The Boeing Model 81 was an American training aircraft built in 1928.
The Model 81 was a development of the Model 64.
It was powered by a newly developed engine, the 125 hp Fairchild-Caminez 4-cylinder radial engine.
Operating at a much lower rpm than most engines (1000 rpm) it required the use of a large high-pitch propeller.
After initial flight tests with the Fairchild-Caminez, the prototype was refitted with a 145 hp Axelson engine, redesignated Model 81A and delivered to the Boeing School of Aeronautics.
There, it was re-engined a number of times, first with a 115 hp Axelson engine, redesignated Model 81B.
It then received a 165 hp Wright J-6-5, then a 100 hp Kinner K-5 and a redesigned vertical tail.
Redesignated Model 81C, it would later be removed from training service, re-engined with an Axelson engine, and used as a classroom trainer.
On 21 June 1928, the second Model 81 built was delivered to the US Navy at Anacostia, Maryland for $8,300, and redesignated Boeing XN2B.
Its trial with the Fairchild engine was unsatisfactory, and on 10 January 1929 it was refitted by Wright Aeronautical with a 160 hp Wright J-6-5 engine.
Despite increased performance, it was not ordered into production.
