On Feb 14, 6:38*am, jan olieslagers
wrote:
Yesterday I was talking to a friend who plans to power his single-seat
slow flyer with an engine from a Citroen Visa. I suppose this engine (a
linear descendant from the famous Citroen 2CV) is not well known in the
US, it is an air-cooled 2-cylinder boxer, in this particular application
it would produce some 45 HP.

My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop. Now I'm sceptical 'cause I heard all kind of bad
things about transmission axles driving propellers, vibration not the
least. But he answers the axle needn't be long, as the engine is only a
2-cylinder.

Any thoughts / ideas / comments / experiences?
TIA,

Not a bad concept. I've spent some time thinking about the same
layout with larger engines. It has several advantages and a few
disadvantages.

Some advantages are that it moves the weight of the PSRU to the rear
of the engine and raises the propeller hub for better prop ground
clearance. It puts the radiator at the front of the engine with the
water pump mounted fan right behind it.

I think the key is that the shaft has to be thin and flexible to get
its resonance well below that of any other part of the drive train.
Going the other way to make a very stiff shaft raises its natural
resonance frequency so it's likely to match some other component
resulting in destructive resonance.