cavuman - thank you, that is really interesting.
May I ask something: I've flown a few Rogallo winged aircraft, and studied them fairly extensively. What I have often wondered about is the relationship between Francis and Gertrude. To what extent where they a true working team of two engineers, and to what extent was Francis in the lead and Gertrude essentially his assistant?
History tends to assume the latter, but I've always rather believed the former. If you were around people who knew them, I'd be really interested in your views.
G