Boeing 307

The Boeing Model 307 Stratoliner was the first commercial transport aircraft with a pressurized cabin. This feature allowed the aircraft to cruise at an altitude of 20,000 ft (6,000 m), well above many weather disturbances. The pressure differential was 2.5 psi (17 kPa), so at 14,700 ft (4,480 m) the cabin altitude was 8,000 ft (2,440 m). The Model 307 had capacity for a crew of five and 33 passengers. The cabin was nearly 12 ft (3.6 m) across. It was the first land-based aircraft to include a flight engineer as a crew member (several flying boats had included a flight engineer position earlier).[1] Development and design In 1935 Boeing designed a four-engined airliner based on its B-17 heavy bomber (Boeing Model 299), then in production, calling it the Model 307. It combined the wings, tail, rudder, landing gear, and engines from their production B-17C with a new, circular cross-section fuselage of 138 in (351 cm) diameter,[2] designed to allow pressurization.[3] The first order, for two 307s (named Stratoliners), was placed in 1937 by Pan American Airways; it was followed shortly by an increase to six by Pan Am, and a second order for five from Transcontinental & Western Air (TWA), prompting Boeing to begin production on an initial batch of the airliner.[3][4] [edit]C-75 conversion At the time the U.S. entered World War II in December 1941, flying across oceans was a rare luxury. The war required government and military officials to do so and most four-engined long-range comme

cial aircraft, including Pan Am's 14 flying boats and TWA's five Boeing 307s, were pressed into service. Additional fuel tanks were added to give them the extra range required; once converted they were designated C-75 for military use. Before World War II ended their production, 10 commercial 307s had been built. TWA flew domestic routes between New York and Los Angeles for 18 months until the Army purchased their Stratoliners for wartime use as long-range, transatlantic transport for various VIPs or critical cargo. TWA converted their 307s to military service in January 1942,[5][page needed] and its Intercontinental Division (ICD) then operated these C-75s under contract to the Army's Air Transport Command (ATC) until July 1944.[2] These were the only U. S. built commercial aircraft able to cross the Atlantic with a payload until the arrival of the Douglas C-54 Skymaster in November 1942. Conversion to the C-75 included removal of the pressurization equipment to save weight, removal of the forward four (or five) of nine reclining seats along the port side, and alteration of the two forward Pullman-like compartments (of four) starboard of the left-of-centerline aisle. Space was thus provided for crew requirements on extremely long flights and for the addition of five 212.5 U.S. gal (804 L; 177 imp gal) fuel tanks. The landing gear was strengthened, the maximum take-off weight was increased from 45,000 to 56,000 lb (20,400 to 25,400 kg)), and the exterior painted military olive drab.