Max Alt of Non Pressurized Aircraft

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ncball

Well-Known Member
My student stumped me today, he asked me if there was a limit to how high we could fly in a non pressurized aircraft. not talking about 91.211 (O2 regs) or service ceiling or anything like that. If a pilot was wearing O2 mask and could keep warm and a plane could do it, is there a physical limit our bodies cant go above or a far limiting alt. I told him my best guess was the engine/plane would max out at its absolute ceiling before we physically couldn't go any higher. even with my understanding of pressurized aircraft there service ceilings are because of the limits of the O2 systems not the engines or a persons body. Any opinions would be welcomed
 
Good quesiton, I don't have an answer. I would say that some of it depends on the certification of the O2 system you are using. That said, I think anything over 25K without sweating out the details *very* thoroughly would be unwise. Even then, I would not be comfortable much out of the teens.
 
The service ceiling of the B-17 was 35,600' MSL according to wikipedia. Those weren't pressurized, but the crews definitely used oxygen. So at least above that.
 
ncball said:
My student stumped me today, he asked me if there was a limit to how high we could fly in a non pressurized aircraft. not talking about 91.211 (O2 regs) or service ceiling or anything like that. If a pilot was wearing O2 mask and could keep warm and a plane could do it, is there a physical limit our bodies cant go above or a far limiting alt. I told him my best guess was the engine/plane would max out at its absolute ceiling before we physically couldn't go any higher. even with my understanding of pressurized aircraft there service ceilings are because of the limits of the O2 systems not the engines or a persons body. Any opinions would be welcomed
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No, once you're into most jets the limit is the wing/engine or combo. Sure you might end up with a cabin alt above 10k, but the limit is almost always not to do with the o2 system. Flying around with a mask on is very annoying though.
 
Blood boil at 59055 feet would be fatal of course.
Considering the height msl of mt everest, and if a person has a source of O2, then I'd say its probably not much higher than everest until the human body needs more than just O2 to withstand the pressure changes.
 
Sosee said:
Blood boil at 59055 feet would be fatal of course.
Considering the height msl of mt everest, and if a person has a source of O2, then I'd say its probably not much higher than everest until the human body needs more than just O2 to withstand the pressure changes.
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Your blood won't actually boil up there (what with it being contained inside your body and under pressure by your heart) - but water boils at body temperature or less above the Armstrong line. It also varies due to pressure variations and so on, but it's somewhere around the 62,000' mark (give or take).
 
Assuming the fuel is kept in the wing, it should stay cold enough that the pressure limit that keeps it from boiling is much, much higher than a humans.
 
ppragman said:
Your blood won't actually boil up there (what with it being contained inside your body and under pressure by your heart) - but water boils at body temperature or less above the Armstrong line. It also varies due to pressure variations and so on, but it's somewhere around the 62,000' mark (give or take).
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Well, if you have water boiling inside you, the suck factor has to be comparable. It would be interesting to feel water boil in your mouth however...
 
z987k said:
No, once you're into most jets the limit is the wing/engine or combo. Sure you might end up with a cabin alt above 10k, but the limit is almost always not to do with the o2 system. Flying around with a mask on is very annoying though.
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From my understanding, the altitude limitation is usually due to how long it takes to come down from altitude for breathable O2 in an explosive decompression. The generators are only good for 14 minutes of O2 IIRC, and getting down from 41000 to 10k can take more than 10-12 minutes in most airplanes. I know in the RJ I fly, that was the exact reason given to us by the training department. The 700/900 have the power AND the wing to make it higher in most weights. I've leveled off in cruise with people in the back at 410 and had 4-5% left (as a rule of thumb, if you have 2% left to maintain .79, you are about as high as you can go, save for the performance data the machine spits out).

Where did you hear that?
 
mshunter said:
From my understanding, the altitude limitation is usually due to how long it takes to come down from altitude for breathable O2 in an explosive decompression. The generators are only good for 14 minutes of O2 IIRC, and getting down from 41000 to 10k can take more than 10-12 minutes in most airplanes. I know in the RJ I fly, that was the exact reason given to us by the training department. The 700/900 have the power AND the wing to make it higher in most weights. I've leveled off in cruise with people in the back at 410 and had 4-5% left (as a rule of thumb, if you have 2% left to maintain .79, you are about as high as you can go, save for the performance data the machine spits out).

Where did you hear that?
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Maybe it would go higher... but you'd have to be crazy light. Less than 65,000 for 400 on the crj iirc. I'm thinking of the lears and hawkers I'm around now, with the lears you still need to be light to get into the upper 40s/50s. Those are not o2 limits. It's performance.
 
z987k said:
Maybe it would go higher... but you'd have to be crazy light. Less than 65,000 for 400 on the crj iirc. I'm thinking of the lears and hawkers I'm around now, with the lears you still need to be light to get into the upper 40s/50s. Those are not o2 limits. It's performance.
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We were told in school the Challenger 601 service ceiling has to do with the emergency descent times.
 
z987k said:
Well by the definition of service ceiling that makes no sense. Perhaps the manufacturer's certified ceiling?
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That's beyond my education. They tell me how high i can go, I don't go higher.
Lear 55 can goto 51, Lear 35 can goto 45, same engine.
 
Also the Hawker is certified to 41 because the engines aren't aft of the pressure bulkhead, it's 43 over in England.
 
mikecweb said:
Also the Hawker is certified to 41 because the engines aren't aft of the pressure bulkhead, it's 43 over in England.
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I heard it was time to descend being the resson, England has different requirements...

Btw our A used to be a B
 
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