|Northrop 2B Gamma Polar Star|
|Developed from||Northrop Alpha|
Design and development
The Gamma was a further development of the successful Northrop Alpha and shared its predecessor's aerodynamic innovations with wing fillets and multicellular stressed-skin wing construction. Like late Alphas, the fixed landing gear was covered in distinctive aerodynamic spats, and the aircraft introduced a fully enclosed cockpit.
The Gamma saw fairly limited civilian service as mail planes with Trans World Airlines but had an illustrious career as a flying laboratory and record-breaking aircraft. The US military found the design sufficiently interesting to encourage Northrop to develop it into what eventually became the Northrop A-17 light attack aircraft. Military versions of the Gamma saw combat with Chinese and Spanish Republican air forces. Twenty Five Gamma 2Es were assembled in China from components provided by Northrop.
On June 2, 1933 Frank Hawks flew his Gamma 2A "Sky Chief" from Los Angeles to New York in a record 13 hours, 26 minutes, and 15 seconds. In 1935, Howard Hughes improved on this time in his modified Gamma 2G making the west-east transcontinental run in 9 hours, 26 minutes, and 10 seconds.
The most famous Gamma was the Polar Star. The aircraft was carried via ship and offloaded onto the pack ice in the Ross Sea during Lincoln Ellsworth's 1934 expedition to Antarctica. The Gamma was almost lost when the ice underneath it broke, and had to be returned to the United States for repairs. Polar Star's second assignment to Antarctica in September 1934 was also futile — a connecting rod broke and the aircraft had to be returned yet again for repairs. On January 3, 1935, Ellsworth and pilot Bernt Balchen finally flew over Antarctica.
On November 23, 1935, Ellsworth and Canadian pilot Herbert Hollick-Kenyon attempted the world's first trans-Antarctic flight from Dundee Island in the Weddell Sea to Little America. The crew made four stops during their journey, in the process becoming the first people ever to visit Western Antarctica. During one stop, a blizzard completely packed the fuselage with snow which took a day to clear out. On December 5, after traveling over 2,400 miles (3,865 km) the aircraft ran out of fuel just 25 miles (40 km) short of the goal. The intrepid crew took six days to travel the remainder of the journey and stayed in the abandoned Richard E. Byrd camp until being found by the Discovery II research vessel on January 15, 1936. Polar Star was later recovered and donated to the Smithsonian National Air and Space Museum.
- Gamma 2A
- First production aircraft, sold to Texaco and flown by Frank Hawks as "Sky Chief", 785 hp (585 kW) Wright radial engine.
- Gamma 2B
- Two-seat version with tandem controls, flown across Antarctica as the Polar Star, 500 hp (373 kW) Pratt & Whitney Wasp radial engine.
- Gamma 2C (YA-13)
- Northrop-proposed attack version to compete with Curtiss A-12 Shrike armed with 4x 0.30 cal machine guns in the wings, 1x 0.30 cal machine gun on a flexible mount for rear defence, and up to 1,100 lb (500 kg) of bombs under the wings, evaluated by USAAC in 1933
- YA-13 prototype redesignated after being fitted with a Pratt & Whitney R-1830-9 engine
- Gamma 2D
- Cargo version used by TWA, three built, 710 hp (529 kW) Wright Cyclone engine. One aircraft was converted into an "Experimental Overweather Laboratory" studying icing, superchargers, radios, and turbulence at 20,000–35,000 ft (6,100–10,670 m), then used by USAAC under the designation UC-100. Another retired TWA aircraft was used by Spanish Republican air force for coastal patrol.
- Gamma 2E
- Similar to Gamma 2C in armament except for a 1,600 lb (727 kg) bomb load, used by the Republic of China Air Force as a light bomber until 1938 with a number of aircraft built in China, one, as K5053, used by the British Aeroplane & Armament Experimental Establishment, and two supplied to the Imperial Japanese Navy Air Service, as the Northrop BXN, for evaluation in 1933.
- Gamma 2F
- Another attack version developed in parallel with Gamma 2C, entered service as Northrop A-17 .
- Gamma 2G
- Two-seat race version, originally with a Curtiss Conqueror engine, later changed to Pratt & Whitney Twin Wasp Jr., then to Wright Cyclone SGR-1820-G-5. Flown by Jacqueline Cochran and Howard Hughes.
- Gamma 2H
- Testbed for Sperry automatic pilot, also flown by Russell Thaw to a third-place finish in the 1935 Bendix Trophy race.
- Gamma 2J
- Two-seat trainer powered by 600 hp (448 kW) Pratt & Whitney Wasp with retractable undercarriage intended for USAAC. North American BC-1 preferred. Only one built.
- Gamma 2L
- Used by Bristol for Bristol Hercules engine testing.
- Gamma 5A
- One aircraft exported to Imperial Japanese Navy (designation BXN1) as a study in modern engineering.
- Gamma 5B
- Two-seat version with the cockpits moved forward, used by the Spanish Republican air force for coastal patrol.
- Gamma 5D
- One aircraft exported to Japan with "Army-type" equipment (designation BXN2), studied by Nakajima, then passed to Manchukuo National Airways which used it for aerial reconnaissance over China and USSR.
- Spanish Republican Air Force – Northrop 2D and 5B Gamma
Specifications (Gamma 2D)
Data from McDonnell Douglas Aircraft since 1920 
- Crew: one
- Length: 31 ft 2 in (9.5 m)
- Wingspan: 47 ft 9½ in (14.57 m)
- Height: 9 ft 0 in (2.74 m)
- Wing area: 363 ft² (33.7 m²)
- Empty weight: 4,119 lb (1,868 kg)
- Loaded weight: 7,350 lb (3,334 kg)
- Powerplant: 1 × Wright R-1820 Cylone 9-cylinder Radial, 710 hp (530 kW)
- Maximum speed: 223 mph (194 knots, 359 km/h) at 6,300 ft (1,920 m)
- Cruise speed: 204 mph (177 knots, 328 km/h)
- Range: 1,970 mi (1,713 NM, 3,170 km)
- Service ceiling: 23,400 ft (7,130 m)
- Rate of climb: 1,390 ft/min (7.1 m/s)
- Wing loading: 20.2 lb/ft² (98.9 kg/m²)
- Power/mass: 0.096 hp/lb (0.16 kW/kg)
Aircraft of comparable role, configuration and era
- Smith 1986
- Eden and Moeng 2002, pp. 74–77.
- "The story of the Polar Star." National Air and Space Museum. Retrieved: June 27, 2013.
- "Fourteen Cylinder Motor In Hawke's New Plane", February 1933, Popular Science
- Francillon 1979, p.153.
- Francillon 1979, p. 154.
- Eden, Paul and Soph Moeng. The Complete Encyclopedia of World Aircraft. London: Amber Books Ltd., 2002. ISBN 0-7607-3432-1.
- Francillon, René J. McDonnell Douglas Aircraft since 1920. London:Putnam, 1979. ISBN 0-370-00050-1.
- Smith, M.J. Jr. Passenger Airliners of the United States, 1926–1991. Missoula, Montana: Pictorial Histories Publishing Company, 1986. ISBN 0-933126-72-7.
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