"Cy Galley" wrote in message
news:SgxDe.190403$nG6.163164@attbi_s22...
Newspaper shims work very well for wood props.

Not to pirate the thread, but I decided to do absolutely everything I could
to insure a safe and comfortable trip to Oshkosh (Leaving at oh-dark-thirty
tomorrow!). I have the honor of being navigated this year by Lt. Col. R.
"Ken" Wheeler, USAF (ret). He flew in B-17's of the 12th. AF out of Italy.
He deserves every amenity my poor Emeraude can offer.

Towards that end, I flew to Thun Field (1S0) this afternoon and engaged the
gentlemen at NW Propellers to dynamically balance my wooden prop.

This prop is an Ed Sterba 74" x 62" which is three years old. I just
refinished it and statically balanced it. I tapped a 3/4" cold-rolled steel
rod through the center hole and suspended that on two jointer blades which
were set up level. Well, the prop vibrated somewhat before I refinished it
and I can't really say it was any better or worse when I got done. I did
feel a bit of vibration at cruise rpm, say 2400, which increased as the
throttle was reduced, peaking out at 1800 rpm when I could actually see
Weird Jim's audio panel blur.

So, off to the prop men. They had me remove the upper cowl and tie the tail
securely. The prop guy installed a transducer on the forward crankcase
center bolt and had me get back in the plane. The procedure would be to
start the engine, let the oil pressure stabilize, then when I was ready, run
it up to 2000 rpm. I did so, he looked at his gauges, shone (shined?) a
strobe at the prop, then signaled me to back off the throttle and cut the
engine.

He looked things over, picked one of the holes on the starter ring
gear/flywheel and added a bolt, nut, and three washers. One of the other
lads hollered over and said, "How close was it?". He answered, "Point six
four". I had no idea what that meant, so he explained. ".64 Inches per
second (IPS) is the extent of the vibration. Most folks show up with about
that or a bit less. Our goal is to get it less than .2 IPS."

We reran the test and he removed a washer. Ditto again. The next time he
spread out the weight over two bolt holes. That did it! The reading now was
..18 IPS. He said that occasionally they get lucky and make .15 IPS, but not
often.

I can't say that the vibration at cruise is a great deal less, but it is
noticeably reduced. Where it makes a big difference is at somewhat reduced
rpm. Now, when the throttle is backed off, the vibration just flat goes
away. I guess the $150 fee is worth it in the long run for comfort, if not
for instrument longevity and fewer cracks in things like the engine baffles.

Rich S.