ShopTalk Forums | Aircooled VW Tech & Restoration Help

Hey jake, do I need to do anything special to convert my motor to airplane duty? I want to have about 110-150hp and be dead reliable. Thanks in advance!

Direct drive to the prop or reduction?

Direct drive

I don't know if you have seen this on ebay. There is a guy selling plans for converting a type 4 engine for aircraft use.


http://cgi.ebay.com/ebaymotors/VW-Type- ... 4889QQrdZ1

We'll see what Jake has to say about this, he seems to do magic with these engines but I think direct drive would be quite a challenge. You would have to make 150hp at 3000rpm or less for direct drive to a prop and that would require 263ft-lb of torque. Thats a lot! Too much in my opinion. You would need an impractically long stroke.

If you use a reduction drive that allows you to make power at something like 5000rpm things get much easier.

You could maybe work toward the lower end of your performance goal and use a low pitch higher rev prop (noisy!) and the largest possible stroke and squeeze it out with direct drive...I'm really not sure. You'll probably want nikies for cooling, reliability and weight reduction. You'll need a trust bearing of some sort on the crank for direct drive. Ram air cooling will have to be figured out. If it were me I would build custom fuel injection and ignition systems that were totally independant per cylinder and be sure it would fly on 3 cylinders. This is not an easy project by any means.

I helped a buddy put a 1.8L Subaru in a home built (by us) amphibian 6 years ago. Its still flying pretty nice but we had to use reduction belt drive to get enough performance.

My problem with those plans is the prop on the pulley end. Stress should go at the flywheel end.
This is something I have been meaning to ask Jake as well, though I would understand if he chose not to reply on an open forum (for liability reasons). What kind of "chugger" would you build?

You need to talk to the RevMaster folks and yes, reduc is the way
to go!

I saw a reduc box for T4 on ESlay last year, went for about $155.
I don't see them often though, or i would HAVE one!


I need 200HP for the plane I want to build.
I just sold the kit last yr, that I had been holding onto for 10 yrs....


Had to make ends meet somehow!


Don

Just don't post pics of the Velocity again...or I'll retaliate with pics of the 1.5 wings I have....

BUWAHHAHAHAHHAHHAHAHAHHAHAHA!

Alas, it was sold, but NOT FORGOTTEN!


I WILL own and fly one one day.....unless I die first, then all bets are
OFF!


Don

No way would I put the prop on the pulley end! And you will need a good thrust bearing assembly IMO to keep the axial thrust off the main bearing.

I have seen no problems at all with the syncro belt reduction on the Subaru I mentioned. Reduction IS the way to go. It eliminates the thrust force problem and lets the engine run at the revs it is suited for.

Thanks for all the replies, it looks like I will need to run a reduction. The plane that I plan to run this in is here http://www.airdromeaeroplanes.com/Default.asp?page=62. It says a 102hp, but I wanted more because it would allow me to run a slightly larger prop to make it look more authentic, and add a little performance. isnt 5000rpm a little high to run constant in a vw? I planned on running FI, but as for ignition, I was thinking a distributor/crank trigger or a dual crank trigger setup.

Something around 5000rpm could be your peak horsepower. This could be 150hp for takeoff and steep climbs but you would cruise at something more like 4000 throttled back to much less hp with no big strain on the engine.

Larger props dont require more horse power. If anything they are more efficient and require less hp for a given thrust. They do require more torque but less rpm. Horse power is torque multiplied by rpm so a bigger prop simply means you need a larger reduction ratio boosting torque to the prop but droping rpm proportionately while delivering the same horsepower.

A slow draggy plane multiplies the problems for a VW:
1. you use a redrive to try to match the best power of the engine with the best speed for the prop = more vital moving parts
2. lower velocity prop wash, farther out = less cooling air for engine
...and there are more. I'm planning, when the airframe is more than a frame, to use something around 2l on my KR2 (slick plastic plane).
Here is the airvw list:
http://groups.yahoo.com/group/AirVW/
They really tend to veer toward T1s and pulley-end, and spend countless hours arguing about ancient magnetoes rather than innovative use of vws.