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Boeing 707B

Sat May 29, 2004 2:34 am

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Photo © Greg Weir

look at that picture. the #1 engine does not have the same vents above the leading edge of the cowling as the other three engines. why is this? is this the case only on this one a/c, or one model of the 707?
"...cannot the kingdom of salvation take me home."
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RE: Boeing 707B

Sat May 29, 2004 2:43 am

You win kudos from me for being observant, but I can't tell you why it is that way.
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RE: Boeing 707B

Sat May 29, 2004 3:31 am

The first 707's did not use bleed air for presurization but used turbo compressors. The number 1 engine was not fitted with a turbo compressor as it was determined that 3 were more than enough. The inlets and ducting for the air for pressurization was fed through the pylon. It was thought at the time by the powers that be, that the bleed air had too much chance for oil contamination.
Hence your first example of a bleedless engine at least for pressurization, but oh wait that is something new for the 7E7.


[Edited 2004-05-28 20:37:45]
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RE: Boeing 707B

Sat May 29, 2004 7:17 am

Most 707-320B/C looked like that, but as I recall they didn't all have three turbocompressors-- one pylon might be empty. A few -320Cs had a #4 pylon like the #1-- AA's freighters, if no others.
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RE: Boeing 707B

Sat May 29, 2004 8:26 am

ALL models of Boeing 707 and 720 aircraft had turbocompressors for cabin pressurization, and in addition SOME also had provisions for engine bleed air for cabin pressurization as well.
If engine bleeds were used, cabin ventilation was rather severely compromised, and descent had to be started much furhter out due to the low volume of bleed air available.
Having said this, if ultimate range was a consideration, using engine bleeds improved SFC by approximately 2.5% with fan engines, 2% for non-fan engines. In this case, turbos needed to be started every hour or so. If this was not done, they might not start at ALL due to cold soak, and be unavailable for use during descent.

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