At that time the USAF used JP-4 primarily. At high altitude the fuel freeze point becomes an issue. JP-4 has an extremely low freeze point (-58C) which is pretty good! Better than Jet A-1, JP-8 or JP-7 which the SR-71 used (-43C.) I’m not sure what the OAT is at 100,000 probably -40C on a standard day. You would have to cruise around a long time to affect your fuel temperature in your tanks. However, I don’t know much about aviation fuel or high altitude performance. The highest I ever cruised around at was 42,000 feet. A few times using JP-8 during the winter our fuel in the tanks dropped below freezing and began to clog up the filters, scary! We had to descend and accelerate to get the temperatures back to normal until the fuel warmed up and stopped bypassing the Filters and allowing ice crystals into the MECs.
lol, what were you in at 42k? The highest I've been is in a C-5 at over 50k over the pond. C-130's are better though. They may only go a little above 30k but with the back door open and nothing between my eyes and the horizon, I've never seen a curve. Always makes me laugh when people say they saw it in a commercial conus flight which is around that altitude. I remind them the windows are curved. My bad, about 6 and not 7. I seem to remember it started with 6....if it went to 7 after, or started with my bad
I think 50,000 ft. might be a typo, I’m sure you meant 40,000 ft. The C-5 has been tested up to 43,000 ft or so but AF rules only allow 42,000 feet max for transport aircraft (There are a few exceptions) the constraint is the O2 masks, the ones installed on transports and airliners don’t work so well above 42,000 ft when depressurized. Also the self contained passenger oxygen systems only last 22 minutes. It takes a transport aircraft about 22 minutes to descend to 10,000 feet without over speeding or over stressing the air frame. I’ve been at 42,000 feet in C-141s and KC-10s trying to get passed thunderstorms. Do not like! I’m more comfortable at or below 39,000. Most of the time we can’t reach those altitudes due to weight and performance limits. Usually only after you’ve burned off a lot of fuel, but by then you are so close to your destination that you don’t want to climb higher just to descend shortly after.
Edit to Add: another constraint is your time of useful consciousness is at those altitudes is 10-15 seconds if you experience a rapid decompression. (Less at higher altitudes.) That’s barely enough time to recognize the situation and get your mask on. One pilot needs to be on oxygen when flying that high. Most aircraft that fly above 42,000 feet require all pilots to be on oxygen, although I’m not sure about the Concorde or Gulfstreams etc.
Never worked on the C-5, just repeating what they said. "Approaching 50k" Whatever, maybe it was show for them. You are too specific to be a "Rando" Who do you work for?
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