Fast Jet Cockpit, Pressurised or not?
 

Recently saw this article about a partial ejection:

Irish Luck - Surviving Partial Ejection from A-6 Aircraft

This has led me to wonder (don't ask how) whether or not the cockpit of a fast jet is pressurised?

An 'educated' (or then again maybe not:}) guess would lead me to say yes for comfort among other things, wondered if anyone could shed some light?

If this is the case then what purpose does the mask serve?

Im sure someone here can be a bit more specific but if what i remember in my trade training is right, That a FJ cockpit is pressurized. Just not pressurized enought for breathing without an oxymask at great height. I cant remember the exact figures. But at a certain height the body requires 100% oxygen supply above a height of roughly 10000 feet or somewhere about that. And that below that height an airmix is used.
Hopefully ive got this atleast in the ballpark. Ill have to have a look at my aviation physiology notes from cosford

Prevents hypoxia. Wikipedia is your friend

NATOPS (OPNAVINST 3710.7) forbids flight above 25,000 feet in unpressurized aircraft. The A-6 can certainly fly above 25,000 feet. Its listed service ceiling was at 40,000 feet.

So yes, the cockpit is pressurized.

The mask ensures getting the mix of oxygen and all else "just right" while you are flying, among other things.

essexlad, you have it about right. :ok:

I can well imagine! Is this the reason flying suits have so many pockets as well? :yuk:

Cheers for the replies.

The pockets on the suits are merely just that. The kit i work on, the oxy mask plugs into a personal euipment cpnnector that connects into the seat, which is also where the anti g trousers are connected into aswell.

So they're not for hungover pilots to vacate the product of a friday night's antics into?? :rolleyes: Dissapointed now!

A service ceiling of 40,000ft for the A-6 was mentioned, is this typical of most fast jets? I wasn't aware that you guys operated that high, with the exception of the U2 etc.

No that's for the Sunglasses, Comb, back up Comb, Mirror, back up Mirror, bottle of water in case something happens to the mirrors so he can still view his reflection, and a book, the pilots abreviated guide to NPT... Narcissistic Personality Disorder and how to increase it.... :p

Every aircraft is different. But generally the higher you go, The more gear and kit youll need to wear to counter the physiological effects against the body

Typically partially pressurised so that pressure breathing is not routinely required.

Even at 100% oxygen, at high altitude there is not enough pressure to avoid hypoxia.

But compared to an airliner, where the air is just a standard oxygen /nitrogen mix and thus has to pressurised a lot, to keep the cabin down at 8000', a fj cockpit does not need to be pressurised as much. Saves weight and air bleed load, thus minimising performance penalty.

Pb

It's all about the Partial Pressure (gaseous concentration) of Oxygen in the lungs.

Only partly pressurising means there isn't an explosive decompression if the canopy/ pressure chamber suffers battle damage.

The RAF flying suit was designed so a four-ship leader in a two-crew FJ can buy his formation a round. Every pocket can take a pint glass (plus one in each hand).
Manoevring is tricky, but that's the real reason for sharpening your balance with ACT.

I'd guess that if you've been partially ejected cockpit pressurisation isn't top of your survival worries.

I seem to remember that in another life, the Canberra cockpit was what they called Combat Pressurised i.e. half the height flown plus 2000 feet with a maximum of 25,000 feet. I also remember a few leaky aircraft that showed well over 25,000 when being flown at 45,000 ft. :*:*

After suffering 3 rapid decompressions in one week during airtests, I was very grateful for the Combat Pressurisation and also the AMTC training.

Heads down, look out for the flack

Half height plus 2 is also what I seem to remember, but it's many a year since I've had to use that so I could well be wrong.

1/2 + 2 is pretty good.

Basic rules are cannot fly above 10K' cabin without Oxy Mask etc. Using above that will be ~17K' altitude (will vary with type). Cannot fly above 25K' cabin due "bends", even with Oxy.

In JP circles, effect is:
JP3/4 unpressurised Max Alt is FL250 (used to go higher before this rule came in) - I have a JP4 manual showing time to FL350 is ~20mins.
JP5 FL350 cruise possible with Oxy.
Spin entry is min FL150, so in modern civvy terms where Oxy not always used, JP3/4 cannot spin without Oxy, JP5 can.

Hawk - I remember getitng one (just!) to FL480.

Even if not using Oxy, a mask is a pretty good idea with ejection seats to protect face / keep helmet on ;)

NoD

- and to speak into.

I managed FL497. :E

Cabin Alt
 

Air is a mix of gasses, oxygen is one. As altitude increases the total pressure reduces and the component pressure of each gas reduces accordingly. At about ten thouand feet the lower pressure has significant effect on some bodily functions and supplementary oxygen is required. Thre is a discernable reduction in some bodily functions at lower levels night vision and colour perception. In a well designed pressure regulator supplying a mask the fraction of oxygen increases with altitude until about 25.000' pure oxygen is available. Above that level even pure oxygen fails to reach the partial pressure exerted by the oxgen at lower levels and pressure breathing must be used to supply pure oxygen at greater than surface pressure.

In the Vs a lower cabin pressure level called "combat" could be selected to reduce the impact of cabin pressure loss. The switch was next to the co pilots right elbow and accidental activation was a frequent source of annoyance

From memory (Daltons law and all that), pure O2 at 200mb (roughly 3 psi) is about the same partial pressure as breathing normal air at sea level. The release of nitrogen into the bloodstream and joints from body tissue is the problem unless you pre-breath for a prolonged period beforehand e.g. "the bends" as already mentioned above.

Is this correct ?