Have you looked to see whether there is a local archaeology or social history society in your area that you could join? They will have individuals involved who are already used to dealing with property owners to arrange research projects, and you might be able to accompany them on the trips they organize. For reference, the archaeological society in my region serves around 400 square miles and typically organizes a low two-digit number of digs every year. There are also some other societies in the same region who focus on preserving and documenting recent history where excavation isn't required.

Another idea: if you don't already have any formal education in history, you could study for some qualifications in the subject. It would probably do much to reassure landowners that you are not going to harm the sites in any way (although I struggle to think of a way you could do so with a UAV!) In any case, good luck; I'd love to see the models!