FL510 and above

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If anyone knows... why is the highest that you'll see bizjets certified up to is 510. I tried to find out how to get certified above that but couldn't find anything.
 
Engines (besides ramjet/scramjet) that will reliably function?
Aerodynamics of keeping a reasonable spread between the two edges of the speed envelope?
 
Trapper John said:
Cost to build structure that can maintain cabin altitude at a tolerable level?


Trapper John
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TMetzinger said:
Engines (besides ramjet/scramjet) that will reliably function?
Aerodynamics of keeping a reasonable spread between the two edges of the speed envelope?
Click to expand...

i was thinking of all three
 
TMetzinger said:
Engines (besides ramjet/scramjet) that will reliably function?
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The U-2 can operate around 70,000 ft, and it has a conventional turbofan engine. F-15s and the like max out around 60,000 ft, I think.

Aerodynamics of keeping a reasonable spread between the two edges of the speed envelope?
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That would be a big consideration, I'd think. A high aspect ratio wing that would work well at high altitude probably wouldn't be very hanger-friendly.


Trapper John
 
I think it's physiological -- blow cabin pressure above that and you're close to blood boiling. That's why we were limited to FL500 in the F-111 without pressure suits even though the cabin altitude was tolerable. They guy who flew the 'Vark (which has turbofan engines, although fairly low bypass compared to modern bizjets) to 63,000 feet during testing was wearing a U-2 type suit.
 
Recall the U-2 was very challenging to fly without the auto pilot working due to it being just above stall speed; it's one explanation for the Francis Gary Powers shoot down; he was low when shot down over Russia because the auto pilot was inop.

============================== The conventional story given to explain the crash of the U-2 and the subsequent capture of Gary Powers is that a surface-to-air missile brought down the plane. However, the U-2 spy plane was constructed to be unassailable by conventional weapons. The major benefit of these high altitude planes was their ability to stay above enemy fire. If the plane was flying at its proper height and had been shot down, many question how Powers could have survived. It would have been very likely that he would have died in the explosion or from the high altitude ejection. Therefore, many individuals question the validity of this explanation. Several alternative theories have been put forward to explain the downing of Gary Powers spy plane:

  1. Gary Powers was flying his plane below the high flying reconnaissance altitude and was hit by anti-aircraft fire.
=======================================

Best,

Dave
 
The Concorde was obviously certified way above 51,000'. I have wondered what would have happened should one of those depressurized at 60K or so. Even if the pilots had military type pressure masks, there's no way they could get down fast enough to avoid severe hypoxia at those altitudes.
 
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Dave Siciliano said:
Recall the U-2 was very challenging to fly without the auto pilot working due to it being just above stall speed; it's one explanation for the Francis Gary Powers shoot down; he was low when shot down over Russia because the auto pilot was inop.

============================== The conventional story given to explain the crash of the U-2 and the subsequent capture of Gary Powers is that a surface-to-air missile brought down the plane. However, the U-2 spy plane was constructed to be unassailable by conventional weapons. The major benefit of these high altitude planes was their ability to stay above enemy fire. If the plane was flying at its proper height and had been shot down, many question how Powers could have survived. It would have been very likely that he would have died in the explosion or from the high altitude ejection. Therefore, many individuals question the validity of this explanation. Several alternative theories have been put forward to explain the downing of Gary Powers spy plane:

  1. Gary Powers was flying his plane below the high flying reconnaissance altitude and was hit by anti-aircraft fire.
=======================================
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Powers was above FL600 when he was hit. Problem was, we didn't think he could be hit up there, but he happened to fly over the test site for the then-experimental SA-2 Guideline system, and they said, "черт возьми, tovarisch, let's give it a shot." It worked. One of his big problems during his trial was letting the folks back home know just how high he was when he was hit without letting the Russians know the actual capability of the aircraft -- see his book for more on that. That gave us a new insight on the SA-2's capability. After that, the B-52's (which were originally designed to go in above 50,000 feet -- they look like gliders, don't they?) had to re-equip for low altitude penetration, the B-58's got phased out, and the high-altitude screamer XB-70 was DOA.
 
Thanks Ron. I just read something recently that stated he was having auto pilot problems and was lower than he could have been, but maybe it was speculation. In any case, not much room to make an airspeed mistake while at altitude. Even the Lears have to watch that.

Best,

Dave
 
Ron Levy said:
I think it's physiological -- blow cabin pressure above that and you're close to blood boiling. That's why we were limited to FL500 in the F-111 without pressure suits even though the cabin altitude was tolerable. They guy who flew the 'Vark (which has turbofan engines, although fairly low bypass compared to modern bizjets) to 63,000 feet during testing was wearing a U-2 type suit.
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That makes a lot of sense. Didn't Concorde drift up to FL550 during cruise, or did it top out at FL510?

Time of Useful Conciousness up there is ridiculously small, too. Any aircraft flying up there would likely require the pilots to have masks on, as "quick-donning" is not gonna be quick enough.
 
I think 60K is still lower than he could have been. low in a U-2 is a relative term.
 
Ron Levy said:
I think it's physiological -- blow cabin pressure above that and you're close to blood boiling. That's why we were limited to FL500 in the F-111 without pressure suits even though the cabin altitude was tolerable. They guy who flew the 'Vark (which has turbofan engines, although fairly low bypass compared to modern bizjets) to 63,000 feet during testing was wearing a U-2 type suit.
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Absolutely correct. At 51,000 feet, nitrogen at ambient pressure, at 37d C boils. Instant stay-puf marshmallow man.
 
According to Wikipedia, Concorde's max cruising altitude was 60,000'. Typical NY to London cruise was at 56,000'. I'm guessing there was a certain amount of politics as well as engineering done to get this plane certified. I hate it when the captain becomes an instant stay-puf marshmallow man.
 
I think it boils down to cost:benefit.
Not much to gain as you go higher, much more expense involved.
 
Lance F said:
According to Wikipedia, Concorde's max cruising altitude was 60,000'. Typical NY to London cruise was at 56,000'. I'm guessing there was a certain amount of politics as well as engineering done to get this plane certified. I hate it when the captain becomes an instant stay-puf marshmallow man.
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A friend of mine flew the SST from DC to Dallas way back when. IIRC, in order to maintain a constant speed, the plane varied altitude. For an example of that pilot technique, see my last flightaware track when AP was off :)

Best,

Dave
 
There are also some requirements regarding the time needed to do an emergency descent which are necessary for certification.
 
I seem to remember FL500 as being the max altitude for F-16's as well. We did a cross country and went up that high to check it out, and it felt like it was mushing along on the edge of a stall the whole time.

The other concern was the physiology, since the pressurization could not keep up with the altitude, and even at 100% oxygen would need a pressure suit.

However, in an emergency, a zoom climb to FL600 was possible to give max glide range.
 
Trapper John said:
The U-2 can operate around 70,000 ft, and it has a conventional turbofan engine. F-15s and the like max out around 60,000 ft, I think.

That would be a big consideration, I'd think. A high aspect ratio wing that would work well at high altitude probably wouldn't be very hanger-friendly.


Trapper John
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I read that the spread between a stall and too fast for the wings (probably meaning something like Va) on a U2 at those altitudes is something like 14 knots. Don't know if it's true, but I did read it somewhere.
 
bbchien said:
Absolutely correct. At 51,000 feet, nitrogen at ambient pressure, at 37d C boils. Instant stay-puf marshmallow man.
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Dr. Bruce, is it technically a "boil"? I know that it's the nitrogen spontaneously coming out of solution, similar to the bends. But since atmospheric pressure does not act directly on the blood (since vessels are sealed and not open to atmosphere, is it technically "boiling," which is a sudden state change from liquid to vapor based on pressure differential?

Not being a smart a$$, I'm really curious about the technical issues here, and I'm not sure I understand this all correctly.

Thanks!
 
While there is truth in all that stuff about "coffin corner" and all, the SR-71 and some other aircraft can operate above FL800. It's all aerodynamics and design, so that's not a bar to bizjets operating above FL510. I suspect there are certification issues involving physiology, pressurization, and emergency descents that provide the greatest barriers to flight above that level.
 
bullwinkle said:
Dr. Bruce, is it technically a "boil"? I know that it's the nitrogen spontaneously coming out of solution, similar to the bends. But since atmospheric pressure does not act directly on the blood (since vessels are sealed and not open to atmosphere, is it technically "boiling," which is a sudden state change from liquid to vapor based on pressure differential?

Not being a smart a$$, I'm really curious about the technical issues here, and I'm not sure I understand this all correctly.

Thanks!
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Yes it is a real boil. Noplace but an obstructed sinus is "sealed" with regard to pressure, and that sinus (bony wall and all) simply explodes. The pressure change is instantaneous everywhere in the body....or you will explode.
 
bbchien said:
Yes it is a real boil. Noplace but an obstructed sinus is "sealed" with regard to pressure, and that sinus (bony wall and all) simply explodes. The pressure change is instantaneous everywhere in the body....or you will explode.
Click to expand...

Cool...in a bad way.

Thanks!
 
There is not alot to be gained by flying above FL510. At that point your above the troposphere typically.

At that point one crewmember must be on oxygen at all times and there are issues as stated before about emergency descent times.
 
Rotor&Wing said:
There is not alot to be gained by flying above FL510. At that point your above the troposphere typically.

At that point one crewmember must be on oxygen at all times and there are issues as stated before about emergency descent times.
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Shouldn't *everybody* be on constant O2 at that level??? Seems like you'd be in for some brain damage otherwise. Or are you just meaning that somebody has to be there to keep things non-catastrophic if the pressurization goes?
 
bullwinkle said:
Shouldn't *everybody* be on constant O2 at that level??? Seems like you'd be in for some brain damage otherwise. Or are you just meaning that somebody has to be there to keep things non-catastrophic if the pressurization goes?
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The latter. Normally, if you have the usual "quick-don" masks, they may be left hanging within easy reach (5 seconds from alarm to masked is the criterion). However, the FAA requires that with a 2-person crew, at least one of them must actually have their mask on above FL410 -- above that point, you can lose consciousness in a depressurization so fast you wouldn't have time to don even a quick-don mask while trying to get the plane headed downhill. Also, if one crewmember leaves the cockpit above FL350 (say, to visit the head), the remaining pilot must be mask-on until the other pilot returns. Reference: 91.211(b).

Obviously, this is for pressurized aircraft with cabin altitudes below 12,500. For unpressurized aircraft, the regular 12.5/14 rule applies for the pilot(s). Reference 91.211(a).
 
Ron Levy said:
The latter. Normally, if you have the usual "quick-don" masks, they may be left hanging within easy reach (5 seconds from alarm to masked is the criterion). However, the FAA requires that with a 2-person crew, at least one of them must actually have their mask on above FL410 -- above that point, you can lose consciousness in a depressurization so fast you wouldn't have time to don even a quick-don mask while trying to get the plane headed downhill. Also, if one crewmember leaves the cockpit above FL350 (say, to visit the head), the remaining pilot must be mask-on until the other pilot returns. Reference: 91.211(b).

Obviously, this is for pressurized aircraft with cabin altitudes below 12,500. For unpressurized aircraft, the regular 12.5/14 rule applies for the pilot(s). Reference 91.211(a).
Click to expand...

Thanks Ron, good to know info about commercial ops!

Doesn't higher altitude put more stress on the pressure bulkheads of the plane, since there is greater pressure differential? It seems airframe life would be degraded the more time you spend at very high FLs in a pressurized bird.
 
bullwinkle said:
Doesn't higher altitude put more stress on the pressure bulkheads of the plane, since there is greater pressure differential? It seems airframe life would be degraded the more time you spend at very high FLs in a pressurized bird.
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Actually, as the folks who designed the Comet found out, the metal fatigue cause by flexing due to repeated pressurization/depressurization cycles (that causes airplanes to expand/contract just like a balloon, although not as nearly much) can be more of a problem than the simple stress due to pressure differential. The stresses can be dealt with by brute force structural engineering, but the metal fatigue is a more complex metallurgical problem. I think you'll find most commercial airliners hit their cycle limits before they hit their hour limits unless they're used only on very long range flights (which are easier on planes that RJ-style pogo-sticking around).
 
This reg is why all the proving runs for part 135 ops are filed for FL340. Also why the POI will always have a scenario that requires a climb to a higher altitude, to be sure the crew will react appropriately with the masks (most rotate at 15-30 min intervals for comfort).

POI's usually get a big laugh when the pilots first don the masks and dust flies everywhere, as though the masks haven't been recently used, even though the airplane has been flying regularly at altitudes above 350.


Ron Levy said:
The latter. Normally, if you have the usual "quick-don" masks, they may be left hanging within easy reach (5 seconds from alarm to masked is the criterion). However, the FAA requires that with a 2-person crew, at least one of them must actually have their mask on above FL410 -- above that point, you can lose consciousness in a depressurization so fast you wouldn't have time to don even a quick-don mask while trying to get the plane headed downhill. Also, if one crewmember leaves the cockpit above FL350 (say, to visit the head), the remaining pilot must be mask-on until the other pilot returns. Reference: 91.211(b).

Obviously, this is for pressurized aircraft with cabin altitudes below 12,500. For unpressurized aircraft, the regular 12.5/14 rule applies for the pilot(s). Reference 91.211(a).
Click to expand...
 
wabower said:
This reg is why all the proving runs for part 135 ops are filed for FL340. Also why the POI will always have a scenario that requires a climb to a higher altitude, to be sure the crew will react appropriately with the masks (most rotate at 15-30 min intervals for comfort).

POI's usually get a big laugh when the pilots first don the masks and dust flies everywhere, as though the masks haven't been recently used, even though the airplane has been flying regularly at altitudes above 350.
Click to expand...

Suppose the plane in question has no LOA for RVSM operations? FL280 would be it, and the masks wouldn't come into question. I suppose the POI could ask for a climb from 280 to 430 to see what the pilots do.

Also, I think you're right. The mask usage requirements are often "forgotten". (Can't speak for 121 ops. They may play this one more by the book, and may have more comfortable masks :rolleyes:.)
 
Lance, I think aircraft may still operate in RVSM airspace as long as ATC approves it. I don't think you can file for it if you are non-RVSM, but may request it enroute...likely to be denied but in theory possible.
 
There are also procedures for non-RVSM aircraft to climb through the RVSM block and then cruise above it.
 
Ron Levy said:
There are also procedures for non-RVSM aircraft to climb through the RVSM block and then cruise above it.
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I've done it a number of times. If you can climb continuously, ATC is happy to give a clearance to FL430 and above. You may have to wait a bit until they have a path where they can maintain non-RVSM separation while you do the climb. However, except for a few special categories, like the military, you cannot get cleared to stop at an RVSM altitude unless you have an RVSM LOA (letter of authorization).
 
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