Ejection seat thoughts

[Manuel_108]

The other day, I was sitting in a plane thinking about how my eardrums would instantly pop if we had an explosive decompression at 39 000 ft. What would happen in a fighter jet though?

 

Imagine, you flew at 42.000 and had to eject, would you be deaf for the rest of your life or does the helmet save you? What do you guys think?

[sobek]

The helmet doesn't maintain pressure on your eardrums and respiratory system, so it wouldn't help.

 

Whether your eardrums will really rupture is a question of how steep the pressure gradient is during such an occurrence, so how much does pressure change in what amount of time, and whether your eustachian canals can cope with the amount of change.

 

Lastly, ruptured eardrums do not necessarily mean that you are deaf. Like most tissues in the human body, eardrums have a limited capability for self repair, although your hearing might be impaired afterwards, depending on how well the rupture heals.

[SilentGun]

Well if you ejected at 42K, I'm pretty sure you would die of hypothermia before you reach 20K.

 

So it really wouldn't matter if your eardrum burst ;)

[karambiatos]

Well if you ejected at 42K, I'm pretty sure you would die of hypothermia before you reach 20K.

 

So it really wouldn't matter if your eardrum burst ;)

The seat won't fully the main parachute until it's at a safe altitude.

[Manuel_108]

Interesting :) Anyway, ejecting at 42k must bring your body to the limits I gather.

[sobek]

Well if you ejected at 42K, I'm pretty sure you would die of hypothermia before you reach 20K.

 

Or decompression/altitude sickness.

[Gate-5]

You might want to look up the Virgin Galactic Spaceship Two crash, Peter Siebold was ejectet out of the spaceship at above 45t feet and mach 1 and survived.

 

http://www.latimes.com/business/la-fi-virgin-pilot-testimony-20150727-story.html

Edited September 19, 2015 by Gate-5

[SimFreak]

The other day, I was sitting in a plane thinking about how my eardrums would instantly pop if we had an explosive decompression at 39 000 ft. What would happen in a fighter jet though?

 

Imagine, you flew at 42.000 and had to eject, would you be deaf for the rest of your life or does the helmet save you? What do you guys think?

 

Part of ejection system has oxygen bottle that either automatically turn on or require pilots action. The pressure of that oxygen last about 10ish minutes....

[sobek]

Part of ejection system has oxygen bottle that either automatically turn on or require pilots action. The pressure of that oxygen last about 10ish minutes....

 

But that does only help with hypoxia, not decompression.

[Manuel_108]

You might want to look up the Virgin Galactic Spaceship Two crash, Peter Siebold was ejectet out of the spaceship at above 45t feet and mach 1 and survived.

 

http://www.latimes.com/business/la-fi-virgin-pilot-testimony-20150727-story.html

 

Wow, sounds like one of the most extreme scenarios one can experience. Can't imagine the pain he must have felt during the decompression.

[Aginor]

In 1958 two pilots ejected from a Canberra flying at 57,000 ft.

They survived. So it seems it works. :)

 

EDIT: Here's the story:

https://docs.google.com/document/d/1Yu2V3IZz87ai73_VNB35FmgJGixgPhPMLKwFYkMm9lU/pub

Edited September 19, 2015 by Aginor

[SimFreak]

But that does only help with hypoxia, not decompression.

 

Correct. So they may experience some symptoms which are not fatal most of the time. Usually USAF would put you in a chamber after experiencing high alt decompression.

[NeilWillis]

So, a little frostbite, a lot of discomfort at high altitude, which reduces as the air pressure rises during the descent, and the Canberra pilot was indeed deaf when he landed.

 

Does anyone know just how much air pressure there is inside a cockpit at high altitude? I presume the cockpit altitude would be well above ground level pressures, so the pressure differential may not be as catastrophic as would be the case if ground level air pressures were maintained?

[SimFreak]

So, a little frostbite, a lot of discomfort at high altitude, which reduces as the air pressure rises during the descent, and the Canberra pilot was indeed deaf when he landed.

 

Does anyone know just how much air pressure there is inside a cockpit at high altitude? I presume the cockpit altitude would be well above ground level pressures, so the pressure differential may not be as catastrophic as would be the case if ground level air pressures were maintained?

 

Which alt pressure inside the pit? That depends on the aircraft. I think U-2 keeps it at 30k ish. While KC-135 can be at 5000-8000. So fighter probably will be somewhere in between.

[sobek]

One should add that the U-2 pilots wear space suits. :)

 

IIRC the A-10 is at 13000 when flying at 20000.

[Backy 51]

Google Aerospace Physiology or Aerospace Medicine for the answer to your questions.

[Manuel_108]

In 1958 two pilots ejected from a Canberra flying at 57,000 ft.

They survived. So it seems it works. :)

 

EDIT: Here's the story:

https://docs.google.com/document/d/1Yu2V3IZz87ai73_VNB35FmgJGixgPhPMLKwFYkMm9lU/pub

 

Interesting read, thanks. 57.000ft that's insane, and the medical board even passed them as fit to continue flying!

Here is a little bit more of the story from the navigators perspective from a book:

 

http://aircrashsites.co.uk/air-crash-sites-5/english-electric-canberra-wt207-lathkill-dale-then-and-now/

[Cobra847]

The eustachian tubes are actually seem fairly good at equalizing quickly when pressure is lowered.

Pressure differentials in water are a good example -- where you can very quickly propel yourself across thousands of kPa with little effect (unless you experience a reverse block due to congestion)

[BlackLion213]

The eustachian tubes are actually seem fairly good at equalizing quickly when pressure is lowered.

Pressure differentials in water are a good example -- where you can very quickly propel yourself across thousands of kPa with little effect (unless you experience a reverse block due to congestion)

 

Yes they do, though there is an element of luck involved. My wife ruptured her ear drum on a rapid ascent from ~45 feet while diving in Monterey Bay. Haven't been able to get her in the water since. :( It varies from person to person, but they are often a bit kinked/closed at rest and open fully during descent of the pharynx (contraction of the omohyoid and strap muscles). :)

 

Like Sobek said, ear drums do heal and my wife's has (it was ~14 years ago). Given all the other issues of exposure, likely high indicated airspeeds, and the violence of ejection (it's a lot of Gs) - I doubt that the ear drums would be a major factor. But there are lots of examples of people surviving ejections even under extreme circumstances - we are pretty hardy when young and healthy.

 

IIRC, the pressure differential between the cockpit and ambient is lower in a fighter than say a commercial airliner. The pilots maintain their oxygenation with a combination of cabin pressure and elevated FiO2 (concentration of inhaled oxygen). So the pressure differential may not even be as much as a rapid ascent for a diver, etc.

 

-Nick

[Jona33]

So, a little frostbite, a lot of discomfort at high altitude, which reduces as the air pressure rises during the descent, and the Canberra pilot was indeed deaf when he landed.

 

Does anyone know just how much air pressure there is inside a cockpit at high altitude? I presume the cockpit altitude would be well above ground level pressures, so the pressure differential may not be as catastrophic as would be the case if ground level air pressures were maintained?

 

For the canberra, half the actual altitude + 2000 ft, so at 44,000 ft the cabin altitude is 24,000.

[JINX_1391]

For what it is worth and somewhat related. A good read anyway if you don't know the story of the Blackbird breaking up at almost 80K altitude.

 

http://theaviationist.com/2015/03/17/sr-71-mid-air-disintegration/

[Aginor]

Yeah, but those guys carried space suits as well, just like the U-2 pilots.

There was that guy you just mentioned with the Sr-71 breaking up, and then that other tale of those two guys who ejected at above 80,000 ft.