Here Caniff depicted Billy Mitchell, an aviation pioneer considered the father of the U.S. Air Force. The painting area is 5.5" x 10".
This same picture was reproduced in Caniff: A Visual Biography in a two page spread devoted to this AHF envelope program (p.312-313). The figure of Billy Mitchell was not on any of the eight existing envelopes.
This next painting is from one of the eight envelopes. The "hat in the ring" gang was the nickname of the 94th Aero Squadron, the first American aviation unit in WWI. Eddie Rickenbacker, America's top World War I flying ace, was one of its members.
They sold for $145 apiece on Ebay. According to Worthpoint's database, they sold for $52 combined in 2008. Quite a nice return. The AHF is now the National Aviation Hall of Fame. You can visit the Hall at the Museum of the United States Air Force in Dayton. Of particular interest there is the wall of honoree portraits, most of which were drawn by Caniff.