O-31, O-35, O-43, and O-46A Observation Monoplanes

O-46A observation monoplane on runwayDouglas' first observation monoplane was the XO-31, an all-metal, single-engine, straight-wing aircraft that won a contract Jan. 7, 1930.

The straight-wing, single-engine O-43 followed the XO-31. It had a deeper fuselage and taller vertical surfaces with an inset rudder. Twenty-four O-43s were built.

Douglas then produced 90 further-improved, single-engine, straight-wing O-46s, built for the U.S. Army Air Corps. The enclosed cockpit O-46 series was the last observation aircraft built by Douglas and was the company's most successful Air Corps program since the O-38 biplane series.

During the same period, Douglas designed the gull-winged, twin-engine XO-35. Similar to its XB-7 bomber counterpart, the XO-35 had two Curtiss Conqueror liquid-cooled engines enclosed in nacelles attached under the wing. The O-35 was never produced in quantity, but six Y1B-7s, serving with the Army Air Corps, delivered airmail to the western zone during the 1934 airmail emergency.

O-46A Specifications
First flight: October 1935
Wingspan: 45 feet 9 inches
Length: 34 feet 6 inches
Height: 10 feet 8 inches
Ceiling: 24,150 feet
Range: 365 miles
Weight: 4,776 pounds
Power plant: One 725-horsepower Pratt & Whitney R1535 air-cooled radial engine
Speed: 200 mph