Oxygen

Hi guys! Can anyone explain me why is necessary the oxygen mask of the cabin us pressurized? Apart from the g issues in maneuvering?

Thamks

Ask that again after getting too close to the other guy with the big gun.:music_whistling:

:D

If your cockpit has been shot to bits (and you survived) the air will leak out and you'll be glad to have an oxygen mask!

In addition to the above, the pressurization capability of the canopy is limited and at a certain altitude, it is necessary to use the mask even with the canopy pressurized.

In addition to the above, the pressurization capability of the canopy is limited and at a certain altitude, it is necessary to use the mask even with the canopy pressurized.

Correct...

Cabin pressure runs through three different modes of operation. The military aircraft pressurization works a bit different from a passenger airliner. This is exactly the same reason one must be baro chamber qualified to go above 16K...at least it is this way in the US.

Explaining further. The three modes of operation are unpressurized, isobaric, and differential. For your first 8K of altitude, the cabin will only maintain the same as your outside pressure. Once you cross the 8K mark, the cabin will continue to maintain pressure at 8K all the way up through 23K(roughtly). At 23K and above, the pressure changes to what's known as a differential pressure. At these altitudes and above, the cockpit is regulated to a 3.2 PSI differential when compared to outside pressure.

Even though the cabin is pressurized, the high threat of hypoxia still exists if not on regulated oxygen. Atleast in the US, our pilots are supposed to be on oxygen at 10K and above at all times.

It seems that the press. system in DCS switches to isobaric after 10K feet.

And you might want to add cabin fire, smoke in cockpit and high alt ejection.

And because all of that your mic is inside the mask, so radio comms too...

But not all fighter jets fly with o2. during shows, the blue angles fly without a mask with a boom mic. On the ther hand, they also fly with a 40 lbs spring to have the nose constantly pitch down, and eithout a g-suitt.

When we are at it, I want to throw another question. Is there any type of air-conditioning present in the cockpit? Imagine a fighter jet at middle east desert where temperature can reach 55 C / 131 F.

Yes, there is. It's right there under the oxygen/pressurization controls.

I always fly with Aircon on it saves the cockpit fogging:D

I bet you will need it in New Delhi :)

I was an Aviation Environmental Systems Technician for a while in the military.

Oxygen

Positive pressure is the key. The o2 regulators in our military aircraft are super expensive. They have the best available components and redundancies. The mask is sealed against your face so the o2 system can fill your lungs for you. Sometimes in a highG or stressful situation, breathing isn't on the top of your priority list. As stated earlier, having an oxygen rich environment in the cockpit can be bad if there's a fire. o2 isn't flammable, but remember the flame triangle... heat, fuel, o2.. increase any one of those and your flame increases. I used to soak cigarettes in liquid oxygen, light them, and watch them go off like rockets.

Cooling

There are two cooling systems we use; Air Cycle Turbines (ram air) and Chemical Condenser (liquid chemical).

The liquid chemical system is similar to what you'd see in a car, but the military uses chemicals that make freon seem drinkable in your morning coffee. In some heat exchange systems they use liquid nitrogen when necessary, but that is super inefficient and dangerous due to the high expansion rate (800:1) of a chemical that is -321F. Liquid nitrogen is just super compressed gas. It's much more efficient to compress a gas or liquid in a closed system where it doesn't have to bleed off.

The Air Cycle system is interesting and super efficient: There's a scoop that takes in ambient high speed air from the outside of the aircraft. It flows through a turbine fan that is connected to a shaft to another turbine fan that turns fast enough to pull clean air from around the outside of the compression section of the jet engine(bleed air). The hot air is forced by that turbine system (ram air), through a small orifice. The physical impact of the super heated air being rammed with such force through a small orifice super cools the air to around -30F. This system also inherently pulls any moisture out of the air. Other valves provide pure hot bleed air to increase the temp of that air if it drops too low, depending on the system or area being cooled. On most weapons systems there are elaborate heat exchangers made of classified materials that this air runs through. A good example of this physical reaction of Ram Air is to blow on your hand with your mouth open (like steaming glasses to be cleaned), then blow on your hand like you're cooling it (small orifice in lips).

I bet you will need it in New Delhi :)

Yeah. Make fun. I'm the one who has to bear the temperature variation of 2C - 45C :cry:

Sound effect for the air regulator would be cool.

Yeah. Make fun. I'm the one who has to bear the temperature variation of 2C - 45C :cry:

Just fly the A10 its got aircon:music_whistling:

Hey Strongharm interesting post. You forget about factors like these in a sim. But it all adds to it IMO Thanks.

Oh and any chance of sending over some liquid nitrogen, phase change cooling O/Cing:thumbup:

It seems that the press. system in DCS switches to isobaric after 10K feet.

And I stand totally corrected on this. I only know of the F-16 and F-15 to this point and based it off those schedules. It seems the A-10 is a little different than those two. Perhaps just flat out designed differently, or a product of a weaker ECS system...not sure

The unpressurized area extends to 10K. And from looking at the chart, the isobaric region goes to only about 18K before switching over to a differential pressure regulation.

I saw that there is a switch on the oxygen regulator that lets you switch from normal oxygen to 100% oxygen.

When would you do so ?

1. If the o2 regulator doesn't automatically deliver 100% o2 above 30k ft.

2. In highG high stress situations more oxygen provides more resources to your brain and body.

3. If you're hung over from the O club the night before, this will completely cure it (why I'm alive).

3. If you're hung over from the O club the night before, this will completely cure it (why I'm alive).

lol