How does it deal Jets with

[alrot]

How does it deal Jets in High altitude? (This is a question I been wonder all the time)
I never heard anything of CO2 and oxigen levels (Or filters at least)in the cockpit , for example how does a pressurise boeing 747 at FL350 with 400 people on board keep all in good levels, Never seen O2 & CO2 oxigen Tanks controls or indicators in diferent parts of the plane(like first class or in the rear ) in the cockpit

Thanks


Alex

[C]

Put in the most simple terms, there will be several large oxygen tanks in the lower fuselage (typically). This combined with several engine driven compressors will provide oxygenated air for cabin pressurisation, typically a cabin alitude of 8000ft. The level of pressurisation is then set and monitored from the cockpit.

[beaky]

The cabin is not sealed. That's the important thing to remember. The oxygen tanks are for the emergency oxygen system (the little masks that pop out if you lose cabin pressure)... the air you breathe on an airliner comes from outside. CO2, etc does not build up to dangerous levels for that reason.

Here's how it works: air is forced in from the slipstream. The compressors mash it into the cabin. In order to maintain a specific pressure, there is a relief valve that will open when the pressure reaches X amount (set by the crew).
The compressor is constantly working to raise the pressure to a point higher than "X", so the valve is usually open. This allows a decent transfer of fresh air, although on long flights it sure seems, sometimes, that you're sealed up in there.

[alrot]

Very Clear Sean , but Imstill confuse ,Make sense of the engine,air compression to the inside and by logic the temperature with should be very low

[Nexus]

[quote]Very Clear Sean , but Imstill confuse ,Make sense of the engine,air compression to the inside and by logic the temperature with should be very low

[Brett_Henderson]

And.....

but at FL300 air?   this air is rare without oxigen..

The oxygen percentage is the same (or pretty close). There's less oxygen because there's less air per cubic foot. Once it's pressurized, all is well..

[expat]

Cabin pressurisation, temperature control and breathing air are all part of what is know as cabin conditioning. I could write a whole book here, and only scratch the surface. So I wont

There is a mixture of correct and almost correct information in this thread.
The aircraft takes off. Pressurisation begines at 300 feet and is progressively increased with the climb. This figure of 8000 feet cabin altitude pressure, though correct, you will not reach that pressure until the aircraft is at about 20000 feet. As I said, it is progressive. Pressurisation  also ends at about 300 feet on approach. The aircraft never lands pressurised. In the event of an emergency evac, cabin pressurisation will put up to 8 tons per square inch on a door. (it always makes me laugh when the papers wet themselves with a story about a passenger who tries to open a door in flight. Arnie and the whole of WWF would not be able to open the door), so for this reason it is dumped. Also I can tell you, being in a pressurised aircraft on the ground is a very, very uncomfortable sensation. I hate doing cabin pressurisation tests.

The short version of the system is.
Air bled from the compressor (the 737-800 from 5th and 9th stage depending on engine speed)
It is very, very hot even though it has come from the compressor (it does not matter if you are on the ground of  30,000 feet, it will burn) it needs to be cooler. It is cooler by the precooler using fan bleed air.
It then passes to the packs. They cool the air, compress it, cool it again and then the water is extracted from it. This water is then sprayed into the heat exchangers to increase cooling efficiency. Once it has passed this it is then heated up to the required temperature using the pack air that is tapped off before it enters the Packs. Once heated it passes to the mixing manifold where it is mixed with recirculated air and then pumped into the cabins. A direct result of this is pressurisation. That is controlled automatically (and with manual backup). At the back of the aircraft we have an outflow valve. This is electrically modulated to maintain a set bleed of air from the cabin in accordance with the altitude of the aircraft. Also we have overpressure valves and negative pressure valves that work in the event of, well what they are titled.
Regulations FAR and JAR sttre that fresh air must be provided at about 0,283 cubic metres or 0,35 kg per minute. So for a 737-800 an air flow of about 70 to 90 cubic metres per minute is required.

This is a short and simplistic version. If anyone is interested, I have systematics of the system.

Matt

[C]

The oxygen tanks are for the emergency oxygen system (the little masks that pop out if you lose cabin pressure)...

Good spot. My mistake...

The cabin is not sealed. That's the important thing to remember

Quite. The aircraft type I'm converting to at the moment is getting on a bit (understatement), and reknowned for being holey (poor door seals, valves etc). Most of the fleet have four compressors, which cope ably, particularly with unexpected leaks during flight, but one or two of them only have two, which struggle like hell!

[alrot]

[quote]And.....


[quote]but at FL300 air?

[Brett_Henderson]

I had to do some research, to be sure..  Since no oxygen is added to a pressurized cabin, I just assumed it...

Here's a quote from this site:


http://www.bmj.com/cgi/content/full/317/7165/1063

Although the percentage of oxygen in inspired air is constant at different altitudes, the fall in atmospheric pressure at higher altitude decreases the partial pressure of inspired oxygen and hence the driving pressure for gas exchange in the lungs.