ngr
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Pressurization

Sun Sep 03, 2006 2:46 pm

Aside from human comfort and breathable air, does an aircraft handle differently if it is pressurized vs. unperessurized at cruise altitude?

All movies seem to portray that depressurization causes instant chaos for the plane--and part of it is probably that a major circumstance occurred to cause the depressurization...but is there any basis to this "myth"?
 
FredT
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RE: Pressurization

Sun Sep 03, 2006 3:27 pm

No, it does not handle differently.

However, if explosive decompression does happen, it is prudent to assume structural damage and fly accordingly.

Rgds,
/Fred
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HAWK21M
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RE: Pressurization

Sun Sep 03, 2006 3:32 pm

No there is no Difference.The Panic is probably more to do with the Pax reaction during a Explosive decompression.a gradual Pressurisation Problem may not be Detected apart from the Ear tinge.
regds
MEL
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RichardPrice
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RE: Pressurization

Sun Sep 03, 2006 7:31 pm

Well, technically it should handle differently, because it will weigh less - a 747-400 pressurised weighs several tonnes more than unpressurised (yes, air does have a substantial weight).

Whether that weight difference is enough to make a NOTICEABLE difference in handling is another question.
 
AirWillie6475
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RE: Pressurization

Mon Sep 04, 2006 4:57 pm

Hollywood gets it all wrong during those decompression scenes, like when people struggle to stay aboard and grabbing on things while others are screaming and just sitting in their seats. If there was a rapid decompression at 30K feet or above a humans only have a usefull consciousness of a few seconds before blackout, so forget about not being sucked out because people will be dead unless they use the oxygen masks.
 
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Jetlagged
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RE: Pressurization

Mon Sep 04, 2006 10:37 pm

Quoting AirWillie6475 (Reply 4):
Hollywood gets it all wrong during those decompression scenes

Hollywood gets it all wrong, period. In fact one of the few pleasures in watching a Hollywood aviation based film is seeing how many errors you can spot.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
Tristarsteve
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RE: Pressurization

Mon Sep 04, 2006 10:56 pm

Quoting AirWillie6475 (Reply 4):
humans only have a usefull consciousness of a few seconds before blackout

If you ever listen to the safety briefing before take off, you will hear the flight attendant say 'Put on your own oxygen mask before helping children with theirs.' There is good reasoning behind this statement!
 
FredT
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RE: Pressurization

Tue Sep 05, 2006 6:24 am

Quoting Jetlagged (Reply 5):
Hollywood gets it all wrong, period. In fact one of the few pleasures in watching a Hollywood aviation based film is seeing how many errors you can spot.

The aviation geek Top Gun party game. Each time you spot something which is out of sync with reality, you... erm... consume a healthy, non-alcoholic beverage.

(There are kids in here)

If that's not enough, try to find a copy of Iron Eagle which hasn't been drenched in kerosene and put on fire. Problem is, you will get way too... erm... healthy before you are half way through.

When I was studying AE, a friend of mine who studied law decided to sit in with five of us aeronautical geeks when Iron Eagle was the only thing on the telly. She left after a while, claiming we spoiled the movie. She would probably have been right... if that movie had been spoilable in the first place! Big grin

Sorry for the off-topic rant.
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Starlionblue
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RE: Pressurization

Tue Sep 05, 2006 6:41 am

Quoting FredT (Reply 7):
If that's not enough, try to find a copy of Iron Eagle which hasn't been drenched in kerosene and put on fire. Problem is, you will get way too... erm... healthy before you are half way through.

When I was studying AE, a friend of mine who studied law decided to sit in with five of us aeronautical geeks when Iron Eagle was the only thing on the telly. She left after a while, claiming we spoiled the movie. She would probably have been right... if that movie had been spoilable in the first place! Big grin

Sorry for the off-topic rant.

Now try the same thing for anything with astronautics. Phil Plaitt has done some of the work for you: http://www.badastronomy.com/bad/movies/#list
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
speedracer1407
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RE: Pressurization

Tue Sep 05, 2006 3:25 pm

Seems to me like much of the "chaos" in hollywood decompression scenes involves the ludicrus notion that pilots suddenly lose control and plummet to earth. My favorite is the otherwise excellent Bond movie, Goldfinger. In one of the final scenes, Bond and Goldfinger wrestle over a gun, it fires, breaks a window, and the very rotund Goldfinger is sucked out its tiny opening. In a moment of contrived hilarity, the plane begins an uncontrolable freefall, Pussy Galore is unable to recover, and the two parachute to safety.

For more absurdity, check out the third (I think) Airport movie featuring Concorde. Can't remember if there's anything about depressurization, but certainly a good flick for aviation silliness.

O
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HAWK21M
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RE: Pressurization

Tue Sep 05, 2006 4:46 pm

Quoting TristarSteve (Reply 6):
'Put on your own oxygen mask before helping children with theirs.' There is good reasoning behind this statement!

Thats one statement which at 1st strikes you as why be selfish  Smile.Then if you think it over makes so much more sense.
In fact it was a question asked to me by a collegue from a non Mx dept a few days ago.
regds
MEL
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N231YE
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RE: Pressurization

Wed Sep 06, 2006 2:57 am

Quoting Ngr (Thread starter):
does an aircraft handle differently if it is pressurized vs. unperessurized at cruise altitude?

I would think that the fuel burn is increased in a pressurized aircraft. Pressurization works by "tapping" compressed air off of the jet engines. As you may suspect, by stealing air from the engines, they have less air to work with, so fuel burn is increased as the engine tries to make up for this.
 
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HAWK21M
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RE: Pressurization

Wed Sep 06, 2006 12:46 pm

Quoting N231YE (Reply 11):

Compared to the need for O2 masks for Pax.It would still be preferred to Use bleed air.
Although Freighters could take a different angle there.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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Jetlagged
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RE: Pressurization

Wed Sep 06, 2006 11:26 pm

Quoting Speedracer1407 (Reply 9):
My favorite is the otherwise excellent Bond movie, Goldfinger. In one of the final scenes, Bond and Goldfinger wrestle over a gun, it fires, breaks a window, and the very rotund Goldfinger is sucked out its tiny opening.

Actually that could happen. There was an incident on a DC-10 many years ago, when debris from an uncontained engine failure broke a window and the window seat passenger (probably not strapped in) was sucked out of the resulting hole. You wouldn't imagine you could get through a hole that size, but air pressure is very persuasive. Goldfinger may have been very rotund, but certainly not incompressible.

Quoting N231YE (Reply 11):
I would think that the fuel burn is increased in a pressurized aircraft. Pressurization works by "tapping" compressed air off of the jet engines.

Not exactly. Pressurisation works by restricting and controlling the air outflow from the cabin. The pressure of the air tapped from the engines is unimportant to this process, so long as sufficient cabin air inflow is maintained.

You can fly unpressurised yet still need the packs on, if you want air conditioning. But you're right that with the packs off there would be slightly less fuel burn.

Quoting HAWK21M (Reply 12):
Although Freighters could take a different angle there.

Not sure anyone would want to fly long haul cargo on full time oxygen  Smile
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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HAWK21M
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RE: Pressurization

Thu Sep 07, 2006 1:42 am



Quoting Jetlagged (Reply 13):
Not sure anyone would want to fly long haul cargo on full time oxygen

Hiding behind an O2 mask for some many hrs is no fun.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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Starlionblue
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RE: Pressurization

Thu Sep 07, 2006 2:46 am

Bottled air and oxygen tends to be pretty dry too. Blech.
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KELPkid
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RE: Pressurization

Thu Sep 07, 2006 6:26 am

Quoting Starlionblue (Reply 15):
Bottled air and oxygen tends to be pretty dry too. Blech.

Especially aviation O2-which as I understand, is 100% moisture-free. I believe it, I flew once with a guy down to Mexico, and we had to return at night IFR (Mexico does not allow night VFR). Well, the MEA on any of the usable airways was 15,000 feet, so we were on Oxygen. I was only in the right seat, but I suffered a terrible nosebleed about 1 hour into the flight.

I was told that the reason aviation oxygen is so dry is to prevent frozen condensation in the O2 supply lines at altitude.
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Starlionblue
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RE: Pressurization

Thu Sep 07, 2006 7:59 am

Quoting KELPkid (Reply 16):
I was told that the reason aviation oxygen is so dry is to prevent frozen condensation in the O2 supply lines at altitude.

In diving tanks, I believe the reason for dry air is to prevent rust in the tank.
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
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HAWK21M
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RE: Pressurization

Sat Sep 09, 2006 8:46 pm

In Aviation the reason for Moisture free O2 is to avoid blockage caused by Icing.
regds
MEL
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Tod
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RE: Pressurization

Sun Sep 10, 2006 12:19 am

Quoting KELPkid (Reply 16):
aviation oxygen is so dry is to prevent frozen condensation in the O2 supply lines at altitude.



Quoting Starlionblue (Reply 17):
the reason for dry air is to prevent rust in the tank.



Quoting HAWK21M (Reply 18):
reason for Moisture free O2 is to avoid blockage caused by Icing.

Everyone is correct today  bigthumbsup 

Tod
 
HKA
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RE: Pressurization

Thu Sep 14, 2006 3:06 am

Quoting HAWK21M (Reply 12):
would think that the fuel burn is increased in a pressurized aircraft. Pressurization works by "tapping" compressed air off of the jet engines. As you may suspect, by stealing air from the engines, they have less air to work with, so fuel burn is increased as the engine tries to make up for this.

So as I understand it, the pressurized air is the atmospheric air,tapped from the engines, pass thru the AC system to the fuselage.

Questions:
1. Air at cruising height say FL350 is thin in oxygen, so how do the passengers feel comfortable.
2. Some airlines maintain relatively cold atmospehere which is sometimes annoying.
3. AC air is very dry. Why don't airlines maintain some humidity in the air. Is it because very little moisture at such height and a humidifier will cost money space ?
 
airfoilsguy
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RE: Pressurization

Thu Sep 14, 2006 3:42 am

Quoting HKA (Reply 20):
Questions:
1. Air at cruising height say FL350 is thin in oxygen, so how do the passengers feel comfortable.
2. Some airlines maintain relatively cold atmospehere which is sometimes annoying.
3. AC air is very dry. Why don't airlines maintain some humidity in the air. Is it because very little moisture at such height and a humidifier will cost money space ?

1. Air is bled into the cabin from the engines causing the air pressure in the cabin to rise. Increased air pressure equals more "air". the more "air" you have the more oxygen you get per volume.

2. I agree

3. Humidifiers cost money. Water for the humidifiers cost weight which uses gas which costs money. Also the more humidity you have in the aircraft the faster stuff corrodes, Which costs lots of money.

On the other side the new 787 is planned to have a cabin with a higher humidity then other aircraft. I am not sure how they accomplish this but am hazarding a guess that they have installed humidifiers since the plane will have a lesser problem with corrosion due to composites used in airframe manufacture.
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474218
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RE: Pressurization

Thu Sep 14, 2006 3:56 am

Quoting HAWK21M (Reply 14):
Hiding behind an O2 mask for some many hrs is no fun.



Quoting Starlionblue (Reply 15):
Bottled air and oxygen tends to be pretty dry too. Blech.

Cures hangovers, or so I have been told.
 
David L
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RE: Pressurization

Thu Sep 14, 2006 7:22 am

Quoting Airfoilsguy (Reply 21):
2. I agree

Wear a jumper.  Smile

But seriously, we always have that problem at work but the fact is that it's easier for someone who's cold to use a blanket or jumper to get warmer. If you're too hot, what can you do without being arrested for indecent exposure?  Smile
 
Tod
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RE: Pressurization

Thu Sep 14, 2006 12:01 pm

Quoting Airfoilsguy (Reply 21):
3. Humidifiers cost money. Water for the humidifiers cost weight which uses gas which costs money. Also the more humidity you have in the aircraft the faster stuff corrodes, Which costs lots of money.

On the other side the new 787 is planned to have a cabin with a higher humidity then other aircraft. I am not sure how they accomplish this but am hazarding a guess that they have installed humidifiers since the plane will have a lesser problem with corrosion due to composites used in airframe manufacture.

In-fight humidity related corrosion isn't a big issue considering all the ground time humidity exposure anyway.

The other problem is the gross stuff that grows when there is enough moisture to support it.

Recycled air that come out of full loads of pax thru the ducts then back into and thru pax and ... (repeat as required)  yuck 

Keep planes dry and just chug all the water you can (between good drinks, of course) Damn TSA, don't F-- with my water bottle.

Tod
 
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HAWK21M
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RE: Pressurization

Thu Sep 14, 2006 6:34 pm

Quoting Tod (Reply 24):
Keep planes dry and just chug all the water you can (between good drinks, of course) Damn TSA, don't F-- with my water bottle

Thats one way.Just avoid getting Dehydrated.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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