User avatar
RayChuang
Topic Author
Posts: 8136
Joined: Sat Jun 24, 2000 7:43 am

PW4084/4090's Are "Moaning Myrtles"?

Mon Sep 25, 2000 10:44 am

Folks,

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."  
 
Guest

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.

TN
 
jim
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!!!!!!!! 

Jim
 
Guest

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.

Who is online

Users browsing this forum: No registered users and 19 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos