Skip,
I can never tell when your around to comment so I will ask this question
while I have your attention, it has to do with the damper on the single
rotor - would you go for harder or softer rubber in a damper for the
single,
because of the greater torque reversals..
George (down under)



On the single rotor we removed the rubber coupling entirely and went
solid mount. All problems that we were experiencing disappeared .All was
good. The more we got use to it we discovered it had one spot as all
rotary gear boxes have is a resonance at 3,000 RPM or somewhere. The
single rotor was at 3,000. You could never get me to run a gear
reduction on a rotary engine.

We have gone back to a belt drive and 1.9 ratio with the best results.

Skip Gorman

Many people have many hours on gear reductions on two rotor engines.
No problem if you somehow mitigate the torque pulses.
The one rotor torque pulse goes negative so a solid or stiff drive is like using
a jack hammer on the gear teeth. The best thing to use is a fluid coupling.
The problem with that is the size and weight.  A rubber coupling is the next
best thing but it must be designed correctly taking into consideration the
resonant frequencies involved. One needs to understand the principles involved in
order to design or choose a coupling properly.

If one does not use a gear box on any small displacement engine one will
never get the required power to weight ratio. There is no replacement
for displacement on a direct drive light aircraft engine. That is because
a prop needs to be about 5 feet in diameter or more to be efficient
AND the tip speed needs to be less than supersonic. That limits the
prop RPM to below 3000 RPM more or less.

On the other hand gear boxes were used on all world war two piston aircraft
engines over 1000 cubic inches and that includes the very large corn cob
engines like the R4360.

A small rotary engine like the Rotamax needs to rev to 6000 RPM or well
above to obtain a reasonable power to weight ratio. Preferably about 7500
RPM for take off.  A 1.9 ratio with a 6000 RPM engine would mean the prop
is rotating about 3200 RPM. Not a good thing for a small 100 HP airplane.
The smaller the airplane with low power to weight ratio need a larger prop
turning more slowly for good take off and climb out results.

This situation is what slowed the acceptance of the Rotamax engine in
the first place as most pilots are fully aware of these facts.

Paul Lamar


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