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The Boeing XN2B-1 was an experimental trainer produced by fitting an experimental Fairchild-Caminez engine to a Boeing Model 64 primary trainer.
The Model 64 was one of many Boeing private ventures, and was designed as a possible primary and gunnery trainer for the US Navy and Air Corps. It was originally built as a two-bay biplane with thin wings (instead of the problematic thicker wings of the Boeing NB). The Model 64 used the standard Boeing construction method of a welded steel tube fuselage and wooden wing structure, all covered in fabric.
The Model 64 made its maiden flight as a twin-bay biplane in February 1926. It was then given new thicker single-bay wings and made its first flight in that format on 31 August 1926. The only Model 64 to be completed was sold into private hands.
Boeing then built two primary trainers based on the thick-wing two-bay Model 64. They were powered by an experimental Fairchild-Caminez 4-cylinder radial engine, and like so many aircraft it would be that experimental engine that was their downfall.
The Fairchild-Caminez engine used cams to link the pistons to the crankshaft. Normal radial engines had a two-turn power cycle, so needed higher crankshaft speeds to produce their full power. The Fairchild-Caminez engine went though a full power cycle in a single revolution, so could produce 125hp from 4 cylinders at 1,000rpm.
The Navy bought the second of two Boeing Model 81 for $8,300. It took delivery of the new aircraft on 21 June 1928, but it soon became clear that the Fairchild-Caminez engine created more problems than it solved. In January 1929 the aircraft was given a 165hp Wright J-6-5 (R-540) radial engine, and this made it a much more capable aircraft, but despite the improvement it wasn't ordered into production.
The first of the two Model 81s was used by the Boeing School of Aeronautics, but only after the Fairchild-Caminez engine had been replaced with a 145hp Axelson engine (as the Model 81A). It later got a 115hp Axelson engine as the Model 81B then a 100hp Kinner K-5 engine as the Model 81C. It ended its life as a ground based maintenance trainer.
XN2B-1
Engine: Fairchild-Caminez
Power: 125hp
Crew: 2
Span: 35ft
Length: 25ft 8in
Height: 11ft 2in
Empty Weight: 1,652lb
Loaded Weight: 2,178lb
Maximum Speed: 103.9mph (113mph with Wright engine)
Climb rate: 515ft/ min (770ft/min with Wright engine)
Ceiling: 12,000ft (13,300ft with Wright engine)
Range: 335 miles