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)
-- Yes, I'm very sure the belt will completely eliminate the vibration - we
have done hours of tests with our prototype belt drive and saw absolutely no
vibration. The first time we saw this engine shake was when we fired up the
Gen II with the gearbox. Later, when we took out the torque dampening
"doughnut" and replaced it with solid aluminum blocks, the vibration was
dramatically reduced - not eliminated, but reduced to the point where I
think you could actually fly it without the engine breaking loose from its
moorings.
Based on this result, I would conclude that the doughnut is enhancing
rather than dampening the resonance caused by the power pulses. A stiffness
change in the doughnut would probably help, by shifting the natural
frequency of the system, but I'm not convinced that you could eliminate the
vibration completely with that approach, and without more tests, it's hard
to say what the stiffness should be. On the other hand, the flexibility of
the belt seems to be exactly what's required to soak up the power pulses
without exciting resonance.
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
The belt does absolutely nothing to change the peak torque
pulse of any rotary or piston engine. They are still there.
The dotted line in the attached chart is the severe torque pulse
from a one rotor engine.
If the belt is working it is doing the same thing as a properly
designed rubber coupling.
Since you did not have over 100 hours on the engine you had no idea
if the gear teeth would take the jack hammer loads impressed on the
gear box teeth without a rubber coupling. It might seem like that
as the gear box will work for awhile. If the rubber
coupling was removed that could have caused the gear teeth to fail
in the Saddler Vampire that crashed if that engine/gear box combo was
the same one tested without the rubber coupling. The gear teeth
could have been cracked or damaged causing a loss of thrust
when they failed.
We changed the rubber coupling in the High Class aviation two
rotor Rotamax engine from 60 durometer to 50 durometer.
That dropped the idle several hundred RPM. That was the softest rubber
coupling we could get from that company. To use a softer coupling to
get the idle much lower would mean a redesign of the entire coupling
system along the lines of Tracy Crook's highly successful rubber coupling.
The gear box ratio was too low so the takeoff performance of the
engine/aircraft combo was unacceptable. The Rotamax 2 rotor engine could
not rev up to its max HP potential. The geared Rotax 912
version of the same aircraft had much better performance.
As far as I could tell Rotamax had no engineers on staff that
understood aircraft engines let alone rotary aircraft engines.
It is a real shame as we had high hopes for the Rotamax engine.
It looked good on paper at first but management basically screwed
it up. Of course they set out with charge cooling which
is not easy to make work. Wankel Gmbh themselves
finally concluded it was necessary to water cool the e-shaft
to make charge cooling work.
Perhaps if they go into bankruptcy someone will buy the assets
and hire some competent engineers. Rotary engines are harder
to design than they look.
Paul Lamar
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