Guest

Boeing 707 Engine Pylons.

Sun Sep 02, 2001 5:52 am

On Boeing 707 jets with turbofan engines, why is the #4 engine pylon shaped differently than the pylons on engines #1-3? What do engines #1-3 have that is not needed on engine #4? You can see the difference between a #3 pylon and a #4 pylon very clearly in Airliners.net photo id#82418, a Boeing 707-323C.
 
EDR 374
Posts: 77
Joined: Wed Dec 06, 2000 5:50 am

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 5:57 am

It' s because of the air conditioning system. I think the air is sucked in by this pylon.
 
Guest

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 5:57 am

Cabin air intakes - the DC8 has its air intakes in the 'scoops' under the nose.
 
Guest

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 6:13 am

I wonder why there are only three of them rather than four. And doesn't it cause a slight aerodynamic drag difference between the left and right wings?
 
EDR 374
Posts: 77
Joined: Wed Dec 06, 2000 5:50 am

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 6:24 am

Hello Flighter1,
I've found something interesting. Look at this page:
http://www.airliners.net/discussions/tech_ops/read.main/15158/
 
Guest

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 7:02 am

Thanks, EDR 374. I'm new here, and don't know all the ways to navigate through archived materials yet. This helps answer my questions. And my thanks goes to all of you others for your posts as well.
 
Spitfire
Posts: 697
Joined: Sat Feb 17, 2001 2:16 am

RE: Boeing 707 Engine Pylons.

Sun Sep 02, 2001 6:22 pm

Ceilidh, for someone who said he flew 707, it's a quite poor explanation.
In fact due to FAA certification in the 50's they do not allow air conditionning and presurization air to be picked directly from the compressor of the engine. They fear to have a mixed of engine oil in this air. So the imposed to have an high pressure bleed air turbocompressor wich take air directly outside the engine.
Here is exactly what is written in the PAN AM 707 Operation Manual (Pneumatic System 707.161 p1 -- Sep13, 1974) :


"TURBOCOMPRESSORS"

After the engine are started, the primary pneumatic source is from engine air-driven turbocompressors. Ambient air enters a turbocompressor ram inlet on top of the engine nacelle, is compressed, and is then routed to the manifold.

Why is there a difference between the engines mount?

Simply because there is only THREE turbocompressors, mounted only on engines 2,3 and 4.

Hope it helps.Rgds.
Sabena ... Never to be forgotten (12 years already , what a shame !! )
 
milesrich
Posts: 1508
Joined: Sun Jul 06, 2003 2:46 am

RE: Boeing 707 Engine Pylons.

Tue Sep 04, 2001 12:44 pm

While the 707-300B/C had three turbo compressors, the 100B and 720B models only had two turbo compressors on the inboard engines.

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