Harley motor in a homebuilt?

Canuck Bob wrote:
This month's Kit Planes talks about a Nieuport replica with a Yamaha
engine as the powerplant. The guy has the engine locked in second
gear to supply his reduction. I saw a site with it a long time ago
but can't find it now. Apparently it has hours on it in the air and
pulls ok. Personally I have no opinion on the feasability but we are
experimenters.

When I first started looking at using a V-Twin motorcycle engine, my
inclination was to use a Jap V-Twin rather than a Harley, mainly because
in motorcycles the Jap engines are 1) smoother, 2) more reliable, and 3)
more powerful. However, the big drawback is that the transmission is
integral with the engine.

The plus side of that is you already have a well engineered gear
reduction system in place. The minus side is you have a lot of extra
weight that you really don't need. I've talked to folks that used other
Jap engines; they removed as much of the transmission innards as they
could, leaving only what was necessary. This involved some tricky
welding, and still left a lot of metal in place that wasn't really needed.

My inclination changed recently after I dropped by a local Harley shop
and started asking questions.

Turns out the Harley motor is separate from the transmission.

Turns out you can get a new-in-the-crate Evo engine for about $2900.
Comes with dual sprockets standard on the crank (just waiting for a
chain drive PSRU).

Turns out it's a dry sump engine; requires a separate oil tank. Can you
say "lots and lots of oil, and an oil cooler to boot"? That'll help a
lot in regard to engine cooling.

Turns out you can get it either carburated or with electronic fuel
injection. EFI means I can keep the simple single lever control
(throttle only) of the original plane, but be able to operate
efficiently at varying altitudes.

So, the only hard part is designing and building the PSRU. I've seen
the one at http://www.hog-air.com/. From the pictures it looks like it
ties in to the cylinder heads, while the engine mounts are at the base
of the cylinders. It seems this would put a bending stress on the
cylinder bases that they were not designed for. I hope to get a first
hand look at it next month and ask the designer about it.
--
David Hill
david at hillREMOVETHISfamily.org
Sautee-Nacoochee, GA, USA