On Mon, 03 May 2004 16:51:07 -0600, mikem wrote:

snip

Prop balancing is done on the ground, with the engine running WOT at
whatever RPM is attainable during a static run. For most aircraft,
you cannot get the engine up to climb RPM during balancing.

snip

I have checked the vibe level in-flight on numerous occasions, on
aircraft that acted "strange" after a standard dy-bal.

The newer balancing equipment can log the vibe signature through a
wide frequency range and is useful in these cases also. The older CH
spectrum analyzer could also do a survey of a range of frequencies.

It would seem to me (and forgive me, it's been a few years) that on a
constant-speed propeller that achieving cruise rpm is quite do-able.
I'm thinking that we useta set the rpm approx. 100 rpm over the
desired "cruise" setting using the throttle, and retarded it using the
prop control.

Our thoughts were that balancing at cruise rpm would tend to reduce
the vibration level at the point that the airplane spent most of its
time in the air.

After several years of balancing inside of a hangar (aircraft securely
chained down), a couple of us could guess the IPS to within about .2
on the initial engine run.

On most singles, a reduction of less than about .4 IPS (at 1/1) is not
noticeable from the pilot's seat. Half-order vibrations are much more
noticeable/visible as instrument panel shake, and seem to be a
"harder" vibration. Unfortunately, a dy-bal doesn't do much for a
half-order vibration.

Never had a light/medium twin that "felt" any different, even after a
..7-.8 IPS reduction.

A proper dy-bal job performed by a knowledgeable technician is a
decent value. We did all the company aircraft mainly because we owned
the box...

TC