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Left: Boeing B.390, a wartime carrier-based STOL design, competing against the XF5U-1. Although less complex and probably more reliable, the B.390 would not have shared the performance capabilities of the XF5U-1. Bill Rose Below left: Appearance of a third-generation Vought Skimmer powered by a gas turbine engine. Capable of VITOL operation, the pilot would fly the aircraft from a prone position. Bill Rose After a period of testing, the first prototype semi-disc shaped, single-seat Boeing B.390 fighter would succeed the B.396. It would be powered by a single 3,500hp (2,610kW) Pratt & Whitney R-4360 28-cylinder air-cooled radial engine, driving a single counter-rotat- ing assembly that used three-bladed pro- peller assemblies. This design was mechanically simpler than the complex power transmission and propeller blade arrangement used by the Vought XF5U-1 and the general reliability was accepted as being significantly better. Although the Boeing B.390 was expected to provide exceptional STOL performance, its capability would never have matched the fully developed Vought F5U, which was designed to hover in a vertical attitude. Boe- ing suggested that the B.390 prototype would be capable of about 425mph (683km/h) and the production version would be fitted with a two-stage supercharger, providing a top speed of about 452mph (757km/h). One rather unusual feature was the ducting of the engine exhaust to the rear of the fuselage, which was expected to provide a small amount of added jet thrust. Designated as the Boeing B.391, the pro- duction fighter would have been armed with four 20mm cannons and capable of carrying a modest bomb load. Needless to say, this Boeing shipboard fighter never progressed beyond being a paperwork study. It seems certain that this unusual aircraft could have been built, tested and put into production; but by the end of World War Two it had been filed away and forgotten. to sell it. Vought were finally obliged toreacha fighter with a broadly similar capability. financial settlement with the Navy for the cost Although not usually associated with fighters, of the silver and forced to confirm the dealer’s _ Boeing’s Seattle design office came up with a legal right to profit from their mistake. series of intriguing proposals for a carrier-based For many years, stories have circulated that combat aircraft with an elliptical planform. scrapping the XF5U-1 was a cover story and Their project would start with the con- the aircraft was actually shipped via the — struction of a one-man, low-speed proof-of- Panama Canal to Muroc Field where it concept demonstrator called the Boeing crashed during an early test flight. While this B.396, which was expected to perform like is an intriguing idea, there is absolutely noevi- the Vought V-173. The B.396 would be dence to support the theory and it can be approximately the same size as the proposed ruled out. combat aircraft, but simplified in design and fitted with a low-power engine that was suffi- Boeing’s Little-Known Rival cient to study its low-speed handling charac- In early 1943, just a few months after Vought teristics. The designation of this proposal had been given the go-ahead to build two — suggests that the B.396 was conceived once XF5U-1s, the US Navy approached Boeing to some initial work was completed to establish design a rival single-engined STOL shipboard _ the viability of a full-sized fighter aircraft. Advanced Pancakes Thomas Clair Smith, who eventually became Vice President of the Woodstream Corpora- tion, joined Vought in 1946 after graduating from Penn State University with a degree in mechanical engineering. Almost immediately, he was assigned to testing components that included aircraft arrester hooks and exploring the bonding abilities of lightweight composites such as Metalite. After clearance by the FBI, Smith was moved to classified development ruled out. Boeing’s Little-Known Rival In early 1943, just a few months after Vought had been given the go-ahead to build two XF5U-1s, the US Navy approached Boeing to design a rival single-engined STOL shipboard 32 Secret Projects: Flying Saucer Aircraft