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Single-engine two-seat low-wing bomber monoplane
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 XA-16 (Gamma 2F) 
The saga of the Northrop XA-16 begins on Christmas Eve of 1934. The mail brought to the fledgling Northrop Corporation, a particularly appreciated yuletide present: official notification that the testing of their Gamma 2C and Gamma 2F had led to a War Department decision to allocate $2,047,774 for the purchase of one hundred ten Northrop A-17 attack bombers. While contract AC7326 was not officially signed until 1 March 1935, the Christmas Eve letter of intent ensured the future of Northrop and concluded an often frustrating 18-month period which had begun on 18 July 1933, when the company had delivered its fifth aircraft for evaluation by the Army Air Corps at Wright Field.
As the performance of its Gamma 2A and Gamma 2B exceeded substantially that of the Curtiss Shrike, The Army Air Corps' then-current attack aircraft, Northrop had decided in early 1933 to undertake as a private venture, the development of an attack version of the Gamma. Retaining the wings and trousered undercarriage of the earlier aircraft, the Gamma 2C (s/n 5) was fitted with a new fuselage housing a pilot and radio operator/gunner under an enclosed canopy located further forward to improve forward visibility. Powered by a 735-hp Wright SR-1820F-2 nine-cylinder radial driving a two-blade propeller, the Gamma 2C was armed with four wing-mounted 0.30-in machine-guns and one flexible, 0.30-in machine-gun firing either outboard upward from the rear cockpit or downward through a ventral hatch. Up to 1,100-lbs (499 kg) of bombs was carried externally on racks beneath the fuselage and center section. Bearing experimental registration X12291, the aircraft was first flown in the spring of 1933 before being delivered, under a bailment contract, to the Army Air Corps for evaluation at Wright Field. These tests, however, indicated the need for several modifications and the Gamma 2C was returned to Northrop in February 1934.
YA-13: When the Gamma 2C was returned to Northrop, a number of minor internal modifications were incorporated. However, a more noticeable modification was made to the vertical tail surfaces, which were changed from the original trapezoidal shape to a triangular shape with the top and rudder trailing edge rounded. In this form, the aircraft was purchased by the Army Air Corps on 28 June 1934, under contract AC6811 and was redesignated YA-13 with Air Corps serial 34-27.
XA-16: With the aim of improving the aircraft's performance and the pilot's forward visibility, the YA-13 was returned to Northrop in January 1935 to be re-engine with the smaller diameter 950-hp Pratt & Whitney Twin Wasp R-1830-7 fourteen-cylinder radial, with a three-blade propeller. Redesignated XA-16, The aircraft was first flown in this form in March 1935. The test results indicated that the aircraft was over-powered and that production aircraft should either have a smaller engine or larger tail surfaces. Later, however, the XA-16 was fitted with a 950-hp Pratt & Whitney Twin Wasp R-1830-9. so powered, it ended his life in an aircraft mechanic school at Roosevelt Field, Garden City, New York.
Gamma 2F/A-17: Powered by 750-hp Pratt & Whitney R-1535-11 fourteen-cylinder radial driving a three-blade propeller, the Gamma 2F (s/n 44) company-owned prototype was delivered on 6 October 1934, for evaluation by the Army Air Corps. In addition to being powered by an engine of smaller diameter than either the R-1830-7 or R-1830-9 of the XA-16, the aircraft embodied several improvements which rendered it more attractive to its potential military users. In particular, the Gamma 2F was fitted with a smaller and longer canopy — the radio-operator/gunner being moved further aft — a more streamlined fuselage and revised tail surfaces. Furthermore, its main undercarriage was made to retract rearward into large fairings. Evaluation of the aircraft by the Army, which began on 6 October 1934, when the Gamma 2F was delivered, proved generally successful, but also indicated the need for additional streamlining. Modifications incorporated when the aircraft was returned to Northrop included the substitution of a fixed undercarriage, with struts and open-sided wheeled fairings, for the original semi-retractable units, and extensive revisions cowling, fuselage lines and tail shape. In addition, the canopy shape was extensively revised, and an unglazed section was added between the sliding canopies covering the pilot's and radio-operators/gunner's cockpits. In this form, the aircraft was delivered to the Army Air Corps on 27 July 1935, as the first A-17 (A.C. 35-51) under contract AC7326.
Northrop Gamma Variants 
Military Variants 
Northrop Gamma Operators 
Specifications — Northrop A-17 [1,3,5]
Weights and Loadings:
Performance (Maximum loading with 1,000 lbs = 450 kg bombs):
Credits and Works Cited
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