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Author Topic: Donald Campbell's Bluebird K7  (Read 53549 times)

Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #25 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 :}

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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #26 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





 
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #27 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.
 
 
 
 
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Flundle (Speedline Models)

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Re: Donald Campbell's Bluebird K7
« Reply #28 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.

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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #29 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.
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #30 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!
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #31 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.
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #32 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.
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Flundle (Speedline Models)

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Re: Donald Campbell's Bluebird K7
« Reply #33 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......
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Flundle (Speedline Models)

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Re: Donald Campbell's Bluebird K7
« Reply #34 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.
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #35 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.
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #36 on: September 04, 2014, 12:47:29 PM »

Here's something I prepared offline......
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #37 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.
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #38 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)
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w3bby

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Re: Donald Campbell's Bluebird K7
« Reply #39 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...

Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #40 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. {-)
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #41 on: September 13, 2014, 02:27:07 PM »

Battle scars (as befits a development model) :}
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Re: Donald Campbell's Bluebird K7
« Reply #42 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
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Re: Donald Campbell's Bluebird K7
« Reply #43 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/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.
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #44 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!!
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Tim_M

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Re: Donald Campbell's Bluebird K7
« Reply #45 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 :}
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #46 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.
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klz

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Re: Donald Campbell's Bluebird K7
« Reply #47 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
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Ramon

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Re: Donald Campbell's Bluebird K7
« Reply #48 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
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ooyah/2

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Re: Donald Campbell's Bluebird K7
« Reply #49 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.
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