W.Green, G.Swanborough The Complete Book of Fighters

NIEUPORT 31 France

   Developed in 1918 to a slightly later timescale than the Nie 29, the Nie 31 was a refined derivative of the earlier monoplane prototypes from which, configurationally, it differed primarily in having an enlarged spanwise auxiliary aerofoil surface. Technically a sesquiplane, but effectively a shoulder-wing monoplane, the Nie 31 (also referred to as the Nie 31 Rh indicating the engine type) was powered by a 180 hp Le Rhone 9R nine-cylinder rotary and was tested during the course of 1919. The wing, which was of exceptionally broad chord, incorporated substantial cut-outs at the trailing-edge roots to provide the pilot with a measure of downward view. The auxiliary surface braced beneath the fuselage provided attachment points for the inclined aerofoil-section wing bracing struts. It also enclosed the undercarriage axle and the upper portions of the wheels. The wooden monocoque fuselage was essentially similar to that of the Nie 29, and the intended armament consisted of two 7,7-mm Vickers guns. Development was abandoned despite excellent performance achieved on comparatively low power, possibly as a result of the rotary engine being by consensus passe by this time.

Max speed, 143 mph (230 km/h).
Endurance, 2.0 hrs.
Empty weight, 1,102 lb (500 kg).
Loaded weight, 1,720 lb (780 kg).
Span, 28 ft 2 1/2 in (8,60 m).
Length, 21 ft 7 4/5 in (6,60 m).
Height, 7 ft 10 1/2 in (2,40 m).
Wing area, 193.76 sq ft (18,00 m2).