Torsional Vibration and PSRU Design

Naaaa. Propellers in disturbed flow can excite the system, but
usually the concern is the opposite. Might be a few rare causes. For
example, I've seen (with telemetry) a variation in torsional vibration
due to a propeller-powerplant whirl mode.


Hi Dan,
Can you say a little more about the example of the whirl mode you saw?

Kent Felkins
Tulsa


*** Posted via a free Usenet account from http://www.teranews.com ***

Hi Kent,
Long time no talk. You still doing balance work?

Seemed to be a whirl mode much like that described for a radial with
a too-loose front propshaft bearing. This was with the 3 cyl Suzuki,
an engine with a natural wobble, again much like the radial. The PSRU
was a cantilever upper axle type, so just a little excess freeplay in
the bearing setup was enough to set it whirling at high power. The
torsional amplitude pulsed at about 2 hertz on the o-scope display.
Took awhile to realize what we were had. You could hear it in the prop
noise and see the whirl at night if you lit the prop disk with a flood.
Didn't explore it much as we had other stuff on the front burner.
Just got rid of the freeplay.

Dan

Hi Dan,
Yes, I'm still busy. Interesting example of the Suzuki.
I lost your email in my last CPU crash. And occasionally have wondered what
you was up to.
I'll write you later.


Btw, I'd to take this opportunity make an announcement to others in this
thread.

I've hung out on RAH since ohh maybe 1998-99 and I still check in a couple
times per week.
Anymore though, when I open the cellar door I hear too much scurrying to
want to come down the steps.

Last time I tried to contribute a little benefit of my experience about
balancing and vibration to a thread, some people quickly turned it personal,
inferred me and my friends were crooks and pieces of ****, or P.O.S. I think
was their term. Others here supported them.
In fact some same people contributed to this recent thread!
They know who they are. .
F Amateurs. Go Get a job.

Kent Felkins





"Dan Horton" wrote in message
oups.com...

Hi Kent,
Long time no talk. You still doing balance work?

Seemed to be a whirl mode much like that described for a radial with
a too-loose front propshaft bearing. This was with the 3 cyl Suzuki,
an engine with a natural wobble, again much like the radial. The PSRU
was a cantilever upper axle type, so just a little excess freeplay in
the bearing setup was enough to set it whirling at high power. The
torsional amplitude pulsed at about 2 hertz on the o-scope display.
Took awhile to realize what we were had. You could hear it in the prop
noise and see the whirl at night if you lit the prop disk with a flood.
Didn't explore it much as we had other stuff on the front burner.
Just got rid of the freeplay.

Dan



*** Posted via a free Usenet account from http://www.teranews.com ***