Paul,
I seem to remember that you planned to have a way of tilting and
gyrating the entire motor mount/engine/prop assy while running it full
tilt? Is this so? Most engine/prop/redrives are tested professionally
that way to check the forces.
[Marc Wiese]

Yes we are but it does not simulate what happens when a blade passes

through a wing

wake.

Paul Lamar

For 'another pair of suspenders' over our safety belts, I'd be willing
to chip in for a vibration analysis by a 'certified' prop shop.  This is
relatively inexpensive & is done regularly by guys who cut down fixed
pitch metal props for homebuilts. The shop could be supplied with the
rpm range expected from the prop and the frequency of torque pulses from
the rotary using all (both?) the common reduction ratios. We might get
some useful info on how the prop would survive Lyc-level torque pulses,
as well.

I'm pretty sure there are some shops out there on the left coast that
can do the job.

This might even be a good thing to do before the engine test. If the
vibration analysis revealed a problem, it might prevent a dangerous
situation on the test stand.

Charlie England

That is a good idea. About what would that cost?
Anybody have any names of outfits that do this?

Paul Lamar

Paul, I had my prop train balanced for a special deal of $100, but most
charge around $250 from what I have heard.  It turns out that there was a
fairly high level of imbalance in mine that my seat bottom had apparently
not recognized, vibration level was noticebly reduced afterwards

Ed Anderson

I had my 182 done and I could not tell the difference. I don't think that
is what Charlie had in mind. Or is it?

Paul Lamar

The test I'm talking about uses transducers to vibrate the prop through
a range of freqs that the prop will see in use, similar to the way an
airframe is ground tested for flutter freqs. About 25 years ago Thorp
T-18 & Mustang II flyers were cutting down a common fixed pitch metal
prop & repitching it for faster cruise speeds.  Several of the cut-down
props shed a blade at almost exactly the same distance from the hub.
Vibration testing using the same model cut-down prop showed a ring node
at that point on the blade.  This problem is far less likely with 'glass
blades, but it's cheap insurance to do it anyway.

Charlie England

 
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