Rick
Topic Author
Posts: 125
Joined: Mon Dec 13, 1999 9:37 am

B757 Reverse Thrust Noise

Mon Dec 13, 1999 9:51 am

I have flown the B757 a lot over the last 7 years as a passenger, mostly the Delta Airlines planes. I must say I love the old paint scheme on those. Back to the point. I have noticed that after landing and the reverse thrust is deployed, there is a loud whooshing noise. This noise happens at the tail end of the reverse thrust sequence as the plane is coming to a stop on the runway or rolling onto the high speed taxi way. A lot of times they have to use the highspeed taxi way in Atlanta as the runways are so hot. My question is What mechanism in the engines causes this noise because I have never heard it on other types of commercial jets I have flown on. I have also noticed this same noise coming from the United Airlines 757's and Northwest 757's, I have never heard it on the American or US Airways 757's. Does anyone have insight to this. I have always liked the 757, interesting Machine!
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: B757 Reverse Thrust Noise

Mon Dec 13, 1999 1:12 pm

It may have to do with the ducting of the exhaust. When the reverser sleeve is extended, all fan air is diverted forward to create the reverse thrust. The core thrust of the engine still goes out the tail pipe, but without the fan air with which it usually mixes. During stowage of the reverser sleeve, the fan air is reintroduced into the exhaust duct. It may be the remixing of the hot and cold airstreams you are hearing.

Different B757's have different nacelle/exhaust installations. This may be why some make your noise and some don't. Help that helps.

Interesting question, as we can't hear a lot of those kinds of sounds up front.

Best Regards,

Buff
 
D L X
Posts: 11663
Joined: Thu May 27, 1999 3:30 am

RE: B757 Reverse Thrust Noise

Mon Dec 13, 1999 1:18 pm

not that I know the answer to this question, but I find it interesting that you noted the airlines you heard the sound on. The ones you heard it on were all Pratt powered. US and AA are Rolls powered. Hmmm...
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: B757 Reverse Thrust Noise

Mon Dec 13, 1999 1:29 pm

Good observation D L X. Maybe the opposite of what I offered is true, and the fully cowled exhaust of the 535E4 prevents this noise. The P&W installation mixes the fan air outside the primary exhaust duct.

Best Regards,

Buff
 
UAL747
Posts: 6725
Joined: Mon Dec 13, 1999 5:42 am

RE: B757 Reverse Thrust Noise

Mon Dec 13, 1999 1:39 pm

I was on a flight from Denver to Boston on a UAL 757 and I also heard this noise. However, I heard it more than once. I heard it right before the aircraft took off and other times during the flight. I don't know if it is the same noise, but I have heard something similar.
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way
 
dl1011
Posts: 315
Joined: Tue May 18, 1999 6:42 am

RE: B757 Reverse Thrust Noise

Mon Dec 13, 1999 4:04 pm

I have also heard that noise on the p&w 2000
powered 757's. Pretty sure that it is caused
by the high and/or low pressure compressor
bleed valves opening and dumping air into the
cold stream.