Boeing Model 81

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.^[1] Operating at a much lower rpm than most engines (1000 rpm) it required the use of a large high-pitch propeller.^[2]

Model 81 / XN2B
Role	trainer
National origin	United States
Manufacturer	Boeing
Introduction	1928
Primary user	Boeing School
Number built	2
Developed from	Boeing Model 64

Closeup of Boeing 81 showing 125 hp Fairchild-Caminez 4-cylinder radial engine

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.^[3]

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.^[4]

Variants

81

Original Caminez-engined aircraft

81A

145 hp Axelson engine

81B

115 hp Axelson engine

81C

100 hp Kinner K-5, redesigned tail.

XN2B

US Navy designation.

Operators

 United States

• Boeing School of Aeronautics

Specifications (XN2B)

Data from Bowers, 1989. p. 144

General characteristics

• Crew: 2
• Length: 25 ft 8 in (7.82 m)
• Wingspan: 35 ft 0 in (10.67 m)
• Height: 11 ft 2 in (3.40 m)
• Wing area: 259 sq ft (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)

Performance

• Maximum speed: 103.9 mph (167 km/h, 90.3 kn)
• Cruise speed: 86 mph (138 km/h, 75 kn)
• Range: 335 mi (539 km, 291 nmi)
• Service ceiling: 12,000 ft (3,660 m)
• Rate of climb: 515 ft/min (2.62 m/s)

References

1. "A diagram of the 4-cylinder Fairchild-Caminez cam engine". Archived from the original on 2017-10-05. Retrieved 2011-11-12.
2. Bowers, 1989, p. 142
3. Bowers, 1989, pp. 144-145
4. Bowers, 1989, pp. 142-144

• Bowers, Peter M. Boeing aircraft since 1916. London: Putnam Aeronautical Books, 1989. ISBN 0-85177-804-6