The Douglas O-31 was the Douglas Aircraft Company's first

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

observation straight-wing aircraft used by the

United States Army Air Corps The United States Army Air Corps (USAAC) was the aerial warfare service component of the United States Army between 1926 and 1941. After World War I, as early aviation became an increasingly important part of modern warfare, a philosophical r ...

Development

Anxious to retain its position as chief supplier of observation aircraft to the USAAC, Douglas developed a proposal for a high-wing monoplane successor to the

O-2 O2, O-2, o2, O2, O2, O2− or O2+ may refer to: Science and technology * or dioxygen, the common allotrope of the chemical element oxygen * , the ion oxide * , the ion superoxide * , the ion dioxygenyl * , doubly ionized oxygen * O2, an EEG ...

. A contract was signed on January 7, 1930 for two XO-31 prototype aircraft, the first of them being flown in December of the same year. A fabric-covered gull-wing monoplane, the XO-31 had a slim corrugated dural-wrapped fuselage, similar to the

Thomas-Morse O-19 The Thomas-Morse O-19 was an American observation biplane built by the Thomas-Morse Aircraft Company for the United States Army Air Corps. Development The O-19 was based on the earlier Thomas-Morse O-6 biplane. It was a conventional two-seat ...

,"United States Military Aircraft Since 1909" by F. G. Swanborough & Peter M. Bowers (Putnam New York, ) 1964, 596 pp. carrying a tandem arrangement of open cockpits for the pilot and observer. It had one

Curtiss GIV-1570-FM Conqueror The Curtiss V-1570 Conqueror was a 12-cylinder vee liquid-cooled aircraft engine. Representing a more powerful version of the Curtiss D-12, the engine entered production in 1926 and flew in numerous aircraft.Gunston 1989, p. 46. Design and deve ...

V-12 engine and fixed landing gear with provision for large wheel fairings."The Complete Encyclopedia of World Aircraft
cover
Editors: Paul Eden & Soph Moeng, (Amber Books Ltd. Bradley's Close, 74-77 White Lion Street, London, NI 9PF, 2002, ), 1152 pp. The XO-31 suffered from directional instability and experiments were made with various fins, auxiliary fins, and rudder shapes, in an effort to cure the problem. The second aircraft was completed as the YO-31, with a geared

Curtiss V-1570-7 Conqueror The Curtiss V-1570 Conqueror was a 12-cylinder vee liquid-cooled aircraft engine. Representing a more powerful version of the Curtiss D-12, the engine entered production in 1926 and flew in numerous aircraft.Gunston 1989, p. 46. Design and deve ...

engine and an enlarged fin, 3" longer cowling, and a two-blade,

dextrorotatory Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...

propeller. Four YO-31A aircraft delivered during early 1932 were modified radically with an elliptical wing planform, a new tail assembly, a smooth

semimonocoque The term semi-monocoque or semimonocoque refers to a stressed shell structure that is similar to a true monocoque, but which derives at least some of its strength from conventional reinforcement. Semi-monocoque construction is used for, among ot ...

fuselage, three-blade propeller, and a canopy over the cockpits. The aircraft appeared with a variety of tail units, the final version (five built) designated O-31A featured a very pointed fin with an inset rudder. The single YO-31B was an unarmed staff transport and the sole YO-31C converted from YO-31A had cantilever main landing gear, and a ventral bulge in the fuselage, which enabled the observer to operate his single 0.3-in (7.62 mm) machine-gun more effectively from a standing position. Five Y1O-31C service-test aircraft were ordered in 1931, and delivered to the USAAC in early 1933 designated Y1O-43. They differed from the final configuration of the O-31A, with a wire-braced parasol wing, and a new fin and rudder.

Variants

_{''Data from:'' "U.S. Army Aircraft 1908-1946" by James C. Fahey

James Charles Fahey (1903–1974) was an American writer best remembered as the original compiler and publisher of the popular American reference ''The Ships and Aircraft of the United States Fleet''.
''The Ships and Aircraft of the United State ...
, 1946, 64pp.} ;XO-31: two built, Curtiss V-1570-25 Conqueror engine ;YO-31: revised XO-31, length increased to , Curtiss V-1570-7 engine ;YO-31A: five built, re-designated O-31A, fuselage construction changed to a built-up

structure of flat sheets, length increased to , Curtiss V-1570-53 engine ;YO-31B: one built, re-designated O-31B, Curtiss V-1570-29 engine ;YO-31C: YO-31A with cantilever gear, Curtiss V-1570-53 engine ;Y1O-31C: five built, wingspan increased to 45 ft 11 in (14 m), became the Y1O-43, Curtiss V-1570-53 engine

Specifications (YO-31C)

References

External links

Boeing HistoryAerofiles
{{Douglas aircraft O-31

Douglas O-31 The Douglas O-31 was the Douglas Aircraft Company's first monoplane observation straight-wing aircraft used by the United States Army Air Corps. Development Anxious to retain its position as chief supplier of observation aircraft to the USAAC, D ...

Single-engined tractor aircraft Parasol-wing aircraft Aircraft first flown in 1930