8 cylinder VW?

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deskpilot

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Look in any forum and you'll find 'wacky' ideas. This may be the wackiest of them all.
Down here in the Land of Oz, we have a governing rule that says one engine, one prop. Now, the engine being the most expensive piece of kit in any plane, we are all looking for 'cheap' alternatives. We all want POWER. To that end, bearing in mind that we don't have 2 pennies to rub together, the thought of coupling engines comes to mind. Problem one is that rule,'one engine only'. So how to get round the powers that be.
My thoughts are to take 2 VW's and connect them in series. Obviously, the coupling between the engines is critical for this idea to work. Not only must the cranks be perfectly aligned, with the cases held so rigidly together that no rotation around the longitudinal axis is possible, but it must also be set so that the firing order is precisely timed with engine 2 firing exactly mid point between relative cylinders of engine1. Following so far? Crazy, ain't it!
Now construct a single ignition system by changing one distributor head from a 4 cyl config to an 8 on one motor. Throw the other distributor out and block off it's mounting/entry hole. Create a single balanced and tuned exhaust system, and repeat for the inlet side of things. Just remember, the more carbies you have, the harder it is to tune. If you really want power, add a couple of turbos to up the anti, but also up the cost.

To all intents and purposes we now have a single power unit, well at least in my mind we do. Have I forgotten anything, don't think so but then, my sanity might be in question.
Would it work? Could it be done cheaper than forking out for a credited aircraft engine. I think so, especially if you're a hands on man/gal who likes experimentation.
 

bob.shea

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Having race monster trucks for, well way to long befor getting into planes. I have spent a great deal of money and time trying to create something better out of something cheeper. I gotta say this is one of those times.
If you could make it work, and you probably could, what do you gain. A motor at least 300 lbs (dead weight) at best only close to 200 hp. rebuild your own aircraft motor. It sounds like you have the ability to do the work.
 

Hot Wings

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Many years ago when the air-cooled VW was much more common I saw versions of just such a "dual" engine. One as you describe and another with the power tapped from between the 2 ....... so it can be done. But I doubt it would be worth the effort.

Tying 2 Rabbit/Golf engies together would be better and even though they are iron blocks they actually weigh less than the air-cooled Tp IV.

When they say one engine one prop would something like this be acceptable?

http://www.infortel.com/cozy/motor_2_grande.jpg
article english
 

lr27

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Anything wrong with the V-8 automotive conversions people are using?

What does the one engine, one prop rule cover? All amateur built? And I guess you can't have two props belted off one engine?

I imagine with your scheme you'd need a very special crankshaft.
 

WonderousMountain

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Why not replace the flywheels with a higher inertia pair, couple them at the reduction gear; tie the throttles together and Bolt/weld it so they can't seperate. You might want some good advice with the coupling, but it should be doible by the layman on a budget.

When a machine needed more power, but the manufactur didn't want to design a whole new engine, this was often done. With well made engines of every size, the practice has become rare. Might be able to sneak past the one propeller requirement with a conter-rotating pair, that would be cool.

Wonderous Mountain
 

BBerson

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VW engines are not real cheap anymore. About $5000-6000 or so each.
As mentioned, the crank is just barely able to handle 4 cylinders where the prop hub attaches.
A twin engine airplane would avoid this problem and create other problems.

This sort of thing is not simple.
 

deskpilot

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Thanks for your replies guys. The 1 engine,1 prop rule covers our Recreational Aviation class, ie, RA.Aus, not GA. Coupling two engines via a common gearbox, via fly-wheels or any other method would still be seen as 2 engines. Coupling 2 props via belts, chains or shafts is still 2 props. Having common ignition, induction and exhaust systems makes it 1 in my opinion.
I have thought of the contra props and a case could be made to CASA, our Civil Aviation Safety Authority that it was a single 'propulsion system' with better characteristics than a single prop. I was thinking on these lines when I wanted to build a replica Westland Wyvern. They could then give me the go ahead and over-ride any objection from RA.Aus. Twin props on the same axis don't have asymmetric problems of the conventional twin (hence their banning).

My reason for thinking this way was that converting an auto V6/8 was way too complicated and expensive in the long run, especially an all alloy one. Besides, the weight of all that cooling system, double radiators etc soon adds up. VW's can readily be found in the breakers yard here, and I'm not talking going the whole hog with twin spark plugs etc so costs are a minor factor. This was to be a cheap way of getting more power and a V8 sound, perhaps.
 

cluttonfred

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Picking up a thread that is a few months old... The one thing the VWs have going for them is a boatload of aftermarket parts available cheap. Instead of this coupled twin idea, why not a custom crankcase and custom crankshaft using all stock VW parts for cylinders, pistons, etc. Eight cylinders, say 4.2 liters and 160 hp? And when it's time to overhaul most of the parts come from the dune buggy catalog. HCI tried to do this with VW parts adapted to a radial configuration...a flat eight seems a lot simpler.
 

MKIV

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Dont see why you couldnt make it work, porsche did much the same in its flat 12 with drive out of the center of crank.
Two issues I can visualise in VW.
1. What will now be center exh ports on each side are going to end up very close to one another [depending on thickness of spacer used in middle between each bell housing].
2. Might be easier to use a gear/belt/ from each crank up to the prop shaft which I would assume would run centerline under intake manifold.
3. Are you going to nose to tail the pair of engines or tail to tail them in which case one will run in reverse, & introduce a few extra challenges.

4. Have you thought of using subarus rather than VW- might be less expensive, but with obvious weight penalty.

Sorry that was Four things & Im already thinking of more...better stop now:)..
 

PTAirco

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Picking up a thread that is a few months old... The one thing the VWs have going for them is a boatload of aftermarket parts available cheap. Instead of this coupled twin idea, why not a custom crankcase and custom crankshaft using all stock VW parts for cylinders, pistons, etc. Eight cylinders, say 4.2 liters and 160 hp? And when it's time to overhaul most of the parts come from the dune buggy catalog. HCI tried to do this with VW parts adapted to a radial configuration...a flat eight seems a lot simpler.

Can't see a flat eight being simpler than a radial; ever looked at the cost getting a forged crank made? And the cam, don't forget. Tons of machining time to make a custom case. The radial crank and master rod and cam disc are comparatively simple and cheap. And lighter.

I have doodled with the idea of coupled VWs toos, but as mentioned before, the end of the crank we drive the prop off is barely adequate for the power of 4 cylinders. Now if you want to complicate your life, how about putting together two Vws , flywheel ends facing each other with a custom housing containing a reduction drive with the output shaft running over top of the front engine? The output end bearing could be secured to the existing generator stand. Now you have more places to run more accesories off than you can think of. (I think Allison did something similar once.)
 

cluttonfred

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What I really want is for Rotec to come out with a 5-cylinder R2000 (guesstimated 70 hp, 180 lbs) to compete with Rotax in the microlight market. Think of all the Rotax-powered bipes and Kitfoxes with a real radial and a round cowl...now that would be fun! Not relevant to this thread, and they have no plans to do so (I've asked), but I can dream, can't I?
 

Starman

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... engine 2 firing exactly mid point between relative cylinders of engine1. Following so far? Crazy, ain't it!
Yep, this was done before on drag bikes. To keep from breaking the crankshaft on the middle engine they used a flexible coupling and had the engines fire at the same time. The flexible coupling consisted of two chain sprockets tied together with a double row roller chain, but you would probably be wanting an elastomeric coupling.
 

Dan Thomas

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If you place one engine behind the other, with the prop driven off one end of the setup, the crankshaft carrying the prop has to do double duty. It has to take all the torque loads from the engine it's in, plus the torque loads applied to it from the other engine. It's a recipe for crankshaft failure. If you look at the cranks in straight sixes or eights you'll see that they are really heavy to resist the twisting that can break them near their output ends.

And if you have two engines driving one prop, you need overrunning clutches so that the failure of one engine doesn't drag the other one down as well. I've seen a setup like that, but the complexity and weight makes the concept expensive and impractical.

Dan
 
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Elmog

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I used to work with salt flat racer that used two big-block Ford engines tied together with a chain drive to power his high-speed car. He said it wasn't that difficult and worked great when a lot of power is needed. I asked a bunch of questions about set up and he said small power differences between the two engines didn't matter. I would think that in an aircraft function any imbalances would be an issue.
I don't feel that it is really worth tying two engine together and that a suitable powerplant could be located for cheap. You are willing to use an automobile engine without a PSRU so I would venture to say that the Aluminum 215 cu.in. Buick V-8 would be the way to go. Probably weighs less than two bug engines tied together and has already flown in a few different designs (Beachner V8, Wittman W-8, Van's RV, Globe Swift) to name a few. You would be light years ahead in terms of simplicity and one can even be sourced from relatively new vehicles such as the Rover or Triumph TR8. You should be able to pay junkyard prices and be in the air long before you put together a "Frankenbug" motor.
 

deskpilot

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Hi Guys, been away for a bit (pc problems) so it was a nice surprise to see my 'Wacky idea' still being discussed. Thanks for your input, especially re crank-shaft strength. I hadn't thought about that. Mind you, if I had the spare cash, I'd still like to try it, not in a plane though.
I have looked at a V8 Rover conversion, but real expensive and soo much plumbing. Maybe it is all alloy, but there's too much weight in the ancillaries.
 

KeithO

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Deskpilot
It seems Japan is not too far away. Why not get a Subaru EG33 6 cylinder boxer engine ? It is about the same size as a continental, there are people in AUS/NZ who build redrives for the Subaru's and you could probably pick up an engine for around $1000. That should be plenty HP for the job and there is quite a long track record for Subarus in airplanes.
 

deskpilot

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Have looked at that option Keith. Not as cheap as you might think. I've also been told that the power is not worth the extra weight? I've only ever seen one 6 pot car here in Oz so no junk yard items available either. I'm sure other would have tried it before if it was worth it.
 

Blind Willy

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...
And if you have two engines driving one prop, you need overrunning clutches so that the failure of one engine doesn't drag the other one down as well. I've seen a setup like that, but the complexity and weight makes the concept expensive and impractical. ..

Dan
This...is the setup that I've pondered for years. Two, in-line, with a common drive system (not a common crankshaft) and a clutch or sprag release drive system that would allow an individual engine to "get you home."

Maybe I'm being naive here (I usually am) but two belts to one common driveshaft (run underneath the powerplants) to a PSRU doesn't seem that complex or involved to me. In my head; the idea of linking two, moderately-tuned, auto engines makes as much sense as using one, peak-tuned, single, powerplant.

I have to say that (being a gearhead and motorcycle nut) I've seen a lot of tandem and triple-engined (ground-based) examples of linked engines (accomplished via in-line crankshaft) in my life. And I know that they are capable of incredible things but, generally, these are only required to run a quarter-mile-or-so at a time. I don't think a setup with a common in-line crankshaft is worth the effort.

My big question; if a dual-engine with a common drive and PSRU (as mentioned above) could even be successfully built and proved itself, where would it stand legally? Would it be like a 337 where the pilot would have to be certified for in-line thrust? ...or...in-line powerplant?
 

deskpilot

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Nice to see this topic opened again.

Whilst looking for info on the VW engine the other day, I came across this:

Emerson Fittipaldi’s Double-Engine VW Beetle | Autopia | Wired.com

So yes, it can be done, will produces LOTS of power, run for a long time and cost a small fortune, I should think. We experimental builders generally don't have a bucket full of money nor a fully equipped workshop to pull off this type of conversion. We can but dream.

BW, as for your last comment, that sort of set-up would still be considered as 2 separate engines here, and therefore, illegal. To be seen as a single engine, both blocks must share common ignition, fuel and exhaust systems. Given that, no special certification would be needed for the pilot.
 
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