Re: 707 engine nacels

From:         Robert Dorsett <rdd@cactus.org>
Date:         11 May 93 01:50:49 PDT
References:   1
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Better late than never...

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In article <airliners.1993.380@ohareChicago.COM> you write:
>I've gotta question about the venerable 707 jet. I've taken a liking
>
>I'm just an airliner fan, no aeronautical engineer mind you, but why would
>the engine attachements to the wings not be identical i.e. symmetrical.

The inlets on top of the engines are ram scoops, for the pneumatics system.
They're connected to turbocompressors which are driven from 16th stage
bleed air.  Only low-pressure air is available from the #1 engine.

Why don't all four have these gizmos?  Guess three was enough!  Why do any
have them?  I would suspect that it was considered desirable to reroute
the air conditioning supply from outside the engine, to preserve mass flow
within the engine and thus eliminate thrust loss--the original engines
on the 707 were rather weak, by today's standards (or even 60's standards).  

In more modern airplanes, bleed air is taken directly from the engine; the 
air conditioning packs have their own, built-in compressors.  My mind
may be playing tricks on me, but I seem to recall some 707 variants with
a completely integrated pneumatics system as well, within the original 
production run (not just the CFM-56 re-engined variants).  Perhaps the
KC-135?



---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd