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VOUGHT XF5U
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.
Charles H. Zimmerman, 1908-1996, conceived a tilt-wing design in the 1950s, decades ahead of the Bell-Boeing V-22 Osprey.
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 was a proof of concept, first flown in November 1942.
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.
The Vought XF5U evolved from the V-173.
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.
My XF5U serves aboard HMSNZS Waikato, an aircraft carrier built for Microsoft Flight Simulator by Severn Reweti.
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.
The modeled XF5U is highly maneuverable.
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).
Given the takeoff signal aboard the Waikato.
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.
My XF5U regularly practices takeoffs (easy-peasy) and landings (challenging) with the Waikato.
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
Simanaitis Says 
It makes you wonder what an XF5U would have been capable of with twin turboprops.
It’s a mystery why the Navy had Vought build this. It did not need the outward-rotating flapping props (which killed it with vibration from the gear train) NACA at Langley before the V-173 found that it did not really help much with efficiency or lift and cost it speed and stablity & control. As good or better performance with props spinning *inwards at the tip*.
The Vought plane was modeled after the Arup which did not have excessive wing-tip vortex drag at high-speed cruise. Arup S-2 flew for the Army and NACA in the ’30s, and helped solidify Zimmerman’s ideas by giving him an extreme STOL plane to try to make a VTOL.
They built in too much complexity trying to experiment with Zimmerman’s idea for VTOL tail-sitting craft, when a simple disc like an Arup (or Boeing 390) would have been effective & fast, and landed slower than 40kts on an escort carrier or converted merchant ship with half-deck. Like a STOL Bearcat with more range, speed, and payload.
Simple normal sort of twin props whether normal or buried (if they can make a drive shaft extension to work well) and it would have been an awesome prop plane like a faster Skyraider with mostly encloses payload and <40kts landing speed. Make it like the foot-print of the navy S-2/C-1 of the same era and it would have taken over the fleet and most of military and now General aviation would be low aspect-ratio (and the most important aviation discovery of the era would have been made in the '20s by a podiatrist in Indiana)
Try to find the Sikorski drawings in Italian of a round-wing like the Vought plane with buried jets. With the experience of the Arups and now the "Little Birds" and others like the Rowe UFO, it's entirely acceptable that it could fly well.