Old aircraft are just amazing, and I wouldn’t have been able to resist a ride in that, either! That may have been a carry over from WW1 aircraft. Hemp fabric covered in an shellac made from acid treated hemp oil called dope, like pipe and thread dope (off subject, but I’ve heard from some aviation buffs that narcotics came to be known as dope from pilots who survived their aircraft catching on fire when shot down). War shortages on materials may possibly have birthed more innovations than any other factor in history.