Peter Cowan/Lexi Cameron wrote:

Do you have a current drawing of Marcotte's "300" (hp) drive?  The attached tif file is a fax he just sent me. What do you think of the design?

Marcotte also gave me the number for Bud Clark in Montana who has the "200" drive on a turbo charged 2.5 l Subaru with about 60 hours. Bud is very pleased with workmanship, noise and vibration levels. He has experience reworking his Ross drive as well.

Peter.

My impression is it is well engineered for an internal spur gear drive.
It is also true that internal spur gear drives are heavier than a
planetary drive of the same torque capacity and cost more.
They also have an undesirable thrust line offset for most aircraft
installations. They lower the engine relative to the thrust line taking
up valuable room needed for a cooling radiator. I don't see the advantage.
Why bother?

Paul Lamar

I see a couple of advantages, Paul.  In the RV-6 there is plenty of cheek room for cooling so the offset simply allows more room on top for manifold and alternator.  You also have to admit that lack of gear noise makes for a more elegant installation.  But the biggest advantage, in my mind, is standard prop rotation allowing the use of a fixed pitch metal prop.  Were it not for the expense and unknown availability of the Marcotte I would have gone with them.

Dave Leonard

If you use the cheek room you complicate the plumbing by having two rads.
Now you are faced with a series or parallel decision. If series the second rad
is less efficient than the first and if parallel you risk getting more coolant flow
through one rad than through the other rad.

Why would you think the gear noise was less? Why would there be a difference?
Can you hear the gear noise over the prop and exhaust noise?

Paul Lamar
 
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