31 December 1938: Boeing Model 307 Stratoliner NX19901 made its first flight at Boeing Field, Seattle, Washington. The test pilot was Eddie Allen. Julius A. Barr was the co-pilot.
The Model 307 was a four-engine commercial airliner that used the wings, tail surfaces, engines and landing gear of the production B-17B Flying Fortress heavy bomber. The fuselage was circular in cross section to allow for pressurization. It was the first pressurized airliner and because of its complexity, it was also the first airplane to include a flight engineer as a crew member.
On March 18, 1939, during its 19th test flight, the Stratoliner went into a spin, then a dive. It suffered structural failure of the wings and horizontal stabilizer when the flight crew attempted to recover. NX19901 was destroyed and all ten persons aboard were killed.
The Boeing Model 307 was operated by a crew of five and could carry 33 passengers. It was 74 feet, 4 inches (22.657 meters) long with a wingspan of 107 feet, 3 inches (32.690 meters) and overall height of 20 feet, 9½ inches (6.337 meters). The wings had 4½° dihedral and 3½° angle of incidence. The empty weight was 29,900 pounds (13,562.4 kilograms) and loaded weight was 45,000 pounds (20,411.7 kilograms).
The airliner was powered by four air-cooled, geared and supercharged, 1,823.129-cubic-inch-displacement (29.875 liter) Wright Cyclone 9 GR-1820-G102 9-cylinder radial engines with a compression ratio of 6.7:1, rated at 900 horsepower at 2,200 r.p.m., and 1,100 horsepower at 2,200 r.p.m. for takeoff. These drove three-bladed Hamilton-Standard Hydromatic propellers through a 0.6875:1 gear reduction in order to match the engine’s effective power range with the propellers. The GR-1820-G102 was 4 feet, 0.12 inches (1.222 meters) long, 4 feet, 7.10 inches (1.400 meters) in diameter, and weighed 1,275 pounds (578 kilograms).
The maximum speed of the Model 307 was 241 miles per hour (388 kilometers per hour) at 6,000 feet (1,828.8 meters). Cruise speed was 215 miles per hour (346 kilometers per hour) at 10,000 feet (3,048 meters). The service ceiling was 23,300 feet (7,101.8 meters).
During World War II, TWA sold its Stratoliners to the United States government which designated them C-75 and placed them in transatlantic passenger service. After the war, the 307s were returned to TWA and they were sent back to Boeing for modification and overhaul. The wings, engines and tail surfaces were replaced with those from the more advanced B-17G Flying Fortress.
Of the ten Stratoliners built for Pan Am and TWA, only one remains. Fully restored by Boeing, NC19903 is at the Stephen F. Udvar-Hazy Center of the Smithsonian Institution.
© 2017, Bryan R. Swopesby