Via (of all the random places) a MetaFilter discussion of WW1 flight sims, four zip files full of PDFs of public domain World War One flying books, about evenly split between period reference books and memoirs/biographies/autobiographies.

Handily, there’s a list of which titles are included in each zip file, so you could use that list, head over to the Internet Archive yourself, and pull individual titles of interest out for yourself.

Or grab the zip files, of course, and instantly have a pretty complete library of Great War aviation titles on your computer.