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THE XF5U “Flying Flapjack” was one of the might-have-beens of aviation history. Its designer, Charles H. Zimmerman, was a talented aerodynamicist and member of NACA, the National Advisory Committee for Aeronautics, predecessor of NASA.
During the 1930s, Charles Zimmerman experimented with wings of extremely low aspect ratio, loosely, the ratio of a wing’s span to its chord, its width. More precisely, aspect ratio is (span)2/area, equivalent to span/chord when the chord is constant. For instance, a Piper Cub’s AR is 7.0. A flying saucer’s, 4/π, about 1.27.
Such small-AR wings inherently have wingtip vortices that generate detrimental drag. Zimmerman, though, countered this by locating the aircraft’s counter-rotating propellers at its wingtips, their rotation mitigating the vortex effect.
The Vought V-173, Zimmerman’s proof of concept, was largely of wood construction, powered by a pair of 80-hp Continental engines spinning conventional propellers (indeed, the same as those on the F4U Corsair). The V-173 proved stable, easy to fly and capable of impressive low-speed maneuvering.
Vought’s XF5U was an all-metal aircraft, powered by a pair of 1600-hp Pratt & Whitney R-2000 radial engines (the same as powering the Douglas C-54 Skymasters). Complex gear drive, destined to be the XF5U’s Achilles Heel, took the power from inboard engine locations to the wingtip propeller nacelles.
The wide-blade propellers—more properly called rotors—were articulated with a small degree of up/down alignment for adjustable thrust and enhanced maneuverability.
The XF5U was designed as a single-seat fighter for the U.S. Navy. Service aboard aircraft carriers would have profited from its advanced capabilities of VTOL/STOL (vertical takeoff, landing/short takeoff, landing).
The XF5U’s control surfaces were “ailavators,” combined ailerons for roll and elevators for pitch. Two “stability flaps” were incorporated into the almost circular wing’s rear.
Vought built a pair of XF5U aircraft for testing. In theory, the aircraft could take off in 710 ft. in still air; 490 ft. in a 17-kt headwind (the sort of thing it would have experienced regularly on an aircraft carrier).
In fact, the real XF5U only made the shortest little hops in taxi testing; it never flew. See http://goo.gl/1BvlWz for a brief look at this testing.
With jet aircraft coming into service, the U.S. Navy cancelled the XF5U program in March 1947. Both prototypes were dismantled; one, apparently, requiring a wrecking ball.
The V-173 prototype still exists, on loan to the Frontiers of Flight Museum in Dallas, Texas.
Flight simmers experience might-have-beens such as the Vought XF5U through Microsoft Flight Simulator. It’s also one of the aircraft in World of Warplanes, a multiplayer online simulation of Wargaming.net. ds
© Dennis Simanaitis, SimanaitisSays.com, 2013