# 8 cylinder VW?

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#### deskpilot

##### Well-Known Member
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

##### Well-Known Member
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

##### Grumpy Cynic
HBA Supporter
Log Member
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

##### Well-Known Member
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

##### Well-Known Member
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

HBA Supporter

#### deskpilot

##### Well-Known Member
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

##### Member
...
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

##### Well-Known Member
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.