I suppose this question is steered towards the Jet guys. But heres my 2 bobs worth. Not cosmic related
I used to fly King Airs at Levels between FL200 AND FL240, on oxygen for 5-6 hours legs. The Aircraft was an A90 not pressurised. It was the optimum altitude though used to get a fuel burn of 350lbs/hr.
The only minus for me was the extended lengths of time on Oxy, it took its tolls, headaches afterwards etc. Ive been told that WW2 Bomber PILOTS used to get enlarged hearts due to prolonged high alt oxy use.
Regads
Sheep
Merry Xmas