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B757 Reverse Thrust Noise  
User currently offlineRick From United States of America, joined Dec 1999, 129 posts, RR: 0
Posted (14 years 4 months 1 week 4 days 2 hours ago) and read 1603 times:

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!

5 replies: All unread, jump to last
 
User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 1, posted (14 years 4 months 1 week 3 days 23 hours ago) and read 1492 times:

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


User currently offlineD L X From United States of America, joined May 1999, 10998 posts, RR: 52
Reply 2, posted (14 years 4 months 1 week 3 days 22 hours ago) and read 1484 times:

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...



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User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 3, posted (14 years 4 months 1 week 3 days 22 hours ago) and read 1483 times:

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


User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 4, posted (14 years 4 months 1 week 3 days 22 hours ago) and read 1470 times:

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.

User currently offlineDL1011 From United States of America, joined May 1999, 386 posts, RR: 2
Reply 5, posted (14 years 4 months 1 week 3 days 20 hours ago) and read 1460 times:

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.


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