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Vought V-173

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American experimental aircraft (1942–47)

V-173General informationTypeExperimental aircraftManufacturerVoughtNumber built1HistoryFirst flight23 November 1942Retired15 March 1947Developed intoVought XF5U

The Vought V-173 "Flying Pancake" is an American experimental test aircraft built as part of the Vought XF5U program during World War II.

Both the V-173 and the XF5U featured an unorthodox "all-wing" design consisting of a flat, somewhat disk-shaped body (like a pancake, hence the nickname) serving as the lifting surface.[1] Two piston engines buried in the body drove propellers located on the leading edge, at the wingtips.[2]

Design and development<br>[edit]

In the 1930s, noted aeronautical engineer Charles H. Zimmerman advocated the concept of "discoidal" aircraft, the so-called "Zimmer Skimmer"[3] and worked on a variety of projects on his own and with the Vought company. After testing using scale models, including a remotely controlled, electrically powered large-scale model, designated the Vought V-162, the US Navy approached Zimmerman and offered to fund further development. Data and concept documentation were given to the Navy in 1939, with wind tunnel tests on full-scale models being completed in 1940-1941.

The original prototype, designated the V-173 (Flying Pancake), was built of wood and canvas and featured a conventional, fully symmetrical aerofoil section (NACA 0015). Designed as a "proof-of-concept" prototype, the initial configuration V-173 was built as a lightweight test model powered by two 80 hp (60 kW) Continental A-80 engines turning F4U Corsair propellers. Later the aircraft was fitted with a pair of specially modified 16 ft 6 in. three-bladed propellers. A tall, fixed main undercarriage combined with a small tailwheel gave the aircraft a 22° "nose-high" angle.[4]

Ground testing of the V-173

The disc wing design featured a low aspect ratio that overcame the built-in disadvantages of induced drag created at the wingtips with the large propellers actively canceling the drag-causing tip vortices. The propellers were arranged to rotate in the opposite direction to the tip vortices, allowing the aircraft to fly with a much smaller wing area. The small wing provided high maneuverability with greater structural strength. The empennage consisted of two vertical fins with rudders, all-moving stabilizers with anti-servo tabs,[5] and two large elevator/trim surfaces on either side of centerline on the trailing edge of the wing planform.[6]<br>V-173 showing all-flying tail Zimmerman chose to include the all-moving stabilizer design because he realized that the increased drag, prop wash, and large wing area would make the aircraft difficult to control at low speeds.[7] Wind tunnel tests would prove that this was a success to an extent. The aircraft would prove to require a lot of force to control at low speeds during in-flight testing but the tail design would prove to make the aircraft controllable.[8]

In January 1942, Bureau of Aeronautics requested a proposal for two prototype aircraft of an experimental version of the V-173, known as the VS-135 . The development version, the Vought XF5U-1, so called "Flying Flapjack" was a larger aircraft with all-metal construction, and was almost five times heavier.[9] Although a prototype was constructed, it only performed brief hops on the runway; it never entered true controlled flight.[6]

Operational history<br>[edit]

Maiden flight, 23 November 1942

The first flight of the V-173 was on 23 November 1942 with Vought Chief Test Pilot Boone Guyton at the controls. The aircraft's most significant problem concerned its complicated gearbox that routed power from the engines to its two long propeller shafts. The gearbox produced unacceptable amounts of vibration in ground testing, delaying the aircraft's first test flight for months. This contributed to the aircraft feeling much too heavy when maneuvering for its light weight. In addition to this on the first few flights, the pilot was never able to achieve enough speed to achieve the correct amount of airflow over the control surfaces to pull the aircraft into level flight. The test pilot Guyton discussed these problems with Zimmerman and they worked to eliminate them. In addition to this Guyton commented that the cockpit design was poor. He explained that in addition to the poor comfort the pilot had limited to no use for the clear bottom panels of the cockpit. He explained that the pilot sat too high in the cockpit to effectively use these lower panels for takeoff or landing.[10] Flight testing of the V-173 went on through 1942 and 1943 with 190 flights, resulting in reports of UFOs from surprised Connecticut locals.[11] Charles...