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JetSaurus
Topic Author
Posts: 58
Joined: Tue May 13, 2003 10:04 am

757 P&W Reverse Thruster

Wed May 25, 2005 6:39 am

I've often wondered why on P&W powered B757's what the sound is when the aircraft is put into reverse thrust.

This past weekend I stayed at the ATL Renaissance and watch a few [sic] planes take off. During that time just about every single Delta 757 that landed had this weird sound after the thrusters were deployed. It happens towards the end of the reverse cycle and sounds like a blast of compressed air and it much louder than the thrust itself.

I've flown many DL 757's over the years and most times you can hear from the cabin also so it's nothing new to me. Just curious as to why it happens and happens only on the PW 757.
Jack/GPT
 
N808NW
Posts: 358
Joined: Sun Aug 22, 2004 5:03 am

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 6:50 am

Yeah... I too have noticed this on NW 757s while spotting at MSP. It sounds as if the engine cowling is coming back into place before the engines are completely idle (almost as if the pilots are hurrying it up). hmmmm.


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optionscle
Posts: 428
Joined: Tue Jun 01, 2004 10:08 am

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 7:31 am

I remember a post on this a while back. If I recall correctly, the difference in fan speed in the various stages of the engine (N1 and N2 ?) causes a lot of pressure to build up inside the engine when the power is reduced from high to idle such as on landing. The sound you hear is the pressure releasing through a valve. I'm sure someone with more technical expertise can explain it in more detail.

-Andrew
 
LMP737
Posts: 6227
Joined: Wed May 08, 2002 4:06 pm

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 7:36 am

If memory serves me correctly that's the 12th stage bleed opening up.
Never take financial advice from co-workers.
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 10:49 am

Quoting LMP737 (Reply 3):
If memory serves me correctly that's the 12th stage bleed opening up.

Actually it's the 14th stage bleed valve.

Dl757Md
757 Most beautiful airliner in the sky!
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 11:01 am

Isn't it also the 2.5 bleed ring opening?
 
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HAWK21M
Posts: 30125
Joined: Fri Jan 05, 2001 10:05 pm

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 4:28 pm

Is it diffferent on the RB211s.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
LMP737
Posts: 6227
Joined: Wed May 08, 2002 4:06 pm

RE: 757 P&W Reverse Thruster

Wed May 25, 2005 11:12 pm

Dl757md:

Thanks for clearing out some of cob webs upstairs. It's been over two years since I've worked on a Pratt powered 757.
Never take financial advice from co-workers.

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