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XB70
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Origins Of Bleed Air For Pressurisation

Thu Apr 03, 2014 6:38 am

I am researching the origins of the use of Bleed Air for Pressurization in Commercial Jet Aircraft and any input would be much appreciated.

With the introduction of commercial jet powered aircraft there was extensive use of turbo compressors as a means of providing air for pressurization and heating. Aircraft like the Comet, Convair 880, VC-10, Boeing 707, DC-8 etc.. appear to have extensively used turbo compressors, a technology introduced on aircraft like the Lockheed L-647/749 Constellation in 1943.

It appears that the French Caravelle was the first commercial jet aircraft to use bleed air directly for pressurization (without turbo compressors) when in flew in 1955. Yet it seems US aircraft continued to use turbo compressors until the Boeing 727 arrived in 1963.

It has been suggested in 2001 and 2005 on this forum that the reason for this was:

"Back in the old JT3D / Conway days the bleed air provided from the engines was too oily to be used directly for cabin pressurization, therefore they used the turbo compressor inbetween."

"In the early jet airplane days, the FAA did not allow engine bleed air to be used for cabin pressurization, they had to use outside air. The turbo compressors used engine bleed air to drive a pump the compressed the outside air and pumped it into the cabin."

I have found at least six reports from the early 50s from Boeing, Douglas, North American etc.. that show their awareness of contaminated bleed air (oil contamination) dates back to the introduction of the J-57 engine and the first use of synthetic jet engine oils. The 1955 North American paper also states:

"“The Separate Compressor As A Solution' – This method of eliminating contamination is considered to be the most positive… also the heaviest, most complicated and most expensive.”

I have also read a 2008 IFALPA Safety Bulletin - 09SAB02 (21 May 2008) - which states:

"The FAA had mandated the use of turbo compressors because of the risk of cabin air becoming polluted due to leaks in the compressor bearings."

However, I cant find any official FAA documentation to confirm this. If anyone has a reference in this regard please let me know.

Thank you.
 
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Jetlagged
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RE: Origins Of Bleed Air For Pressurisation

Thu Apr 03, 2014 11:08 pm

The VC-10 didn't use turbo compressors, it used mechanically driven compressors. It was possible to use bleed air for pressurisation on the 707 so it's use can't have been prohibited by the FAA. Not using bleed air was a precautionary measure, and also a continuation of existing technology from piston engined aircraft. Contemporary British jet aircraft to the VC10, the Trident and BAC 1-11, used bleed air.
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wingscrubber
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RE: Origins Of Bleed Air For Pressurisation

Fri Apr 04, 2014 1:55 pm

Also don't forget to mention the 787 - I believe it's gone with electric compressors instead of bleed air supposedly for improved efficiency, but incidentally it does also help to protect against fume events.

The BAe 146 has had a lot of fume events due to the bleed air system, http://aerotoxic.org/ is a good website about the topic, if a little scaremongering.
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zeke
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RE: Origins Of Bleed Air For Pressurisation

Mon Apr 07, 2014 3:16 pm

Quoting wingscrubber (Reply 2):
but incidentally it does also help to protect against fume events

Does not stop engine or APU exhaust from entering the packs.
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m1m2
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RE: Origins Of Bleed Air For Pressurisation

Wed Apr 09, 2014 8:18 pm

I don't think he meant engine or APU exhaust fumes. This would only be a problem on the ground when the aircraft has no forward speed.

I'm thinking he meant from oil leaks, or other contamination. I'm not sure how the packs run on the 787, but I'm assuming they still have an ACM being driven by the electric compressors. Having said that, most of the contamination I've seen in air conditioning systems came from oil leaks within the ACM itself.

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