Thanks to Murry for finding this.

It looks like we can just use the Ford splined part to mount the SGF
damper and an .090" thick 4130 plate to hold the ring gear. This is
easy to make with nothing more than a lathe and easy try.

Paul Lamar


 Looks like the driveshaft coupling I mentioned once. How well will it
 dissipate the heat?

 Dale Davies

 Good question. On second thought we are in this for the long haul.
 It might be a mistake to depend on just one part like the SGF that might
disappear.

 Probably better to build our own. Another advantage to that is we
 can tailor the durometer of the rubber bushings to our needs.

 Paul Lamar

 Hi, they are used in high volume production cars: Mercedes, Corvettes,
BMWs, etc. also sold for marine use.


 Murry I Rozansky

There are many sizes. I don't think they all use the 300 ft pound version.

Paul Lamar

After reading about all the failures related to the damper, I started
to research into the subject of torsional resonance and found this
article on how they have solved their problem on Bede 5. The original
PDF is rather long so I just copy part of it for you to take a quick
look. You can find the original file here
http://ibis.experimentals.de/downloads/torsionalvibration.pdf

The part that I think is of most interest is reproduced here:
"THE FREEWHEEL CLUTCH
The idea for a freewheel clutch came from our machinist, Ray Johnson,
and I must give him the credit. He came in one day and told me that
when he was a kid, his dad had a thrashing machine on the farm They
would run the belt from the tractor to the thrashing machine and it
had a freewheel device on it so that any vibration coming from the old
two cylinder John Deere would be somehow taken care of. The minute he
said "freewheel clutch", it rang a bell. After previously seeing the
oscillating torque reversals of the prop I knew we needed some way to
allow a torque reverse to occur without the bounce back. I had been
looking at centrifugal clutches, manual clutches, etc. that could be
used to disengage and allow some slip. We even tried a test with a
super loose belt with idler pulleys but the slop still wasn't enough.
The torsional amplitude was just too great at the low system frequency
we were dealing with.

Immediately after Ray mentioned the freewheel clutch, I started
investigating and found a Borg Warner clutch that was used in
automatic transmissions It was a double cage, full phasing sprag
clutch. The double cage caused all the little cams inside to engage
precisely at the same time. I had previously had experience with
freewheel roller type clutches at Avian but we had problems with the
brinelling of the clutch races when one roller would engage before the
others and momentarily take the full torque, causing eventual clutch
failure. The double cage full phasing, sprag clutch solved this
problem."

From there, I wonder if Tracy's original design really works or not? I
am not sure if enough on the subject of torsional resonance has been
done. May be even a different approach is necessary?

Also, from my readings, it seems that many people recommends more
cylinders for smoother torque curve. In my simple mind, a smoother
torque curve alleviates the problem. The 2 rotors have one firing
every 180 degree, similar to a four stroke so torque curve is not
smooth. (See information on EPI Inc. on this subject)  A 3 rotor is
similar to an in-line 6 at 120 degrees so may be 20B is more
suitable/reliable for aviation? A 4 motor would be even better. Many
great airplanes in WWI are V12s and they would not have a lot less
problem with torsional vibrations.

I am not a mechanical engineer, so anyone out there please correct me
as much as they can. I am not building yet, not even a license to fly.
But sure hopes to find time to do it soon.

Henry Nee