The title more or less says it all! The engine is a 912ULS with 600 hours total
and the propeller is an Airmaster which is serviced/greased every 100 hours as
specified and is well balanced. The carburettors are regularly checked with
a CarbMate electronic synchroniser and maintained as perfectly matched as
possible.
The aircraft is delightfully smooth to fly, yet there is a "fly in the
ointment".
During the last 50 hours or so of flying, a constant "wow-wow-wow" sound, akin
to that of a piston twin aircraft with unmatched rpm, has gradually increased.
For most flights since the sound first appeared I could level off in the
cruise, select "Manual" on the propeller control and reduce engine speed to
about
4700 rpm, which reduced the sound oscillation to almost nil.
But recently it has become more intrusive, to the extent that further reduction
of engine rpm doesn't eliminate the problem. So I'm thinking of removing the
gearbox and getting it checked over professionally, in case the dogs or their
springs could be the culprits. By the way whenever I do the friction torque
check,
it always results in a reading of around 45 to 50 N-m.
Within the last approx. 20 flying hours I've replaced 2 exhaust springs in
different
locations, which might be indicative of undesirable vibrations
Any advice please before I resort to gearbox removal. I've done it before and
know
what's involved, but if you believe that it might be a wasted exercise please
tell me soon, thanks
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496910#496910
|