Northrop YA-13

Last revised July 7, 2000

The Northrop YA-13 attack plane of the mid-1930s has a very convoluted and complex origin. Sit back and get yourself a cup of coffee while I tell you its story.

The design of the YA-13 can be said to begin back in January of 1932, when John K. Northrop and Donald W. Douglas joined forces to set up the Northrop Corporation as a partially-owned subsidiary of the Douglas Aircraft Company. The new company was based at El Segundo, California.

One of the first products of the new Northrop Corporation was the Gamma special-purpose and mail-carrying aircraft. The first two examples built were known as the Gamma 2A and Gamma 2B. The Gamma 2A was built for the well known pilot Frank Hawks and the Gamma 2B was built for the Lincoln Ellsworth Trans-Antarctic Expedition. Each plane had an enclosed cockpit set on top of the fuselage aft of the wings. The two planes were completed in August of 1932.

The Gamma 2A was a low-winged, cantilever monoplane powered by a 785 hp geared Wright GR-1510 Whirlwind fourteen-cylinder air-cooled radial driving a three-bladed propeller. It was initially registered X12265 and was a single seater with the pilot's cockpit located aft of the wing and enclosed by a streamlined canopy. The wings were of multi-spar construction with the center section built integrally with the fuselage and the outer panels being bolted to the center section. The main landing gear was fixed and enclosed in large streamlined trousers. The tailwheel was spatted. Initially, the Gamma 2A was fitted with a set of full-span flaps and "park bench" ailerons which were mounted above the wing trailing edge. However, more conventional ailerons were later installed and flaps of reduced length and area were adopted. A large compartment was provided in the fuselage forward of the cockpit, but this was not normally used.

The Gamma 2A was purchased by Texaco on December 6, 1932 and was put at the disposal of Frank Hawks for record-breaking and advertising purposes. It was given the civilian registration NR12265, and flew with the Texaco Sky Chief logo prominently displayed. It set a number of records, including a nonstop flight between Los Angeles and New York in 13 hours 27 minutes at an average speed of 181 mph on June 2, 1933. In 1934, Texaco sold the Gamma 2A to industrialist Gar Woods, who entered the plane in the 1936 Bendix Trophy Race from New York to Los Angeles. Unfortunately, during this flight the plane caught fire in the air and the pilot, Joseph P. Jacobson, was forced to parachute to safety. The Gamma 2A crashed near Stafford, Kansas, and was completely destroyed.

Its stablemate, the Gamma 2B (registration X122269) was handed over to Lincoln Ellsworth on November 29, 1931. It was named Polar Star, and had been ordered for a proposed flight across the Antarctic continent. It differed from the Gamma 2A in having a longer transparent cockpit canopy that could house a second crew member in addition to the pilot. It was powered by a single 500 hp Pratt & Whitney Wasp SD nine-cylinder air-cooled radial engine driving a two-bladed propeller. Since the Gamma 2B was intended for use in Antarctica, it could be fitted with skis in place of the main and tailwheels, and could be fitted with twin Edo floats replacing the trousered main undercarriage. It was initially flown with full-span flaps and "park bench" ailerons, but these were replaced by conventional ailerons before the plane was shipped by boat to Antarctica.

The Polar Star flew several pioneering mapping and survey flights in the Antarctic continent, including the discovery of mountain ranges and islands that were previously unknown. It succeeded in making the first crossing of the Antarctic continent in November of 1935. The Polar Star is now on display at the National Air and Space Museum in Washington, D.C., occupying a place of honor for making one of the epic flights in aviation history.

Since the performance of the Gamma 2A and 2B substantially exceeded that of the Curtiss A-12 Shrike, Northrop decided in early 1933 to undertake at its own expense the development of an attack version of the Gamma, the Gamma 2C. The Gamma 2C retained the wings and trousered undercarriage of the previous two Gamma aircraft, but differed from them in having a new fuselage with a new two-seat enclosed cockpit. The cockpit was moved much further forward, with the pilot now sitting slightly behind the wing leading edge. The Gamma 2C was powered by a 735 hp Wright SR-1820-F2 nine-cylinder air-cooled radial driving a two-bladed propeller. It was fitted to carry up to 1100 pounds of bombs externally between its trousered main undercarriage units. The Gamma 2C was armed with four wing-mounted 0.30-inch machine guns and one flexible 0.30-inch machine gun firing either upward from the rear cockpit or downward through a ventral hatch underneath the fuselage.

The Gamma 2C was flown for the first time in the spring of 1933. It bore the civilian registration X12291. It was then delivered under a bailment contract to the Army Air Corps for evaluation at Wright Field in Ohio. Flight tests revealed the need for some modifications, and the Gamma 2C was returned to Northrop in February of 1934.

While at Northrop, a number of internal modifications were made to the Gamma 2C. In addition, the vertical tail surfaces were changed from the original trapezoidal shape to a more triangular shape. In this form, the US Army purchased the Gamma 2C on June 28, 1934. It was designated YA-13, and was assigned the serial number 34-27.

In order to improve the aircraft's performance and the pilot's forward visibility, the YA-13 aircraft was again returned to Northrop in January of 1935 to be re-engined with the smaller diameter 950 hp Pratt & Whitney R-1830-7 fourteen-cylinder air-cooled radial. This engine change resulted in the YA-13 being redesignated YA-16.

While waiting for the Army to make up its mind, 49 export versions of the YA-13 were built for the Chinese Government as light bombers. They were known as Gamma 2E, and were generally similar to the Gamma 2C in its original configuration. They were powered by 710 hp Wright SR-1820-F3 engines driving two-bladed propellers. The Gamma 2E was fitted with a partially retractable bomb-aimer's tub underneath the fuselage just aft of the wing that was operated by the bomb-aimer/gunner sitting in the rear seat. The armament consisted of four forward-firing 0.30-inch machine guns in the wings and one 0.30-inch machine gun operated by the bomb-aimer/gunner. A maximum bombload of 1600 pounds could be carried. The first Gamma 2E was delivered to China on February 19, 1934. The first 24 Gamma 2Es were manufactured and assembled by Northrop, but the remaining 25 were delivered to China in kit form and assembled by the Central Aircraft Manufacturing Company (CAMCO) at Loiwing.

The Gamma 2Es were in action with the Chinese Army Air Arm against the Japanese when they invaded China in August of 1937. However all, all 49 aircraft were rapidly destroyed either in training accidents or by the fury of the Japanese onslaught.

A single civilian version known as the Gamma 2ED-C was built in July 1934 as a demonstrator aircraft. It was powered by a 735 hp SR-1820-F53 radial. The initial civil registration was X13760. In early 1935, it was piloted by Frank Hawks and G. H. Irving in a 20,000 mile tour through Central and South America to locate suitable airfields for a proposed "Round America Air Race". X13760 was later sold to the British Air Ministry in 1935 for evaluation, where it was assigned the RAF serial number K5053. It was tested by the A & AEE at Martlesham Heath. Its ultimate fate is unknown.

Specification of Northrop YA-13:

Engine: One 735 hp Wright SR-1820-F2 nine-cylinder air-cooled radial. Performance: Maximum speed 207 mph at 3300 feet. Cruising speed 198 mph. Initial climb rate 1300 feet per minute. Service ceiling 21,750 feet. Maximum range 1100 miles. Weights: 3600 pounds empty, 6463 pounds loaded, 6575 pounds maximum. Dimensions: Wing span 48 feet 0 inches, length 29 feet 2 inches, height 9 feet 2 inches, wing area 363 square feet. Armament: Four wing-mounted 0.30-inch machine guns and one flexible 0.30-inch machine gun firing either upward from the rear cockpit or downward through a ventral hatch. Up to 1100 pounds of bombs could be carried on external under-fuselage racks.


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