Indeed, once resonance does take hold, the energy which must be dissipated
quickly
destroys rubber donuts. This is the reason that rotax only got away with them
on two strokes which have trivial reverse torque pulses. Automotive applications
are a different paradigm altogether as the ground presents an infinite
damping load reducing the frequencies involved vs a free air propellor although
the analogue does still exist: the situation when a student manual transmission
driver pops the clutch at idle and the car lurches back and forth with
increasing
amplitude until it either stalls (a good thing) or something breaks.
In aircraft applications, the lightly loaded and under damped (in air) propellor
mass can quickly increase the positive feedback resonance amplitude and thus
power in the system until things break or the mechanical wear (dogs for example)
becomes destructive (creating exasperating dog-pockets for example). All at
low power input settings by definition. Give full power and the air provides
sufficient damping load to avoid positive feedback resonance - and why this
phenomenon
is not seen in marine drives (water is a terrific damping medium). The
very efficient slippery europa design feeds into this problem vs those draggy
bush plane applications.
Auto conversions with simplistic rubber dampers (read: viking) are inadequate
imhoand
time will tell as fleet time builds. The sprague solution in the yamaha/teal
world are already seeing excessive low time field failures - as predicted
by that website i had quoted.
Fwiw,
Cheers,
PeteZ
> On Dec 27, 2022, at 8:27 AM, JohnFrance <77alembert@gmail.com> wrote:
>
>
> I agree about the donuts, my triumph GT6 Mk2 had them on the drive shafts.
> I also know someone who used them on his ultralight which used a car diesel
> engine.
When it failed he lost drive to the prop and the forced landing totalled
the aircraft. That may be why Rotax didnt use them in the gearbox.
> A very interesting thread this one all the same.
>
> --------
> Europa mono Nr 192
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> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=509810#509810
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