PM
I googled it. The one on the right is correct. Another piece of useless information  {-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 28, 2014, 10:25:35 AM
There's a bit of a lull in proceedings here while I wait for my new ESC to arrive ('up to 45 days' <:(). I wanted to add a water cooled heatsink to my ESC while the glue was drying on the sponson mods. When I stripped it down, I decided that the soldering was very scruffy where I had repaired it after the previous 'meltdown' and there was a good risk of causing a short if I put metal anywhere near the board.  After a massive struggle, I managed to get two wires stripped and re-fitted. On the third one, I dislodged a tiny chip and (of course) lost it.  >>:-( Subsequently, Castle Creations explained that it's impossible to do DIY repairs on their boards as you need specialist equipment to deal with the solder. They are not wrong there! Anyway, if anybody has the skills and access to the right equipment, an 80A ESC is yours for the cost of a stamped addressed jiffy bag (PM me). Be aware that I have almost certainly damaged it beyond repair and there is a chip capacitor missing!

I have been working on re-aligning the sponsons. When I designed the model, I had to use my imagination. I made the planing shoes a little wider (not wide enough, it turns out) and I also increased the angle of attack. That was a mistake and the effect was to lift the bow far too early, burying the prop deep under water where it couldn't work properly. I'm now down to about 5 degrees incidence (thanks, George) so we'll see how that goes. Don't worry that the mod looks a bit flimsy. The booms are attached to the internal structure of the sponsons; the power bulges are cosmetic (not very cosmetic, I'll grant you).

I've also been working on the MkII design on the computer. I have so far made what I believe to be an accurate conversion of the Nexus plan into 3D. Now I am working on modifying (a copy of) that model to correct some of the things that are wrong in the plan and to add 'un-scale' features that are needed to make the model work (no rear wedge, modified planing shoes etc.). I enjoy computer modelling pretty near as much as working on the bench. Everything fits perfectly, the glue dries instantly and the finish is perfect  :D Oh, and you can 'undo' your mistakes.

MkI still has a big role to play. I need to find the best position for the CG, tune up the sponsons and check out the prop angle. Once she's up and running sweetly, I will have the information I need to put into MkII.

One of the biggest mysteries to me is what is the best angle for the prop. The current set up has 'a bit of down'. I reckon it's about 8 degrees and that is the minimum I can get with the shaft completely straight. I have the opportunity to play around with that because I'm using a flex shaft and strut. I would rather like to use a straight (rigid) shaft in MkII. The minimum angle I would be able to achieve with that would be around 5 degrees (and that is using a very long shaft). If that turns out to bee too much then I will use a flex and strut again.

I understand that the Octura X4 props have 'medium lift'. If anyone has experience of these props and how to set them up properly, now would be a good time to share it! (Please)



 
Title: Re: Donald Campbell's Bluebird K7
Post by: John W E on September 28, 2014, 10:54:06 AM
 :-))
will this be of help to you ? from the real plans of Bluebird

aye
john
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 28, 2014, 11:39:23 AM
Hey, thanks John! That's brilliant!

I'm using a combination of the Nexus plan, photo's in 'The Bluebird years' and photo's on line. (especially those on the Bluebird restoration project website. You drawings are a huge help. I shall download them before the internet breaks  O0

Rgds,
Title: Re: Donald Campbell's Bluebird K7
Post by: EJL on September 28, 2014, 07:36:24 PM
Its now approaching 20 years since I did all the development work to get the very first Touchwood K7 to work. Time goes past too quickly.(I also did the development work for the working Touchwood K4 and K3)
Having got the first K7 to work  I prepared a set of intruction to Touchwod which were sent out with the kits. Early version had a modified 540 hot motor on a geabox. I later converted it to brushless power but never got around to doing an ammended set of intructions for Touchwood however I did help a lot of people privately on lin via e mail.
The kit was too heavy and I replaced the heavy fin/seat and sponson planing wedges with my own made from lite ply. My grandson now owns the model and recently the family cat kocked it of the top shelf in his bedroom resulting in some minor damge but the sponsons remained intact due to how I built it.I have recently run it with a hot Leopard motor on 2S lipos(lighter than nim cells) and its sill very fast, much too fast for an 8 year old.
 
I have followed this thread with interest and its good to read interest is still out there.
The original sponsons on the full size boat had a chamer to reduce the wetted area. I spoke to ken Norris the designer of Bluebird 20 yeas ago and he said the chamfer idea was a mistake. After listening to him and in the knowledge we cannot scale water all my Bluebird models, including the big gas trubine one on youtube, dont have the chamfer  and I believe thats why they run well. I have 4 a various scales..
By the way. If using an Octura X series prop the shaft needs a bit of down angle and the cetre of the prop needs to be on the same horizontal plane as the rear most part of the sponson planing suface. The COG is important, about 20% of the distance between the rear part of the front planing wedge and the centre of the prop. Too far back and it will run tail heavy.
 
Cheers
Ernie Lazenby
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 28, 2014, 08:26:48 PM
Ernie, I'm honoured!
As the acknowledged 'guru' of K7 models and all things fast I'm delighted that you have been following the thread (and probably chuckling as you watch me stagger up the learning curve). I corresponded with you way back in 2001 or thereabouts and you offered me advice then too.

I shall continue to develop the model I have following the advice I receive on this forum, which has been invaluable and then move on to MkII (a lighter version incorporating all the modifications from the start). I plan to make that a very 'open' project from the initial design stage onwards so that others can contribute. I will follow guidance and, who knows, perhaps some of my own ideas may be of interest to others.

PS. Love the turbine job. I really don't know how you build models that good!

Thanks for your interest and best wishes,
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on September 28, 2014, 11:36:07 PM
Tim ,
The bulges on the forward sponsons don't look too bad, in the early development of K7 there were very large bulges on the forward sponsons as shown on a pic that I have in a book when D.C. tried Lake Ullswater in 1956 and these were obviously dispensed with at future development, In Touchwoods cat there is a pic of these bulges
( http://www.touchwoodmodels.com/water-speed-record-models/1-43-bluebird-k7.html ), please keep us posted on developments.

ERNIE.
it's so good to read that you are following this K7 thread, you were such a help when I built mine especially the article in ASTEC Models.
I think it was in 2002 that we spoke at Windermere when I had my flashsteamer there, pity it didn't perform particularly well at the time but it now has a new engine but it's just too fast to run it on R/C. at 40 + mph and at 26lbs all up weight.

I do hope that you are felling much better and glad that you are in the background to advise on building and running a K7,
Keep well.
 George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 05, 2014, 03:59:57 PM
Still waiting for the new speed controller to arrive, The tracker says it's in the UK (and has been for well over a week). No doubt sitting in a customs shed somewhere.......

So, meanwhile I've started work on the design of the MkII version. I decided to re-model it from the original plans (rather than the Nexus version) at 1/8 scale and add certain adjustments to make it work as a model. No rear wedge. The sponson shoes are angled at 5 degrees and are 62mm wide at the step. These measurements may change when I see how MkI runs. The steps are set 30mm from the bottom of the hull. I think that's enough to clear non-scale ripples. I have compromised on the front booms as I want to use some 20 x 15 aluminium tube I have in the garage and it's a tad too big to go inside true scale booms. Also, I have the top of the sponsons horizontal, not sloping down. Stand off scale. If you don't like it, stand further away {-).

What I have so far is the 'plug' that I will carve up to create the basic frames. I think it's reasonably accurate (remembering I'm going for stand-off rather than true scale) but if anyone can see any glaring errors, now is the time to shout!
Title: Re: Donald Campbell's Bluebird K7
Post by: nigeltyoung on October 06, 2014, 10:26:25 PM
Hi Tim,

I have just found this topic and what a great build. I am now subscribed and looking forward to see how your K7 develops even further!

At the moment I too am building an RC 1/12 K7 and will hopefully get a heads up on running issues from your excellent reports - good luck and looking forward to more progress.

Nigel
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 07, 2014, 12:11:33 PM
The speed controller (Aquastar 160A water cooled), programming box and cooling jacket for the motor arrived yesterday. Yay! :D

Unfortunately, they didn't come with instructions. >>:-( The online instructions are incomplete and in Chinglish. I've read a few reports of these things blowing up on the bench so I'm waiting for HK to clarify just what I plug into where and what I do to make the motor turn. I've found them pretty good in the past so we'll see how that goes.

I have to say the ESC looks well-made (from the outside). Good quality wires supplied as well. If it performs as well as it looks, we're on to a winner!

Lots of draws on my time this week but the water is looking closer.........
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 10, 2014, 06:42:58 PM
Phew! The motor's turning. No sparks, no bangs, just a drop of sweat and some palpitations as I connected the battery. I had to make a slight mechanical mod to my Rx because the plug would not fit my 40 year old JR gear. (They don't make 'em like that any more. Just as shiny as the day it was bought and it looks really classy!). I can sleep again.

So the power train is sitting on the bench, ready to go back in with new plumbing. Everything is just about ready for another trial. Am I going to get on the water this weekend? Methinks the weather has other ideas.  {-) Never mind. My very belated birthday present from #1 daughter arrived today. An airbrush kit with compressor! Just have to learn how to use it...............

All in all, a good day. :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 12, 2014, 04:46:30 PM
And she's off! Bluebird has had her first run without breaking down. That doesn't mean without breakage....... {-)

Went to the lake this morning only to find that the model yacht club were in residence. Given that they have been sailing there for 100 years or more, I thought it better not to intrude. After lunch, despite the dodgy weather (windy) we set off again.

Bluebird now has a new speed controller and the planing shoe angles reduced to 5 degrees. Straight away, the difference was obvious. No more tail dragging and the prop started to surface pierce on about two clicks of throttle. At 1/4 throttle, she was planing and at half throttle running straight, clean and smooth. And rather too fast for my liking!

I tried full throttle a couple of times and whilst the speed was impressive, the stern started to leap about a bit. Could be that I have too much 'down' on the prop or maybe it was just that the water was way too rough for high speed running. One thing is clear. I have ample power and the boat runs 'easy' now.

I still have a bit too much throw on the rudder but I can turn that back on the Tx. Most of the twitchiness is actually down to bad driving. I have the eye-hand coordination of a snake. (Which is why I gave up aero modelling many moons ago. At least with a boat you can stop to get your head sorted out). I have set the water outlet high up so I can see if the cooling is working. It isn't, so that is something to look into.

Now, the yacht club had left two marker barrels in the lake. Quite small, bright orange. You couldn't possibly hit one of those, could you? Damned thing was like a wood magnet. I clipped it once, slowly, and then went back for another go at high speed. That's gonna take some glue. {-) I think it's the 'you go where you are looking' syndrome that causes bikers to ride into trees and horse riders to dump themselves in hedges. You should never look at the obstacles!

There's a scrappy video here: http://youtu.be/dhnnJWXCJRI


Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on October 12, 2014, 06:06:11 PM
Hi Tim,
It's good to hear that you have your K7 running true and straight, not so good that the glue bucket will have to be brought into play.
For some reason I can't access your you-tube vid, keeps saying access denied.
The pic of the boat running looks fine but the water is a bit rough and this can cause the tail dancing but please take care on rough water or it will take off at full throttle and it's imperative that you cut down rudder throw, another cause of tail dancing due to twitchy fingers.

In your thread asking advice on setting up your E.S.C. you say that the motor shuts of immediately you pull the stick down, I would leave it at that as it will act as a very efficient brake to stop the boat in emergencies, especially when heading straight for orange markers or swans !!!!!!!!!

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: essex2visuvesi on October 12, 2014, 06:14:15 PM
Youtube Video says it is private :(
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 12, 2014, 06:39:19 PM
Sorry chaps,
I posted on Mayhem while the video was still uploading. It took nearly two hours!

Should be OK now; I've just viewed it.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on October 12, 2014, 07:22:44 PM
Sorry chaps,
I posted on Mayhem while the video was still uploading. It took nearly two hours!

Should be OK now; I've just viewed it.

Tim,
Just viewed it, that's what I call an " OUCH " moment, put it down to pilot error.

Your K7 sits on top of the water and not like mine bury it's self when full power is applied from stop before coming up onto the plain, must be something to do with the bigger scale.

It's the rough water that's causing the bounce, if I had to apply full power on water like that it would flip over.

I can't see anything wrong with the boat's set up, it's running well but cut down the rudder throw.

Is the damage to the sponson repairable ?

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 12, 2014, 07:31:44 PM
Anything is repairable! :-)) This models looking pretty beat up but not to worry. It's the test bed for MkII.
I'll put some splints inside the sponson  and with a bit of luck it'll hold up.

BTW, I hadn't ignored your earlier advice ref. the rudder. I had already shortened the throw mechanically. I can afford to cut it down more and I realised I have a dual rate switch for that channel of the Tx. I can keep a bit in reserve for parking, just like the car!

Driver error? Got that by the bucket load, old chum!
Title: Re: Donald Campbell's Bluebird K7
Post by: klz on October 12, 2014, 10:35:48 PM
Hi Tim your model is looking good, I have now added one to my very long list of models I want to build keep up the good work.

KLZ
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on October 12, 2014, 11:55:57 PM
Anything is repairable! :-)) This models looking pretty beat up but not to worry. It's the test bed for MkII.
I'll put some splints inside the sponson  and with a bit of luck it'll hold up.

BTW, I hadn't ignored your earlier advice ref. the rudder. I had already shortened the throw mechanically. I can afford to cut it down more and I realised I have a dual rate switch for that channel of the Tx. I can keep a bit in reserve for parking, just like the car!

Driver error? Got that by the bucket load, old chum!


Tim,
Forgot to tell you that I whacked the far end of our lake which has a concrete edge all around when U started out on my tests.
At least I have the age advantage at 75 although still good eyesight,still if I was nearer I could dip into your bucket.

K7 M1 has turned out great so I look forwards to Mk 11.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 02, 2014, 04:27:58 PM
Round about now, I had planned to unleash the MkII build project on an unsuspecting Mayhem. My PC, however, had other ideas. Down side is I am considerably poorer than I was a couple of weeks ago. Up side is that the hard disk was OK and I managed to recover all my files and here is my new work bench. Not quite as powerful as the laptop but that screen is sooooooo much nicer to work on!

As for Windows 8? The jury's still out. Does anybody know how to get rid of the 'trovi' hijack that comes built in??
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 02, 2014, 04:39:15 PM
So, in the meantime there has been a small amount of progress on MkI. She is recovering nicely from major surgery. The sponson repair was quite determined but is now looking reasonable. Smooth as a baby's bottom. Baby elephant, maybe. Even 'Donald' looks surprised! I was thinking of leaving it red (and painting the other on green) to help me with my (lack of) steering ability but decided later to have a go with my new airbrush. And the result? Let's just say I have a lot to learn before I go anywhere near a real model.......
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 02, 2014, 04:50:04 PM
I had a look at the cooling. There was a lot of back pressure in the plumbing! I managed to open up the feed in the rudder from about 2.5mm diameter to 4mm. That's almost three times the area! Carrying on, I looked at the speed controller. The holes in the nipples are a rather disappointing 2.5mm diameter. I was going to drill them out but fortunately I took one out (rather than drill in situ). The thread is small and there's not enough material left to drill out the holes. Luckily I didn't plough ahead without looking. Nothing that can be done there. The motor cooling jacket is very restrictive. It's nicely made but the gap between the motor and the shell is really too tight. Again, nothing to do there. I've decided to plumb everything in parallel rather than in series and I'm waiting for some little Y shaped unions to arrive from Hong Kong. Couldn't find anything locally but they were dirt cheap, even with the postage.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 02, 2014, 05:01:39 PM
 ( I'm making multiple posts to get the pictures and words to stay together - if that's not the right thing to do, can somebody tell me?)

Finally for today, just to prove that I have been thoroughly bitten by the modelling bug, here is a sneak preview of next year's 'big build'. It's another subject that I've wanted to tackle for ever and I have finally managed to get a reasonable start on the CAD model. It's going to be a major challenge!

Extra points for anyone (else) who knows what it is  O0
Title: Re: Donald Campbell's Bluebird K7
Post by: Mad Scientist on November 02, 2014, 10:08:48 PM
Why, it's a Westland SRN2 hovercraft, of course! O0

Tom
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 03, 2014, 08:03:59 AM
Wow, a reply from Canada on the mystery model. Of course, the SRN2 underwent trials on the St Lawrence river back in the day. For me, it's still the most elegant hovercraft ever built and I spent many a childhood hour on the jetty at the ferry terminal staring across at the Westland slipway waiting for it to lift off. You really could see all the way underneath before they started adding skirts. Elegant, impractical, unstable, mega difficult to model - but it just has to be done  {-) 
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 03, 2014, 08:21:23 AM
That's one awesome project ahead Tim but could I respectfully suggest you create another thread on it and not allow it to encroach and possibly deviate this superb thread on your Bluebird  ok2


I guess I'm not the only one awaiting further progress on that and more on the Mk2 version as that develops. Every time I stand at our pond which is just over 400ft long - but walled - I wonder about whether it would be a viable project to take on


Posted with the best intention in mind


Regards - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 03, 2014, 10:12:40 AM
Yes Ramon, The SRN2 will be a completely separate thread in due course -  I will put the build on Mayhem (eventually) because although it's not a boat it is the 'Saunders Roe Nautical 2". I only posted the glimpse of the future because I was chuffed with the CAD model. That's the furthest I've ever got after many attempts!

K7 Mk II will be a new thread too. Just have to get the plans finished before I open it up to the public.

Appreciate your interest in the K7 build!
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on November 03, 2014, 02:29:10 PM
That's one awesome project ahead Tim but could I respectfully suggest you create another thread on it and not allow it to encroach and possibly deviate this superb thread on your Bluebird  ok2


I guess I'm not the only one awaiting further progress on that and more on the Mk2 version as that develops. Every time I stand at our pond which is just over 400ft long - but walled - I wonder about whether it would be a viable project to take on


Posted with the best intention in mind


Regards - Ramon

Ramon,

I get about an 8 sec run in my club pond and at 40 mph that's about 150 yds, if my maths are correct.
You do need a bit of space, Loch Lomond is my favorite on a calm day but at 26" long and a brushless motor with 3S Lipo's if I run flat out it will take off, so just a touch below full throttle.

Very exciting little boat and what a crowd puller, everybody knows  Bluebird K7.

George
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 03, 2014, 11:25:12 PM
Tim, been following it from your first post - keep it coming  ok2


George - been thinking about doing this for so many years it's untrue - hence the interest in Tim's and others models.

Haven't got there yet but Tim's accounts of his endeavours are having a distinct influence  %)

I need to keep focused on the 'Wide a Wake' first though


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 04, 2014, 09:52:40 AM
I've got a question.
Reading Graham's log on his Krik Lisa M reminded me that I needed to ask about motor mounts etc.

Modern motors use ball bearings. It's generally not a good idea to put an axial load on a ball bearing (unless they are specifically designed for it - the races have a slightly different profile - and my guess is that Chinese motors don't use top-notch bearings). If the motor is fixed and the shaft is a fixed length, there will be an axial load on the bearings - no getting away from it. 'Thrust washers!', I hear you cry. Nope, that's not going to work. You would have to build the driveline so that the balls were centred in the races (impossible in practice) and the slightest wear on the washer or change in temperature  results in the load being carried by the bearings, not the washer. We are talking microns here - bearings are made with incredible precision.

In 'real' drives, it's normal practice to arrange for a proper thrust bearing and include some sort of sliding or compressible coupling (typically a splined 'telescope') to keep the axial load away from the motor shaft. I've looked around and there's nothing on the market that would fit the bill for a model (size, price, rpm capability). My approach with Mk1 was to make a sliding motor mount - there is a picture way back in the thread. I was surprised that nobody challenged that. I'm planning to do the same with MkII. Apart from anything, it makes setting up the drive line so easy!

I've added a couple of picture of what I plan to do. Yes, I intend to hang the motor under the mount. That gives me scope to get the minimum angle on the prop shaft. (Still need to find the optimum angle from Mk1 trials). The motor mount is actually simple but I will probably have to compromise a bit on the fancy shapes as my 'machine tools' are a hacksaw and file.  :-))

All this leaves me with three options:
1) I've got the basic engineering wrong. (I doubt that - it's my job to know this stuff!)
2) I am the first person to have thought about his. (I seriously doubt that - boats have been around (even) longer than me).
3) It doesn't matter. I'm being a pedantic old ***. (I'm renowned for it). The bearings will outlast the rest of the boat  - especially with my driving. What matters at work doesn't matter for hobby use. I know that my motor has some end float in the shaft anyway - perhaps it's worn out! (I still think there are people making money out of selling PTFE washers that are a complete waste of time though  {-))

I joined the forum mainly to get advice from those who know. Go ahead  please - but try to keep the abuse minimal  {-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 05, 2014, 08:26:10 AM
Tim - check your messages - PM sent


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 08:03:40 AM
Quick vote chaps - I'm almost ready to start logging the Mk II design and build. Shall I start a new thread or carry on with this one??
(It's getting a bit long!)
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 09, 2014, 08:51:51 AM
I'm up for continuing Tim - a natural progression.


As I see it the length of the thread is not such an issue for anyone interested in the subject. That said others may have other views and prefer a fresh start. Should you refer back though it will mean having two threads open.


Whatever you decide I shall still be following - looking forwards to it  :-))


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on November 09, 2014, 10:07:59 AM
Tim,

I'm with Ramon.
Stick with the same thread, sometimes another thread on the same K7 subject can get lost.
This way you can always read back without too much hassle.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 11:29:01 AM
This is where it will go then  :}

I will try to upload some pictures of the (design) progress later. (After I've changed a set of brake pads and done the shopping!)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 06:53:59 PM
Mk I is in the garage convalescing and waiting for new plumbing.

It's time to launch the Mk II log  O0

Let me preface this by saying that I still know very little about model boats. I'm indebted to those who contributed to getting Mk I off the shelf and into the water and everything that has been learned so far has led to the starting point of Mk II. I'm not trying to teach anybody how to build a model here, just sharing what I'm doing and there is an unashamed engineering bias to my approach. I've decided to post early in the project on the grounds that "Why don't you...?" is far more useful than "You should have..."

Are you sitting comfortably? Then we'll begin.

The first was to build a 3D solid model of the outside of the boat at 1/8 scale using the original drawings kindly sent to me by a fellow Mayhemer. I've got it pretty accurate to the prototype but there is no rear wedge and the sponson shoes are wider - this time, less of a guess and more based on what works on Mk I. It looks like this:
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 07:06:08 PM
The next stage is to create the framework of the model by cutting the frames from the solid. In CAD, the best way I can describe it is a 'reverse saw cut'. I slice down through the model where I want the frame and get the program to give me only the slice where the saw cut would be. Make sense? (Actually, each frame still has a copy of the whole model attached to it. If I want to move a frame, I just edit the cut position and the shape of the frame updates to suit. Very cool! This approach means I have a lot of data in the final model but my modest PC can cope with it just fine)

After a LOT of chopping and trimming I have something like this:
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 07:25:58 PM
Coming on nicely. What you can't see, unless you have amazing eyesight, is that I made a bit of a cock-up around the air intakes. The cowling is circular cross section until it approaches the front, where it changes to elliptical. I got the solid model right but managed to cut the frames out with the cowl upside down  <*<. Not a major issue, I just have to re-model a couple of frames and the stringers.

The basic design is similar to Mk I; two closed boxes running down the outside, which makes the model very stiff. I have decided to make one major change though. The cowling was very difficult to build on Mk I, it made the model a nightmare to handle during the build and the scale (ish) access hatch made the inside inaccessible! This part of the boat serves no great structural purpose in the model so I am going to split the model in two right along the cowling.  It gives me another advantage in that I can seal the hull with a simple, watertight internal hatch that is invisible when running. Not scale, but then neither is sticky tape to seal the scale hatch. :-)) I can do it on this scale of model because there is enough room for all the hardware under the hatch. It probably wouldn't work at a smaller scale.

I will reduce the size of the hatch and make it simpler when I know just where things will be inside but for now I've put the biggest one in that I can fit, just to see what's possible
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 09, 2014, 07:59:26 PM
You can see that I have already put the motor and battery into the CAD model. There's two reasons. Obviously, I'm designing the structure around the hardware but also, at a later stage, I will get the CAD system to calculate the CG position. The weight of the motor and battery is included in their models.

I spent a fair bit of time considering where to put things inside the boat. One thing that lets down many models is that they look too 'twitchy'. That's because you can't scale time. (Or you can, using video. I've seen some amazing videos on UTube where they are slowed down just a tad and the models look totally convincing). What I wanted to do was increase the mass moment of inertia of the model as much as possible. "Ooo - er," I hear you say. " He's gone off on one....." If you are not familiar with moments of inertia, he's a little demonstration you can do in the workshop or just in your head. Take two hammers - come on, we all have at least two hammers  {-) -. Hold the heads together in one hand , with the handles sticking out. Now try to spin them like an aircraft propeller. OK, turn the hammers round so you are gripping the ends of the handles and the heads are outboard. Now try to spin them. A lot more difficult, isn't it? You still have the same mass (weight) and the CG is in the same place (in your hand) BUT it's a lot harder to get those hammers moving.

I wanted to spread the weight out as far as possible in the boat. The heavy bits are the motor and the battery. The CG on Bluebird is just behind the back of the sponsons. I thought about putting the motor way up front, almost under the forward boom. That would allow me to put the battery a long way back. However, that would require another hatch between the booms (difficult to seal), there's not much room that far up front to offset the motor and I would need a very long (expensive) prop shaft. The last straw was that all the wiring would lie in completely the wrong directions. I decided to stick with what works on Mk I. The battery is up between the booms but this time it will live in a drawer, designed in front the start. It goes in under the aft boom nicely and this allows me to use my simple hatch. If I can move the motor back a bit (once the CG calcs have been done) I will but for the moment I'm sticking with my existing hardware. I'm back to where I was but at least I'm satisfied that I have explored the possibilities rather than just copy what I did before.

You may notice that in the 'exploded' picture, the cowl frames are solid but in the assembled view, the centres have been cut away. They are two different models of the cowl that are part of the cunning build plan. I'll cover how I plan to build the cowling in another post and let you all rip it to shreds.

Just in case you are thinking I rely too much on CAD I would point out that I could (just about) still generate the design the old fashioned way - drawing it out and projecting all the sections. However, that wouldn't give me a fraction of the information I can get from 3D CAD - and it's much harder! Besides which, I'm not sure quite how well Mrs M would take the installation of an A0 drawing board in the dining room  %).

For now, I need to carry on trimming and fitting the parts together. The solid parts will eventually be used to create 2D drawings as templates for the real wood. (Yes, a set of full scale, printable plans will be posted in due course for anybody that wants to have a go). This thread will grow slowly but I'll try to keep you posted on where I've got to and why I'm going that way.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on November 10, 2014, 08:28:45 PM
Tim,
Can I suggest that you consider .

1--Moving the battery position to the sides of K7, if you look back at my K7 you will see that I have  2- x 3s Lipo's to
     give a longer run time, you could then put the E.S.C. in that forward position as it doesn't need to come back out.
     If you position them as your drawing you will find it difficult to get them out and in.
 
2--Consider beefing up the skins of the bow where the sponson supports come thro' to prevent the hull cracks that       have in mine due to a lot of use.
  Say epoxy some 1/4" thk ply plates to the inside of the hull

Just some thoughts.

George.
 
 

   
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 10, 2014, 09:09:54 PM
Hi George. The battery is there for the moment because that's where it needed to be on Mk I to get the CG right. Later on when the whole structure is modelled, I will be able to get an fairly accurate prediction of the CG from the computer (I'll have to make some guesses when it comes to weight of the waterproofing, paint and glue). I can then look at moving the battery if need be. Actually, it's not hard to get the battery in and out on Mk I but I shall design in a proper sliding drawer for it so I don't have to pull it out by the wires  >>:-( (if it stays where it is  ;)) If I go this route, the ESC will be hung from the hatch to keep it out of the wet. Not that my boats ever leak.... {-)

Now the booms. Yes, I did read your earlier advice. In this model, however, the booms are not going to be connected to the outer hull except by a little silicone sealer. The load is taken by the box between the inner frames. The box will be extended to meet the hull (to keep the water out) but between the frame and the hull skin it will be in clearance. I'll cover the details of my proposed arrangement in a later post.

Yeah, I have a bit of a weird approach but I see the functional structure in my mind and the hull sort of hangs off it. Quite the opposite of starting with a hull and building everything off that. I take all your comments on board and I'm still prepared to be shot down in flames later but I think you will understand my strange logic as the post progresses.

Just finished correcting the model of the cowling. That was hard work! Too late to post tonight but it's the next topic for discussion.
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 10, 2014, 11:06:29 PM
Tim - Can I just say that I find your detailed accounts of your thoughts and the reasoning behind it makes for interesting and informative reading. I fear I will have little to add but if I may make the following comment.


As a regular poster on another forum sometimes, when one sees the number of visits relative to the number of replies, it can get a bit dispiriting if you begin to feel you are talking to a vacuum. So, speaking for myself - I know I won't be having much to say nor likely to have much input but I do know I shall be following you every step of the way - you're doing a fine job  :-))


Regards - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 11, 2014, 08:12:39 AM
Thanks Ramon. I'm not concerned about the ratio of views to replies; I read a lot of other posts and just admire the work. A lot of them leave me speechless anyway - the craftsmanship is staggering! When the comments come in, they are always helpful and welcome.

I was thinking about what George said on batteries last night  (this modelling lark tends to take over a bit!). I'm using a 5000 mAh battery. If I find that I want to spend longer on the water I think I might invest in a second battery but swap them over mid-session rather than carry one round in the boat - I'm aiming for low weight after all. On the other hand, if the battery stays where it is, which depends on where the CG comes out, there is enough space between the existing battery and the motor to drop another one in. (I have designed the boat so that the battery slides back into that space to be removed and also so the battery position can be simply adjusted to get the balance right). Guess what? If I add a second battery just in front of the motor, it will be sitting right on the CG. No major re-trimming needed.

Of course, I planned it that way....... {-)

I haven't run the boat long enough to flatten the battery yet. Only time will tell what course I take. (Bit like my steering).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 11, 2014, 10:37:54 AM
I mentioned earlier that I'm going to split the cowling right down the boat. On Mk I the cowling was an integral part of the hull. That made it difficult to build, made the
model extremely diffucult to handle during the build and made access to the inside a nightmare, especially round the transom when I was going through a series of modifications such as moving the prop strut around. The rattling sound I hear when I pick the boat up now is all the lost M3 nyloc nuts floating around in there.

My approach on Mk I was to plank the frames with balsa strips, about 15 mm wide. I used CA glue and quickly learned what you all know already. The glue lines were harder than the wood, which made it very difficult to sand the skin smooth. I didn't use any stringers either so there was a tendancy for the skin to balloon outwards where the curves got tight. To this day, you can still see a slight 'barrel' effect (flat patches) when the light catches the cowl.I used a lot of glue and filler on that cowl, which may go some way to explaining why Mk I is, like her builder, a bit heavy in the rear end.

'Make it from fibreglass', I hear you shout. No, that's not going to happen. I hate the smell, the mess and the feel of fibreglass. I've never made any good out of it. I enjoy
working with wood even though I'm not very good at it. Why use a material you hate when a hobby is supposed to be fun?

My plan for Mk II is this. I will cut the frames out as per the picture, mark out the final hollow shape but leave them solid for the moment. The frames will be assembled onto
a sturdy 'spine' sticking out of the bottom (not shown) that I can grip in the vice. The 1/4" square stringers are not 100% accurate in the CAD model but are close enough for
the CG calculations.I want to be sure that the join between the removable cowl and the fixed part is good. There are two sheet stringers shown in red and green in the picture. They will be glued to the frames but not to each other. In fact, they will be separated by the thickness of a knife blade. (I've got loads of blunt ones to use as spacers - never throw anything away).These lie on the split line. Below that there is one last stringer shown in orange. This one is curved in both directions and is the line where the cowl meets the deck. (Once again, the power of CAD allows me to extract that weird shape from the solid model easily).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 11, 2014, 10:42:41 AM
I am hoping to skin the frame using quite large sheets of 3 mm balsa, joining them on the stringers (chubby orange peel segments, if you like). The curves are not too severe
and I hope that with some steam or soaking and a lot of patience I can persuade the wood to take the double curvature. I can work out the shape of the segments by measuring off the curve length round the frames and create a flat pattern for each peice. I will then fit the peices to the frame one by one (but not glue them) and form them to shape before final trimming. I won't glue the skins on until they have had a chance to settle into their curved shape and have dried completely. I don't want to build a lot of
stress into the skin and have it springing off. This is going to be a slow process and I will start the build with the cowl so that it can be drying while I get on with other stuff.

If anyone has experience of this style of build and can pass on any tips, I'm all ears.

I intend to treat the skin and frames to a dose of Ronseal Wood Hardener. Yes, it does exactly what it says on the tin! Originally intended for rescuing rotten wood, such as
window frames, it's a water-thin polyester resin that soaks into the wood and sets rock-hard.It strengthens the wood (you end up with wood reinforced plastic instead of glass
or carbon RP), it repels water and gives a good surface for sanding. It should help keep the cowl in shape over time too. This time round, I will use it sparingly - it does
not evaporate so it adds to the weight. I used loads on Mk I and the structure came out heavy. I also recall it caused some problems when I applied Zap-Poxy to the hull before painting. The epoxy went off much too fast. (What I can't remember is whether this was a reaction on the dried surfaces or whether there were traces of wood hardener in the pot I used to mix the epoxy. I will need to check). 

The skin will initially continue beyond the deck stringers. Once it is all glued up, shaped and sanded, I will trim it back to the deck stringers and cut back the bottom of the frames to their final shape - they will now have legs between the split line and the deck stringer. I will adjust bottom of the cowl to fit the hull. This isn't a super-critical fit because there will be a fillet of filler added later at that joint. The next stage is to cut through the skin from the inside at the split line, leaving the frames intact for the moment. Now you know why the stringers were spaced apart (if you hadn't already worked that one out). I used a similar approach on Mk I to create the access hatch and it worked well. It keeps all the curves smooth.

The whole thing then gets glued to the deck and when it's all set, I cut through the frames with a razor saw from the outside (using the cuts in the skin as a guide). I'm doing it this way to make sure that the fixed part of the cowl doen't spring out of shape and everything is perfectly aligned.

The final stage is to cut out the centres of the frames in the detachable cowl using a Dremel (and put it in a safe place).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 11, 2014, 10:44:36 AM
The fixed part of the cowl will be trimmed up on the inside so it's all nice and tidy and the radius between the deck on the cowl will be formed with filler. The curve is far too tight to make from bent wood and the weight of filler required is minimal.

Next topic will be the booms. Bet you can't wait  {-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on November 11, 2014, 06:44:46 PM

Tim - Re the method of covering the cowl - 'Moulded balsa' has been used very successfully to shape complex compound fuselage halves. The balsa is soaked in hot water (ammonia used to be added but is now apparently difficult to obtain - besides it smells awful) and then carefully wrapped to a 'buck' or former using soft bandage. Left to dry, the balsa will retain the shape providing a very strong but very light component.
I Googled 'Moulded Balsa Fuselages' and found this [size=78%]http://www.clapa.org/windy2.htm (http://www.clapa.org/windy2.htm)[/size] - it's by someone considered in the control line aerobatic world to be an absolute master at it. Unfortunately there are no images but further searching will reveal the idea.


I know you said you do not want to go down the fibre glass route but if something like this type of balsa shell is covered with the very lightest F/G cloth say .6oz/sqyd it becomes immensely strong and very water proof. You do not have to use F/G resin - I have used two pack resin fuel-proofer to put this on with which works just as well. You can also use the thin epoxy vailable for the same purpose. The cloth is laid over the finished balsa and the resin gently painted through it with a flat soft haired brush working outwards all the time from the high point. The good thing about using fuel-proofer is that the pot time is long but the dry time is relatively quick. It will be much lighter that using the wood hardener I'm certain.


This is a technique used by many yacht hull builders - a search on here will produce the results.


Hope that's of use - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 11, 2014, 07:27:06 PM
All 'ammunition' is welcome Ramon! It's lodged in my 'things to try' department. Thanks!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 12, 2014, 01:20:29 PM
BOOM!

Did that get your attention? We come to an interesting area of the design that has developed round several things:
1)   George's operational experience
2)   My build experience from Mk I
3)   A bit of engineering
4)   How the prototype worked

In Mk I, the booms were made up as wooden U sections reinforced with aluminium tubes held in with fibreglass (yeuk!). The booms were fitted into a box in the hull and then the sponsons were attached. Finally the booms were built up with block balsa to give the final shape. One area of the build that gave me a lot of jip was trying to blend the booms into the hull and sponsons. I used a fair bit of filler but it was all inaccessible for finishing. In short, I made a pigís ear of it and I was never happy with the result.

Now, Iíve said before that I see the model in my engineering mindís eye from a slightly different perspective to others. The prototype boat had a structural space frame inside and everything hung off that. My model is somewhat similar. There are two big beams running the length of the boat and the booms attach to that, not to the skin of the hull. For the structural part of the boom, I am planning to use some 15 x 25 x 1 mm thick aluminium tube I found in the garage (an old shower curtain rail). To be honest, you could substitute a piece of wood here, perhaps spruce. It would be plenty strong enough and only weigh a few grams more (I checked!).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 12, 2014, 01:52:26 PM
The booms are going to be fitted after the model is painted.
Really??
Yes. I want to leave the hull as clean and accessible as possible for sanding and painting. Iím not very good with a paint brush and Iím an absolute menace with a spray can. I need all the help I can get! (I hope to get the hang of using an airbrush by the time I get round to painting this model but we will have to see). So how is that going to work without getting glue all over the boat and still make a good joint?

Cunning plan. The weight of the boat is carried by the top of the boom, so that is the bit I need to attach to the frame. The structural box (between the main beams) has a flat top and is deeper than is needed for the boom to fit. The bottom face slopes up towards the centre on both sides. Between the main beams and the hull, there is another box, 1-2 mm bigger than the boom all round. Slow-set epoxy is applied to the top face of the boom where it fits the box (with a smear on the sides too) and the boom is then slid into place across the bottom floor of the box so the adhesive is not wiped off. The ends of the boom are supported on level blocks and the hull allowed to drop onto the top of the boom, maybe with a bit of ballast for good measure. The whole lot will be trued up and checked then left to set. So far so good. The boom is attached where it needs to be attached but the joint is a little vulnerable. Adhesives are good in compression (thatís how it is being used here) and pure tension, good in shear (if the boom tries to slide out sideways) but much less strong in peel and cleavage. If I were to push down on one end of the boom while holding the hull still, the adhesive would be put under a peeling/cleavage load and thatís a likely fail. To get round this, after the epoxy has set, I will insert two glued-up wedges under the boom to make sure that this loading condition canít happen. So thatís why the box floor slopes!

We still have the Ďoversizeí boxes open where the boom comes out through the skin. I will apply a little low-modulus silicone sealer to seal this area to keep the water out, though itís not strictly necessary. The booms can flex all they like now and not transmit any significant force to the hull skin.
There you go, George, I was listening!   :-))

Instead of sheathing the booms in place, I am going to make up some cuffs that slide over the tube. They will be pre-painted to and only attached to the hull by a little silicone. (If I glued them to the hull, I would Ďshort circuití the silicone gap round the structural booms). Iím not going to try to blend these into the hull or sponsons, just make them a neat fit. Oh dear, that requires some skill so it will take a long time.

The sponsons will be fitted in a similar manner. In this case though, itís the bottom face of the boom that gets attached to the sponson structure and there will be a wedge above. That wedge will have to be part of the Ďcuffí. Oh dear, oh dear. More accurate building needed. I have some reservations about the attachment of the sponsons; itís quite a small joint to rely only on adhesive. I will make a judgement when I see the sponson structure. I could add a dowel down through a hole in the top of the sponson and patch the paint up afterwards if necessary. On the other hand, if there is a crunch, it would be better to have the sponson fall off rather than rip the whole side of the boat out.

The pictures below speak more than my thousand words.

I now have a lot of design work to do so please be patient. Eventually, I will get some good predictions of the weight and CG out of the solid model and then it's on to the drawings so that I can cut real wood!
Title: Re: Donald Campbell's Bluebird K7
Post by: Mad Scientist on November 12, 2014, 09:06:30 PM
Thanks for sharing your design process with us, Tim. I, for one, find it fascinating! :-)

Tom
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on December 07, 2014, 11:38:43 AM
Hi Tim - any 'latest news' on the design work ?


Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on December 07, 2014, 01:53:03 PM
Timely enquiry, Ramon; I was planning to post today.

Unfortunately, this project is currently stalled - NOT abandoned. I'm not sure if time is accelerating or my brain is slowing down but I have no spare time whatsoever at the moment! Changing computers seemed to take about three weeks, changing phones a whole weekend...... Mrs M has decided to make up for the schooling she never had as a child and she's studying ferociously every evening. As a one-time teacher, of course I get the privilege of helping. To cap it all, I am changing jobs in the new year, which means going back to a daily cross-Solent jaunt. (That's the second to last thing I wanted to happen. The last thing I wanted to happen was to find myself suddenly out of work, which was looking like a real possibility. Better to jump ship when the water's reaching the gunwales, I say).

I did manage to make some progress on the sponsons. The picture below looks simple enough but belies the work behind it. Just a soon as I get the time, I shall carry on working on the frames till I get to the point where I can pull of the drawings, then find a big printer. I will publish the drawings too as soon as they are done. Good chance I will get a few hours over Christmas but you never know round here!

Realistically, It will probably be around Easter before I get round to cutting wood, depending on how the new job goes. I've been told that I won't need to travel much but I've heard that one before!

So, don't despair! Mk I will be back in the water when the weather (and daylight) permits. Mk II remains a work in progress, albeit slow progress at the moment.

Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on December 08, 2014, 06:14:43 PM
Hi Tim, Sorry to hear that the dreaded work has got in the way - know (or rather, knew) what that was like but the joys of retirement has seen that banished forever now :-))


A thought on the sponsons - would there be any advantage of bolting them on in such a manner that their angle of attack and possibly their height was variable in order to establish optimum position? Might require a small amount of metal work but would be glad to help if you thought it might be beneficial.


Glad to hear it's not abandoned - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on January 18, 2015, 07:43:39 PM
Happy New Year chaps!
(Chaps includes those of the feminine persuasion, just so as to avoid offence!)

There has been a little progress on the CAD work. Extracting all the parts from the solid is a fairly painful process but it just has to be done.
As things stand, the CAD model predicts a weight of around 2 1/4 kg, including the motor and battery but no prop strut or rudder and no allowance for glue and paint. At least it's starting in the right ball park. The CG comes out just a few mm forward of where I want it. That will move back when I add the prop.

One of the pictures shows two hatches; one in red and one in purple. The purple section I will sheet in and secure with silicone once I am happy with the work round the transom. The red hatch is the watertight access. Another picture shows the removable cowl (not watertight at all).

I thought About Ramon's comment about adjusting the sponsons. Normally, I would built in adjustment but in this case it's not practical because there is no space. I have done the tuning on Mk1 so I'm pretty confident this version will run OK. If push comes to shove, I'll adjust the planning shoes.

Not much of a post but at least you know the project is not dead. Must dash - Mrs M will be home from work in a minute and wanting her dinner!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 05, 2015, 02:01:18 PM
Long time no see. Hope you are all fit and well  :-))

By now you would be forgiven for assuming this is just another fly-by-night abandoned project but finally, after six months of chaos I found a couple of hours to sit down and look at the CAD model. I was a lot further down the line than I realised. My original idea was to produce proper, commercial standard drawings for every part so that anybody else could build the model. I realised that not only would that entail a huge amount of work, it wasn't necessary. Instead, I have taken sections through the assembled model to produce the cutting templates I need. I will produce the others as I need them. If anybody else wants to have a go at the build, you have the same information as me. It is, after all, a scratch build. Some things will be worked out on the fly. (Oh, if anyone wants a copy of the solid model - stp or iges, let me know)

I've uploaded the first three drawings. One shows the details of the cowl, one shows the main hull frames and the third is a general assembly. I've managed to get the frame drawings so they will print 1:1 on A3 paper; should be easy enough to get that done by a shop if you don't have access to an A3 printer. If you want to print the GA, you're going to need an A0 plotter! We have one at work, I just need to creep round the right person........ 

And just lookit what arrived on Wednesday  %% along with a couple of shiny new router bits for my Dremel. Yes, it's now Sunday afternoon and  I've have only just found time to open the parcel. Such is life round here. That's a lot of wood for one Bluebird but I decided to buy ahead for this and the next project. The delivery cost was about 15% of the order, even delivered to work on the mainland. Delivery to the IOW would add an extra 20 quid! The filler? Not that I ever bodge anything.... the design actually calls for a bead of filler along the cowl-hull joint so I got a proper lightweight one while I was ordering the wood.

The cowl gets built first. Far and a way the most complicated part of the build involving 3D forming of the skin, which will need plenty of time to dry out. Never done that before so it could get exciting.

I would like to say I'm off to the cave now to start tracing the frames onto ply but I haven't printed the drawings yet so I guess I'll have to do the ironing instead. >>:-(. I'll keep a photo log as I go along and keep you posted. I can't do a Krishna (I LOVE those foam and scrap boats!!) and produce a model every day but we should see some progress now. Watch this space (but don't hold your breath).
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on July 05, 2015, 05:08:12 PM
Hi Tim - Pleased to see you back on this. I know exactly how it is -I'm having a break from my launch too  :-)

My offers still good on the mount - not doing any machining at this precise moment but keep me in the picture as to when you need it by at the latest.

Looking forwards to the build - I'd love to do one myself but have more that enough waiting to do as it is - nice thought though ok2

Regards - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: klz on July 05, 2015, 05:09:08 PM
Hi Tim, I am glad to see you back I have followed this from the beginning only the other day I was wondering if you was continuing with the build.

Keep the pics coming, I have just down loaded your PDF's I have no idea what to do with them as I have never built from scratch but you never know there is always a first time.

Kelvin
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 05, 2015, 05:32:53 PM
Back so soon?

Half way through the ironing I remembered that I was going to draw all but two of the frames onto the wood rather than trace them. They are all circular, except the front two. I only needed a couple of dimensions for each frame. I should have put them on in the first place as a check (you can't be sure a '1:1' print really is 1:1 unless you measure it). Printed them off on A4 and hid myself in the garage.  I have uploaded 'Issue 2' of the drawing.

I chuckled as I set to work. The ruler still has splashes of blue overspray from when I built the first model about 15 years ago. The only problem is that the millimetres have got an awful lot smaller. I will need to print the front two frames and trace them onto the ply. Then I need to find the bits for the Dremel (I'm sure I have a trammel attachment for it). Before I start cutting I need to re-set my head. My 'spring project' was a table - started out as a piece of mahogany, 10" x 2" x 5ft long. Gotta think delicate, gently does it!

Ramon, I'll keep you posted  :-))

We have progress!


Title: Re: Donald Campbell's Bluebird K7
Post by: John W E on July 05, 2015, 07:30:12 PM
Hi ya Tim

Watching with great interest :-) what ply are you using here?   Already downloaded and going to talk to the Mrs to see if she can print the images off at work.

aye
john
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 05, 2015, 10:26:20 PM
That's 2mm lite ply. More common for aircraft but weight is critical on this model.
Title: Re: Donald Campbell's Bluebird K7
Post by: F1 madness on July 06, 2015, 07:58:00 AM
Sweet build watching with interest  :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 06, 2015, 07:46:43 PM
Does this put it in perspective  {-)
(Sorry about the knees)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 11, 2015, 07:17:44 PM
First Cut.
I found the trammel attachment and, to my delight, in amongst the kit of a million and one useful things to attach to your Dremel, a parallel routing fence that goes with it. I started by cutting the slots in the frames where the joint will be. The actual position isn't critical but they all need to line up. A parallel fence needs something to bear on both sides of the cutter so I cut the slots while I still had a sheet. (The very observant will notice that the frames are not the ones I showed last time. Although the position of those slots isn't critical I cut the slots and then realised I was about 7mm out from where they should be. I'd relied on memory instead of checking the drawing. :embarrassed:  I wasn't sure if I would be creating problems later so I just joined up the slots and re-drew the frames. By now, I have 1:1 prints so it didn't take long)

I then used the trammel to cut the frames out. They are circular so it was a doddle. You'll notice I decided to sacrifice a square of ply as a disposable cutting board. The new router bits are great but they're also six pounds a pop so I don't want to ruin them hacking into chipboard. The red spot on the trammel is, by the way, A neg. That point is really sharp! I have a couple more frames to cut that are not circular (different router attachment).

I've decided to change the design slightly. You may recall that I was going to keep the frames as sheets during the build then remove most of them later. I realised that this would entail a lot of difficult keyhole surgery and I've opted to add lightening holes now (cut with hole saws). Much easier and leaves the frames stronger - now I have the wood, I have a better feel for the strength. Is it worth it? I weighed the disks that I removed. 10 grams total. OK, sounds like nothing but the frames themselves weigh 80 grams so it's over 10% weight saving.

Oh yes, I weighed three sheets of ply while I have them intact. They weighed about 975 grams. From that I calculate that the density of (my) lite ply is about 445 kg/m3. That's a note for me as much as anything - I'll check what number I used in the CAD model later.

Hopefully, more progress tomorrow.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 12, 2015, 02:10:28 PM
On we go...........
I was thinking about all the details I had to cut in those frames today and, to be honest, not relishing the thought. It would be so much easier if I had a table router.
Aha! Half an hour later I have a table router! And I didn't destroy anything to make it (unusual for me). I have one of those conical router attachments for the Dremel. I just routed out a rebate in a piece of MDF so the cutter pokes through the right amount, fixed the router attachment with some wooden blocks and Bob's your uncle. Works really well. Go on you need one!

All the little notches and slots cut. Time to tackle frames A and B, the ones I had to trace because they're not circular. Where did I put them? You remember that piece of ply I sacrificed as a cutting board? Guess what was on the other side.  :embarrassed: Never mind. A quick re-draw and we're off. By now, I have also found the spring bow I bought as an apprentice. Beautiful instrument; 45 years old and as good as new. Brought back memories of getting a right royal rollicking from the (pipe smoking) drawing office manager for turning up to work without a tie.  {-)

Notice how I cut one of the frames on the table router. Actually easier than using the trammel.

By the way; my garage isn't really as messy as it looks in the photo's! And yes, that one of those Chinese sailing boats in the background. Whatever the experts say, for a total amateur it's a nicely made boat and great fun to sail, if ever I find the time.

Quick rub down to make the frames look respectable and on to the next stage.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 12, 2015, 02:36:06 PM
Onto the building board.

Or, in this case, the building stick! I got a piece of 2x2 from the local wood shop. Fortunately, the chap was patient enough to find me a straight bit. It's only when you look you realise that most of what's on sale is a bend as the proverbial donkey's. The position of the frames is marked on and the end of the stick tapered away so that it doesn't protrude outside the last frame.

I've been using  Gorilla glue for some full size jobs lately and I really like it. On well-fitted joints it give a super-strong result. It's also quite forgiving as it expands while curing to fill gaps (which is just as well because 99/100 of my joints are not well-fitted). OK, you have to use it sparingly because otherwise it foams out of the joint but it's easy to remove any ooze later. I spotted the same brand in a cyano and decided to use it to fix the frames to the building stick.

Nope. The frames need to be a reasonable fit on the stick but not a tight fit because they will buckle. Needles to say, the cyano did not take up any gaps and I only managed to tack the frames in place. It worked out better, actually. There was a fair bit of adjustment required to get everything nice and true; that first spline helps a lot to reveal the alignment. I ended up adding proper Gorilla to the joints and it's curing as I type. By the way, do not glue the frames to the top of the stick, just the sides. (Obviously) the stick comes out later and it would be very difficult to remove if you glue the top.

The clamping isn't as drastic as it looks, I just don't have any smaller clamps. They are not that tight.

You will have realised that I'm posting as I build rather that waiting till the end to report how things went. I suppose from the reader's perspective it might be better to consolidate everything at the end but I rather like the idea of have some experts looking over my shoulder as I go. You may even be able to stop me before I do something stupid! It kind of adds focus - and gives me something to do while the glue is curing. :-)) I reckon things will be dry by now so I'm off to fit some more stringers.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 13, 2015, 08:01:04 PM
All strung out.................

I had serious misgivings yesterday about the wisdom of building this boat again when I saw the size of the task for real. Never mind, we are well underway now. The stringers went in quite well. If anyone else decides to try the build, I would not notch the front two frames until you see just where the stringers 'want' to lie. I had to do a fair bit of adjustment to the notches to get them to fit so it's better to mark off from the wood. (The stringers in the CAD model are 'cut' from the solid plug. A piece of initially straight wood does not follow quite the same curve; it's a spline).

You can see the old knife blades used to space the two sheet stringers apart where the canopy will eventually split. Those paper clips are really handy, by the way. Very strong clamps.

The next step was to sand the stringers back. I don't know of any easy way to do this; you have to follow the circle of each frame but also follow the longitudinal curve. I used a long sanding block, which helped, but I still managed to get a few 'flats' on the frames. I'm not unduly worried about that (yet) because I think the stringers will form the skin rather than the frames. (Thinking about it, it might even be better to make the frames deliberately under-flush so they can't cause wrinkles). Three of the stringers were nice, hard balsa. The other two were rather soft. If I lived anywhere near a model shop I would have replaced them but as I don't, they have been given a liberal dose of (..................drum roll......................) Ronseal wood hardener! You just knew I was going to get that in somewhere during the build. {-)

You will also see that I have added some 1/4 balsa block between the first two frames. That area gets cut back to virtually nothing to form the engine intakes. It's a lot easier to fill that are now and sand it out later. Oh, and that square-ish block in the tail? I used that to support the rear frame, just tacked in with a tiny spot of cyano. Now I have the stringers on - I can't get it out! I was going to try to cut it up in situ but I've decided to leave it there till the canopy comes off the stick. Much safer but it does give a disconcerting rattle every time you pick the frame up!

At this point, I decided to take a time out to sort out the lighting round my bench. I have two 150W halogen floodlights over the bench, which is great, but when I'm working on stuff that is facing me, it's in its own shadow. Not so great and my excuse for many a cock up. I now have another floodlight behind me. Is it just me, or is it hot in here? (Will be nice in the winter though).

And so, the next job is to add the final 'deck stringer' and then it's on with the skin. This is new territory and I have no idea how that's going to work out. I have the wood, I have the bandages. I am sure I can't do the whole thing in one piece but I have edge joined two sheets of balsa to give me a 6" wide sheet for starters. I need to soak it in hot water but we do not have a bath in the house. I'm thinking swing bin or...........Dishwasher!  %%Yeah, I reckon that would work - take it out before the 'dry' part of the cycle. It will be interesting to see if the glue holds up. Now, when is Mrs M working next??? ;)

I did try steaming a small scrap of balsa (with a small steam cleaner). I wrapped a 1/8 sheet round a 40mm pipe without it splitting. That's going to come in useful  later. There's another 3D skin to form that is much more difficult than the cowl. Worked out what yet??

I'll leave you in peace for a while now as the next parts will be rather slower than the frame build.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 19, 2015, 01:07:00 PM
The learning curve has a few slippery patches............

I would like to say that the cowl skins went on without a hitch but that's not the case. On the plus side, I found out that popping the balsa in the dishwasher for half an hour really did the job. The wood comes out soft and pliable and it will conform to just about any form to strap it to. That will be very useful when I come to make those concave curves in the lower aft part of the hull. On the minus side, I found out that popping the balsa in the dishwasher for half an hour really did the job. The wood comes out soft and pliable and it will conform to just about any form to strap it to. Yes, you did read that right. I fitted (not glued) one double-width sheet and two single width sheets to the cowl frame. It was quite an effort to pull everything in with the bandages and I had to make a split towards the stern as there was just too much wood. I had my doubts when I looked at the bandaged shape and so I took a look today. The skins had pretty much taken the curves but had stayed flat between the formers (obvious in hindsight). I might have got away with a lot of sanding and some filler but I was not happy with the result. I have seen the level of craftsmanship that 'plank on frame' builders apply on here and I would be ashamed to leave it as a total bodge.

I had a think. Plan 'A' had been to use a number of segments to form the skins. That has to be the way to go, I realised. Having thunk, I also realised that I need to make sure the segments retain some 'spring' as they come off the formers. So, I rough cut two segments and glued them edge to edge and flat to the top former, following only the long curve. When that was dry, I tacked some 1/4 balsa strip to protect the edges and then pulled the skins down to the next former, having first applied steam for a few seconds. This time I bandaged in two stages - first layer pulled everything more or less into place, second layer pulled everything down tight - and I mean tight! That 2x2 stick is working hard! I put a couple of the first try skins over the frame too to protect it and give the bandages something to bear on.

The idea is that by gluing the skins together down the former I will get better 'tangency' and by leaving the wood hard it will follow the other curve better, not flatten out. I will find out next week if it worked. If it did, I will add each segment in turn. If it didn't I may cry.

That means skinning the cowl is going to be a long, slow process. Fortunately, the cowl and the hull are two completely separate things so I can crack on even though the cowl is going to take about a month, bit by bit.

Nothing more nautical for today; I have husbandly duties to fulfil  :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Perkasaman2 on July 19, 2015, 06:49:49 PM
Have you thought of thickening the frames and planking/skinning the other way to achieve the shape. You could also possibly use 1/32 ply for added strength and rigidity to the monocoque if the shape allows. Just a thought.
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on July 19, 2015, 08:31:30 PM
Tim,
Though I haven't done this method of moulding balsa to this degree before I am very familiar with the approach. I think the problem you face is simply too much space between the supported areas. The pressure of the bandage will pull the sheeting into the air space between stringer and former. When used for developing fuselages for control line aerobatic models the form or 'buck' is usually made from block balsa or higher density blue foam carved to shape. This supports the balsa completely. Fuselages made like this have nice contours and are extremely light and very strong whilst having little internal structure to support them.
It's been quite a while since I last looked at such but some very accomplished proponents of this method were Windy Urtknowski, Joe Adamusko and Al Rabe. Googling their names along with 'control line aerobatics' might prove beneficial - you could try 'Stuka Stunt Works' - 'moulded fuselages' too as I'm sure something will come up.

If you really don't want to go down that route then I think it's likely that to get the best curvature of your formers and stringers is to apply the sheeting as thinner planking - preferably diagonally and two layers. That will produce the curvature you seek but will prove immensely strong for low-ish  weight though not quite so low as a single moulded sheet.

Hope this is of use - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 19, 2015, 08:50:10 PM
Thank you very much for the advice chaps. I took a quick peek under the bandages tonight and things are looking promising for the first two segments. Yes, the former should ideally be solid or at least have a lot more stringers. I will be using solid forms for some of the other parts and I'm very confident that will work. I'm trying to get as few joints as possible. It looks like 30 degree segments has a good chance of working. That will give me six skins to fit. I'm so glad it's not four.

I'll keep you posted - mistakes and all!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on July 26, 2015, 01:39:06 PM
This week's thrilling instalment............

The skins are on. It was a slow process; each piece was glued on one edge and left overnight, then steamed, pulled into place with bandages and left overnight and finally the second edge glued down. I managed to work on the two sides in a different sequence so it all happened in a week. The result is that I'm pretty confident I'm into reasonable sandpaper and filler land. The photo (rather unflattering) was taken straight after gluing the last pieces on so I haven't started to sand yet. I have resigned myself to the fact that I will need to add a very light glass finish otherwise I'm sure I will get cracks coming through at some time in the future.

I can't put my hand on heart and say that I thoroughly enjoyed this part of the build. It was pretty difficult but I did manage to re-use the wood from my first trail using a wide sheet. My advice to anyone embarking on this build would be to look at your own skill set and preferences (Oh dear, that sounds like management speak!) before deciding how to go about the build. It is, after all a scratch build so you can do whatever you like! The plank on frame boys will walk all over this. I reckon double-diagonal planking would work a treat if you know what you're doing. You could skin it with a series of rings and then sand out the bumps. The fibreglass department could knock up a plug (you do have a lathe that can swing a 8" X 2ft lump, don't you?).

In retrospect, if I were starting again, I would make a wooden former - not the whole thing, just a 30-40 degree segment - and pre-form the skins pieces over that before gluing into place. That is what I will be doing later for some of the other parts.

I've now given the whole thing a light spray with water (hardly needs it in this weather!) and I will leave it alone for a week or so to relax before I start to sand. Fortunately, I enjoy sanding. But the build isn't stalled there. You may notice the hull floor is lurking in the background, marked out ready for the frames. Next week I will be cutting the frames and starting to build something more boat-ish.

Ramon? Any time you like my friend! It won't be long before I want to line up the drive train. (But I can do it without the motor mount  so no pressure)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 01, 2015, 09:58:28 PM
Today's thrilling instalment..............

Things are starting to happen. In the week, I found time to cut out the hull frames. I've started assembling the hull now. You can see I like things well anchored down. {-) That transom isn't going anywhere in a hurry! I doubled up the transom to 4mm and I will be adding a carbon fibre plate on the inside later (only because I have some). The frames look a bit skwiffy but the edges are glued in the right place. The ply is moving around all over the place as the temperature and humidity change. You can leave the frame and come back half an hour later and all the free bits have moved. It will be OK when everything is tied together properly.

I've also started to sand the cowl. It's looking pretty good so far; most of the lumps and bumps are out. It's got to the stage where it's difficult to see what's going on because of the wood grain, shades and joints so I have now given it a thin coat of emulsion so I can see the high and low spots. I'm still working on shaping rather than finishing. Up to this point, the best indicator has been feel. Mrs M gave me a very sideways look when she caught me fondling the cowl out in the garage. Don't get me wrong; my wife is the nicest person you could wish to meet but she does not understand modelling.
"I don't get it"
"What, dear?"
"You spent hours and hours making these models".
Yes , dear."
"Then you take them down to the boating lake and crash them."
"Yes, dear."
"And start again!"
"Yes,dear   :}...................And your point is????"

I don't understand why anybody needs 25 handbags, so we'll call it a draw. (At least, I will {-))

I digress. The glass cloth and Aerokote resin for the cowl arrived. Had to shop around a bit for that as most websites stated they could not post the resin. RC World did the business and it arrived in 24 hours.

And how about this for a rudder! I wanted a twin-feed rudder and spotted this on Ebay, from Hong Kong. About £15 all in and it arrived in 8 days! It's rather big (160mm) but I can cut it down a bit if I need to. Nicely made, too. Even got brass bushes in there. The reason I went for this one is that the bracket is in two parts. I'm planning to attach the rudder to the back of the prop strut again and this will work really well - just lose (hoard) the right angle section of the bracket.

I also got some white Letraset. Might be a bit too big but certainly better than writing 'DO NOT STEP HERE' in Tippex It will be a long time till I get to that point but I like to be prepared.

I'm on holiday for  couple of weeks so things should move along. There's some interesting stuff coming up; what this space!
Title: Re: Donald Campbell's Bluebird K7
Post by: F1 madness on August 01, 2015, 10:25:01 PM
Looking good and coming together nicely
Couple things on the rudder
Use small file and open up the water intakes so they do the job effectively as they quite restrictive
Other 1 makes sure you thread lock the grub screw that holds the pin in place as they do come loose
I learnt the way on both and nearly the expensive way   :D
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 04, 2015, 01:29:25 PM
I'm taking a short break from building as I have glue, wood and resin drying in the garage. Nothing I can work on!

Progress is far better than I expected. I've deviated from the original plans in a couple of places - nothing major. Mainly I had a bit of a re-think about how all the various bits of wood join together around the bow and just tapered the longitudinal beams in at the front.

I have the bow section built up now and I have built the boom boxes. There's no heavy wood in there, the stiffness and strength comes from the shape. That whole area is really stiff now. I have also built the battery box and fitted the runners that guide it. It may seem a bit early in the build to be thinking about battery location but you may remember the battery is 'moveable ballast' in this design. The CAD model (and experience from Mk1) says that the battery needs to go right up under the cockpit. Now is the time to build (and waterproof) that area - while I can still get to it!

My biggest dilemma is what colour curtains to put over the opening.  {-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 04, 2015, 01:51:20 PM
I'm feeling like the cat with two tails at the moment. One of the tricky shapes to build on this model is the convex cut-away from the transom running forward. In geometric terms, there is a constant radius swept along a curve that lies at an angle to the centreline. (How many times did you read that?  {-)). Whatever. This bit gave me some jip on Mk1 and I didn't even try to do the 'double curve' shape.

I made a former from a lump of 3x2. I started by cutting the big curve then formed the radius on one edge. If you have a router with a 21mm rounding bit that would work fine but I don't. I set to with my trusty, new spoke shave (4 quid from Toolstation!). I have to tell you that making that former was a complete joy. I love using a spoke shave! Next, I soaked a piece of lite ply, bound it to the former with bandages and clamped a hefty lump of timber on for good measure. I left it for a couple of days. I decided to use ply rather than balsa because it's quite a tight radius and a pre-feel suggested that balsa would probably split. I was pleased when I removed the dressings to day. The form had taken well. Even more impressed when, after the required trimming, it fitted! That's where the weird shape of the floor comes from.  The waviness in the free edge is not a problem. That will pull into place easily when the side skin and deck are added.

So today I cut the opposite radius on the former and have soaked (dishwashed) and bound another piece of ply for the other side. Hope this one goes as well, otherwise I may end up feeling like the cat with no .......

Oh, forgot to mention. I've switched from Gorilla glue to Resin W for most bits now. I think it will be tougher, dries quicker and is less messy on the hands.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 04, 2015, 02:08:10 PM
The cowl.
I found the best way to sand this was to take a long band of sand paper (I always buy mine on the roll) and wrap it around the cowl, sanding across the grain. I worked away until I had removed most of the 'revealer' coat of emulsion, then touched in with filler and finished it off. I did find one area that went paper thin so I filled it from the inside with some two-part filler. That worked well. I'll remove the excess later.

I have now applied the 0.6 oz glass cloth using easycote fuel proofer. Worked a treat! Thanks, Ramon. One more coat of resin I think then cut back ready to prime.

The next job on this bit will be to  cut the air intakes, remove the cowl from the stick, attach it to the hull and finally split it. Carefully!

And with respect to the rudder, Lookit the dust on that!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 04, 2015, 02:12:57 PM
I forgot...........

I tried an experiment adding panel lines to a scarp of balsa before applying glass cloth. I tried scribing the lines with a ballpoint, a pencil, a scalpel and sandpaper. None of it worked. The glass cloth obliterated my efforts.

Any suggestions on how to add some panel lines after the glass?
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on August 04, 2015, 11:16:20 PM
Tim - I realise you did it before glassing but personally I wouldn't consider trying making panel lines into the glass covered surface using any kind of scribing method - I fear this would create stress lines and affect the strength of glass at that point (and consequently effect the wood beneath).

This may be of use ........

The recognised method panel lines were/are created on control line aerobatic models was to draw them on using a drafting pen. The paint surface is matted down using 1000-1200 grit wet and dry, the panel lines drawn using masks/tape as guides then the whole coated with fuel proofer - works very well indeed. It's difficult to get consistent adhesion on a gloss surface hence the need to matt it down first - Another visit to a control line site should help -http://stunthanger.com/smf/index.php?topic=25024.0 (http://stunthanger.com/smf/index.php?topic=25024.0)

Hope that helps

Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: JimG on August 05, 2015, 12:59:49 PM
A standard method used on aircraft is to use 1/64 inch wide chart tape. After the first coat of primer has been smoothed down the panel lines are added using the tape. It is then resprayed with primer , after sanding the tapes can be removed leaving the lines. You need to make sure that you don't overdo the top coat or it will fill in the panel lines.

Jim
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 05, 2015, 01:14:58 PM
Thanks for the advice on panel lines, Ramon and Jim. I get the point about not cutting into the glass cloth. Should've thought about that!

The idea of selective masking looks feasible. I'll give that a try on some scrap and see how I get on. I hope to be using an airbrush/tiny spray gun for the top coat. My daughter gave me the kit over a year ago and I haven't used it yet. I have run up the compressor - nice! Something else to learn.

More progress today, will post later when I have a bunch of updates.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 06, 2015, 03:24:42 PM
More glue drying so time to post the progress.

I hacked out the air intakes using a dremel sanding drum. The edge is nice and thin but quickly tapers out to about 1/4" thick for strength (I put the blocks in before skinning the cowl if you remember). Looks really cool, or at least it will do when I finish smoothing. I'm going to close off the opening at the first remaining frame. Although the main hatch should be watertight (interesting - just upgraded to Windows 10 and now the smileys don't work...) I'm not going to push my luck by deliberately flooding the inside of the cowl. There is more work to do on the back end, once I decide how to model the engine.

The cowl is pretty much split now ready to attach the lower part to the hull. Wonderful thing this CAD. It fits!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 06, 2015, 03:36:14 PM
The port deck has been attached and while I was waiting (again) I made the new cockpit canopy. I posted about the method elsewhere but it's very simple. I have the vac-form plug that I made fifteen years ago for Mk1. I modified the shape slightly and stuffed it, along with a tapered packer - the end of the now-redundant building stick, inside an empty coke bottle (PET plastic). Carefully heat it up with a heat gun, starting from the packer side, and the whole lot tries to shrink back to the shape of the original parison the bottle was made from. Really simple and ultra cheap! I reckon you could make a lot more bits and pieces this way. Just need to ensure the label residue is on the waste side of the former. Cut it off the former with a razor saw and there you go. (This is actually much thicker than the PC version I had made 'properly' by vac forming so it's more robust.

At the moment, the port side skin is clamped in place with the glue drying. That will take overnight, I think, because I have some serious trimming to do in situ. Don't want to rush and have the whole lot fly off in my face.

Oh yes, I ordered some tape for the panel lines. I could only find 1.5 and 0.5 mm (in the UK). I will experiment and work out how I will do it.
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on August 06, 2015, 04:07:55 PM
Nice work on the canopy Tim - It's quite amazing how well it shrinks around the form isn't it - made quite a few aircraft canopies that way too - I can remember getting some funny looks in the local supermarket when I was scrutinising different coloured bottles for their suitability - contents immaterial!

I haven't seen anything smaller than 1/32" in the past and I think that was for masking printed circuit boards but try 'Jammy Dog' micro masking tapes - they do a range from .5 mm onwards. I haven't used Jim's method on larger models though have done something similar on plastic models and would agree it is certainly feasible way to achieve what you are after - what I would add is you might be better using a white primer rather than the standard grey. White tends to have a higher build which would give you higher definition - as Jim says it's easy to lose it when sanding  %)

Regards for now - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 06, 2015, 06:14:13 PM
Funny you should say that Ramon. The tape is on its way from Jammydog and the only primer I could find in the local hardware shop was.............White!

Who's building this model??

Got the other scalloped skin fitted this afternoon. Stb deck and outer skin tomorrow, maybe. Then we will have something that resembles a boat rather than a pile of G clamps.
Title: Re: Donald Campbell's Bluebird K7
Post by: JimG on August 06, 2015, 09:46:14 PM
A source for the 1/64 Chartpac tapes is Fighteraces http://www.fighteraces.co.uk/products/finishing-materials/ (http://www.fighteraces.co.uk/products/finishing-materials/).

Jim
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 07, 2015, 04:11:50 PM
There's a pattern developing here - glue, clamp, post.

The cat has still got two tails and all of his....... The port side deck and skin went on well and I have cut back to the scallop. Still a little more sanding to do as the glue line is really hard and the shape is difficult to work on. The stb scallop went on easier (I used a slightly smaller radius on the former to allow for spring back so there was less fighting to get it into place. Inside the scallops has been waterproofed (wood hardener - not too much). I had been toying with adding foam (polystyrene or polyethylene) in the closed boxes but decided to risk it without. I've got eight or ten closed chambers inside the structure. What are the chances of breaching too many at once? (Titanic springs to mind but at least these chambers are sealed all round, no bulkheads to overflow). Let's just hope I never find out.

Right now, the stb deck is glued up. When that's dry I can trim up and add the sbd skin. Turns out I didn't over order on the wood. I still have two sponsons to make and it's touch and go whether I will have enough ply. Not to worry, I have plenty of balsa sheet left. Strange; I haven't wasted much but the boat itself doesn't seem anywhere near as heavy as four sheets of ply. I'll find out tomorrow when I weigh it.

Thanks for the info on tapes, Jim. The 1.5 and 0.5 mm tapes arrived today. I'll try those first.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 07, 2015, 04:47:29 PM
Something else turned up today...........

And I got caught. Mrs M was not working this morning and she accepted the parcel. Fortunately, she had decided to try out the sewing machine I bought for her a couple of weeks ago so she couldn't be too cross. I think she may even be starting to discover the joy of creating things!

I had been umming and aahing for weeks on this one, waiting for it to come into stock in the UK. I started doing the maths and it actually wasn't any more expensive to get it from Hong Kong, just that there could be a six week delivery. My finger slipped and I ordered it. Eight days ago!!

Nine channels for a boat????

The rationale is this. I have been using my trusty JR 35MHz 6 channel set for 35 years or more. A lovely piece of kit that still looks like new (cue nostalgic photo). The receiver has survived several aircraft (crashes), hovercraft (that didn't hover very well) and boats. It even recovered from a recent dousing in Mk1. I know I shouldn't be using 35 MHz for a boat (though there are no model aircraft around here) but the clincher is the antenna. Three feet of wire poking out of the top of a K7 looks ........ naff. It was time to get with it and go for 2.4 GHz. I was toying with the 6 channel version (that Martin has for his BAT land yacht) but I didn't like the plastic handle (call me Mr Fussy!). Plus, this one is described as 'full range' as opposed to 'Park Flyer'. I have to say that the pictures on the Hobbyking website don't do it justice; it's really rather nice! My next mega-project is the SRN2 hovercraft. That will need at least 5 channels and mixers. The old set will be permanently consigned to my sailing boat, where the antenna doesn't show!

It's amazing how the prices have changed over the years. The JR cost me around £150 pounds (a couple of weeks wages). This new one was about £50; less than the weekly food shop. Now all I have to do is learn to drive it (Chinglish online manual).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 09, 2015, 01:32:18 PM
Not much to post today as we are making the most of the weather together.

This is the first time the hull and cowl have met. The cowl has not been trimmed yet but considering the parts were built completely independently and they are BIG I am very pleased with the fit. The back is kicked up a little because the deck is cambered but the stringer on the cowl is horizontal. When things are trimmed back, I think I will have a very good fit. To be honest, I could live with what I have now but I can see how to get it right.

I shouldn't be surprised. The parts were generated from the same CAD model so all I had to do was cut them to the drawing; they 'could not' be wrong. Nevertheless, when you look at the combination of curves and cambers it's impressive. I would have struggled to do that with a pencil!

For the record (for me as much as anything) the weights so far are:
Bare hull = 555 g
Bare Cowl  = 263 g
(Total) = 818 g

I can't remember the weight of the hardware (I did log it somewhere but I've lost it) but I recall about 1 kg for the motor and battery. If I estimate another 500 g for the sponsons I'm well on track for a significant weight reduction on Mk1 (over 3.5 kg all-up); predicted is about 2 1/2 kg. She'll FLY!
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 13, 2015, 02:05:29 AM
I've had a quick look, and can find no comment, but forgive me if this has been mentioned. Scale speed, your calculation at Design Philosophy stage is incorrect. You mention you'd welcome correction.  To achieve a scale speed of 300 mph an 1/8th scale model would have to travel at around 106mph.  Your 37.5mph model speed would yield a scale speed of a little over 98 mph.

If you've got this T shirt no problem, I'll get my coat  ok2
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 13, 2015, 12:00:15 PM
Hi Jerry,
You have my interest! I don't really know how to calculate scale speed for a model. I worked on the premise that the model should cover 1/8 of the distance the real boat covered in the same time. Of course, that isn't correct in terms of the hydrodynamic forces. I remember doing dimensional analysis at tech college but it was so long ago that the example we used was Noah's ark. I would really appreciate it if you could explain where your figure comes from. I'm here to learn! (I'm sure others will be equally interested).
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 13, 2015, 02:16:18 PM
The scale speed is derived by multiplying the actual speed by the square root of the scale factor.

Now I did the calcs in my head before but here it is properly

I.E. at 1/8 scale
Square root of 8 = 2.828427124
At an actual speed of 37.5 mph ◊ 2.828427124 = 106.0660171 mph scale speed


I'm not knowledgeable enough to be able to explain the meat behind the formula, all I can say is that I believe it comes from models used by development engineers in wind tunnel and tank tests. My attention came to it when I started thinking about the margins of some speeds, where some of the numbers just don't look right using the simple scale approach.

For example, if a little tenth scale speedboat wanted to do a scale speed of 100 mph then it would only be doing an actual 10 mph, and in my mind watching a boat at a trotting speed is not representative of 100 mph in scale. So that was why I looked into it really, and when you apply the formula the perception of a models speed as a small rendition of reality when watching models it all fits.

So, if you need to know a target model speed to reproduce a scale speed the formula changes to scale speed divided by the square root of scale factor.

I.E. at 1/8 scale,
Square root of 8 = 2.828427124
A target scale speed of 300 mph ų 2.82847124 = 106.0660171 mph actual speed

So it turns out that the scale speed of your estimated figure is the actual speed needed to get the target scale speed of 300. That pans out in all examples.

Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 13, 2015, 04:57:11 PM
Glue, clamp, post.........

What's holding me back today is that I have run out of clamps! I have built up the sponsons; one of them has the outer skin fitted (clamped!) and the other is waiting. I built them as a pair; it's more important that they are the same as opposed to dead accurate. I've used polyethylene foam as reserve buoyancy (having seem first hand what happens if you get water in the sponsons and they are the most vulnerable part of the model  - when I'm driving, that is). It's nice because it cuts very easily and doesn't crumble like polystyrene. Plus it's what I had to hand.

I had thought of using the bandaged-ply method to make the top deck of the sponsons but I chickened out. It's a very tight radius with little margin for error (I need lots of margin for error!). Plus it's a slow, difficult technique. Oh, and I've run out of ply!! I opted to use block balsa for the curvy bits. Looks like I have added a lot of weight but in reality most of it gets carved away later.

I have also attached the cowl to the hull. I got the join within a couple of mm all round. I was going to go further for my own satisfaction but stopped myself as there was a good chance I would ruin a pretty good job. Photos to follow when the duct tape comes off.

Thanks for the info on scaling speeds, Jerry. What you've described is dynamic scaling and that I do understand (or did!). That gets the hydrodynamic (or aerodynamic - same thing, different fluid) forces right, which is why you rightly say it's used for wind tunnel and test tank models. I spent many happy (and scary) hours running serious model hovercraft and ships down test tanks as an apprentice. Sitting on the carriage at about 30 mph indoors and wondering if the automatic brakes were going to work today called for the right coloured trousers. I guess the best scale for a model is what looks right! To me, most models look a bit too fast and twitchy (because time is not scaled). Just my opinion. Tell you what though - my K7 will NOT be doing 100 mph! On my local lake I reckon that would give me about a  five second run (OK, maybe ten by the time it gets up to speed and, hopefully, slows down again). What I would like to figure out is how to get it to kick up some impressive rooster tails from the prop and sponsons. I'm even contemplating adding some tiny 'scoops'. Anybody got any ideas?

Answers Please.............
Rudders. On Mk 1 I put the rudder right behind the prop. It seemed to work well (too well??) and looked OK. I know many people fit the rudder alongside the prop. I could do that too with more or less the same hardware. Given that K7 is intended to go in a straight line only (apart from lining up), is there a clear best choice? (I'm expecting two different schools of thought here).

Decals. I've made my own decals in the past for craft projects. I looked online (Crafty Computer Papers) and I now have three choices. Inkjet decals, that have to be waterproofed after they are fitted, laserjet decals that are inherently waterproof, or 'rub down' transfer decals. I think the inkjet option is out because I don't want patches of varnish. Laserjet would be OK as we have the right printers at work. I rather fancy the rub-down option. Anybody had experience of those?

Finally, Paint. I was kindly informed of the correct colour (Mercedes Himmelblau). Now, I want to use an acrylic rather than a solvent based paint (fumes, clean up, you name it....) and I'm going to attempt to use an airbrush. Anybody recommend a product/colour that is similar enough and readily available?

Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 13, 2015, 05:34:02 PM
Scoops work well to create rooster tails. Racing airboats have them to stop flipping when the engines are throttled off quickly, the high thrust line of the aero engines forces the bow down normally, remove that and troubles can ensue. We fitted an active brake to my lad's airboat, here it is deployed:

(http://i706.photobucket.com/albums/ww65/jes437/Img_5150.jpg)

It slows the boat a little and undermines the steering, but you'd only need little ones to create a nice effect I would think. I'll dig up images of the device itself if its of use to you.


I agree with your approach to speed for this project entirely. It does make you appreciate the speed of these original machines I must say, it must have been an amazing spectacle to witness.
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 13, 2015, 06:16:16 PM
Just remembered this video, within it is the airboat above with brake on and off showing:

https://youtu.be/IhgnAs8RnKw


Rudders immediately behind surface piercing props give lots of effect at high speeds and less at lower speeds simply because of the thrust directing/cavitation thing. So a surface prop needs to start being on song before the rudder has must water pressure to direct, when suddenlybit has a lot. So either low throw with limited low speed ability, which is firmly what one of my boats has but is fine to live with, exponential settings on the radio gear, or mixing between throttle and steering. Different throttle settings also create changing steering trim. Frankly I find sound control overcomes the disadvantages for sports use, racers would have a very different perspective.

For smoother, more speed proportional, and for less drag an offset rudder is the way to go. Less affected by  planing height, clear of propwash and placed on the stbd side is the best match for prop torsion issues meaning right turns are best, in most cases. As the Bluebird K7 was about locked in straightline ability I think this is the option I'd be looking at. In essence this boat is a 'Rigger', so what those guys are doing may help with ideas perhaps.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 13, 2015, 08:47:28 PM
That's the fella, Jerry! I'm thinking perhaps some tiny 'winglets' on the front fins. Something to think about. You get just the 'foamy' effect I'm looking for (even though your purpose is quite different).

Regards the rudder, I intend to offset the prop about 15-20 mm stb (as per Mk1). That would put the rudder way off centre but as the bracket will attach to the strut, it's possible. I tried dual rate on Mk1, which tamed the over steer. Throttle rudder mixing? Mmm...........well, I have that new fancy radio now. Perhaps I will have a go at that! I knew there was a reason for buying it.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 14, 2015, 03:56:26 PM
Just for a change, I'm not waiting for anything to dry (except, perhaps, the weather; it's grim!). I have just come to a natural pause.


Yesterday, I attached the cowl to the hull. Today, I detached it. No, I don't mean I messed it up; I cut along the split line and lifted the top half away. What d'you know? It worked! Just look at all that lovely space I have to work in! Later, after I have tidied up and arranged the running gear, I will add a couple of frames to stiffen the open section and then the inner deck and hatch. (I have a cunning plan for that hatch - I'll tell you if it works  {-)  ) (Oh good, got the smileys back. they don't work in Microsoft 'Edge')


The sponsons have been rough sanded to shape. I'm very pleased with the way they turned out.


I weighed everything today:
Bluebird K7 Weights 14-08-2015 (g)
Hull and Cowl                                       835
Sponsons (2)                                      345
Motor                                                   475
Battery                                                 380
Speed Controller                                  135
Booms                                                  125
Rudder                                                 50 - 110 (depending on what bracketry I use)
Servo                                                    45
Prop and flex                                        50
'All up' (everything piled on the scales)      2361
That motor is a real lump! OK, there are still a few bits to add, some wood to take off and the finish to apply but the current weight at 2.4 kg is huge reduction from Mk1 at over 3.5 kg. Bodes well for easy running.
The past couple of weeks have been intensive on the build, to put it mildly. Now I need to slow down - way down. The build so far has gone better than I could have hoped for and I  have the foundations of a half-decent model - or a heap of junk. Now it's down to attention to detail and careful finishing (never my strong point). I'm not going true 'scale' - though the basic shape is pretty accurate - just aiming for a model that 'captures' the real thing. My interest is firmly in design and build rather than running so now it's time to get my money's worth out of the materials. I think it will keep me entertained for quite some time. I will still post the progress but it won't at the same pace. I'm sure you will forgive me!
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 15, 2015, 04:08:52 PM
The scale speed is derived by multiplying the actual speed by the square root of the scale factor.

Now I did the calcs in my head before but here it is properly

I.E. at 1/8 scale
Square root of 8 = 2.828427124
At an actual speed of 37.5 mph ◊ 2.828427124 = 106.0660171 mph scale speed


I'm not knowledgeable enough to be able to explain the meat behind the formula, all I can say is that I believe it comes from models used by development engineers in wind tunnel and tank tests. My attention came to it when I started thinking about the margins of some speeds, where some of the numbers just don't look right using the simple scale approach.

For example, if a little tenth scale speedboat wanted to do a scale speed of 100 mph then it would only be doing an actual 10 mph, and in my mind watching a boat at a trotting speed is not representative of 100 mph in scale. So that was why I looked into it really, and when you apply the formula the perception of a models speed as a small rendition of reality when watching models it all fits.

So, if you need to know a target model speed to reproduce a scale speed the formula changes to scale speed divided by the square root of scale factor.

I.E. at 1/8 scale,
Square root of 8 = 2.828427124
A target scale speed of 300 mph ų 2.82847124 = 106.0660171 mph actual speed

So it turns out that the scale speed of your estimated figure is the actual speed needed to get the target scale speed of 300. That pans out in all examples.

Firstly to Tim,
What a great job of building your K7, top marks.

Jerry,
Thanks for to the speed conversion formula.

My K7 at 1/12 scale does approx 40 m.p.h. but to get a true scale speed it would need to be 86.7 m.p.h. which is mind blowing.

Earlier in Tims thread I said that I get about a 7 sec run from one end of my club lake to the other at 40 m.p.h..

Last year in the summer on a very flat calm day I had my K7 at Loch Lomond  and I was able to send it 100 yds to my right and  100 yards to my left.
I had Mrs T  with the camera but unfortunately she finds it hard to shut one eye and focus thro' the lens of the camera with the other, hence the pic enclosed doesn't show K7 flat out.

What actualy happened was that as I openned full throttle K7 took off ( literaly ) as it wound up speed with the amount of run that it had, just as it was level with me it took off just like D.C.'s K7, as it's a prop drive the torque of the prop started to turn it over to starboard and I was quick enough to snap the throttle shut and it flopped down on the starboard sponson which saved me a swim in a very cold loch.

I have a book by Neil Sheppard ( DONALD CAMPBELL AND THE FINAL RECORD ATTEMPT ) which does a very technical study by him and a Dr Kieth Mitchell with so many titles and P.H.D's to his name I will leave out and although a medical man his pastimes are the areodynamics and design of large R.C models and Hydroplanes in particular D.C.s Bluebird K7.

After much study of the last attempt he concludes that at 320 m.p.h. K7 was actually flying and shows some pics of K7 riding on it's stabilising fins and the hull is above the water with only the rear wedge touching and with the long held thought that as the engine cut out and  there was no thrust to keep it level the stern dropped down , wind underneath and K7 took of with the resulting disaster and at the speed it was travelling at was way out of it's design criteria.

I seam to have let myself get carried away a bit hear but  if you look at the video link with my K7 you can see as it comes at you she is clearly riding on the edges of the sponsons and the prop C/Line and well out of the water and is producing quite a Rooster tail.

I don't think that we should be aiming for a scale speed as you rightly say that Tims K7 would need to acheive 106 + m.p.h. to get up to full size speed.and the spray from the prop will create a rooster tale not unlike the Jet powered K7 of D.C. and Ernie Lazenby's Turbine powered K7 ,  can't say that I approve of a brake to create a spray as it will only take more power to get it up on the plane.

Hope that this is of interest and the book is well worth the cost to any Bluebird K7 fan and what ever you do Tim don't try to turn your K7 at speed, it just will not do it, I have the TEE shirt to proove it.

George.

Pic at Loch Lomond and link to you-tube.

https://www.youtube.com/watch?v=fGPMBKTA1Wo (https://www.youtube.com/watch?v=fGPMBKTA1Wo)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 15, 2015, 06:14:50 PM
Hello George! I was concerned by your silence. All is well, it seems  :}




HELP!
I decided to take a break from building and check out the new radio (just in case it was faulty).
After a LOT of searching and direct contact with Hobby King I managed to get a sort of manual, but it only goes so far. With a lot of bleeping (literally and metaphorically) I have managed to enter the model name and set it up as a basic aircraft (sorry George). I could not get any response from the motor but eventually realised that the throttle is at zero in the mid position. Surely that's not right? Aircraft don't go back'ards, do they (except the ones I tried to fly)? I then managed to stop that 'model' working completely again by messing about with the throttle end points, so I'm using another memory.


Long and short of it is I could REALLY use some guidance on setting up the radio. It's a Turnigy 9x. (OK, I should have known better and bought an expensive one). Anybody got any experience of this model? I guess any programmable radio would work in the same way....


What makes me a bit cross is that anything that carries the CE mark has to be provided with instructions in the language of the country it's sold in by law.  >>:-( Seems Hobby King know different.
Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on August 15, 2015, 06:23:18 PM
Hello George! I was concerned by your silence. All is well, it seems  :}




HELP!
I decided to take a break from building and check out the new radio (just in case it was faulty).
After a LOT of searching and direct contact with Hobby King I managed to get a sort of manual, but it only goes so far. With a lot of bleeping (literally and metaphorically) I have managed to enter the model name and set it up as a basic aircraft (sorry George). I could not get any response from the motor but eventually realised that the throttle is at zero in the mid position. Surely that's not right? Aircraft don't go back'ards, do they (except the ones I tried to fly)? I then managed to stop that 'model' working completely again by messing about with the throttle end points, so I'm using another memory.


Long and short of it is I could REALLY use some guidance on setting up the radio. It's a Turnigy 9x. (OK, I should have known better and bought an expensive one). Anybody got any experience of this model? I guess any programmable radio would work in the same way....


What makes me a bit cross is that anything that carries the CE mark has to be provided with instructions in the language of the country it's sold in by law.  >>:-( Seems Hobby King know different.

Hi Tim,
Yes alls well at present with the exception of the arthritise in my neck which gives me quite a bit of greif with shoulder pains and head aches, this is all a back lash from my early years as a design draughtsman , in those days it was a flat board on wedges and a small stool to let you get to the top.

I have been following your build and I do admire your enthusism in the wood work and the Computer drawings of K7, I have found no reason to comment other than well done , I hope that when you get her out on the water I may be of more use then.

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: black magic racing on August 15, 2015, 07:02:24 PM
Hello George! I was concerned by your silence. All is well, it seems  :}




HELP!
I decided to take a break from building and check out the new radio (just in case it was faulty).
After a LOT of searching and direct contact with Hobby King I managed to get a sort of manual, but it only goes so far. With a lot of bleeping (literally and metaphorically) I have managed to enter the model name and set it up as a basic aircraft (sorry George). I could not get any response from the motor but eventually realised that the throttle is at zero in the mid position. Surely that's not right? Aircraft don't go back'ards, do they (except the ones I tried to fly)? I then managed to stop that 'model' working completely again by messing about with the throttle end points, so I'm using another memory.


Long and short of it is I could REALLY use some guidance on setting up the radio. It's a Turnigy 9x. (OK, I should have known better and bought an expensive one). Anybody got any experience of this model? I guess any programmable radio would work in the same way....


What makes me a bit cross is that anything that carries the CE mark has to be provided with instructions in the language of the country it's sold in by law.  >>:-( Seems Hobby King know different.
http://static1.squarespace.com/static/51e8d916e4b0aabd69a1d776/t/545baa9ae4b0a69b3b66e12d/1415293621723/TH-9X+Manual.pdf (http://static1.squarespace.com/static/51e8d916e4b0aabd69a1d776/t/545baa9ae4b0a69b3b66e12d/1415293621723/TH-9X+Manual.pdf)
hope this helps?
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 15, 2015, 09:18:05 PM
Thanks for that Mr Magic! I've seen that one and HK sent me a link to another, slightly more understandable: http://www.hobbyking.com/hobbyking/store/uploads/529892926x11510x2.pdf

The issue I have is that I have always assumed that the throttle stick goes all the way down to stop, all the way up for flat out. My radio at the moment is only using half the travel, which means I have to put the stick in the middle to get neutral before the ESC will arm. It wasn't like that on my JR set. I have set the radio to Mode 2 so it should be right. It just isn't :(
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 17, 2015, 07:10:13 PM
I finally managed to get the throttle working as I want it to. Whilst the solution was simple, getting to it was not and I had to go to HK online chat to get the answers. I thought I would log the solution here for my benefit and  because others may have the same problem. Advice seems to spread virally on the net.
This applies the the Turnigy 9X v2 Tx and Rx ,, mode 2 and the Turnigy Aquastar 160.
There are two important things to understand first:
1) The Turnigy 9X 'Mode 2' transmitter is physically constructed as mode 2 (throttle stick on the left) but the firmware defaults to mode 1. When you start to set up a model, you need to go to the 'Stick Set' menu and select 'Mode 2'. Be careful; to select the setting you scroll down and then give a SHORT push on the 'menu' button. A long push (for good measure) does not save the setting! (One nice feature of the radio is that you can go to a 'display' screen and check which stick is doing what).
2) The Aquastar 160 cannot be recalibrated. It automatically adjusts to maximum throttle but the neutral point cannot be adjusted.
If you want forward and reverse, then you are good to go but I want forward only, full stick travel.
After a lot of playing around, it turns out the set up is simple.  Set the ESC to 'Forward Only' Make sure the Tx really is set up in Mode 2. Adjust the throttle stick trim to full up. Adjust the throttle sub trim to maximum positive. Leave the end point settings alone. Done.  The ESC will arm with the stick fully down and the motor will start to spin just about as soon as you move the stick up (i.e.  you have the full stick movement available)
Sorry if this is **** obvious. It wasn't to me and, judging by the number of internet posts on the subject, it isn't obvious to others either. The procedure is different, by the way, if you have an ESC that does get calibrated for a new set-up. You just need to be sure the Tx is really in mode 2 then follow the instructions for your ESC.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 22, 2015, 07:01:14 PM
Lots of interesting things have turned up this week including a new servo, more glass cloth, resin and fittings and new collets for my Dremel (hint: do not put a broken off needle file in a Dremel to open up small holes  :embarrassed: ). But nothing quite as exciting as the beauty in the pictures below.


Those who have been following the thread will know that one of my pet obsessions (I have many) is thrust washers/bearings. The only way I know to ensure a thrust washer is actually working is to allow longitudinal float in the drive train; a sliding coupling or a sliding motor mount. Back around Christmas I posted the design of a sliding motor mount as an improvement on my previous efforts. A fellow Mayhemer, who wishes to be known as Mr Nonny Mouse, on account of he would be inundated with requests, volunteered to make the mount for me.


The result is quite something. You can see the quality of the machining, sure, but what you can't see is the level of craftsmanship that went into making this. The mount slides backwards and forwards as smooth as silk and there is absolutely so sideways play. That's going above and beyond just working to the drawing.


Needless to say, I am extremely grateful to my distant friend. You meet the nicest people on here.  :}
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 22, 2015, 07:27:30 PM
There has been quite a lot of progress on the build this week, little by little. I'm still sanding to shape but things are getting close to the point where I start sanding for finish.


Most importantly, I've done a dry fit of the hardware and I would welcome any input before I start making brackets and stuff.


I've got two choices; offset rudder or in-line (right behind the prop). As the prop is offset about 15 mm starboard (I need to check the number from Mk 1), I'm planning to offset the rudder to port. It fits quite well there. I can't offset to stb (conventional) because there isn't enough room. Bearing in mind K7 is only intended to go in a straight line (apart from low speed lining up) I'm going to go with this unless somebody tells me it will be a disaster.


Yes, the motor mount goes this way up! I want to get the motor close to the floor so I can have a straight driveline  with a bit of 'down' on the prop. If I put the mount the other way up, the angle on the shaft is too much. The ESC and receiver will also be mounted high up just in case of any leaks (what leaks??). Plan A is that the ESC and Rx will be on a hinged panel so they swing up out of the way to get at the battery, which is way up front. Hard to tell at the moment but I may be able to put the ESC alongside the motor instead - it depends how the wires behave when the motor is bolted in - then I won't need the hinged panel.


My thoughts:
1) OK, I agree the prop is a tad high  {-)
2) That rudder is HUGE. I've already cut it down as much as I can below the water pick ups. I think I will probably cut it off a bit more  re-drill the pick up holes from the front and plug as required (The water channels cross, of course, just to make it more difficult. I think if I drill at a slight angle I can get the pick ups to break out a bit further back from the edge too then make the rudder narrower.
3) The rudder isn't really in line with the prop. Will that matter for straight line running? If it needs to go further back, I will abandon part of the 2-piece bracket and make a new one. (At this rate there won't be much left of the rudder apart from the nipples and the pivot - but that's what I bought it for!)
4) I'm using a 3 mm carbon fibre push rod, only because it was cheaper to buy a set that to buy a steel rod and the fittings separately. I was quite shocked when I saw the size of the servo but it is higher torque (4 kg.cm - stupid unit!!) and faster than the old JR one I used in Mk 1. Metal gears and digital too.


OK chaps, put me right before I start hacking out holes. :-)) 


(Sorry about the quality of the photos - they're only for technical. Sorry about the feet too. They're mine, as is, unfortunately, the belly.)
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 23, 2015, 01:14:52 AM
Forgive me if I've missed things but I'll continue from an assumed position. A lot of this sounds dramatic, but I'm cutting to the chase here.


Your radio gear should ideally be protected enough to permit complete submersion of the boat. Placing it high feels right but not if the boat ends up upside down. I guess it's normal practice for displacement type models to have open gear but in my view that should be limited to displacement hulls, anything fully planing can, and probably will at some point, end up inverted. Generally a waterproof radio box will be less than half the price of a basic receiver, as much as a budget servo, and a quarter of a sound quality ESC, no contest for me. For interest the last two models I've made, and continuing forward on the results I'm getting, used waterproof servos, so the the radio box is tiny, and it's easier to seal a servo cable than a pushrod through the box.



If you're aiming for surface piercing prop drive the usual starting point is the bottom of the strut level with the bottom of the hull. If that's the intended prop it's a 'Cleaver' style which will have lots of lift, you could have an unstable back end if you run it submerged, and it'll cavitate for a pastime if running at decent RPM, if not it'll be because of the motor being pulled down, which will kill it in time if it's the right size for the motor.
If you plan to used a rigid shaft then a 'Stinger' drive may be better.


Leave your rudder as it is, it may be long but the chord on race rudders is small. Fitting the rudder to Stbd is all very well, but on a three point hydro it's less important than a mono, the boat should turn flat so the thing about keeping the rudder in the water is academic. With it to Port the wash off will compress the water a little on that side of the prop, but again immaterial as this boat will only be turning at low speed to setup for a straight run right? So it's not an issue in my view. The primary reason rudders are run to Stbd is that the boats race on right hand turn circuits, a product of the direction of rotation of the engines, which being derived from aero engines back in the day means that they are backwards facing and run contrary to the real world where most courses need left turns, for the same reason of dealing with prop torque reaction trying to rotate the boat.


Your carbon rod should be OK, it's an unbalanced rudder as far as I can tell so turning forces will be higher than a balanced or partially balanced one, but so long as your rod ends are secure to the CF it will be fine, I use them on boats with 10cc engines no problem, at least with partially balanced rudders. Here's one on one of my home made rudders.The CF rod is epoxied into a threaded ferrule for connecting to the rod end, I put heatshrink over it to colour it.


(http://i706.photobucket.com/albums/ww65/jes437/2014-05-21223545sm.jpg)





Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 23, 2015, 01:54:00 AM
By the way, again this may have been covered, but are you aware that flexible shafts shorten under load? Your motor mount is lovely, a good idea, but it would be wise to bias the relaxed motor position forward to ensure there's room for the shortening. A very rough guide for a 1/4" shaft in a boat of your size is that the shaft will shorten 1/4" under full load.


Just in case  :-)
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 23, 2015, 08:07:47 AM
Hi Jerry,
thank you very much for taking the time with your detailed reply. First thing that's not clear from yesterday's post is that all the hardware will, in fact, be enclosed under a waterproof hatch. There are some more frames and decking to go in once the hardware is positioned so that all the mechanics will be sealed off. The upper hull (cowling) is purely decorative on this model. I will be adding another waterproof box for the receiver too. Been there, done that, got wet legs.  :-))


Prop height is something that has given me concern but what I ended up doing on my previous build, under guidance, was to set it about 35 mm from the bottom of the boat (same height as the forward planing shoe edges). The original K7 had a planing wedge on the stern. Under advice, I took that off and the stern lifted nicely. The back end of the boat is completely out of the water once it gets going. By the way, the CG on this model is a long way forward, perhaps more than conventional. It seemed to work on my Mk 1 so that is my starting point for this model. (I'm not after high speed, strange though it might sound. I want the model to get up onto three points and look right at a moderate speed - something I can control and get more than a couple of seconds run on a 200 m lake (with ducks. Lots of ducks.))


I looked at the photos of the rudder again last night. I'm reassured that you agree it can stay on the port side and that it really isn't much too big. Yes it's a single sided horn; that's how it came. And yes, it will increase the load on the servo (but not the torque). Have to make sure I have a decent bracket! I have a cunning plan for sealing the push rod - keep watching. {-)


The main reason for the sliding motor mount is to cater for shaft wind-up. I've got about 10 mm free float in there. The thrust washer will touch  - in other words it will BE a thrust washer - but the shaft will never go into tension. Only wish I could make something like that myself! (By the way, that's a pretty serious boat in your photo! Awesome!)


All your comments have been taken on board. It's reassuring to know that most of them are already built in to the build plan! Many thanks again.
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on August 23, 2015, 10:05:05 AM
Ideal, you are clearly on top of things.

I guess you shaft will see a some tension every time you throttle off, recently I adopted a method many folk use to protect their props which has revealed to me how much tension there can be. A piece of silicone tubing is placed between the prop and the prop nut, the idea being that in an impact the prop can compress the tubing and disengage itself from the drive dogs, hence stop rotating during contact. Whilst first trying to set this up I found it surprising how much compression is needed on the tubing to stop unwanted disengagement, on throttle off the prop would release from the drive leaving me essentially in neutral, as the prop would not re-engage reliably. By the time the tubing was compressed enough to ensure this didn't happen I came to the conclusion that the prop would still be damaged so abandoned the idea. But, my point is that it revealed that the tension put on the shaft must be significant. The concept is used by racers anyway, where the odd climbing over someone elses boat occurs. I don't race, not least because of that reason,  so its not needed so much. I'm also not trying to protect £50 props  :-)

If your original boat and this one rides on the prop alone then all the more reason to leave the rudder length, prop walk becomes a bigger issue on a flying hull. On the K7 though I'm guessing that's not such an issue, it'll just show itself as neutral trim variation.  It's common for a race boat to show Port trim when trolling or running on idle, then to straighten up under full throttle (assuming the boats was trimmed at full speed) 'driving' the boat compensates for that, but a deep rudder naturally will assist.

You come across as an astute person, and if there's anything that will allow you to really open up opportunities in model making it's having access to a lathe and milling machine. I'm a model builder, some are model assemblers, I measure modelling achievement by the rewards folk get from the activity so the approach is not the issue for me, but I like to make as much as I can and I imagine a chap such as yourself would see great benefits from some small machines. Take a look in the Sports R&D section for my build of a dummy outboard that doesnt exist commercially, it may interest you.

Loving the desert camo shorts by the way  :-).
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 23, 2015, 06:11:12 PM
Hi Jerry,
Tension on throttle down. I'll confess I hadn't thought of that! Don't think it will cause a problem though. The motor mount has a limit to its travel and that should stop the shaft pulling out of the bearing. Might jump when I start going forward again though. Mmm, you learn something every day.

Machine tools. Ah yes, one day! I still remember my days as a boiler-suited apprentice, milling, turning, welding, filing. Ooh I hated filing! I've been following your outboard thread with interest. Lovely workmanship, good idea. Inspired by that I decided to renew my knackered buffing mop (I use it to polish the burners on the cooker after they've been cleaned). I was also inspired by Toolstation prices! For £4 you get 3 small wheels, an arbor and two polishing soaps! Not pro quality but they do the job. I've also decommissioned my bench grinder. Last time I turned it on it was clear that the wheels were well out of balance - it's been in my damp garage for years. Nothing like a burst grinding wheel to spoil your day. For another £3 I got a 6" buffing wheel. It fits the old grinder a treat so I will be getting another one and use them for coarse and fine soaps.

K7 is indeed a 'prop rider'. I've given some thought to the prop position after your comments. I won't try to explain what I'm doing here but it will all become clear when I get it built and take some photos.

BTW, the flip flops are also desert camo. Nicely coordinated........
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on August 31, 2015, 08:15:52 PM
Slow but steady...............


The hull is pretty much sanded to shape (not finish) and the last couple of weeks have been spent sorting out the 'mechanicals' of the model. There wasn't a lot of point in posting every little cut and fit along the way.


Drive
Rather than a fixed tube and skeg, I'm using a centreboard. I'm sure other people have done it before. I have two pins that fit the tube; one fits the motor collet and the other fits the strut. They're both a snug fit ('turned' up in the electric drill :-)) ). The lateral position of the motor and strut are fixed (15 mm off centre). When the time comes to put the drive in place (after painting, which is a huge benefit) I set the prop depth and motor height. The prop tube finds its own line to set the a angle and the motor bearers (already fitted to the motor mount) are glued it wherever they end up. The prop tube is sealed to the centreboard box with a formed-in-place silicone grommet (aka a blob of sealer) and the skeg gets locked into place with a single pinch bolt - not glued. I haven't fitted the top, back or front to the centreboard box yet so it's easier to see how it works. It's not intended for adjustment 'on the fly' but it makes setting up a doddle and if my predictions for prop position turn out wrong I can change it without major surgery. Moving the prop on Mk1 wrecked it![size=78%]


Steering
The push rod passes through an oval tube. I'm going to fit the bellows seal on the inside of the boat because I don't want to see it. Plan A was to use a finger from a rubber glove but I have ordered a 'large' bellows 'cos it looks better. If it doesn't fit then it's back to plan A. (Not quite as daft as it sounds; you get a really soft gaiter - in both directions - using a rubber glove finger. Just seems a bit crass). Yes, the servo is mounted inverted. That's just the way everything lines up.


The second oval tube is where the water pipes will run. They will be sealed in with silicone.


I took a look at the rudder bracket. It was totally out of proportion to the strut and very heavy. I set to with the drill and file and did some pretty drastic weight reduction; there was a lot of redundant material there. I got it down from 68 g to 35 g. Not much in the great scheme of things but worthwhile as the bracket is so for from the CG. There's still ample meat left on it. If it breaks I will be a) very surprised, b) hugely impressed with the strength of my transom  :-)) . I think I will probably finish the rudder and strut in matt black. I love the sight of all the brightly coloured shiny hardware hung on the back of a racer but it isn't supposed to be there on K7. I'd like it to be as discreet as possible.


Layout
Everything has a home now. The ESC will be hung from a hinged bracket so it swings out of the way to get the battery in and out. The bracket isn't shown in the photos but it is made. This gives a nice easy run to all the cables. The receiver will be getting its own waterproof box.


Remember, all of this lot will be protected by a waterproof hatch as well, which is the next item in the build. I think the reasons for what I've done will be a lot clearer once you see how that hatch fits :-))




 [/size]
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 06, 2015, 07:33:51 PM
Plodding along.


Steady progress this week but nothing very exciting to report I'm afraid. The problem is I use slow glue  {-) . I have two types of cyano (Gorilla and Zap a Gap) but I really don't like either of them. Useful for fixing small parts or tacking but I find the joints are just too brittle (probably because they are not very good joints). Resin W for me.


The nature of the build has changed tack a little. The early part of the build was rather like assembling a kit. OK, the parts weren't pre-cut but basically all I had to do was cut all the bits to the drawings and stick them together. I'm now very much into scratch building; sorting out all the details that aren't in the CAD model and working out how to do things as I go. Fun but slow.


This week I have concentrated on building the coaming and hatch (yawn....) - a vital part of this design. I made the coaming up around some tree wood formers and then wrapped the hatch sides around them so it all fits together pretty well. I'll share something that didn't work. There is a lip around the coaming and the hatch where they meet. My cunning plan was to stretch an elastic band around that lip so it would both hold the hatch on and form a good seal. Mmm............ It worked really well on the corners but not on the straight bits. I should have seen that one coming but foresight is never quite as clear as hindsight. I still think it would work very well on a circular hatch if you ever have the need.


After some thought, I decided to substitute some silicone tube for the elastic band, split along its length (fiddly to do). The tube is stuck to the underside (only) of the lip on the coaming - one time when cyano works really well. Plan B (given that plan A didn't work) is to put the hatch in place and then pull the tube round the lip using a little hook tool. I tried it on the bench and it worked well. Not sure how it will work in situ as there is not a lot of room round the coaming. If it's not practical then Plan C is to just put the hatch down on top of the tube and clip it in place. The slit tube gives a nice compliant seal. If all else fails, it's Plan D - tape it up like everybody else does  :-))  The coaming is now fitted to the hull but I want to tidy up a bit before I photograph it - and the glues not dry yet {-) [size=78%].[/size]

I've made the hinged bracket for the ESC and the rubber bellows has arrived. That just about fits the oval tube but it's a bit of a stretch. I may try to get some smaller conduit for the sake of neatness. All in all, I should be able to get the mechanics dry-fitted completely in the week.

[/size]I had a go with the airbrush today. Ooh, that's fun! I think even I can get a half decent paint finish with that; very controllable. I have a question though. I want to use water-based paint (partly because I don't want to use gallons of thinners cleaning out the airbrush). Hobbycraft do 'Crafters' brand acrylics; they are cheap and they also have just the right colour (I may need to mix two blues together) but the finish is matt. Anybody know of a water-based gloss that would work? Otherwise I guess I need to paint and then apply a water-based varnish afterwards. (I thought about using the Aerokote two-part resin I'm using for the glass cloth but I think that is pretty much a recipe for a ruined airbrush).

[/size]Don't worry, it will get more exciting. O0
Title: Re: Donald Campbell's Bluebird K7
Post by: Ramon on September 09, 2015, 06:05:46 PM
Hi Tim - Haven't looked in for a while but it's all looking very good indeed  :-))


A couple of things that may be of help. I have been using TiteBond 111 (as opposed to TiteBond and TiteBond 11) for some time now. Apart from the fact that it's totally waterproof the thing I like most about it is it's extremely quick grab time 20 -30 mins in a warmish environment - can't recommend it enough and no, no connection  ok2


Airbrushing - as someone who does a lot of it virtually on a daily basis at present a constant need to strip and clean the brush is a major part of use. Using any two pack or one pack varnish through it will not be a problem providing it's thin enough but be aware - when using two pack you really do not want to breath the fumes.


There are many acrylic paints suitable for airbrushing that you can use though may be the colour match might be a problem. Tamiya do a gloss aerosol spray with a reasonably close blue but that may not be near enough - check out Tamiya TS spray paint - but personally I would go the matt route then finish with a clear coat. There are some 'Floor Finishes' that make superb topcoats. The last I used on model aircraft was a two pack from a national paint company called Morrelli. If the airbrush is cleaned immediately after use with cellulose thinner you should have no problems - shooting cellulose thinner through the brush is not the same as cleaning it BTW  ok2


One thing to be aware of with using Acrylic colour coat is that if applied over a heavy-ish cellulose base coat eg sanding sealer there's a very good chance it will eventually craze like an old pottery glaze. I believe this is due to the cellulose always slowly moving whilst the acrylic being very hard and inflexible doesn't - definitely got the tee shirt on that disaster  %)


Hope that might be of use


Regards - Ramon
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 14, 2015, 06:26:38 PM
My Goodness! (family forum rule  :-)) ). That hatch gave me some jip. In the end I wasn't happy with the external seal so I ripped it all off. I now have an internal ledge that may use to support a pipe 'O' ring type seal. On the other hand, I will probably tape it shut  - like everybody else. {-)


Time got the better of me this weekend but I did manage to do a complete dry fit of the hardware. The hinged ESC mount works well; you might notice that I had intended to mount it at right angles to where it ended up (from the slots). Turned out the water pipes needed a lot more room. The Velcro strap will be a tie-wrap in the finished version. I also found the best space for the Rx was further back. I'll need to extend the lead from the ESC but it's been damaged anyway so I'll do a proper job on that later. I looked around for something interesting to put the Rx in but in the end I've settled for a simple wooden waterproof box (under construction). I shall do something to protect the servo too (not sure what yet). You can see the tube for the pushrod with its internal bellows and the second tube for the water pipes. The entire rear compartment gets sheeted over once all the rear-end hardware is fitted. The top is fitted to the centreboard box now too.


Next work is to tidy up the cowl joint and work out the latching and then it's sanding ready for glass and paint. Lots of sanding!


By the way, I have been using two-part filler where I need a strong material. I wanted to dispense small amounts onto edges and into holes and I found you can do it easily with a disposable syringe. Best bit is, it doesn't stick to the syringe so you can clean it out easily and use it again. I expect you already knew that but maybe someone didn't ok2
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 14, 2015, 06:42:21 PM
Thought for the day......


Straying slightly off-topic, you have often heard me banging on about universal joints -  Hooke's Joint - and how they cause vibration. I was reading yet another post complaining about vibration from a UJ and blaming the quality of the component. It doesn't matter how much you spend on a UJ, it WILL cause vibration if there is the slightest angle on it - it's a geometric thing and you cannot get away from it. (2 works better but you still have the shaft between them speeding up and slowing down on every rev so you still get vibration).


What you need is a Constant Velocity (CV) joint, like in your car. I was thinking 'if only somebody made them for models'. Like a car - model. MODEL CARS! They have CV joints. (I even checked on the chassis I have hung on the wall as a source of interesting bits).

Me, I prefer straight lines but I'll be interested to see if any of the bent shaft boys take this one up....................

I'm sure if this is in the wrong place one of the mods will move it (please).
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on September 14, 2015, 07:42:47 PM
I've thought about it a little, bought a few for the purpose, and continued to look at them in the packaging since mostly to be honest. I baulk at the idea when it comes to lubrication mostly, with concerns about what power can be put through them. There's a seed of an idea in there somewhere though.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 14, 2015, 08:10:40 PM
Hi Jerry,
Yes, but you are talking SERIOUS horsepower in your boats! My guess is that some of the off-road competitive hardware would handle the average fast electric. You, my friend, would have to knock something up. Well within your capability, I reckon!
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on September 14, 2015, 10:17:14 PM
I've taken a peek at the shafts I have properly Tim and it turns out none of them are CV joints. As much as they look like them mine are differently made universal joints with the problem Mr Hooke found with them. So a gimbal arrangement. Do you know of something different?

To be honest if it were looked into closely the fact that IC engines are not constant velocity themselves would have to be taken into account,  that element is already more demanding on the power train needing tougher stuff than a same power electric motor, where their margin of velocity shift is so small.

So, if we assume an electric, whatever the power, two universal joints with appropriate positioning will result in a constant velocity output but with the intermediate shaft being the only potential source of vibration, if a true CV joint isn't out there.

I hope there is a solution, I'm not a lover of flexible shafts.
Title: Re: Donald Campbell's Bluebird K7
Post by: w3bby on September 19, 2015, 06:28:01 PM
Check out the wire drives (http://www.offshoreelectrics.com/proddetail.php?prod=jw-wire062) that are making waves.... Even being used for ic petrol nowadays (not exactly similar but the idea is the same).

Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 20, 2015, 04:16:55 PM
( I've seen some CVs on the net that look like proper jobs and plenty more that are definitely not. Oh well; I need to get this thread back on track before I get told off  ;) )


This week has seen progress on some of the detail work. There's no particular build order at the moment; I can just do what takes my fancy on a given day. I made the little box for the Rx. How many clamps can you get on a 50 x 70 mm box? Quite a lot, as it turns out  {-) . I tidied up the joint between the cowl and the hull and, having got a nice sharp edge on the cowl, I decided to give it another layer of glass to protect it. That went well and it's looking pretty smooth now. Plenty of time for me to ruin that when I start painting. I've also formed the fillet between the lower cowl and the deck. A little more work to do there.


The nose of Bluebird is like the Mona Lisa's smile - enigmatic. I've looked at dozens, perhaps hundreds of photos and in every one the nose looks different. Over the weeks, I have gradually worked on the nose until I ended up with a pleasing shape. Unfortunately, when I looked again yesterday that pleasing shape was nothing like the original. Miles out. I'm not a scale fanatic but there was only one thing for it. Rhinoplasty! I slapped on some 2 part filler and set about reshaping the bow. I've now ended up with a shape that looks pretty close to the original, perhaps closer to the replica. Did I get it right? Haven't got a clue to be honest. It looks right to me but then it looks completely different in the photos  :o . Anyway, that's how it's staying because I'm starting to break through to fresh air - and my fingers are worn out. I'm sure it will look OK once the badge goes on.


For the benefit of anyone who's contemplating this build, I finally worked out the geometry of the nose (I think) and this is how you create it:


To start with, forget about the radius between the deck and the sides. That comes later. Form the longitudinal curve of the deck first. The sides are flat. Starting from around the forward boom box, the sides get an increasing chamfer until they meet at the bow. At this point, you should see a characteristic curved V form where the sides and deck meet. My photo was at slightly the wrong angle; the chamfer is steeper than it looks. Once you are happy with the V shape, add the radius, starting from the kink in the deck and increasing uniformly to the bow, where the radii from the two sides will meet. Then it's down to your own interpretation, eyes and patience. Worked for me, anyway. BTW, does anybody want about half a pound of used filler? Very low mileage.


Next step is to clean up and glass the hull. I'm not going to do that today as I've had enough and I'll only mess it up!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on September 27, 2015, 06:16:25 PM
Nothing to see here.............
Just a verbal check-in this week because the boat looks exactly as it did last week. There have, however been some changes. The hull and cowl are glassed, sanded and are pretty much ready to paint, which came as something of a surprise to me. I had allocated a couple of weekends for the sanding. In the event it took about an hour to do the glass coat (bottom one evening, the rest the following night) and just an hour to sand it. There is just a slight suggestion of 'weave' in the surface when the light catches it right. That seems good to me - the surfaces are flat and I haven't taken all the glass off. But it looks as if I've done nothing!


I fought long and hard against using glass but I'm glad I gave in in the end. I'm surprised how easy a process it turned out to be and the results are very pleasing. Hopefully no more corner joints popping open on this model.  :-)) .


Photos will follow when there is something to show. Meanwhile, you might want to check out my rowing machine post in R&D.  :}
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 18, 2015, 07:17:48 PM
Slow but steady progress. All the major bits are now made and this week saw them coming together for the first time. I reckon that merits a photo  :-)) . Last couple of weeks I have been working on the boom covers. They seemed to take an extraordinary amount of time for quite small pieces - especially as it took two attempts to get the rear ones half decent. I lost two weekends along the way too. We've had my wife's mother staying for the summer and last weekend was taken over by a big 'going away' party. This weekend was a 3 a.m. start to get her to Heathrow. Unfortunately, she arrived home at just the same time as Typhoon Lando. Not a nice trick to play on a first-time traveller but she got there in one piece so all's well.


Back to the boat. Everything is glassed. Next job is to work on the fillets where the front boom joins. Remember, with this model the booms get fitted after painting so I need to make a decent job of the joint. Then lots of wet sanding and start throwing paint at it. The reports will be a bit slow coming as I have to take my time now; everything from here on will show on the finished model. The woodwork has gone well (far beyond my expectations) but painting has always been my weak point. Steady as she goes! is the order of the day.
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on October 19, 2015, 06:29:02 PM
Looking good.


I seem to be a bit of a nay sayer on this one, but I would not wet sand it yet. I don't know what paint you're planning to use, but even a small beach of the glassing could result in a whole load of back pedalling. I would get through the priming process dry first. Once you have a reliable full coating which does not breach dry sanding, apply a further coat and wet sand it from there. All wet sanding offers is waste clearance to reduce abrasive clogging, not such a big issue on a model sized painting project.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on October 19, 2015, 08:19:18 PM
Thanks for the advice Jerry. I'll just take off the lumps where I was clumsy with the resin and start to built up rather than take off. I'm looking forward to/dreading the paint job in equal measure!
Title: Re: Donald Campbell's Bluebird K7
Post by: Stavros on October 19, 2015, 11:36:08 PM
I DONT advocate wet sanding at all this is because all primer is porus so WHY introduce Damp into your paint


Dave
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on November 08, 2015, 06:55:14 PM
Contrary to what you might think, I have been beavering away on K7 in every spare moment.


I guess every project reaches a point when you think "My goodness; why on earth did I every undertake such an endeavour?" (or less family-friendly words to that effect). Hopefully, this project has just passed through that stage. Me vs the boom covers. Those four little parts took a ridiculous amount of time to get half-decent. I don't need to tell anyone on this forum how difficult it is to form those fillets. Filler on, filler off, on-off, on-off. Same with the paint. Getting them right without cutting into the flat parts is so tricky! They are not perfect but, as my mum used to say "A blind man would be glad to see it." (She had a few more flowery sayings too....). A little more paint and they'll do for me. (I'm losing the will to live!)


Speaking of paint........... I had already wet-sanded the hull before I got advice. I was very careful not to cut into the glass and it turned out OK. So, why the multi-coloured hull? I started off using UPol #5 Hi build primer. I've used it before and found it very good. However, after a few coats on the boom covers and one coat on the hull I had an empty can and a whole lot of painted newspaper. At twelve and a half quid a can, I needed a plan B. I decided to used a brushing primer, at least for the first coats. Following the instructions on the can, I used a generously loaded brush and laid the paint on in one bold stroke. Non of that brushing out and laying off malarky - it dries too quickly. My kind of painting  :-))  It looks pretty grim at first but after an hour or so, the brush marks go away. Most importantly, the paint is on the model, not all over the bench.


I struggled with dry sanding at first because the paper clogged instantly. Discovered I needed a much lighter touch. Sorted.

I have started using the airbrush now. I have a lot to learn about that joker!. Struggled at first but found the paint needs to be much thinner than I imagined. I then noticed some splodges coming through. Water! I had chosen today (wet and wild) to try spraying. Twit! [size=78%] :embarrassed:  [/size]The water was condensing in the nozzle as the air expanded and cooled. Not a disaster but a light rub down and more coats required. I need to work on a dry day (I wonder if I can get a cheap air dryer?). I also need to knock up some sort of spray booth before I do the hull. I have a proper mask but I think my garage may end up completely light grey. Even at this stage, I can control an airbrush much better than a spray can. Looking hopeful.

A while back I knocked up a dummy engine. I was toying with an empty beer can and a bottle top (like you do.....). I noticed that the reflection of the top gave a pretty good impression of looking up the dangerous end of a jet engine when the light caught it right. (Come to think of it, both end are somewhat dangerous if you get too close......) Very hard to catch it on camera - you'll have to take my word for it. Turned out that a mini coke can was the perfect size. Just cut it up with a pair of scissors, reversed the bottom and put it back together with a mallet. I kept the rolled edge of the can intact in the interests of retaining all my fingers in the future. (I may have to build a larger scale model at some point so I can use a proper beer can. Preparing your raw materials is half the battle......)It's just a case of soldiering on with the painting for now (weather permitting). One day I will get round to some fitting out. Who knows? One day this model may even get wet!
Title: Re: Donald Campbell's Bluebird K7
Post by: Jerry Hill on November 08, 2015, 09:51:58 PM
What size airbrush do you have? A model of this size is not really airbrush territory.
Moisture usually forms upstream of an air tool, and the solution is an inline moisture trap or water separator. Many of these are mounted on the compressor, but it's better to have a length of airline between the compressor and the trap to allow the water vapour to condense fully before being separated. Basically the cooler airline acts as a condenser. Bear in mind the airline will probably still have moisture in it, so it'll need drying if reused post separator.

Some airbrushes will not pass anything with a viscosity higher than milk, really fine ones struggle even with that. Upping the air pressure can force atomisation, but this causes many other problems. A good indicator is the comments of spray cans. Spray some into a lid and check it's viscosity, that's about the upper limit of any spraygun that could be called an airbrush.

For a way of generating a smooth transition from radius to flat try rubbing off the flat into the radius at up to 45 degrees. Helps to avoid those grooves.

If your abrasives are clogging too easily it may not be coarse enough a grade.



Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on March 06, 2016, 10:14:46 AM
Long time no see.............. :}


I got sidetracked (side swiped?) The second Tuesday in November (I remember it well) I came down to find the entire contents of my central heating system distributed all over the ground floor - kitchen, dining room, lounge and hall. The 30+ year-old boiler had finally rotted out. Time to get the men in. Needless to say, they couldn't put a new boiler where the old  open-flue one had been so after a major rearrangement (boiler upstairs) I was left with a nice new heating system and a wrecked kitchen. The floor-up refurbishment took me right through Christmas. Along the way, I had to replace my drill and router and then the dishwasher died. As I said to Mrs M, everything in this house is getting old and worn out. She just looked me up and down and walked off. Revenge is pending.


It was February before I could even think about modelling but at long last Bluebird is ...................................... Grey.


It took ages. I could blame the materials, the tools, the weather or the light but the truth is I am rubbish at painting. I tried various spray cans to no avail. I ended up using an airbrush and Halfords grey primer (cellulose based). I agree that an airbrush is not the ideal weapon for a model of this size but I found by a process of trial and error (mainly the latter) that I could get the paint consistency and setting right to allow me to walk the fine line between getting the surface wet and getting runs. I looked at buying a mini spray gun but my compressor is not powerful enough. I lost count of how many coats I put on. I guess it's the equivalent of about two good coats by a competent sprayer. Whatever. I have had to take a reality check. The surface is not perfect but I'm not building a museum-quality model here (I couldn't). It's a toy and it will no doubt pick up a few dings and scratches along the way (going on my past driving record). If I try too hard, this boat will never hit the water.


I learned one important lesson the hard way. Mix your paint properly! Preparing the paint for what was to be the last coat, I found a lot of sludge in the bottom of the tin. I mixed it in and thinned the paint for spraying. Next day it had dried like crazy paving and had to come off. I guess what happened was that the sludge contained all the heavy solids but not enough of the binders and other chemicals to make the paint work properly. Adding thinners just made it thinner. I started again with a fresh tin of paint and made a swizzle stick to stir it with the electric drill. You have been warned  :-))


I have added some panel lines; they really bring the model to life (though they don't show well in the photos. Rivets heads? No chance!


Next step is to get some colour on. I'm using water-based acrylic; it's cheap and readily available. I am optimistic. I tried one coat on the boom covers and I was amazed how well it covers with just one coat. Of course, it's matt but I intend to blow a coat of water based varnish over the top once the decals are fitted (tried it on some scrap and it looks OK). Then it's on to assembly and fit-out. Actually, that's not quit true. The next stage will be to make a stand. Once I start fitting out, there will be all sorts of stuff hanging down below the nice, convenient flat bottom. She has to go up on the blocks.


With Easter on the way there is a chance of progress!
Title: Re: Donald Campbell's Bluebird K7
Post by: Martin [Admin] on March 06, 2016, 04:41:12 PM
 
Nice finish!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on March 26, 2016, 05:25:30 PM
And now it's blue......... (and decorated)
Many coats of acrylic and then I started to apply water-based varnish. That didn't work very well; no real shine. I resorted to 'full fat' polyurethane (Blackfriars gloss), slightly thinned. And that worked much better. The decals proved tricky. I bought the paper years ago for something different and it worked well. The prints looked fine but.................. the ink wasn't waterproof! (Cheap 'compatible' cartridges). I tried the sheet that I had printed at work on a posh laser. Also not waterproof. I wasn't about to rush out and buy 'genuine' cartridges (who can afford those these days? You can buy a whole printer for the same price!) so I tried blowing a light coat of Humbrol varnish (bought at the same time as the paper) over the sheet first. Worked fine. Not sure if the Rolls Royce badge existed on the original but it looks pretty cool.


Somebody take Stavros off to a darkened room - he's not going to like this bit. I was trawling the net looking for a replacement needle/nozzle for my gravity fed airbrush; I had wrecked it learning how to dismantle an airbrush. A came across a '0.3 mm airbrush, gravity fed spray gun, 100ml cup' on ebay, UK stock. (Item ID: 151716939279 I was tempted. Turns out this thing can handle quite thick paint and (even better) varnish. Any good? The only problem, apart from the fact it comes with a full-size airline bayonet, is that my tiny airbrush compressor struggles to keep up with it. Spraying in quite short sessions and allowing the pressure to rebuild in the tank, you can get away with it. It certainly worked better on the larger parts than an airbrush. An the cost? £7.50 plus £1 P&P. That's why I was tempted! With a large compressor, I reckon it would be really good  - but then if you have a large compressor, you probably already have a good  spray gun.


The finish on Bluebird is far from perfect but it's good enough for me. I know I will only make it worse if I try to make it better. The next stage is to build a stand then on with the fit-out and detailing. Mrs M is on the other side of the world at the moment so she doesn't know how long I am spending in the garage  {-)


Oh, I forgot to mention that I found the perfect pilot. Blue overalls, goggles and even a teddy.  :-))
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on March 26, 2016, 05:27:30 PM
I don't know what the splodges are in the close up of the nose - they don't show in real life!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on March 31, 2016, 03:51:35 PM
Looking quite purposeful now. I had planned a week of intensive modelling but Storm Katie had other ideas. Three days of outdoor repairs................ >>:-(


Question:
I noticed the LiPo is looking a bit strange after the winter (I left it with a 'storage charge'). There's a bit of a bulge on one side that seems to be a gas bubble. Anybody seen this before?
Plan A is to charge it up again outdoors. If it blows, it blows. Then I think I will make some sort of test rig and put it under load to see what happens - unless somebody tells me I'm on a hiding to nothing. I'm reluctant to throw it away as it's only run for about an hour but, on the other hand, I don't want to see Bluebird explode.


Meanwhile I have a heap of small bits to make and fit.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on April 04, 2016, 04:53:15 PM
A small step forward; the shaft tube is fitted. There are snug fitting pins in each end so the strut and motor are aligned to the tube. The skeg/centre board was slotted into place and then the motor and strut fitted to the pins. Glue was applied to the motor mount and the whole lot was then adjusted to get the prop height right and the motor nice and low.  A single bolt locks the centre board in place. All the bolt holes had silicon applied before assembly and the 'formed in place silicone grommet' (blob of sealer) made. When this lot is all dry, I have to cut the tube at both end to remove the pinned sections. Finally, I will do a leak test and once everything is OK the rear section will be sheeted in and sealed for life.


The finish on the bottom? Blue Bird meets Blue Peter. Stainless steel effect fablon! According to the manufacturer, it's waterproof and has a guarantee of three years out of doors. Well, it looks pretty good and saved an awful lot of masking and painting. The underlying surface is fully waterproof anyway; it won't be the end of the world if it peels off. Not sure I will use it on the sponsons as the area is quite small.


BTW, I decided to play it safe with the battery and ordered a new one. I may still investigate the old one but this way if it works it's a bonus rather than being tempted to push my luck and run with it.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on April 30, 2016, 11:43:03 AM
Just Add Water.................


That's it, for better or worse. Just need to charge the battery and sort out the channels on the Rx before sealing the box (it's held it with velcro), tape down the hatch and throw it in the lake. Now is a good time to get some pictures. Those of you who have followed the build log will know that thanks to my (lack of) driving skills, this may be the last time we see Bluebird in one piece. I shall wait for a dead calm day and take it easy.  :-))  Oh, I do have to build a transport cradle. The stand I used for building is so heavy, I'll slip a disc if I try to put it in the car.


On the whole, I'm pleased with the end result. The paint job is not good but it is about ten time better than I hoped to achieve. Scale? I don't think anybody would be in any doubt as to what the model represents. The front booms are a bit chubby (because of the tube I used inside) and the 'double curved' scoops in the hull are definitely a figment of my imagination - they do look nice though! Of course, the sponsons are not scale and there's all that stuff hanging off the back. Unavoidable, I'm afraid. In retrospect, I should have ditched the prop strut and used a solid shaft. Something went a bit awry and I noticed the sponson edges are set about 20mm below the hull floor. It should have been more like 35mm. My adjustable prop design came in handy sooner than I expected. Having sheeted in the rear deck, I promptly had to cut an access panel in it, raise the prop to match the sponsons and fit a cover (with silicone). I'm not convinced the hull will ride clear of the water yet but we'll see. If need be, it will be easy to add some running shoes.


You can see the battery tucks away right up front. The CG comes out just about right with this arrangement, maybe a tad too far back. Again, we'll see. The rudder has twin water scoops and the feeds for the motor and ESC are kept separate. I also split the feed to the ESC and have two discharge pipes (plus another for the motor). The little funnel is where the antenna sits and I've put the main switch through the hatch cover. I'm only a mile from the lake and will probably seal everything down before setting off from home.


The flotation test was OK. I didn't run the prop as the inhabitants of the pond are very inquisitive. I have better things to do on a Saturday than clean minced fish off the side of the garage...........


Once we get a good day, it's off to the lake with camera (and 'Rescue 1')  ready.
Title: Re: Donald Campbell's Bluebird K7
Post by: Captain fizz on April 30, 2016, 12:16:38 PM
I say Tim, that all looks rather good.
Looking forward to your test runs.


Simon.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on May 29, 2016, 09:30:22 PM
At long last, the elusive combination of good weather and spare time.


The maiden voyage turned out well. Low speed steering is a bit iffy (won't turn right for some reason) but once she starts to plane the steering is very good. She rises up onto the plane easily and rapidly gathers speed. Not sure how fast it will go when I really open it up - my nerves were in tatters after the medium-speed runs.


I have uploaded a rough video so you can at least share the first run. Note the afterburner in action at the end  %) . Nipper couldn't keep up with the higher speed trials but credit where it's due - he did manage to get some video of a fast-moving object ans a cracking 'still'.


https://youtu.be/vqWwuV4NOec



Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on May 30, 2016, 09:07:30 PM
Hi Tim,

Your K7 looks the part and I don't think you will have any trouble when you apply full throttle, just keep your concentration at top level, if anybody speaks to you when you are sailing K7 just snap the throttle shut and ask the person not to talk to you when you have the boat under control as it only breaks your concentration.

In my early days as I was going up my lake at full throttle a guy asked a question and I tried to answer him only to smack my K7 into the concrete wall at the end of the lake doing 40 m.p.h. so you can imagine the damage and my answer to him !!!!!!!!!

Great job it was worth the efforts maybe you will manage to get on a lake which is larger than yours and have no Geese for company and you can really let her go..

George.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on May 31, 2016, 07:07:50 PM
Hi George,
I think you're right; I will be able to open her up a bit more once I get used to it. It just a little unnerving seeing all that work flying on the tips of the sponsons and trying to remember which is left and right as it goes past  {-) . This model came out a good half kg less than the first, which helps. The success of the first run is, of course, due in no small part to all the advice you passed on based on your own experience. I appreciate that a lot!


Unfortunately, there is only one boating lake on the IOW and somebody ruined that by sticking an island in the middle of it as a bird sanctuary. There is a picturesque natural lake a few miles away but access is very poor. I think I would have to be very confident in the model before I let it go there. There's always the river Medina, but a safety boat would be essential. Never mind; I enjoy watching K7 as it transitions from floating to flying. Once it's flying, it tends to go out of sight anyway! I hope to get some good video footage over the summer and will post again.


Rgds,

Title: Re: Donald Campbell's Bluebird K7
Post by: ooyah/2 on May 31, 2016, 08:39:36 PM
Hi Tim,

I would be reluctant to try the river, as you know rivers run out to the sea so I would stick to lakes.
 With the engine bay top fixed on over a sealed engine compartment do you have any water ingress ?

Don't think left and right, think Port and Starboard , it becomes easier to remember.

I find that my K7 responds better to Starboard as the rudder is more to Port and the wash from the prop helps a great deal, but on no account try to turn K7 at high speeds.

You will get used to the speed , if you crash it it's 2- off the belt for you.

Take care

George. 
Title: Re: Donald Campbell's Bluebird K7
Post by: ballastanksian on May 31, 2016, 09:04:48 PM
She looks very real Tim. You have sorted the balance issues out and probably better than the real thing.

Mind you, with a Minion driving, you may have to wrestle the controls back on occasion!
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on June 02, 2016, 07:54:54 PM
One thing that was a success was the sealing. When I took the hatch off, it was bone dry inside - not a drop! Mind you, I did obsess a bit over that part of the design. The 'engine intakes' are closed off so it's very difficult for water to get anywhere near the hatch. There's a deep coaming and the hatch gets sealed with tape before the top goes on. As for the river, I'd only take the boat there if I had a full size safety boat to go after it. Nearly ended up in open water many times as a kid  ok2


Ian - keep your voice down! Bob is very sensitive and if he gets upset I'll never see my boat again!
Title: Re: Donald Campbell's Bluebird K7
Post by: ballastanksian on June 02, 2016, 09:01:21 PM
Don't worry Tim, Bob, Nick and I had a good conflab last weekend at Wicksteed and he is a lovely chap. The frustration of such catastrophic problems appearing in the middle of the water rather than on the bench would have had me vexed somewhat.
Title: Re: Donald Campbell's Bluebird K7
Post by: Tim_M on June 04, 2016, 09:03:30 AM
Crossed line I think, Ian. My Bob is a minion. Who's yours?  {-)