Vought V-173 "Flying Pancake"

The Vought V-173 design features a circular airfoil with large-diameter propellers on the wing tips. Its designer, Charles Zimmerman, reasoned that the drag, which is created by disturbed airflow near the tip of conventional wings, would be minimized by placing the propeller at the wing tip. By maintaining a uniform flow over the entire span, he felt that it could take off and land at exceptionally low speeds and still have good high-speed performance. These qualities seemed to be especially desirable for Navy fighter aircraft operating from aircraft carriers. After pursuing this idea with NACA (NASA's predecessor) he was encouraged to go to private industry and develop it further; as the Agency did not feel that it could subsidize the work needed to prove the concept. Although noted for its conservative approach to aircraft development, Vought responded by building and testing a quarter-scale model and then persuaded the Navy to fund a full-scale aircraft.

A proof-of-concept vehicle, this design, the V-173, it had a circular wing 23.3 feet in diameter and a symmetrical NACA airfoil section. A huge three-bladed prop was mounted at the tip of each airfoil blanketing the entire aircraft in their slipstreams. The wing/fuselage had a complex empenage consisting of two normal-looking horizontal stabilizers and elevators, two rudders, and two large elevators on the midpoint of the fuselage. In a 139-hour test program it was found that it had unusual flight characteristics and control responses but could be handled effectively. It could almost hover and it survived several forced landings, including a nose-over, with no serious damage to the aircraft or injury to the pilot.

The Navy was so impressed with the project that it ordered the construction of the Vought XF5U-1. It was substantially the same design as the V-173 but much more rugged and equipped for service work, and powered by two Pratt &Whitney R-2000 radial air-cooled engines mounted inside jet-intake-like nacelle openings. Power from the 1,600-hp engines was transmitted to the two four-bladed props through heavy transmission gearboxes and some intricate cross-shafting. Although it was completed, it was never flown; the Navy cancelled the project because of its decision to switch to turbojet engines. The tests of the V-173 proved Zimmerman's ideas to be practical but unfortunately the useful potential of high-speed performance with turbojet engines was greater than the remarkable low-speed performance attainable with the flying wing.