Boeing 314 Clipper

The Boeing 314 Clipper was an American long-range flying boat produced by Boeing from 1938 to 1941. One of the largest aircraft of its time, it had the range to cross the Atlantic and Pacific oceans. For its wing, Boeing re-used the design from the earlier XB-15 bomber prototype. Twelve Clippers were built, nine of which served with Pan Am. Pan American had requested a truly trans-Pacific flying boat with unprecedented range and double the passenger payload of the airline's Martin M-130. Boeing's bid was successful and on July 21, 1936, Pan American signed a contract for six. Boeing engineers adapted the cancelled XB-15's wing, and replaced the Pratt & Whitney Twin Wasp radial engines with the Wright Twin Cyclone. Pan Am ordered six more aircraft with increased engine power and capacity for 77 daytime passengers as the Boeing 314A. The huge flying boat was assembled at Boeing's Plant 1 on the Duwamish River in Seattle, and towed to Elliott Bay for taxi and flight tests. The first flight was on June 7, 1938, piloted by Edmund T. "Eddie" Allen. At first the aircraft had a single vertical tail, and Allen found he had inadequate directional control. The aircraft returned to the factory and was fitted with the endplates on the ends of the horizontal tail in place of the single vertical fin. This too was found to be insufficient and finally the centerline vertical fin was restored, after which the aircraft flew satisfactorily. The 314 used a series of heavy ribs and spars to create a robust fuselage and cantilevered wing, eliminating the need for external drag-inducing struts to brace the wings. Boeing also incorporated Dornier-style sponsons into the hull structure. The sponsons, broad lateral extensions at the waterline on both sides of the hull, served several purposes: They provided a wide platform to stabilize the craft while floating, they acted as a gangway for boarding and exiting, and they possessed intentional shaping to contribute additional aerodynamic lift in flight.