Corky Scott wrote:

On Tue, 09 Mar 2004 03:18:59 GMT, Peter Dohm
-KNOW wrote:

At the moment, the Geshwender drive (which is back in production despite Mr G's
death) looks like the most reliable scheme for much more than 100 horsepower,
any may still be the best value in the long run.

I agree, but add that this psru was originally designed for high
output engines, engines that start with around 400 horsepower.

For those interested, the reason Fred designed the psru in the first
place was to provide a less expensive engine alternative for crop
dusters. The engine he used was a Ford big block V8. I think that
smaller psru's may be available now but I haven't checked for a while.

When I called him to talk about his psru a year before he died, he
talked me out of using it because it was overkill to use that psru on
an engine putting out only 190 or so hp.

Corky Scott

I agree about it being overkill. An it is not cheap either. However, it looks
like something you can trust.

It's really an interesting dilemma that I will have to face when I get ready to
build. If you don't require true short field capability, and only need a two
seater; you can give up a little power and thrust, and build a v6 version of
Steve Wittman's Tailwind installation.

I admit that I am willing to give up a lot of "utility" for the few features
that I think I need. I really don't consider landing speed very important, but
want adequate cabin width at my own elbows and shoulders.

The basic point is that I believe that I can power my first project with direct
drive. Probably an engine in the 3.8 to 4.3 liter displacement range turning a
56 to 60 inch diameter prop and developing 130 to 150 horsepower. That should
be enough for a cruising speed of about 130 kts tas.

To be really blunt about it, I could probably design a better airplane with
similar performance around a 110 hp corvair engine--if I knew of a source for
*new* heads and crank cases.

I also recognize that such an installation won't work on a Christavia MK4, which
needs a longer prop. Therefore, you really don't have a choice. You are
building the airplane that those 2400 to 2500 rpm engines were designed for! If
you use an automotive conversion, you need a psru. Hypothetically, you could
get about 170 hp from a 350 cid v8 turning a 72 inch prop at crankshaft rpm; but
you would be lugging the engine, so the smaller engine with the psru would last
longer and would still be at least 50 pounds lighter after allowing for the
drive shaft and thrust bearing adapter on the v8.

Peter