Jeff;
Hard to tell, but sounds like something
vibrating at the particular frequencies set up under those conditions. There
are times I also hear strange noises on descents, and very low throttle
settings – sometimes there, sometimes not. You finally just accept them
as normal.
Not likely anything to do with the
thrust bearing. I have a pusher and you’d think the forces are
reversed; although I guess if the engine is being driven by the prop rather
than vice-versa, the result is the same. If there is
some issue about steep descents, I’d like to know as well.
Al
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Jeff Whaley
Sent: Thursday, April 15, 2010
7:13 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Weird sound
during descent
I have been hearing a weird buzzing sound usually
detectable on base leg at low power settings. It is hard to describe in
text but is repeatedly as zzuuzz, zzuuzz, zzuuzz .
I thought it was wind noise escaping between the
fuselage and gear legs, as there are no fairings between the fuselage and top
of the cub-style gear.
Last night it was bit bumpy and during one descent
there was a good bump that lifted me against the seat belts -- the noise
stopped.
Tracy had cautioned me against low power steeps
descents, something about thrust bearing and/or snubber – maybe refresh
me on that one Tracy?
However, an approach speed of 500 fpm, 80 mph, 3000
rpm, mp <10”, is not what I’d consider steep.
Anyone care to give me a clue as to what I might be
hearing?
If I get a chance to fly this weekend, I’ll
experiment to see if I can stop/change the noise with speed or attitude
adjustments.
Jeff
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