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Author Topic: HMS Dreadnought. Using Dental Drills as model ship turbines  (Read 10013 times)

Colin Bishop

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HMS Dreadnought. Using Dental Drills as model ship turbines
« on: April 12, 2016, 09:01:18 pm »

In the latest issue of Model Boats (May 2016), there is an excellent article by Dr Marcus Rooks on his model engineering project build of HMS Dreadnought in metal. Although interesting in its own right, I was particularly intrigued by his intention to use dental air drill motors as 'turbines' under steam power, particularly as these motors only cost around £20 each. This does seem to raise some interesting possibilities for other models too. I have put up a couple of pics of these motors with captions from the article on the Model Boats Website:
http://www.modelboats.co.uk/forums/postings.asp?th=116653&p=1

Colin
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ballastanksian

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #1 on: April 12, 2016, 10:42:21 pm »

I have been thinking about turbines in model ships, certainly since seeing the article published in Model Boats last year showing the model of the Warspite, also of all metal construction, with a pair of turbines and wondered about making miniature turboines. This seems an elegant method.

As long as the boiler can provide the oomph to turn the props and provide some extra emergency power then they will be excellent for all but the smallest model ships.
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Colin Bishop

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #2 on: April 12, 2016, 11:02:02 pm »

The only thing I wondered is if the motors are intended for dry air operation, will using steam cause any problems with seals and joints etc.

Colin
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ballastanksian

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #3 on: April 12, 2016, 11:14:11 pm »

Interesting point Colin.

I would think that the motor and it's components would have to have an element of water resistance given that condensate from an air compressor seems to find its way through most air systems even with moisture traps, also there is the issue of fluids, saliva, rinisng water etc getting onto and into parts of the drill (the main reason for not using electric motors to drive the drills I presume).

The ability of the motors to work damp would be to the shipmodellers benefit both for reliability and saving the expense of replacement seals and joints.
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southsteyne2

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #4 on: April 13, 2016, 01:02:36 am »

Very interesting would probably need gearing down as speed would be high but power low so where would these be purchased for 20 quid?
Cheers
John  O0
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #5 on: April 13, 2016, 05:53:14 am »

There are plenty of workshop air-powered drills available for a couple of quid thay might be worth experimenting with that have more torque and run at more useable speeds. What is the cfm steam capacity of a model steam boiler?
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #6 on: April 13, 2016, 08:27:08 am »

(the main reason for not using electric motors to drive the drills I presume).
[/size]
[/size]Also the possibility of electrocuting the patient {-) {-)


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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #7 on: April 13, 2016, 08:30:08 am »

Some sort of glitch on my last post  >>:-(


Another reason for air drills is not to electrocute the patient  ;D ;D


Ned
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Colin Bishop

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #8 on: April 13, 2016, 10:01:40 am »

Plastic has made a good point, it's possible that the steam consumption could be quite high and that it might be difficult to fit sufficient boiler capacity within the hull. Very interesting project though.

Colin
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #9 on: April 13, 2016, 10:36:07 am »

My dentist has a 240V air compressor out back that drives their tools - it's quite big - probably 15cfm.

Steam technology is well understood.
I'm thinking that the size of boiler required to supply 4 little turbines could be huge - they are literally like open-ended piped with very little through-resistance, not like piston engines with separate cycles and control valves.

A diving-type compressed air tank as a reservoir may be an easier supply but run time may not be huge.
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #10 on: April 13, 2016, 12:33:59 pm »

These little turbines run at approx quarter of a million rpm with very little torque, it is in theory, possible to stop them with your fingers(never tried). Nemesis
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #11 on: April 13, 2016, 01:32:07 pm »

These drill/die-grinders are adjustable to 15,000rpm @ 4cfm consumption for £20 from Screwfix - they will have a lot more usable output for a propshaft..
A dive cylinder works out as 80 cubic feet so 4 motors flat out = 5 minutes run time?
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #12 on: April 13, 2016, 04:28:58 pm »

The real steam turbine wasn't just a straight-through loss of pressure. Using condensers (and sea water cooling) the steam was liquified and bunged back in the boilers.

If that could be made to work in a model, running the working liquid as a closed-loop, almost loss-less system, presumably the real factor in driving a model turbine is having burners big enough to counteract the scale efficiency losses and provide enough steam to drive them?

Andy
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John W E

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #13 on: April 13, 2016, 07:13:55 pm »

Having read this article in this month's Model Boats - it is going to be interesting to actually see how this model performs as far as efficiency is concerned.   As having pulled a few air powered tools apart, I know basically you have a drum with angled holes in it - which the air passes through to drive the drum around, creating the drive and as has been mentioned this solely relies upon air pressure behind it.  In industry it is normally at 100 psi that is supplied to the air tools. 

As has been mentioned, can we maintain the volume at this pressure?   Where on real steam turbines the diameter of the blades start off very small and as they go along the shaft the diameters of the rota blades increase - the reason for this - steam turbines obtain their energy/power not only from the power of the steam, but also the steam expanding, which gives it - its greater power.   

The steam will naturally expand as it cools down inside the air tool - but will not affect its performance, due to the fact that there is only 1 diameter size hole in the drive drums of the air tool.

The other thing is there is a vast gear ration on these tools as well, to give them the torque they require to drive drills and soforth.

But, we will have to wait and see :-)

John 
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ballastanksian

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #14 on: April 13, 2016, 09:25:44 pm »

All the 5inch gauge locos at my model engineer club ran at around 90PSI with boilers of between 12 and 18 inches in length (approx) so a boiler for a model battleship would have to be pretty robust and of suitable capacity as mentioned before. This would add weight that would be dificult to accomodate in a amsl hull. How big is Dr Rook's model going to be?
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Colin Bishop

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #15 on: April 13, 2016, 09:57:24 pm »

1:100 scale, hull length 63 inches.

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #16 on: April 13, 2016, 10:04:06 pm »

 
   An interesting project this and if a dental motor could be geared appropriately and stand steam heat it may work . The motor in the ordinary industrial air tool doesn't rely on angled holes to generate power from the air supply, that would be just a plain impulse turbine and not particularly efficient. Rather, the air enters into the narrowest part of the  rotor chamber where the rotor is offset from the chamber axis and the sliding vanes, usually 4 of them, allow the air to expand as the rotor turns, and exits at the point of maximum volume, hence making the tool feel cold. So if steam were used then that too would expand and cool, but I would think that a pretty large boiler and burner would be require for air tool motors, which might not fit a 63" hull, the average 3/8 drill or die grinder motor uses about 4 c.f.m of free air somewhat more than a dental drill.

                           Trevor
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #17 on: April 24, 2016, 04:30:13 pm »

Dumb Question Time--Just scribbling on a paper napkin here, but:

I'm assuming "flash steam" boilers put out more CFM than regular boilers--can anyone confirm/deny that for me?

Assuming flash steam boilers put out more CFM than our more traditional, small, 30-40psi boilers of (unknown to me) CFM, perhaps that would be an option, to run a air/steam "turbine"--be it sourced from the dental industry or elsewhere?


Alternatively, I know there are actual JET engines (burning some type of chemical fuel) in model-scale, flying aircraft.  They can certainly handle far more heat than steam would ever produce!

So my (second) question is:  are there any actual model fuel-burning TURBINE "prop jet" (i.e., a gas turbine turning a PROPELLER) engines, in the model RC aircraft world?

IF so, I wonder if they could be "driven" by steam/compressed air, instead of by burning fuel inside of them?

Because at least you'd have a realistic set of graduated-sized turbine blades, to take (mechanical?) advantage of the decreasing pressure steam, as it expands, and leaves the engine....

Again, just shots in the dark--please feel free to set me straight--I'm here to learn and, if possible, contribute.

Thanks,

GreenSteam

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #18 on: April 24, 2016, 05:27:21 pm »

Most model jet engines and gas turbine prop-jets run at a constant high speed - no stopping or reversing so probably more suited to a plane or helicopter than a boat.

The turboprops or turbo-generators I have seen have a free-wheeling fan disc that sits in the blast from the turbine exhaust so the gas forms a type of fluid coupling connected to the output shaft. Lots of revs, low torque.

The reduction gearbox requirements would be expensive and complicated (and well balanced) to connect to a low-speed boat prop with reversing capability.
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #19 on: April 24, 2016, 05:45:11 pm »

Quests, 'HOW DO THEY DO IT' series had a segment where they built a jet engine for model planes - may be available on line.
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #20 on: April 24, 2016, 06:20:28 pm »

 Agree with plastic here, and as far as I know there isn't a currently available model turbo prop engine commercially available, I think that there was a Russian model once, though there are drawings to construct the Shreckling engine available, but you will need very good engineering facilities and skills, particularly in the fabrication of your gearbox which will be more complex than an aircraft gearbox as it will have to reduce the c70K rpm of the turbine down to  a mere few hundred rpm for your boat prop., and as plastic says, have reversing capabilities .
     Another thing to consider is the amount of heat that is generated by even the smallest model turbine, there's an awful lot of it and in a (model) boat you will not have a good volume of cooling air flowing around the engine casing/jet-pipe.
  There would be even more heat around if you were to try to drive the turbine by generating steam in a separate boiler, remember the laws of diminishing returns because of each system,s inefficiencies. Not only that, but (model)gas turbines generally have only a single stage turbine wheel to drive the compressor by the vast amount of very hot gas generated by combustion of kerosene, your idea of passing steam through it would need a very large flash steam generator, and probably a steel hull to put it in!

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #21 on: April 24, 2016, 09:49:15 pm »

Agree with plastic here, and as far as I know there isn't a currently available model turbo prop engine commercially available,
There are several model turbo props commercially available, There are at least three manufacturers at present, one even makes a turbo prop system for boats.

Quote
     Another thing to consider is the amount of heat that is generated by even the smallest model turbine, there's an awful lot of it and in a (model) boat you will not have a good volume of cooling air flowing around the engine casing/jet-pipe.
                                                    Trevor       

Most model aircraft use a double walled jet pipe where the turbine exhaust draws cooling air between the layers keeping it cool when stationary.

Jim
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #22 on: April 24, 2016, 10:23:12 pm »


 Thanks for the corrections Jim, I'm obviously out of date it's quite a while since I dabbled in jets, things have obviously moved on a bit since then, using exhaust induced flow makes good sense. I thought that the Wren had stopped making the turbo prop version, is the marine installation you mentioned a development from engines used in the model  helicopter world where they too need relatively low rpm output shaft ?

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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #23 on: April 24, 2016, 10:35:27 pm »

These are the type I'm talking about - the inlet to the turbine is at the back and the exhast gasses pass forwards and spin the disc connected to the propeller gearbox.

There is no mechanical connection from the turbine engine to the propeller, just the exhaust gasses.
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Re: HMS Dreadnought. Using Dental Drills as model ship turbines
« Reply #24 on: April 24, 2016, 10:45:42 pm »


 but would you not need yet another reduction stage on the gearbox to get the rpm down from the usual air prop range, say 10k-12k? to prop speed for a battleship, not a speed-boat,

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