bildan wrote:
You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

You must have missed the fact that this all took place in the early
sixties and seventies. Even if they had practical wireless sensors for
this, they didn't have the compute power available economically to
process it. Having said that, you still have to account for the effects
of the sensor. For that matter I think that wireless sensors and
attendant equipment are still not practical for the average modern
homebuilder.

High speed shafting is as old as the industrial revolution. Solutions
to torsion oscillations are just as old. Yes, there are potential
problems but there are also well tested solutions. The trick is
knowing what they are and how to use test instrumentation.

The other thing that jumps out about the Bede saga is that fact that
they were trying to put an experimental engine/prop drive into an
experimental airplane before it was de-bugged and they were doing it
under a deadline.

That's snakebite country. Even things that work everywhere else are
almost certainly going to bite you under those conditions.

It's vital to work one problem at a time. If it's an experimental
engine and prop drive, work on that until it's been running sweetly
for a long time. Then, maybe, think about designing an airframe
around it.

Sometimes an experimental airframe demands an experimental engine.
Engineering is seldom one dimensional, which is why I was poking at the
use of a long flexible shaft as a guaranteed solution. As far as
deadlines go, thats may not be a factor for a homebuilder, as many
projects get completed post mortem, but it is a factor form commercial
endeavors (Moller notwithstanding)

Charles