The Vought XF5U based on the V-173 aerodynamic research aeroplane. The XF5U had a basically circular wing with twin vertical surfaces at its rear ‘corners’ outside two stability flaps and inside two projecting ‘ailavators’ for pitch and roll control. The primary structure was of Metalite, a material of bonded aluminium and balsa that offered exceptional strength with great lightness. The powerplant comprised two 1600-hp (1193-kW) Pratt & Whitney R-2000-7 radials buried in the thick inner portions of the wings and driving, via a complex double right angle transmission system of shafts and gearboxes, two 4.88 m (16 ft) four-blade propellers located on the forward ‘corners’ of the wing. The propeller blades were articulated and could be moved fore and aft on their shafts in the manner of a helicopter’s rotors, permitting the craft to ‘hang’ on its propellers in a semi hover at low airspeed.

Vought XF5U-1 Article

Vought’s specification for the Flapjack called for a maximum speed of 811 kph (504 mph) at 6100m (20,000 ft), while the landing speed was to be as low as 32 kph (20 mph). A proposed turbine engined variant would have been even faster. The aircraft was to have been armed with six 12.7 mm (03 in) machine guns or four 20 mm cannon, or two 454 kg (1000 lb) bombs.

The prototype XF5U 1 33958 first began engine tests in August 1945, but it was not until 1947 that the articulating propellers became available and the Flying Flapjack began taxying trials at Vought’s Stratford, Connecticut plant.

On 17 March 1947 the US Navy had cancelled the programme in favour of jet powered fighters, and the prototype, the sole XF5U was ordered scrapped, but a crane’s wrecking ball merely bounced off the tough little prototype, and it finally took workers with blowtorches to reduce it to salvageable scrap.

Engines: 2 x Pratt & Whitney R-2000-7 radials, 1600-hp (1193-kW)
Wingspan: 32’0″
Length: 27’10”

Navy chiefs ordered a full-size flying model to be built to evaluate the flying characteristics of the proposed fighter, and this aircraft, the Vought V 173 designed by Charles H Zimmerman, made its first flight on 23 November 1942 piloted by Boone T Guyton. The V 173 (unofficially dubbed Flying Pancake or Flying Flapjack) was constructed of wood with fabric covering, and had two wingtip-mounted 80 hp Continental engines driving a pair of 5.03 m (16 ft) three-blade, laminated-wood propellers.

Compared to a typical taildragger’s resting deck angle of around 5 degrees, the V-173 sat at an extreme 22 degrees. This would eliminate all forward vision if not for the addition of windows on the underside of the nose by the pilot’s feet. When on the ground, the pilot simply looked downward, past his feet, and could see the path ahead.

To further reduce takeoff and landing distances, two enormous propellers bathed the entire airframe in propwash, generating lift even at a standstill. The result was a landing speed of only 22 mph and the capability of taking off nearly vertically with typical wind over a ship’s deck.

The V-173 prototype would ultimately weigh just over 3,000 pounds fully loaded, with a massive 427 square feet of wing area. The V-173’s wing loading was just over 5 pounds per square foot.

With such ample lift, only modest power would be required. Zimmerman chose two small and light 4-cylinder Continental A80 piston engines. Their small size enabled them to be buried within the saucer-like fuselage.

Zimmerman had US patent #2,431,293 of 18 November 1947.

The engines of the V 173 were barely adequate, but the Flying Pancake took off in 15 m (50 ft), or much less with a steady wind, and could cruise at 222 kph (138 mph) despite its low power. Guyton and other pilots who flew the aircraft (including Charles Lindbergh) found it impossible to stall or spin, and full control could be maintained even at a 45 degree angle of attack.

The V-173 confirmed that the type offered viceless handling characteristics as well as an exceptional speed range between 20 mph (32 km/h) and 460 mph (740 km/h). The Vought XF5U was based on the V-173.

At one point, a vapor lock resulted in a forced landing on a beach. While the airplane flipped over onto its back, neither the airplane nor test pilot were significantly harmed.

The one V-173 built, 02978 in 1942, completed 171 flights for 131.8 hours flight time.

The V-173 placed into long-term storage. Charles Zimmerman went on to become a division chief for Project Mercury at NASA.

In 2003, the Vought Aircraft Heritage Foundation began a nearly 10-year-long restoration of the aircraft, stripping it down to its wooden airframe and replacing the fabric entirely. Today, the resplendent V-173 stands proudly on display at the Frontiers of Flight Museum in Dallas.

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Engines: 2 x 80hp Continental
Wingspan: 23’1″
Length: 26’0″
Wing area: 427 sq.ft
Speed: 138 mph
Landing speed: 22 mph
TO distance: 200 ft
Landing distance: 50 ft