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Pressurization  
User currently offlineNgr From United States of America, joined Apr 2001, 176 posts, RR: 0
Posted (8 years 3 weeks 4 hours ago) and read 2461 times:

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"?

25 replies: All unread, showing first 25:
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (8 years 3 weeks 3 hours ago) and read 2458 times:

No, it does not handle differently.

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

Rgds,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 2, posted (8 years 3 weeks 3 hours ago) and read 2458 times:

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



Think of the brighter side!
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 3, posted (8 years 2 weeks 6 days 23 hours ago) and read 2416 times:

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.


User currently offlineAirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1
Reply 4, posted (8 years 2 weeks 6 days 2 hours ago) and read 2303 times:

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.

User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 5, posted (8 years 2 weeks 5 days 20 hours ago) and read 2277 times:

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.
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4009 posts, RR: 33
Reply 6, posted (8 years 2 weeks 5 days 20 hours ago) and read 2272 times:

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!


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 7, posted (8 years 2 weeks 5 days 12 hours ago) and read 2235 times:

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.



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17044 posts, RR: 66
Reply 8, posted (8 years 2 weeks 5 days 12 hours ago) and read 2233 times:

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."
User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 9, posted (8 years 2 weeks 5 days 3 hours ago) and read 2176 times:

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



Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 10, posted (8 years 2 weeks 5 days 2 hours ago) and read 2166 times:

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



Think of the brighter side!
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 2 weeks 4 days 16 hours ago) and read 2113 times:

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.


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 12, posted (8 years 2 weeks 4 days 6 hours ago) and read 2065 times:

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



Think of the brighter side!
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 13, posted (8 years 2 weeks 3 days 19 hours ago) and read 2032 times:

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.
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 14, posted (8 years 2 weeks 3 days 17 hours ago) and read 2003 times:



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



Think of the brighter side!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17044 posts, RR: 66
Reply 15, posted (8 years 2 weeks 3 days 16 hours ago) and read 1995 times:

Bottled air and oxygen tends to be pretty dry too. Blech.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKELPkid From United States of America, joined Nov 2005, 6388 posts, RR: 3
Reply 16, posted (8 years 2 weeks 3 days 12 hours ago) and read 1965 times:

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.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17044 posts, RR: 66
Reply 17, posted (8 years 2 weeks 3 days 11 hours ago) and read 1949 times:

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."
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 18, posted (8 years 2 weeks 22 hours ago) and read 1831 times:

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



Think of the brighter side!
User currently offlineTod From Denmark, joined Aug 2004, 1725 posts, RR: 3
Reply 19, posted (8 years 2 weeks 18 hours ago) and read 1813 times:

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


User currently offlineHKA From Canada, joined Jan 2006, 148 posts, RR: 1
Reply 20, posted (8 years 1 week 3 days 16 hours ago) and read 1655 times:

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 ?


User currently offlineAirfoilsguy From , joined Dec 1969, posts, RR:
Reply 21, posted (8 years 1 week 3 days 15 hours ago) and read 1645 times:

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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 22, posted (8 years 1 week 3 days 15 hours ago) and read 1637 times:

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.


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 41
Reply 23, posted (8 years 1 week 3 days 11 hours ago) and read 1592 times:

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


User currently offlineTod From Denmark, joined Aug 2004, 1725 posts, RR: 3
Reply 24, posted (8 years 1 week 3 days 7 hours ago) and read 1565 times:

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


User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 25, posted (8 years 1 week 3 days ago) and read 1537 times:

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



Think of the brighter side!
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