| XF5U | |
|---|---|
 The XF5U-1 during testing | |
| General information | |
| Type | Fighter |
| Manufacturer | Vought |
| Designer | |
| Status | Cancelled 17 March 1947 |
| Primary user | United States Navy |
| Number built | 2 |
| History | |
| Developed from | Vought V-173 |
TheVought XF5U "Flying Flapjack" was an experimentalU.S. Navy fighter aircraft designed byCharles H. Zimmerman forVought duringWorld War II. This unorthodox design consisted of a flat, somewhat disc-shaped body (resembling a flyingflapjack/pancake, hence its nickname) serving as the lifting surface.[1] Two piston engines buried in the body drove propellers located on the leading edge, at the wingtips.
A developed version of the originalV-173 prototype, the XF5U-1 was a larger aircraft. Of all-metal construction, it was almost five times heavier, with two 1,400 hp (1,193 kW)Pratt & Whitney R-2000 radial engines. The configuration was designed to create a lowaspect ratio aircraft with low takeoff and landing speeds but high top speed.[2] The aircraft was designed to keep the low stall speed and highangle of attack from the V-173 prototype while providing for better pilot visibility, cockpit comfort, less vibration, and provisions to install armament. This included a cockpit redesign moving the cockpit from the leading edge of the wing to a nose nacelle that extended further in front of the leading edge. The arrestor hook was changed to a dorsal hook that would diminish the drag from the apparatus.[3]
Normally, a wing with such a lowaspect ratio will suffer from very poor performance due to the degree ofinduced drag created at the wingtips, as the higher pressure air below spills around the wingtip to the lower-pressure region above. In a conventional aircraft, these wingtipvortices carry a lot of energy with them and hence create drag. The usual approach to reducing these vortices is to build a wing with a high aspect ratio, i.e. one that is long and narrow. However, such wings compromise the maneuverability and roll rate of the aircraft, or present a structural challenge in building them stiff enough. The XF5U attempted to overcome the tip vortex problem using thepropellers to actively cancel the drag-causing tip vortices.[4] The propellers are arranged to rotate in the opposite direction to the tip vortices, with the aim of retaining the higher-pressure air below the wing. With this source of drag eliminated, the aircraft would fly with a much smaller wing area, and the small wing would yield high maneuverability with greater structural strength.
The propellers envisioned for the completed fighter — unlike the torque-reducingcounter-rotating propellers of the V-173 design — were to have a built-incyclic movement like ahelicopter'smain rotor, with a very limited ability to shift their center of lift up and down to aid the aircraft in maneuvering. Initially, the aircraft used propellers originally designed for theV-173 prototype.[5] These propellers would be replaced with propellers taken from theVought F4U-4 Corsair. An ejection seat was fitted to allow the pilot to clear the massive propellers in the event of an in-flight emergency.[2] Although the prototype was unarmed, a combination of sixM2 Browning 50-caliber machine guns or fourM3 20 mm cannons would be mounted in the wing roots in service.[2]
The V-173 and F5U design was considered promising, and possibly capable of great maneuverability and speeds of up to 452 mph (727 km/h).[6] Two prototypes were constructed. Taxi trials of the XF5U-1 at Vought's Connecticut factory culminated in short "hops" that were not true flights.[7] Suggestions that the XF5U-1 flew were likely a result of confusion with the V-173, which underwent flight tests until 1945.[8] During these ground runs the XF5U-1 reportedly experienced severe vibration problems.[7]
By 1946, the project was long over its expected development time, and well over budget.[2] With jet aircraft coming into service, the US Navy officially canceled the F5U project on 17 March 1947. The only completed XF5U-1 proved to be so structurally solid that steel ball with which the breakers attempted to smash the Flapjack with just bounced off its Metalite-skinned wing with scarcely a dent, and blow-torches had to be used to cut it apart.[9] The prototype V-173 was transferred to theSmithsonian Museum for display.
General characteristics
Performance
Armament
Related development
Aircraft of comparable role, configuration, and era
Related lists
