Most of the aircraft in the contest were popular sport planes of the late 1920s, that took part in the previous contest as well, like de Havilland Gipsy Moth DH-60G, which was the main aircraft of the British and Spanish teams. These aircraft had mostly open cabs, and were built in mostly low-wing (29) or high-wing (17) layout, only 13 were biplanes (and 1 mid-wing). Only five were of all-metal construction, most were all-wooden. On contrary to a previous contest, there appeared also some special aircraft, better suited to meet the Challenge demands. First of all, they were German BFW M.23c and Klemm L 25E, being new variants of successful machines of 1929 – wooden low-wing monoplanes with closed canopy, belonging to lighter category, yet fitted with powerful Argus engines, having better chance in technical trials. All aircraft in the contest had fixed conventional landing gear and had no wing mechanization (slats or flaps) yet.