Ian Stirling wrote:
Richard Lamb wrote:

Ian Stirling wrote:

Ernest Christley wrote:


Ian Stirling wrote:



Best tool available to the amateur is a variable speed strobe - Party Light!

That way you can actually look and SEE what's happening.


That'll spot ordinary vibrations.
Torsional ones are a little bit harder.

Especially if you want, as you probably should, a graph of maximum stress
anywhere in the shaft/PSRU/Prop system vs RPM.

A few fine white lines down the length of the shaft will clear up that
problem.


Will they?
It'll obviously show huge torsional movement, but many, especially
shorter shafts may fail before it becomes visible.


Ian, if it won't stay together long enough to turn on the strobe,
it probably needs a little more work...




I suspect you know what I mean.
But to clarify in any case, any shaft will have a given torque/torsional
bending ratio.
Say a half a degree at maximum safe load (or whatever) per 10 diameters.
If the shaft is half a diameter long, it's going to be much harder to
observe, than if it's 100.

The discussion was about long shafts. Rear mounted engine on tractor
airplane. No, it won't do much good on a 6" shaft.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."