flyrotary@lancaironline.net Mailing List Archive

Wind noise is easy to check. Get up a few thousand feet and fly a fake downwind and base leg just as you would if you were at pattern altitude. Once the noise starts, leave the throttle and MP alone but see what happens as you change attitude. If it's wind related you should be able to figure it out pretty quickly. Likewise, once the noise starts, level out and do some slow flight. See if it hangs around. Increase throttle to see if that makes it go away. If it's a harmonic thing in the muffler you'll find out pretty quickly too.

Good luck.

Dwayne

From: Al Gietzen <ALVentures@cox.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Thu, April 15, 2010 11:33:39 AM
Subject: [FlyRotary] Re: Weird sound during descent

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.

-----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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