The Northrop A-17 series of single-engined attack bombers were the backbone of the USAAC's attack aircraft strength during the late 1930s. The A-17 was well-armed, had a good performance, was reliable and dependable, and was widely exported. Although a fairly advanced design when it first appeared, the A-17 was rapidly eclipsed by advancing technology and soon became obsolescent. Even before American entry into the Second World War, the A-17 had been taken out of front-line service with the USAAC and largely relegated to training roles. It saw no combat in American colors, but its export versions did see some action.
The direct ancestor of the A-17 series was the Northrop Gamma 2F. The Gamma 2F (c/n 44) was a private venture prototype for a two-seat attack bomber. It was a development of the Gamma 2C two-seat attack bomber prototype, but differed from the Gamma 2C in having a 750 hp Pratt & Whitney R-1535-11 Twin Wasp Junior fourteen cylinder radial driving a three-bladed propeller. This engine had a smaller diameter than either the R-1830-7 or 9 of the XA-16, which made the forward view much better. In addition, the Gamma 2F had a smaller and longer fully-glazed canopy, with the radio operator/gunner being moved further aft. The fuselage was more streamlined and the tail surfaces were revised. The main undercarriage was partially retractable, with the main members retracting rearwards into large, bulky underwing fairings.
The Gamma 2F was delivered to the Army for evaluation on October 6, 1934. The results of the evaluation were generally favorable, but the Army wanted additional streamlining. The aircraft was returned to Northrop for modifications. Since the semi-retractable undercarriage Had resulted in only a slight improvement in performance, it was replaced by a fixed undercarriage, with struts and open-sided wheel fairings. In addition, the cowling, fuselage lines, and tail shape were all refined to obtain better aerodynamic streamlining. The shape of the cockpit canopy was extensively revised, and an unglazed section was added between the sliding canopies that covered the pilot's and gunner's cockpits.
On December 24, 1934, the Army announced their intention to purchase 110 production examples of the Gamma 2F under the designation A-17. Although the A-17 was well armed and had a good performance, perhaps its most salient selling point was its low cost--under $19,000 apiece, minus government-furnished equipment. This made it especially attractive in an America struggling with the Great Depression. The contract was officially signed on March 1, 1935. This was the largest prewar Army attack contract, and was a bonanza for the new Northrop branch.
It had been hoped that the larger GR-1820 Cyclone or the R-1830-7 Wasp could be installed in the production A-17, so the YA-13 prototype was returned to Northrop for fitting with this engine. However, the YA-13 was significantly overpowered with the R-1830-7, and to prevent disruption of production, it was decided that the production A-17 would retain the smaller R-1535.
In modified form, the Gamma 2F aircraft was delivered to the Army Air Corps on July 27, 1935 as the first A-17 (serial number 35-51). 109 production A-17s (35-52/160) were delivered between December 1935 and January 1937. They were powered by the 750 hp R-1535-11 and were armed with four wing-mounted and one flexible 0.30-inch machine gun. They differed from the prototype in being fitted with three-segment perforated air brakes which extended between the ailerons.
The first true production A-17 (35-52) was sent to Wright Field in December of 1935. The A-17s were initially evaluated at Wright Field and by the Technical Training Command at Chanute Field, Illinois. Beginning in February of 1936, A-17s were delivered to the 3rd Attack Group (8th, 13th and 90th Squadrons) based at Barksdale Field, Louisiana. They were also supplied to the 17th Attack Group (34th, 37th, and 95th Squadrons) based at March Field, California, which had recently converted from P-26A pursuits.
The A-17s were powered by the 750hp Pratt & Whitney R-1535-11 radial. They Were armed with four 0.30-inch machine guns in the wings and a single 0.30-inch gun on a flexible mount in the rear fuselage. The ventral firing system tested out on the prototype was deleted on production examples. Up to 20 30-lb bombs could be carried in small bomb bays in the fuselage.
Within a year, the A-17s were supplemented in these two groups by faster retractable-undercarriage A-17As. Shortly thereafter, the A-17s were transferred to training and auxiliary units. By the time of Pearl Harbor, the A-17 was thoroughly obsolete, and the surviving examples were being used only as advanced trainers or as squadron hacks. Most of them ended their lives at mechanics' schools during the early war war years.
A-17 35-122 was used by the National Advisory Committee for Aeronautics (NACA) to investigate the characteristics of laminar-flow aerofoils. New highly-polished surfaces were built over and around the existing wing structure. The new surfaces were highly polished and protruded ahead of the leading edge and behind the trailing edge, nearly doubling the wing chord inboard of the ailerons. A two-bladed propeller driven by a small auxiliary engine was mounted on each side forward of the new leading edge to increase the speed of the airflow over the wing. However, it was found that it was much easier to obtain the same data by using conventional wind tunnels, and NACA discontinued the project.
35-051/160 Northrop A-17 c/n 44, 75/183
Engine: One 750 hp Pratt & Whitney R-1535-11 Twin Wasp Junior fourteen-cylinder air-cooled
Performance: Maximum speed 207 mph at sea level. Cruising speed 170
mph. Landing speed 67.5 mph. Initial climb rate 1530 feet per
minute. An altitude of 5000 feet could be reached in 3.8 minutes.
Service ceiling 20,700 feet. Absolute ceiling 22,150 feet. Normal
range 650 miles with 654 pounds of bombs. Maximum range 1240 miles.
Dimensions: Wingspan 47 feet 8 1/2 inches, Length 31 feet 8 5/8
inches, Height 11 feet 10 1/2 inches, Wing area 363 square feet.
Weights: 4874 pounds empty, 7447 pounds loaded.
Armament: Four wing-mounted 0.30-inch machine guns, plus one flexible
0.30-inch machine gun operated by rear cockpit gunner. Normal bomb
load included twenty 30-pound fragmentation bombs carried in chutes
inside the fuselage and four external 100-pound bombs. Maximum
bombload was 1200 pounds.