Paul,
Thank you for the press and discussion about our customers who appeared
at OSH. We are impressed and humbled by the fine job Joe, Jim and Gerry
have done in building exceptional aircraft and presenting them at OSH.
There is no doubt that without the patience, hard work and
contributions of all our customers the project would be significantly
more difficult.

A couple of comments:
I believe you are right that the side by side comparisons with the
Vans' aircraft are not completely fair but alas they are the best that
we have. The RPM range that they were tested at may be ideal for the
Lycoming and not for the rotary. As you pointed out also, the 3 blade
props may not be a good speed match to the two blade props. Especially
at high RPM the three blade prop clearly is at a disadvantage. On the
other hand they are great for climbing and acceleration. The MT props
are currently the only option we know of for an electric CS prop that
can handle our power. The best fixed pitch prop we have found is 74
inches long and 85 inches of pitch. As new options become available we
will test to see if they offer any advantages.

A note about torsional vibration. Torsional vibration is not directly
about power, nor directly about power pulses. It is about a harmonic
that exists in the engine. The simple analogy is to think of the
demonstration of a wine glass that is shattered when a certain tone is
played. The glass goes into an oscillation that grows and eventually
shatters the glass. It does not matter how strong or thick the glass
is, if the glass goes into an oscillation it will shatter. The volume
(power) of the tone, though important, is not the critical component,
the "pitch" (frequency) is. So in this simplified analogy you can see
that the number of power pulses has little to do with whether or not
the engine could be in danger of damage due to torsional vibration. All
engines (regardless of the number of cylinders) are equally in danger
if there is a vibration frequency in the system that is of the same
frequency (pitch) as the engine system. To remove the dangers of
torsional vibration from an engine system either a dampener must be
introduced or, a the system must be designed such that the potentially
damaging harmonic is outside of the operational range. (Either a
torsionally soft or torsionally stiff system.)

Pardon me for the over-simplification. It really is much more
complicated than this. Also an engine system may actually have multiple
critical harmonics/pitches in the system. Anyone who is really
interested in this issue will find a lot of resources by typing
torsional vibration into a Google search. For example here is a link;
http://www.prime-mover.org/Engines/Torsional/

We are excited to see the growth in the number of rotary engines
presented by all builders and we hope that the trend continues.
Regards,
Tedd James

The torsional resonant frequency of the two rotor shaft is far above
the possible  12,000 RPM upper limit of the engine. The upper RPM limit is due
to rotor bearing centrifugal loads. In other words unlike a piston
engine the shaft is extremely stiff in torsion. Fortunately that is
not and never has been a problem in the rotary engine.  Any torsional
resonant  problems we have had in the past are solely due to the spring
clutch plate used in the Ross gear box.

Everett Hatch broke a dyno shaft which had to do with the torsional
frequency of the shaft itself and not the mild pulse characteristic of
the rotary engine. In other words all his prior experience had been with
aircraft engines that had a max pulse repetition rate of 5400 pulses per minute.
When he connected a 13B rotary to the dyno the pulse repetition rate went up to
13,000 pulses per minute at 6500 engine RPM which apparently happened to be
in the torsional resonant frequency range of the shaft he was using to connect the rotary to the dyno. Consequently the coupling shaft broke.

Also consequently he misinterpreted this result and attributed the shaft failure
to severe pulses from the rotary. The truth is the power pulse from the rotary is
less severe than that from a four cylinder aircraft engine.

As far as PSRU gear life is concerned it pays to cushion the gear impact loads
with a rubber coupling that absorbs the shock pulses and damps out the coupling resonance or moves the coupling resonant point down to below the idle frequency. Dozens of rotary powered aircraft around the world with hundreds of accumulated
total hours over the past couple of decades have proved that point.

BTW Dave Lemon at Mazdatrix has hundreds of high power 13b hours on his dyno with
no problems. He uses a BMW drive shaft rubber coupling. Midwest rotary engines
now owned by Diamond Aircraft uses a similar rubber coupling on their two
rotor engine.

Paul Lamar