Carl Zuckmeyer's play 'Des Teufels General', which is claimed by some to be based around the life of WW1 flyer Ernst Udet, contains various flying songs.

I don't have access to a text, so cannot comment on their authenticity but if my recollection is correct they are only given in part, suggesting that the complete words were well known and in general circulation. Perhaps one of the German natives/residents may be in a better position to research this than I.

Though the play is set in WW2, the most famed part of Harras's career was in WW1, and the songs in which he indulges might be presumed to date from the same time.

Flying was in its infancy during WW1, very much a high-risk occupation, and with (relatively) low numbers of participants. As a result there are not likely to be too many authentic songs to be found, making each one that much more precious.