Here's an article by Barry Schiff about limitations of airplanes. The caption photos are of a Skymaster being tested at Cessna. Nice photos that show the actual structural testing of the 337. The article is a good read, although, most of the information is basic it still describes the foundational limitations and how they are determined of aircraft. Not specifically the Skymaster but just aircraft in general. It is however interesting that they used the photos of a Skymaster being stressed to the limit.