 OT: Airliner air conditioning, I know someone here will know this... |
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| URY914 |
  Nov 5 2004, 02:17 PM
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#1
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I built the lightest 914 in the history of mankind.  Group: Members Posts: 121,116 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None  |
On a car the a/c compressor runs off the engine.
In a house the a/c compressor is run by an electric motor. (you can figure out my next question, can't you?) How is the compressor on a airliner (737, 747,etc) powered? I've never noticed a big v-belt on the engine before. If it is powered by a electric motor, if so how is the generator powered? Is there some type of power take off from jet engines? Thanks, Paul |
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| Cano |
Nov 5 2004, 02:21 PM
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#2
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Member Group: Members Posts: 110 Joined: 29-September 04 From: Goshen, KY Member No.: 2,854 Region Association: None |
It is my understanding, from watching something on the History Channel on the history of HVAC (It was more interesting than it sounds, really) that jet engines compress the air coming into them, and that this compressed air is taken from the engines before fuel is mixed in and burned. Hopefully someone else can elaborate a bit more.
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| GaroldShaffer |
Nov 5 2004, 02:26 PM
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#3
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You bought another 914? Group: Benefactors Posts: 7,624 Joined: 27-June 03 From: Portage, IN Member No.: 865 Region Association: None 
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I thought the pilot just opened a window (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/cool_shades.gif)
Ok ok I know (IMG:style_emoticons/default/slap.gif) |
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| Allan |
Nov 5 2004, 02:27 PM
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#4
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Teenerless Weenie Group: Members Posts: 8,373 Joined: 5-July 04 From: Western Mesopotamia Member No.: 2,304 Region Association: Southern California |
Engine bypass air.
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| URY914 |
Nov 5 2004, 02:29 PM
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#5
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I built the lightest 914 in the history of mankind. Group: Members Posts: 121,116 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
QUOTE(Headrage @ Nov 5 2004, 12:27 PM) Engine bypass air. WTF does that mean. I was on a plane last week an it hit me that the real cool stuff doesn't start until we get in the air with the engines really humming. |
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| Allan |
Nov 5 2004, 02:35 PM
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#6
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Teenerless Weenie Group: Members Posts: 8,373 Joined: 5-July 04 From: Western Mesopotamia Member No.: 2,304 Region Association: Southern California |
On all the planes I worked on, they had ducting that would divert engine intake air to a turbine that was used for the hvac system.
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| SLITS |
Nov 5 2004, 02:37 PM
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#7
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"This Utah shit is HARSH!" Group: Benefactors Posts: 13,602 Joined: 22-February 04 From: SoCal Mountains ... Member No.: 1,696 Region Association: None |
Also, consider the temp of the intake air at altitude - real a/c
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| URY914 |
Nov 5 2004, 02:38 PM
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#8
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I built the lightest 914 in the history of mankind. Group: Members Posts: 121,116 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
So the turbine would only be spinning with enough speed to power the compressor when the plane is in the air.
Correct? |
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| 2-OH! |
Nov 5 2004, 02:45 PM
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#9
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Senior Member Group: Members Posts: 552 Joined: 17-October 03 From: Santa Clarita, Kalifornication Member No.: 1,253 |
On the ground, air is bled off the APU (auxillary power unit - small jet engine) ducted into the heat exchangers and then fanned into the cabin...Once the engines are running, (APU off) air is bled off the 13th and 6th stages of the compressor (on each engine) then run through the heat exchangers and fanned into the cabin...The reason it's not so cool is because the bleed air is around 450 degrees and so it just cannot cool fast enough before it goes into the cabin...Ambient air also plays into the equation...The hotter the day, the hotter the bleed air, the longer it takes to cool it down...However, the air speed through the duct system is constant, so it does not get to linger or re-circulate through the exchangers again...
Once in the air, outside RAM air comes in to help and very quickly when you figure 35,000 feet is around 40 below 0...Also, the tube (airframe) becomes cooler instantly at that temp... Except for the Concorde...That airplane growns 11.12 inches in flight due to heat expansion...Every flight...Remember, metal has memory...What happens to a paper clip after you bend it 100 times... 2-OH! |
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| Kerrys914 |
Nov 5 2004, 02:45 PM
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#10
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Dear, the parts I just sold paid for that part ;) Group: Members Posts: 1,568 Joined: 26-December 02 From: Williamsburg, VA Member No.: 16 |
Well in flight. How about no compressor at all (IMG:style_emoticons/default/ohmy.gif) (IMG:style_emoticons/default/ohmy.gif)
The air outside the plane is cold enough to cool the cabin. They more then likely need to add heat to it before it enters the cabin. This is kind of the same concept large buildings use for cooling requirments in the winter season so they don't need to run a chiller. Cheers (IMG:style_emoticons/default/beer.gif) |
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| maf914 |
Nov 5 2004, 03:39 PM
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#11
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None
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QUOTE(Kerrys914 @ Nov 5 2004, 12:45 PM) Well in flight. How about no compressor at all (IMG:style_emoticons/default/ohmy.gif) (IMG:style_emoticons/default/ohmy.gif) The air outside the plane is cold enough to cool the cabin. They more then likely need to add heat to it before it enters the cabin. This is kind of the same concept large buildings use for cooling requirments in the winter season so they don't need to run a chiller. Cheers (IMG:style_emoticons/default/beer.gif) Sounds good, but remember at 35,000 feet the air is pretty thin. The stewardesses may like the idea of unconscious passengers, but I don't think that would fly with the flying public! (IMG:style_emoticons/default/laugh.gif) |
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| redshift |
Nov 5 2004, 03:48 PM
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#12
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Bless the Hell out of you! Group: Members Posts: 10,926 Joined: 29-June 03 Member No.: 869 |
lol
m |
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| spare time toys |
Nov 5 2004, 03:50 PM
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#13
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hooked on grilling food. Group: Members Posts: 4,059 Joined: 3-April 04 From: West Plano Tx Member No.: 1,884 Region Association: Southwest Region |
It takes air off the compressor section. Depending on what stage it is coming off of it could be upwards of 490 Deg. F( if over that you should get a pack trip) It then goes into a precooler at the pylon. From there it goes into two big heat exchangers and an air cycle mechiene ( think a big turbo) and past the 35 degree valve then into a water seperator. The 35 deg. valve injects hot air back in so the water seps dont freeze.After that it goes into the distribution bay at the back of the forward bag bin then off to cool little Timmy on his way to Grandmas. The out flow valve at the rear closes to start presureization. but as you climb the pres actually decreases from ground pres. The cabin altitude will climb to aprox 10000 feet while the airframe is at 30000+ when you come down it increases the cabin pres to field elevation. That is basicaly it. Hope this helps.
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| SLITS |
Nov 5 2004, 04:00 PM
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#14
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"This Utah shit is HARSH!" Group: Benefactors Posts: 13,602 Joined: 22-February 04 From: SoCal Mountains ... Member No.: 1,696 Region Association: None |
And if you board a plane in Norfolk, VA in the summertime, it blows snow (IMG:style_emoticons/default/sad.gif)
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| J P Stein |
Nov 5 2004, 04:00 PM
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#15
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
The new CF 7E7 is gonna eliminate bleed air ducting.
They'll use a hellforstout APU to do the work conventionally done by bleed air. This makes the airplane MUCH simpler to build and, with the CF fuselage, they can raise the humidity in the cabin to a much more comfortable level. |
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| spare time toys |
Nov 5 2004, 04:11 PM
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#16
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hooked on grilling food. Group: Members Posts: 4,059 Joined: 3-April 04 From: West Plano Tx Member No.: 1,884 Region Association: Southwest Region |
QUOTE(J P Stein @ Nov 5 2004, 05:00 PM) The new CF 7E7 is gonna eliminate bleed air ducting. They'll use a hellforstout APU to do the work conventionally done by bleed air. I would be willing to bet this idea gets scrapped. The airlines will not want to run an APU in flight just to run the packs when they have good engines they can pull air off for virtually no cost |
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| Elliot_Cannon |
Nov 5 2004, 05:37 PM
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#17
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Senior Member Group: Retired Members Posts: 1,922 Joined: 26-March 03 From: Orange County Ca Member No.: 480 Region Association: None |
Bleed air ain't free.
Cheers, Elliot |
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| Dominic |
Nov 5 2004, 06:05 PM
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#18
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Dominic Group: Members Posts: 992 Joined: 14-January 03 From: Vacaville, CA Member No.: 149 Region Association: Northern California |
QUOTE(spare time toys @ Nov 5 2004, 01:50 PM) It takes air off the compressor section. Depending on what stage it is coming off of it could be upwards of 490 Deg. F( if over that you should get a pack trip) It then goes into a precooler at the pylon. From there it goes into two big heat exchangers and an air cycle mechiene ( think a big turbo) and past the 35 degree valve then into a water seperator. The 35 deg. valve injects hot air back in so the water seps dont freeze.After that it goes into the distribution bay at the back of the forward bag bin then off to cool little Timmy on his way to Grandmas. The out flow valve at the rear closes to start presureization. but as you climb the pres actually decreases from ground pres. The cabin altitude will climb to aprox 10000 feet while the airframe is at 30000+ when you come down it increases the cabin pres to field elevation. That is basicaly it. Hope this helps. (IMG:style_emoticons/default/agree.gif) Except for the cabin altitude part....35000 FT at 8.2 psi differential pressure is around 5500 FT cabin altitude. I spent a lot of hours in the air controlling the pressurization (IMG:style_emoticons/default/biggrin.gif) |
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| J P Stein |
Nov 5 2004, 06:26 PM
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#19
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
QUOTE(spare time toys @ Nov 5 2004, 02:11 PM) I would be willing to bet this idea gets scrapped. The airlines will not want to run an APU in flight just to run the packs when they have good engines they can pull air off for virtually no cost It's a done deal....but I will bet 50 bucks if you insist (IMG:style_emoticons/default/laugh.gif) |
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| Elliot_Cannon |
Nov 5 2004, 07:18 PM
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#20
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Senior Member Group: Retired Members Posts: 1,922 Joined: 26-March 03 From: Orange County Ca Member No.: 480 Region Association: None |
Martin,
That's why you get the big bucks. cheers, Elliot PS Congrats. |
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