Re: Difference between engines 1 & 4 of the boeing 707

From: (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         17 Dec 95 02:11:49 
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In article <airliners.1995.1933@ohare.Chicago.COM> "Marcelo F.Cosi" <> writes:
>Does somebody know why the engines-arm were different in most of the

Engines 3-4 had turbocompressors for use by the pneumatics (and thus
pressurization) system.  This was supplemented by normal bleed air from
the engines themselves.  The designers felt they didn't need four of them
(but engine 1 could still provide bleed air).

Modern engines have much higher airflow, and can "bleed" all necessary air
from within the engine for the same purpose.

The above, of course, depends on which engines the airplane has.  CFM-56
retrofits, for instance, have no need for the turbocompressor so they're
not there.

Robert Dorsett                         Moderator, sci.aeronautics.simulation