Michael McGee wrote:

Hi Francois: A question on your engine mount hardware:

You have a dynafocal style mount on the Mistral engine similar (or
identical) to the Lycoming mount.  Did you guys have the vibration damping
mounts made for the rotary engine or are you using mounts from a Lycoming?

The reason I ask is the frequency response of the mounts would be different
by a factor of 2-3.  From what I've learned looking into vibration mounts
the frequency response is part of engineering the mount.  Analogous to a
capacitor in a filter, a mount tuned for a 2500 rpm engine (about 42 hertz)
would be too much for 6000 rpm (100 hertz).  Perhaps the aerobatic mounts
that are stiffer would be more appropriate.

Paul: The Barry mounts we have been looking at on here (22000 series) are
designed for 10-20 Hz.  I realize the rotary is almost vibrationless
compared to the Lycoming.  However, the right mount would make it feel like
a turbine.

I have yet to talk to Barry tech support or Lord tech support.  I'm still
working on my "this is not for an airplane" dialog.  Since I'm using a
standard dynafocal mount it's going to be a tough sell.  I would like to
see what it would take to get the right frequency response designed into
the isolation mounts.

Open to any and all ideas...

Mike

Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode, RD-1C, EC-2

Also the plain of the vibration is different in a rotary. What you have mostly
is torsional vibration about the e-shaft center line  due to the two
combustion
events per rev. At 6000 RPM that is 200 hertz. Well above the 10 hertz
resonance
of the Barry mounts. Perry Mick's engine is bolted solidly to the airframe and
you can only feel a slight buzz.

The Mistral rotary engine is very smooth in the Piper.

All sorts of modes are happening in a piston engine.

Paul Lamar

-

Mike

Maybe I can help out here. An acoustical design engineer I have been working
with on varied projects (eliminating vibration) for over 24 years now is a
genius in this area. His specialty is noise reduction in assembly production
lines. He would want to know the weight you are dealing with and the amount
of torque the mounts would be subject to.

Doug- 

 
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