Design and Development
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 26 March 1930, two designs were ordered by the Army Air Corps. Due to minor differences between the two aircraft, one was designated XO-35 and the other XO-36. Because these two aircraft had much better performance than most of their predecessors, they were a promising alternative to the slow, bulky Keystone Aircraft Corporation biplanes that made up the entire Army Air Corps bomber fleet at that time.
Impressed by the pair of aircraft submitted by Douglas, the Army Air Corps chose to complete the XO-36 as a bomber. It was redesignated B-7, and was equipped with bomb racks capable of carrying up to 1,200 lb (544 kg) of bombs. In August 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 1932, where testing commenced. A few months later, the first Y1B-7s were delivered. The Y1B-7s were differentiated by having more powerful Curtiss Conqueror engines with streamlined nacelles, and by having three-bladed rather than two-bladed propellers.
The prototype XB-7 was a bomber, carrying only 1,200 lb (544 kg) 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).
Read more about this topic: Douglas Y1B-7
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