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b707 turbocompressors

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b707 turbocompressors

Old 4th May 2004, 11:58
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b707 turbocompressors

hi all,
just was wondering,since i'm not that familiar with the 707's airframe & technical details,if anybody could tell me why the 707 lacks a number one engine turbocompressor?
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Old 4th May 2004, 23:00
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Three sources for pressurization are a plenty for the two packs installed.
In addition, for the times when all turbocompressors fail enroute (an unlikely occurance), 9th stage bleed air is available on most models, expect the freon air conditioning equipped aircraft.
Have personally (when maximum range was required), switched OFF all turbocompressors and used engine bleeds for pressurization (3% improved specific fuel consumptioin). This is OK for freighters, but results in rather low cabin ventilation rate with pax aircraft.

IIRC, the 707 used by the USAF to transport the president, had 4 turbocompressors installed.
Nothing but the finest for the boss, I guess.
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Old 5th May 2004, 18:28
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And all DC8s came out of the factory with 4 TCs.
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Old 6th May 2004, 02:13
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Ah, well Glueball,
Indeed they did.
But did they have engine bleeds available as well?
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Old 7th May 2004, 13:31
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Boeing 720Bs only had two!

What about the early 707-120s. Did they have Turbo Compressors?
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Old 9th May 2004, 23:40
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Yes, normally three.

Turbocompressor and bleed air normally could not be mixed, either one or 'ta other.

If bleeds were used, turbos needed to be started every hour to warm 'em up...otherwise they might not be available for descent.

Descent with bleeds only was rather difficult, to say the least.
Then, the Flight Engineer earned his salary...big time.
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Old 10th May 2004, 09:53
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Question

Out of interest why did that type of eng use a turbocompressor?

I would think that it adds lots of weight/maintenance.

What’s the advantage?
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Old 10th May 2004, 10:11
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The TCs on the 707 were its achiles heal. Always packing up.
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Old 10th May 2004, 15:49
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Oddly enough, only one time did I have a turbocompressor fail on the 707, and I operated several of the early models (with JT4A engines) as well as the -320B advanced.
Turbocompressors were needed because insufficient bleed air was available from the engines at lower RPM's to keep the cabin pressurized during descent. Also, using bleeds reduced the climb performance greatly, whereas the TC's were more efficient at delivering cabin air.
In addition, engine bleeds did not supply enough air for sufficient cabin ventilation with a full (189) pax load.
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