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NACA wind tunnels: Above, left to right: 15ft Spin Tunnel at NACA Langley 1934; 15ft Spin Tunnel at NACA Langley 1935; This photograph shows NACA Langley’s 15ft Spin Tunnel building during the construction phase in 1934. All pictures NASA Left: 24-inch High-Speed Tunnel, 1934, NASA The Army were impressed with his con- cept, but finally turned down a development proposal, probably because Chance Vought was primarily a US Navy contractor and inter- service attitudes made them reluctant to pro- ceed in this direction. But the following year, after a merger with Sikorsky, senior officials at Vought managed to attract Navy interest in Zimmerman’s work. This led to a series of wind tunnel tests at Langley Field using scale models and a US Navy contract to build a sin- gle ‘proof of concept’ prototype known as the V-173. This was essentially a scaled-up, man- carrying V-162, powered by two modest pis- ton engines. The first proposal for the V-173 featured a prone position for the pilot to improve NACA wind tunnels: The Army were impressed with his con- cept, but finally turned down a development proposal, probably because Chance Vought was primarily a US Navy contractor and inter- service attitudes made them reluctant to pro- ceed in this direction. But the following year, after a merger with Sikorsky, senior officials at Vought managed to attract Navy interest in Zimmerman’s work. This led to a series of wind tunnel tests at Langley Field using scale models and a US Navy contract to build a sin- gle ‘proof of concept’ prototype known as the V-173. This was essentially a scaled-up, man- carrying V-162, powered by two modest pis- ton engines. The first proposal for the V-173 featured a prone position for the pilot to improve streamlining and before long a wooden mock-up of the cockpit had been built. By the time assembly of V-173 began, horizontal sta- bilisers had been attached to the tail of the air- craft and the cockpit was fully redesigned so the pilot could sit in a more conventional upright position. In late 1941, the V-173 proto- type was shipped to Langley and tests began in the Full Scale Wind Tunnel, with two- bladed propellers fitted. As a consequence of this lengthy series of trials, various modifica- tions were made to the aircraft and the two- blade propellers were replaced with a three-blade type. than a remarkably simple 20in (508mm) rub- ber band-powered model. In 1937 these projects caught the attention of United Aircraft Corporation’s President Eugene Wilson and, although Zimmerman was now the head of NACA’s Stability and Control Section, he accepted a designer's job at the company’s Chance Vought Aircraft Division, situated at Stratford, Connecticut. This gave Zimmerman the opportunity to construct an advanced model-sized circular- winged demonstrator called V-162. Company records indicate that this electrically-pow- ered tethered model flew extraordinarily well inside a hangar and showed remarkable STOL potential. In February 1938 Zimmerman filed a US patent (2,108093) for a semi-circular low aspect ratio aircraft, which he called the Aeromobile. The design was driven by twin propellers, which provided an estimated per- formance range of 0-200mph (0-322km/h) and carried a pilot and two passengers in prone positions. By the time his Aeromobile design had been finalised, Zimmerman had progressed to a military utility version, called the V-170, which Vought offered to the US Army in late 1938. 24 Left: 24-inch High-Speed Tunnel, 1934. NASA. Secret Projects: Flying Saucer Aircraft