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PW4084/4090's Are "Moaning Myrtles"?

Mon Sep 25, 2000 10:44 am


I was at the end of SFO's Runway 1R today and saw several UA 777-200/200ER's take off from this runway.

One thing I immediately noticed about these 777's: the Pratt & Whitney PW4084 and PW4090 engines mounted on the UA 777's make a very distinct high-pitched "moaning" sound during taxiing. That sound disappears when the engines are revved up to full power to start the takeoff run. It's relatively constant, unlike the high-pitched "mooing" sound coming out of the center RB.211 engine on an L1011 that comes and goes.

Is this "moaning" sound because at certain fan blade speeds there is a "resonance" frequency that generates this noise?

P.S. No awards for where I got the phrase "Moaning Myrtle."  

RE: PW4084/4090's Are "Moaning Myrtles"?

Mon Sep 25, 2000 1:44 pm

Maybe it's from the accessory drive. Anybody else? I'm just throwing out ideas.

Posts: 448
Joined: Thu Jul 29, 1999 8:12 am

RE: PW4084/4090's Are "Moaning Myrtles"?

Tue Sep 26, 2000 5:15 am

I'd have to disagree with the idea of the accessory drive. Once a jet engine has lit off, there is no other noise (except the engine its self) to be heard outside the aircraft.

I have read where even the designers aren't really sure WHY a jet makes its particular noise. Some scream, some growl, some moan, some buzz. Each type is different, and that's what makes Stage 3 so much fun!!!!!!!! 


RE: PW4084/4090's Are "Moaning Myrtles"?

Sat Sep 30, 2000 9:35 pm

I don't care about no prize, but you got that from the Harry Potter books.

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