paco1980
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Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 11:39 am

Hi all,

Just a small question, what are the drawbacks of getting outside air during flight for air conditioning purposes?

Does it increase drag? I would assume so, as it would "somehow" disturb the air flow...
Any balance to find between the authorized volume of outside air and flight performance or Air conditioning systems in particular ?

Cheers,

Paco
 
oly720man
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RE: Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 1:24 pm

If it's from the engine then there's a thrust/sfc penalty and you can poison the pax if there's an engine problem.

http://www.flightglobal.com/articles...cabins-ignored-by-authorities.html
wheat and dairy can screw up your brain
 
Tristarsteve
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RE: Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 1:30 pm



Quoting Paco1980 (Thread starter):
Just a small question, what are the drawbacks of getting outside air during flight for air conditioning purposes?

99pc of jet airliners draw air conditioning air from the engine compressors. It is outside air, it has just been compressed in the engine.

Many years ago the air was drawn from outside, and compressed by a machine of some sort (Rootes blower was one on the VC10) and on the B787 it will come from outside.

The advantage of drawing it from outside a la B787 is that the air is cleaner, the disadvantage is that you need a big motor to drive the compressor.
 
Mir
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RE: Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 3:59 pm



Quoting Paco1980 (Thread starter):
Does it increase drag? I would assume so, as it would "somehow" disturb the air flow...

There will be some small drag penalty, yes. On the other hand, you can use all the air going into the engines to produce thrust, rather than siphoning some off in the compressor to go to the packs. And that makes the engines more efficient.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
KELPkid
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RE: Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 8:28 pm

Another disadvantage is that, in winter operations at nothern lattitudes, you must be aware of where the ozone layer begins. You don't want to be sucking ozone into your cabin, or it might start smelling like Kinko's and causing some people respiratory distress  Wow!
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
skoker
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RE: Drawback Of Getting Outside Air In Flight

Fri Feb 27, 2009 11:26 pm

And of course, and I'm surprised that this hasn't been mentioned already, you get some super-dry air up the higher you go. Cold, too.
 
Tristarsteve
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RE: Drawback Of Getting Outside Air In Flight

Sat Feb 28, 2009 12:04 pm



Quoting KELPkid (Reply 4):
Another disadvantage is that, in winter operations at nothern lattitudes, you must be aware of where the ozone layer begins. You don't want to be sucking ozone into your cabin, or it might start smelling like Kinko's and causing some people respiratory distress



Quoting Skoker (Reply 5):
And of course, and I'm surprised that this hasn't been mentioned already, you get some super-dry air up the higher you go. Cold, too.

Come on guys lets get one fact straight. In all aircraft, the air that you breathe in the cabin comes from outside. Sometimes compressed by the engine, sometimes by an air compressor.
The only exceptions are some fighter pilots on oxygen, and the space shuttle that makes its own.
No airliner yet has a rebreathing system that replaces the CO2 in the air with O2, although most airliners recirculate the air, all that happens to it is that it is passed through a filter, its composition is not changed.
Maybe one day continuos oxygen generators, that are used on fighter aircraft, may grow into the airline world, but it hasn't happened yet.
 
skoker
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RE: Drawback Of Getting Outside Air In Flight

Sun Mar 01, 2009 2:08 am



Quoting TristarSteve (Reply 6):
Come on guys lets get one fact straight. I

How did myself or KELPkid not get this right?  Confused
 
Tristarsteve
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RE: Drawback Of Getting Outside Air In Flight

Sun Mar 01, 2009 7:56 am



Quoting Skoker (Reply 7):
How did myself or KELPkid not get this right?

OK you are both right, but there is not much you can do about it. When you get above the clouds the air is dry, theres not much you can do about it (except carry water on board) and ozone is there. Its the air quality about an airliner, it doesn't matter how you draw it in, its the same air.
 
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DocLightning
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RE: Drawback Of Getting Outside Air In Flight

Sun Mar 01, 2009 11:32 pm

There aren't drawbacks of getting outside air in flight. The other option would be to can the air for the entire flight and that would be prohibitively heavy.

There are some issues, however. The air out there is very cold and very thin. If you lost cabin pressure at altitude, you would pass out within a matter of minutes and freeze to death in a few more minutes. So it needs to be compressed quite a bit to provide a breathable atmosphere. The compression heats the air up quite a bit, however, so then it needs to be cooled in order to not cook the occupants of the plane (passengers tend not to want to fly your airplane if the result of a flight is a bunch of roasted corpses). This all requires a fair amount of energy.

All current aircraft pull the air from the engine compressor, which reduces engine thrust efficiency, but does provide compressed, hot air. This is useful for de-icing and a few other uses, as well as atmosphere. The 787 will not do this. Instead, it will pull air directly from outside, compress it, air condition it, and then use that for the cabin. De-icing and other uses for hot air will be replaced with electricity.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
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JoeCanuck
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RE: Drawback Of Getting Outside Air In Flight

Mon Mar 02, 2009 9:03 am

The drawback to not getting outside air during flight is asphyxiation.
What the...?
 
Tristarsteve
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RE: Drawback Of Getting Outside Air In Flight

Mon Mar 02, 2009 9:34 am



Quoting DocLightning (Reply 9):
If you lost cabin pressure at altitude, you would pass out within a matter of minutes

When you listen to the safety briefing, the flight attendants say, Pull the mask to you and put it over your nose and mouth. Breathe normally. FIX YOUR OWN MASK BEFORE HELPING OTHERS.

The reason they say this is that you will pass out in about 4-10 seconds without the mask. If you lean over to help your child, you will pass out.

There was an accident report in the UK a couple of years ago about a B737 Captain who passed out in the cockpit. The aircraft had depressurised due to a cargo door failure, he put on his oxygen mask, and knocked off his glasses. He took off the mask to lean down and pick them up and passed out. Luckily the flight attendant could come in and pull him off the control column.
 
pilotpip
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RE: Drawback Of Getting Outside Air In Flight

Tue Mar 03, 2009 5:58 am

A number of groups have researched time of useful consciousness and have found it to be much less than previously believed.

In the Mid 30s you might have 10-15 seconds before you're out if you're lucky. I never want to find out. This is one of the reasons that you have to wear the mask above a certain altitude if you're single pilot.
DMI
 
sgtusmc96
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RE: Drawback Of Getting Outside Air In Flight

Tue Mar 03, 2009 11:37 am

During my aircrew training in the Marines, we had to go to a high altitude camber. I don't remember the altitude we reached but, after 20 seconds hypoxia had set in and I almost passed out before the instructor put my o2 mask on. I was unable to even figure the O2 mask out. So, it doesn't take long at all.

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