Tag Archives: Martin XB-907

16 February 1932

Martin XB-907 in flight. (U.S. Air Force)

16 February 1932: First flight, Glenn L. Martin Co. Model 123, designated XB-907 by the U. S. Army Air Corps. It was powered by two Wright Cyclone SR-1820-E engines rated at 600 horsepower, each. The engines were covered by Townend rings to reduce drag and improve cooling.

Martin XB-907

The prototype was tested at Wright Field.  The airplane reached a maximum speed of 197 miles per hour (317 kilometers per hour) at 6,000 feet (1,829 meters). Recommendations for modifications were made, and Martin upgraded the prototype to the XB-907A configuration (Martin Model 139), which was then designated XB-10 by the Air Corps, with the serial number 33-139.

Martin XB-907A, right profile. (U.S. Air Force)

Martin increased the XB-907A’s wingspan from 62 feet, 2 inches (18.948 meters) to 70 feet, 7 inches (21.514 meters). The engines were upgraded to Wright R-1820-19s, rated at 675 horsepower. Full NACA cowlings were installed.

The Army then ordered 48 production airplanes.

The XB-907 would be developed into the Martin B-10 bomber.

U.S. Army Air Corps Martin B-10B of the 28th Bombardment Squadron, Philippine Islands 28 November 1939. (U.S. Air force)

© 2019, Bryan R. Swopes

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27 November 1933

Martin YB-10 (Model 139), 33-140. (U.S. Air Force)

27 November 1933: The United States Army Air Corps accepted the Glenn L. Martin Company’s first service test YB-10 bomber, serial number 33-140. This was the first all-metal monoplane bomber with an internal bomb bay, retractable landing gear, rotating gun turret and enclosed cockpit. It flew faster than pursuit aircraft of the day.

The prototype Martin Model 123 (XB-907) in flight, 1932. (U.S. Air Force)

There had been a single prototype, the Martin Model 123. It was powered by two Wright R-1820-19 engines rated at 600 horsepower, each. This was designated XB-907 by the U.S. Army Air Corps when tested at Wright Field in 1932. Recommendations for modifications were made, and Martin upgraded the prototype to the XB-907A configuration, which was then designated XB-10 by the Air Corps. The Army then ordered 48 production airplanes.

Martin XB-907A (XB-10 33-139). (U.S. Air Force)

The first group of 14 airplanes were designated YB-10. The YB-10 (Martin Model 139) had enclosed canopies for the pilot and top gunner, and a nose turret. The crew consisted of a pilot, radio operator and three gunners.

These airplanes were powered by two air-cooled, supercharged, 1,823.129-cubic-inch-displacement (29.876 liter) Wright Cyclone SGR-1820-F2 (R-1820-25) 9-cylinder radial engines with a compression ratio of 6.4:1, which were rated at 750 horsepower at 1,950 r.p.m. at Sea Level. The engines turned three-bladed Hamilton Standard adjustable-pitch propellers through a 16:11 gear reduction. The R-1820-25 was 3 feet, 11–13/16 inches (1.214 meters) long, 4 feet, 5-¾ inches (1.365 meters) in diameter, and weighed 1,047 pounds (475 kilograms).

Martin YB-10. (U.S. Air Force)
Martin YB-10 at Wright Field, 1933. (U.S. Air Force)
Martin YB-10, left profile. (U.S. Air Force) 060511-F-1234S-008
Martin YB-10, right rear quarter view. (U.S. Air Force)

The bomber could carry two 1,130 pound (513 kilogram) bombs, or five 300 pound (136 kilogram) bombs in its internal bomb bay. Alternatively, a 2,000 pound (907 kilogram) bomb could be carried externally. There were three .30-caliber (7.62 mm) Browning M1919 machine guns for defense.

Martin B-10B in flight. (U.S. Air Force)

The first full scale production version was the B-10B, which was very similar to the service test YB-10s. These airplanes were 44 feet, 9 inches (13.640 meters) long with a wingspan of 70 feet, 6 inches (21.488 meters) and height of 15 feet, 5 inches (4.670 meters). The B-10B had an empty weight of 9,681 pounds (4,391 kilograms).

The engines installed in this variant were Wright Cyclone SGR-1820-F3 (R-1820-33), rated at 700 horsepower at 1,950 r.p.m. at Sea Level. Dimensions, weight and propeller gear reduction for this engine are the same as the R-1820-25, above.

The B-10B had a cruising speed of 193 miles per hour (311 kilometers per hour), and maximum speed of 213 miles per hour (343 kilometers per hour) at 10,000 feet (3,048 meters).

33-140 was converted to a B-10M for towing aerial targets and was assigned to the Tow Target Detachment at March Field, Riverside, California. Piloted by Robert E. Phillips, 33-140 was damaged in a taxiing accident, 8 April  1942.

Martin B-10 (U.S. Air Force)

© 2018, Bryan R. Swopes

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