B-10/B-12 Martin 139 - Major Variants
Serial production of bombers began in Cleveland. The order for the first 12 pre-series machines XB-10 was received on January 17, 1933. Then there were modifications of the YB-10 (the brand designation Martin 139, 14 planes built) with the engine R-1820-25 and YB-12 (7 aircraft were built) with the R-1690-11 engine. The latter developed a speed of 341 km/h.
The Martin YB-10 (Model 139) was an improved version of the XB-10. The major change was the addition of canopies enclosing the pilots and rear gunner's compartments. In 1933 the Army Air Corps made its initial order for 48 basic Martin airframes in four different types, including 14 YB-10s. The difference between the two was the type of engine installed. Martin also built the YB-10 for export. Various versions of the Model 139 were sold to Argentina, China, Netherlands, Soviet Union, Siam and Turkey.
The Martin YB-10A was essentially a YB-10 with turbo-supercharged radial engines added. The aircraft was the fastest aircraft built in the B-10 series (B-10, B-12 and B-14); however, only one aircraft was built and it served mainly as an engine test aircraft.
B-12
The Martin YB-12 was a Martin YB-10 airframe modified for Pratt & Whitney R-1690-11 Hornet radial engines. These engines were slightly more powerful than the Wright Cyclones used on the YB-10 and gave the YB-12 a speed advantage of about 5 mph. Seven YB-12s were ordered in 1933 for service test and 25 more similar aircraft were ordered as B-12A.
The series of 25 B-12A aircraft was equipped with an additional fuel tank in the bomb bay, and in 1934 the last serial modification, the B-10B, featuring the R-1820-33 engine, appeared. Until the end of the year, 91 copies were built (according to other sources, in the year 1934 the deliveries amounted to 88 vehicles), then the Air Force in 1935 and 1936. issued an additional order for 15 and 2 aircraft, respectively. After that, the production of B-10 / B-12 bombers ended. At the stage of prototypes there were variants of YB-10A (two planes with R-1820-11 engines and turbochargers), XB-14 (with engines YR-1830-9, this modification developed the speed of 380 km / h) and Martin 146 (with engines R -1820-G5). Order
The Martin B-12A was the production version of the YB-12. The A model had an extra fuel tank (365 gallons) installed to increase range, reducing the top speed by a few miles per hour. In January 1931 the U.S. Army took over the responsibility for coastal defense as a result of the MacArthur-Pratt agreement. This would allow the U.S. Navy to take on a greater role in long-range sea offensive operations. The Navy, like the Army, was very limited in size in the 1920s and early 1930s. With the acquisition of coastal defense duties, the Army converted some B-10 and B-12 aircraft to float planes.
B-13
The XB-13 was a version of the Martin YB-10 powered by two Pratt & Whitney R-1860-17 radial engines of 700 hp each. Ten aircraft on order were canceled before construction began.
B-14
The Martin XB-14 was essentially a YB-10 airframe modified for Pratt & Whitney YR-1830-9 Twin Wasp radial engines. The aircraft was ordered in 1933 along with the YB-10, YB-10A, YB-12 and B-12A as part of an order for 48 aircraft. The only major difference between all these aircraft were the engines installed.
Other Variants
In May 1934, an assault version of the XA-15 was proposed on the basis of the YB-10 bomber. The aircraft was virtually identical to the original design and, according to the project, was to receive Wright R-1820-25 (750 hp) engines. With a maximum flight weight of 5,605 kg, its speed would be 344 km/h. From the practical implementation of this project was rejected in favor of a specialized attack aircraft Curtiss XA-14. Also, the YO-45 front-line reconnaissance project was not implemented.
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