Northrop XP-948
single-engine single-seat low-wing pursuit monoplane

Northrop Gamma 3A, (c/n 44, XP-948) (Northrop photo)

Overview — Northrop Gamma Series

The Northrop Gamma was a single-engine all-metal monoplane cargo aircraft used in the 1930s. Towards the end of its service life, it was developed into a light bomber.

Design and Development — The Northrop 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 Northrop Alphas, the fixed landing gear was covered in distinctive aerodynamic spats, and the aircraft introduced a fully enclosed cockpit.

Operational History — The Northrop Gamma saw fairly limited civilian service as mail planes with Trans World Airlines, but had an illustrious career as 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 Nomad light attack aircraft. Military versions of the Northrop Gamma saw combat with Chinese and Spanish Republican air forces. Twenty Five Northrop Gamma 2Es were assembled in China from components provided by Northrop.

On June 2, 1933 Frank Hawks flew his Northrop Gamma 2A Texaco 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 Northrop Gamma 2G making the west-east transcontinental run in 9 hours, 26 minutes, and 10 seconds.

The most famous Northrop Gamma was the Northrop Gamma 2B Polar Star. The aircraft was carried via ship and off-loaded onto the pack ice in the Ross Sea during Lincoln Ellsworth’s 1934 expedition to Antarctica. The Northrop Gamma 2B was almost lost when the ice underneath it broke and it had to be returned to United States for repairs. The Northrop Gamma 2B Polar Star’s second return 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. The Northrop Gamma 2B Polar Star was later recovered and donated to the Smithsonian National Air and Space Museum where it resides to this day.

Overview — Northrop XP-948 (Gamma 3A)

In early 1935, the US Matériel Division announced a design competition for single-seat fighters to replace the Boeing P-26 Peashooter, then the most advanced aircraft equipping Army Air Corps Pursuit Groups. Manufacturers were invited to submit private venture prototypes for evaluation at Wright Field beginning on 27 May 1935. Initially, three companies decided to enter prototypes in the forthcoming competition: the Curtiss Wright Corporation, which designed its Model 75, the prototype of the P-36 and H75 series; the Seversky Aircraft Corporation which planned to develop a single-seat variant but initially delivered a two-seat prototype, the SEV-2XP, the forebear of the P-35 series; and the Northrop Corporation, which proposed its Model 3A.

To obtain the necessary performance, while hastening the development of the new aircraft, an engineering team led by Ed Heinemann decided to design a retractable undercarriage variant of the of the XFT-1/XFT-2 naval fighter prototype. In spite of this time-saving approach, the Northrop 3A was too late to be delivered to Wight field and the Matériel Division decided to adjourn the competition until August 1935 rather than award a production contract to Curtiss whose Model 75 had been the only entry available on the specified date. However, the stroke of luck which appeared to give a new lease of life to the Northrop 3A was of short duration.

The Northrop 3A (XP-948, c/n 44), powered by a 750-hp Pratt & Whitney Twin Wasp R-1535-A56 fourteen-cylinder radial driving a three-blade propeller, was completed in July 1935. the aircraft was finished in contemporary Air Corps colors, blue fuselage with yellow wings and empennage. The aircraft was unarmed, but had provision for two fuselage-mounted 0.3-inch 0.50-inch machine-guns. After completing preliminary manufacturer’s trials at Mines Field (now LAX), the 3A was ferried to Wight Field in July 1935. However, limited evaluation by Air Corps personnel confirmed the Northrop test pilot’s report that the aircraft was rather unstable and prone to spinning. Accordingly, these 3A was returned to Mines Field were Northrop hoped to find some quick solution to the stability problem before entering the aircraft in the August 1935 competition trials. Intent on testing the modifications made to the aircraft before its scheduled return to Wight Field, First Lieutenant Frank Scare took off on 30 July 1935, for a test flight over the Pacific and failed to return. No trace of the Northrop 3A or its pilot were ever found.

The loss of the prototype effectively removed Northrop from consideration as supplier of the next generation of fighter aircraft for the Army Air Corps. Consequently, to recoup some of its investment in the project, the company sold its design to Chance Vought Aircraft which developed it into the equally unsuccessful V-141 and V-143.

Northrop Gamma Variants

Civil Variants

• Northrop Gamma 1E: Single-engine (Pratt & Whitney Hornet) two-seat closed-cabin low-wing land monoplane, 1 built, Sweden A.B Aerotransport, c/n 29.
• Northrop Gamma 2A: Single-engine (Wright Whirlwind) single-seat closed-cabin low-wing land monoplane, 1 built, Texaco Sky Chief, c/n 1.
• Northrop Gamma 2B: Single-engine (Pratt & Whitney Wasp) two-seat closed-cabin low-wing land monoplane, 1 built, Ellsworth Polar Star, c/n 2.
• Northrop Gamma 2C: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, 1 built, USAAC light attack aircraft YA-13, c/n 5.
• Northrop Gamma 2D: Single-engine (Wright Cyclone) single-seat closed-cabin low-wing land monoplane, 3 built, TWA cargo aircraft, c/n 8-10.
• Northrop Gamma 2E: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, light attack bomber, Chinese Military, c/n 14, c/n 46, c/n 48-72.
• Northrop Gamma 2EC: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, light attack bomber, Chinese Military, c/n 17-22, c/n 45.
• Northrop Gamma 2ED: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, light attack bomber, Chinese Military, c/n 15-16, c/n 23-27, c/n 30-37.
• Northrop Gamma 2ED-C: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, shipped to USSR, c/n 47.
• Northrop Gamma 2F: Single-engine (Pratt & Whitney R-1870-7) two-seat closed-cabin low-wing land monoplane, 1 built, USAAC light attack aircraft XA-16, c/n 5.
• Northrop Gamma 2G: Single-engine (Curtiss Conqueror) two-seat closed-cabin low-wing racing land monoplane, 1 built, Jacqueline Cochran, c/n 11.
• Northrop Gamma 2H: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing racing land monoplane, 1 built for Marron Price Guggengeim, flown by Russell W. Thaw, c/n 12.
• Northrop Gamma 2J: Single-engine (Pratt & Whitney Wasp) three-seat closed-cabin low-wing land monoplane advanced trainer, 1 prototype built, USAAC advanced trainer competition, version of Army A-17 Nomad, c/n 186
• Northrop Gamma 2L: Single-engine (delivered without engine) two-seat closed-cabin low-wing land monoplane, 1 built, sold to Bristol Aeroplane Company for Hercules engine testing, c/n 347.
• Northrop Gamma 3A: Single-engine (Pratt & Whitney Wasp) single-seat closed-cabin low-wing land monoplane fighter, 1 built, USAAC XP-948, c/n 44.
• Northrop Gamma 5A: Single-engine (Pratt & Whitney Wasp) two-seat closed-cabin low-wing land monoplane, 1 built, exported to Japanese Navy 1935, c/n 187.
• Northrop Gamma 5B: Single-engine (Pratt & Whitney Twin Wasp, Jr.) two-seat closed-cabin low-wing land monoplane, 1 built, Spanish Republican Air Force, c/n 188.
• Northrop Gamma 5D: Single-engine (Pratt & Whitney S3H-1) two-seat closed-cabin low-wing land monoplane, 1 built, exported to Japanese Navy, c/n 291.

Military Variants

• Northrop YA-13: Single-engine (Wright Cyclone) two-seat closed-cabin low-wing land monoplane, 1 built, USAAC light attack aircraft, Gamma 2C (A.C. 34-027, c/n 5).
• Northrop XA-16: Single-engine (Pratt & Whitney R-1870-7) two-seat closed-cabin low-wing land monoplane, USAAC light attack aircraft, redesigned & re-engine YA-13 (A.C. 34-027, c/n 5).
• Northrop XP-948: Single-engine (Pratt & Whitney R-1870-7) single-seat closed-cabin low-wing land monoplane, 1 built, aka Northrop 3A, USAAC pursuit adaptation of Navy XBT-1 (c/n 44).
• Northrop XFT-1: Single-engine (Wright XR-1510-8) single-seat closed-cabin low-wing land monoplane, 1 built, USN experimental fighter (BuNo 9400, c/n 6).
• Northrop XFT-2: Single-engine (Wright R-1535-72 single-seat closed-cabin low-wing land monoplane, re-designed and re-engine XFT-1, 1 converted, USN experimental fighter (BuNo 9400, c/n 6).
• Northrop A-17: Single-engine (Pratt & Whitney R-1535-11 Twin Wasp, Jr.) two-seat closed-cabin low-wing land monoplane with fixed landing gear, 109 built, USAAC light attack bomber (A.C. 35-051 to 35-160, c/n 75-184).
• Northrop A-17A: Single-engine (Pratt & Whitney Twin Wasp, Jr.) two-seat closed-cabin low-wing land monoplane with retractable gear, 129 built, USAAC light attack aircraft (A.C 36-162 to 36-261, 38-327 to 38-377).
• Northrop A-17AS: Single-engine (Pratt & Whitney R-130-41 Wasp) three-seat closed-cabin low-wing land monoplane with retractable gear, 2 built, USAAC staff transport (A.C 36-349 and A.C. 36-360, c/n 289-290).
• Northrop XBT-1: Single-engine (Pratt & Whitney R-1535-66) two-seat closed-cabin low-wing land monoplane, 1 built, USN experimental dive-bomber (BuNo 9745, c/n 43).
• Northrop BT-1: Single-engine (Pratt & Whitney R-1534-94) two-seat closed-cabin low-wing land monoplane, 54 built, USN dive-bomber (BuNo 0590 to 0626, 0628 to 0643, c/n 293 to 329, 331 to 346).

Northrop Gamma Operators

Military Operators

• China
• Japan: as BXN
• Spain: Spanish Republican Air Force - Northrop 2D and 5B Gamma
• United States: United States Army Air Corps

Civil Operators

• Manchuria: Manchukuo Manchurian Air Lines
• United States: Trans World Airlines

Northrop XP-948 (Gamma 3A) Specifications and Performance Data

Type:

• Single-engine single-seat low-wing pursuit monoplane

Power Plant:

• 750-hp Pratt & Whitney Twin Wasp R-1535-A5G driving a three-blade propeller

Dimensions:

• Wingspan: 33 feet 6 inches (10.21 m)
• Length: 22 feet 3 inches (6.78 m)
• Height: 9 feet 1 inch (2.77 m)
• Wing area: 187 ft² (17.37 m²)

Weights and Loadings:

• Weight loaded: 3,900 lbs (1,769 kg)

Performance:

• Maximum speed at S/L: 270 mph (434 km/h)
• Maximum speed at 10,000 feet (3,050 m): 258 mph (415 km/h)
• Cruising speed: no data
• Landing speed: no data
• Climb to 10,000 feet (3,050 m): 3.3 minutes
• Service ceiling: 31,600 feet (9,630 m)
• Endurance: 3.1 hours

References

• Photo: Northrop photo via the John Shupek Collection
• Wikipedia: Northrop Gamma
• Northrop 3A: Francillon, René J., McDonnell Douglas Aircraft since 1920: Volume I, Putnam Aeronautical Books, London, 1995, ISBN 0-85177-827-5, pp. 193-195.
• Allen, Richard Sanders, The Northrop Story 1929-1939, Orion Books, New York, 1990, ISBN 0-517-56677-X, pp. 143, 150-155.
• Green, William and Gordon Swanborough, The Complete Book of Fighters, Smithmark Publishers, Inc., New York, NY, 1994, ISBN 0-8317-3939-8, p. 455.