Not sure if this link has been posted before but you can read his memoir "Fighting The Flying Circus" online and it is in easy format to be printed. Quite an insightful read.

http://www.richthofen.com/rickenbacker/

Very cool ...thanks

Great! I read a few chapters. Fascinating to read of his climbing up to 22,000 feet in his Nieuport. He only mentions how freezing cold it was (I can just imagine), but nothing about fin ding it hard to breath.
I havent read that book for decades. It's a good one.

Always wondered how WW1 pilots where managing too get up too such extreme altitudes without dying in the process. They had no pressurised cockpits an no masks. Yet by ww2 they where flying on O2 above 12000ft. Is it the wind in youre face that gives you the oxygen you need too stop the ill effects? Propwash and forward motion? Or was it extremely hard too breath? McCudden mentions going up to 27000ft on his last sortie. He mentions the numbing cold and the agony when he got back but nothing about breathing.

I haven't kept up with this sim, but glad I stepped in here. I'm going to give that one a look when I get home.

About the oxygen, haven't people climbed Everest with no oxygen before? I think they're in pretty bad shape when they come down, but perhaps taking a powered ride at a relatively slow rate of climb allows you to do it. No strenuous physical excertion and no quick changes in breathable air?