Paul Wrote;

The torque fluctuation is not as bad as a two cylinder piston engine.

What kind of flywheel or prop do you have? Seems like a prop
should damp some of that shake. This may be one case where
a heavy prop would help.

Rodger Hilyard wrote:

[Image] Reference torque curve "F" in the chart.
Notice how much and how long the torque is opposing normal e-shaft rotation.

My estimate is the reverse (negative) torque integral is approximately
1/4 of the forward (positive) value, and of sufficient duration to
not be masked by the rotational inertia of the driven system, indeed,
a heavy driven system (i.e. prop) would provide a "stiffer" force
for the positive and negative torque's to react against and would
add further to the torque pulses tending to rotate the engine block.

 The magnitude and duration of the negative pulses are there at
all power and rpm's, so even if the engine seems to run quite
smoothly  off idle, the ability to damage gear drive systems
exists continuously.

Hence my advice to not recommend single Rotor engines for
Aircraft systems.

Rodger

What was the diameter and weight of the prop you used?

It is not that much worse than a two cylinder four cycle aircraft
engine with PSRU of comparable HP and there are several of those 
being used in the ultra light community. It all depends on what 
connects the engine to the PSRU. I am still not willing to give up 
up on a one rotor direct drive or otherwise. Solve the problem!
If the direct drive prop loosens, enlarge the flange. Design a 
rubber coupling for the PSRU that will absorb the torque fluctuations.

Heck back in the old days they had very large one cylinder four stroke
engines. Have you ever seen a John Deere tractor? 
They only fire once in awhile.
 
Paul Lamar

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