Alitalia744
Posts: 3777
Joined: Thu Mar 30, 2000 8:22 am

DL PW 757 Engine Noise

Sun Nov 07, 2010 6:06 am

Being on a DL 757 almost every week, noticed the PWs make a noise which sounds like an open bleed air valve pointing directly at the fuselage. Always during taxi out. Seems more noticeable in colder temps...

Any DL pilots or 757 fans have an idea what this is?
Some see lines, others see between the lines.
 
Dalmd88
Posts: 2447
Joined: Fri Jul 28, 2000 3:19 am

RE: DL PW 757 Engine Noise

Sun Nov 07, 2010 4:49 pm

My guess is the fan air valve. It is a type of bleed valve. I can't recall the parameters for it to be open, but I think it is low power. It is near the top of the engine on the left side and the number 2 engine exhaust does point at the cabin.
 
Alitalia744
Posts: 3777
Joined: Thu Mar 30, 2000 8:22 am

RE: DL PW 757 Engine Noise

Mon Nov 08, 2010 6:09 pm

Dalmd88,

Thaks, was def the #2 engine that was making the noise, very audible. Seems more often in colder weather, but that could be a perception.

-G
Some see lines, others see between the lines.
 
maddogjt8d
Posts: 207
Joined: Wed Oct 21, 2009 3:37 pm

RE: DL PW 757 Engine Noise

Mon Nov 08, 2010 9:09 pm

What does the noise sound like? Have plenty of 757 videos over the years and would like to see if I can hear it. Am also flying another 757 in a few weeks and would like to see if I can pick up on it any better in the colder weather.
 
Alitalia744
Posts: 3777
Joined: Thu Mar 30, 2000 8:22 am

RE: DL PW 757 Engine Noise

Mon Nov 08, 2010 11:50 pm

MadDogJT8D,

It sounds as tho a rush of air is hitting the fuselage (my better half describes it as the sound a hand-dryer makes with your hands up close or the sound a vacuum makes when you block it with something - not very scientific I know).

We (not sounding arrogant) always sit up front and it is definitely noticeable there.
Some see lines, others see between the lines.
 
maddogjt8d
Posts: 207
Joined: Wed Oct 21, 2009 3:37 pm

RE: DL PW 757 Engine Noise

Tue Nov 09, 2010 3:43 pm

Interesting - I think I know the noise of which you speak of. Does it cut out when the engines rev up from idle? If so then I know exactly what you're talking about. I sit 50/50 up front vs. in the back, so I'll check out some of my videos for it. Thanks!
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: DL PW 757 Engine Noise

Sat Nov 13, 2010 2:51 am

It's the 14 stage bleed valve. It bleeds air off of the high pressure compressor. The exhaust for it is on the left core cowl of the engine so the bleed from right engine will be louder in the cabin than that from the left engine but both are clearly heard from inside the cabin. Some have suggested it is the 2.5 bleed (fan air bleed) but the pressure from that is relatively low and it dumps into the bypass duct so the noise from it is muffled and not easily detected from inside the cabin. The 14th stage bleed valve opens to unload the compressor during start and shutdown, and provide compressor stall protection at certain low power setting conditions, engine transient conditions(acceleration-deceleration), and reverse thrust.

DL757Md
757 Most beautiful airliner in the sky!
 
Okie
Posts: 3608
Joined: Wed Jul 16, 2003 11:30 am

RE: DL PW 757 Engine Noise

Sat Nov 13, 2010 5:14 am

Quoting dl757md (Reply 6):
The 14th stage bleed valve opens to unload the compressor during start and shutdown, and provide compressor stall protection at certain low power setting conditions, engine transient conditions(acceleration-deceleration), and reverse thrust.


I have noticed many a time during taxi but not every taxi, seems they throttle up to gain speed and you hear the turbine come up on speed and when they drop the throttle back toward idle is when I normally hear it. I have heard it on CFM's on 737 but seems to louder on the left side of the cabin.
Still can not beat sitting right behind the wing on 732 monitor the flaps and reverser buckets along with a pretty good ear-full during landing.

Okie
 
AA737-823
Posts: 4955
Joined: Wed Mar 01, 2000 11:10 am

RE: DL PW 757 Engine Noise

Sat Nov 20, 2010 9:53 pm

Quoting dl757md (Reply 6):
and reverse thrust.

Here in Anchorage, in COLD weather, you can hear the Northwest (errr... Delta) 757's landing and turning off the runway because of this noise. And I work across the airport from them!!!
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: DL PW 757 Engine Noise

Sun Nov 21, 2010 1:22 am

Quoting AA737-823 (Reply 8):
Here in Anchorage, in COLD weather, you can hear the Northwest (errr... Delta) 757's landing and turning off the runway because of this noise. And I work across the airport from them!!!

My current assignment at Delta requires that I'm often very near that engine during maintenance runs, sometimes at takeoff power. When the 14th stage bleed opens coming down from high power the sound is so loud that ear plugs and ear muffs together aren't enough. It's easily the loudest sound I'm regularly exposed to and all I work is engines on wing.

DL757Md
757 Most beautiful airliner in the sky!

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