If you are ever in Arkansas, and have a bit of time, stop by the ASU campus library, and ask to the Cass Hough Collection

the Cass S. Hough Aeronautical Collection, which has been described as the single most valuable collection of aviation materials in private hands

It's comprised of 4800 books, and other materials

None of it's been digitized, nor is it likely to be, as there are only 2 people in the library archives. I just talked to Melissa, and they aren't ever going to get the time, people, budget, or motivation to scan and make the Cass Hough collection available online

http://www.astate.edu/a/library/archives/