Jonathan,
By putting the Airmaster in MANUAL mode the prop is fixed, so hunting of the
prop
is unlikely if the warble persists at any RPM. As for blade tracking, if the
blades are still firm and not twisting, that rules out a tracking issue
normally.
I left some super thin painters tape on all three blades one time after a
touch-up.
I know, a good preflight and proper workmanship would have prevented this...
I couldn't figure it and quickly took the brand new plane down to the dealer.
After hauling the plane down to have the gearbox checked, Lockwood could
find nothing. When picking up the plane, I found the thin painters tape, pulled
it off and behold, a good sounding engine again and I had a much lighter
pocket book.
Another "brain fart" I'm not proud of, an owner came in with a blade that was
beginning
to show signs of leading edge wear. The thin metal leading edge guard
was slightly dented and pitted on his Warp Drive. I didn't notice it was
becoming
de-laminated (slight bubble). I should have caught it on a close inspection
but didn't. This was not a warble sound from the outside, it was a sharp
hum or buzz, but inside it seemed to have a warble. Rebuilt the blades (fairly
cheap) and all was good. If your leading edges are unevenly worn or pitted,
and or the trailing edge of your leading edge tape even slightly loose, refinish
the blades.
Folks are right, the book says for most gearboxes, an overhaul at 600 hours is
required for continuing maintenance. Gearboxes are normally sent off for the
overhaul (which takes 30 minutes at Lockwood). I pull the prop, the gearbox and
drive down and have lunch with the boys, then come back. Nice visit and about
$3-400 if no main gear parts are needed. The time is one hour and the new
seals and bearings are quite cost effective.
Exhaust resonance is tough to find. Exhaust leak soot and spring failures
generally
point the way that something is amiss. One must be very careful trying
to troubleshoot this during ground runups.
A problem with the sprag clutch can cause noise, but that is clearly heard
around
an idling engine, so I doubt that is an issue.
Vibration noise from the airframe is tough to track. Loose gear components,
speed
kits, and anything that vibrates in flight will pick up a power plant frequency
and resonate along with the other vibrations. A slight difference in frequency
will cause a distinct increase and decrease (like that propeller sync
example) giving you fits troubleshooting those type things.
Keep us all posted.
Bud Yerly
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