Brodhead Pietenpol Association

Original Posted By: jkahn(at)picasso.dehavilland.ca (John Kahn)
I spoke with a gentleman in GA mon who built a poplar piet- powered bya GM engine...Got to thinking...has anyone ever really rated thehorsepower,or perhaps more importantly the torque, of different autoengines-AT The RPM they would operate aat in an aircraft- assumingdirect drive is used- I know corvairs generally are direct drive-aforemention poplar piet was direct.. I have been planning to use acorvair as I have several engines handy at the right price_Free! Andalso a lycoming 65HP off of an airboat(which I would rather save foranother project... I would really love to know how the twocompare..either by numbers or better yet- by seat of thepants-testing(which is know to be far more accurate:). Anybody everflown both?Paris________________________________________________________________________________

Original Posted By: Phil Phillips
Just about any engine can be expected to produceabout 1/2 hp per cubic inch in the mid 2000 rpms withthe right cam. That is what most a/c engines produce.So a 2 litre (122 cu/in) car engine will make around 60 hp at 2700 rpm, although very mild cam grind would probably be necessary to getthe torque peak down to the desiredrange.Any number of the newest all-aluminum inline foursin the 2-2.5 litre range would probably do the job.I would be inclined to check out the newer Honda Accord2.2 litre fours. You should be able to get 70hp outof one direct drive. Hopefully it might be a littlelighter than a model A, but I bet the weight saving isn't all that great.The problem is that the cranks are not designed to takethe thrust and gyro loads from a prop. The gyro precession forces when the airplane yaws and pitches quickly are tremendous, and these forces will bend the crank. (Get the tail up quickly on a big taildragger likea C-180 and the nose swings quite a lot as the precessionof the propeller pulls the nose left). On an aircraftengine or a Model A the bearing at the prop is long enough to absorb all the bending force instead of transmitting it to the next main bearing. Car engineshave a normal narrow main bearing at the flywheel.VWs and corvairs deal with it by using fairly small wooden propellers (very small in the VW's case)to keep the forces down. I think an extension shaft and bearing carrier like usedin the Wittman V-8 conversion is necessary personallyif you want to run a 72 inch prop...The Model A is just about the only car engine that canreally deal with a big propeller just as it is.johnk________________________________________________________________________________