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Type: Bomber
Origin: Douglas
Crew: 4
Models: N/A
First Flight: 1931
Service Delivery: 1932
Final Delivery: N/A

Model: Curtiss V-1570-27 "Conqueror"
Type: 12-Cylinder Vee
Number: Two      Horsepower: 675 hp

Wing span: 65 ft 3 in (19.9 m)
Length: 45 ft 7 in (13.9 m)
Height: 12 ft 1 in (3.7 m)
Wing Surface Area: 621.2 ft (57.71 m)
Wing loading: 16.02 lb/ft (78.42 kg/m)
Empty weight: 5,519 lb (2,503 kg)
Loaded weight: 9,953 lb (4,515 kg)
Max takeoff weight: 11,177 lb (5,070 kg)

Maximum speed: 182 mph (158 knots, 293 km/h)
Cruise speed: 158 mph (137 knots, 254 km/h)
Stall speed: 78 mph (68 knot, 130 km/h)
Combat radius: 206 mi (180 nm, 330 km)
Ferry range: 632 mi (549 nm, 1,020 km)
Service ceiling: 20,400 ft (6,200 m)
Rate of climb: 1,100 ft/min (5.8 m/s)
Power/mass: 0.136 hp/lb (224 W/kg)

Guns: Two .30 in. Browning machine guns

Bombs: 1,200 lb (540 kg)

The original XB-7 was an experimental version of a set of monoplanes made by Douglas, which were designated XO-35 and XO-36. The plane was built as a competitor to Fokker YO-27, which eventually led to the Fokker XB-8. The Douglas plane had a single set of wings, which were mounted relatively high (hence their nickname 'gull wings'). The wings were covered by corrugated duralumin. On 1930 March 26, two planes of the design were ordered by the Army Air Corps. Due to minor differences between the two planes, one was designated XO-35 and the other XO-36. Because these two planes had much better performance than most of their predecessors, they were a promising alternative to the slow, bulky biplanes Keystone Aircraft Corporation that made up the entire Army Air Corps bomber fleet.

Impressed by the pair of planes submitted by Douglas, the Army Air Corps chose to complete the XO-36 as a bomber. It was redesignated XB-7, and was equipped with bomb racks capable of carrying up to 1,200 lb of bombs. In August of 1931, the Army Air Corps ordered seven Y1B-7 bombers for service testing (along with five Y1O-35s, which became the O-35 in operation service with the 9th Observation Group). The XB-7 was delivered to Wright Field in July of 1932, where testing was commenced. A few months later, the first Y1B-7s were delivered.

The prototype XB-7 was a Light bomber, carrying only 1,200 pounds of bombs. The skin of the fuselage was corrugated for ease of production. The gull wing was braced externally to increase strength. While this brace also increased drag, the XB-7 was still faster than any of its biplane predecessors. The crew complement consisted four: a pilot, copilot, and two gunners (one in the nose and one at the tail).

Operational History:
Despite positive evaluation, the Y1B-7 was never entered into mass production because of its small bomb load and because newer, more capable aircraft, such as the Martin B-10, were under development. Nevertheless six of the B-7 prototypes, the XO-35 prototype, and the five O-35s all participated in the Airmail Emergency of 1934. All of the O-35's survived and remained in service during the latter 1930's, but four of the B-7's were lost in crashes delivering the mail.
    Source: Wikipedia