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The Douglas O-31 was the
Douglas Aircraft Company The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated a ...
'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 con ...
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,"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 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 engine and an enlarged fin, 3" longer cowling, and a two-blade, dextrorotatory propeller. Four YO-31A aircraft delivered during early 1932 were modified radically with an elliptical wing planform, a new tail assembly, a smooth semimonocoque 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, 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 semimonocoque 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 Single-engined tractor aircraft Parasol-wing aircraft Aircraft first flown in 1930