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I believe that brings the thread full circle.

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You're right, and discovered just now that I had missed Dan Horton's post
dated 4/15/06 at 7:16pm where he stated in part:

" The JN-4C project had several goals. A friend wanted to proof
custom software written to model torsional vibration in a complex
aircraft drive system (a pusher with with long shafts, might I add). I
wanted a new and improved PSRU. So, we modeled the old drive and then
altered the model for optimum predicted results. Then I designed a
drive to match the model inputs, built it, and ran it with telemetry to
check the accuracy of the predictions. Along the way we developed a
damper and tested it, ran two different props while I had the
telemetry, played with strobing linear vibration, and a whole bunch of
other stuff. End result was proven software and a pretty good PSRU,
plus an education."

So it appears that there is a solution, which may or may not be for sale or
rent...

Peter