|Model 81 / XN2B
||Boeing Model 64
The Boeing Model 81 was an American training aircraft built by Boeing 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.
- Original Caminez-engined aircraft
- 145 hp Axelson engine
- 115 hp Axelson engine
- 100 hp Kinner K-5, redesigned tail.
- US Navy designation.
- United States
- Boeing School of Aeronautics
Specifications (XN2B) 
Data from Bowers, 1989. p. 144
- Crew: 2
- Length: 25 ft 8 in (7.82 m)
- Wingspan: 35 ft in (10.67 m)
- Height: 11 ft 2 in (3.40 m)
- Wing area: 259 ft2 (24.06 m2)
- Empty weight: 1,652 lb (750 kg)
- Gross weight: 2,178 lb (988 kg)
- Powerplant: 1 × Fairchild-Caminez, 125 hp (93 kW) each
- Maximum speed: 103.9 mph (167 km/h)
- Cruise speed: 86 mph (138 km/h)
- Range: 335 miles (539 km)
- Service ceiling: 12,000 ft (3660 m)
- Rate of climb: 515 ft/min (2.62 m/s)
- Bowers, Peter M. Boeing aircraft since 1916. London: Putnam Aeronautical Books, 1989. ISBN 0-85177-804-6