The Curtiss O-40 Raven was a sesquiplane observation aircraft produced in tiny numbers for the US Army in the early 1930s. It was produced in response to an Air Corps requirement for a modern observation aircraft, but was something of a interim design. Its modern featured included the metal monocoque fuselage, metal framed and metal skinned wings and retractable undercarriage. Less modern was its sesquiplane wings - it had a larger upper wing and a shorter narrow-chord lower wing, connected to the upper wing by one set of struts. It was armed with one fixed forward firing .30in machine gun in the right upper wing and one flexibly mounted .30in gun in the rear cockpit.
The YO-40 was delivered in February 1932, but it was then damaged in a crash on 20 May 1932. It had to be returned to Curtiss where it was rebuilt and returned to the Army with stronger wings as the YO-40A.
The YO-40 was followed by four improved service test aircraft. These were originally ordered as the Y1O-40A but the design underwent significant changes and these four aircraft were delivered as the Y1O-40B.
The main change on the Y1O-40B was the removal of the lower wing. This turned the aircraft from a sesquiplane into a parasol wing monoplane. A stub of the lower wing had to be retained as it contained the retractable landing gear. The engine was upgraded and the wingspan reduced by 2ft 4in. The new aircraft were heavier than the original prototype, and their performance was generally worse. The aircraft were used for service tests and were then redesignated as the O-40B. The last one was still intact in 1939.
Engine: Wright R-1820-27
Span: 41ft 8in
Length: 28ft 10in
Height: 10ft 8in
Empty weight: 3,754lb
Gross weight: 5,180lb
Max speed: 187.7mph
Climb Rate: 1,660ft/ min
Service ceiling: 23,100ft
Range 324 miles
Armament: One .30in machine guns