On Feb 15, 11:43*am, Charles Vincent wrote:
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.

I didn't miss it. I did tests like this in the early 1960's. Load
cells are just Wheatstone Bridges and the wireless tech WAS available
then - it just used discrete components instead of IC's. It needs no
computer power whatsoever since it's an analog signal. If you don't
like wireless tech, slip rings are available.

The sensors are very light and have little or no effect on the shaft
under test - if they did, no one would use them. In any event, you
can put an accelerometer on a shaft bearing housing and see if it's
output changes when you remove the torque sensor.

The only reason they didn't use instrumentation must have been that
Bede was cheap and in a hurry. It was definitely available and not
expensive.

Torsional resonance instrumentation is absolutely practical for home
builders and it doesn't cost all that much. The oscilloscope is
probably the most expensive thing and you could probably borrow one.

If I were going to do the auto engine shaft drive thing, I'd buy a
cheap running engine from a junk yard. If it ran rough, so much the
better. I'd build up the firewall forward drive system on a trailer
with a club prop. Then I'd run it to find and eliminate resonances.
Only then would I build an exact replica of the flight article using
new components and run that on the test stand.