|Model 200 and 221 Monomail|
|Model 221 of United Airlines|
|First flight||6 May 1930|
|Primary user||United Airlines|
|Developed into||Boeing YB-9|
Design and development 
The aircraft marked a departure from the traditional biplane configuration for a transport aircraft, instead featuring a single, low set, all metal cantilever wing. Retractable landing gear and a streamlined fuselage added to the aerodynamic efficiency of the aircraft. A single example was constructed for evaluation by both Boeing and the US Army (under the designation Y1C-18) but no mass production ensued, and the aircraft eventually joined Boeing's fleet on the San Francisco-Chicago air mail route from July 1931.
A second version was developed as the Model 221, with a fuselage stretched by 8 inches (20 cm) that sacrificed some of its cargo capacity to carry six passengers in an enclosed cabin; however the single pilot sat in an open cockpit. This version first flew on 18 August 1930. Both the Model 200 and the Model 221 were eventually modified for transcontinental service as the Model 221A, with slight fuselage stretches to give both a cabin for eight passengers. These aircraft were flown on United Air Lines' Cheyenne-Chicago route.
The advanced design of the Monomail was hampered by the lack of suitable engine and propeller technology. By the time variable pitch propellers and more powerful engines were available, the design had been surpassed by multi engined aircraft, including Boeing's own 247.
- Model 200
- mailplane (1 built)
- Model 221
- mailplane with capacity for 6 passengers (1 built)
- Model 221A
- Model 200 and 221 converted as 8-passenger airliners
Specifications (Model 221) 
- Crew: 1
- Capacity: 6
- Length: 41 ft 10 in (12.75 m)
- Wingspan: 59 ft 1 in (18 m)
- Height: ()
- Max. takeoff weight: 8,000 lb (3,628.7 kg)
- Powerplant: 1 × Pratt & Whitney Hornet B, 575 hp (428.8 kW)
- Maximum speed: 158 mph (254 km/h)
- Cruise speed: 135 mph (217 km/h)
- Range: 575 mi (925 km)
- Service ceiling: 14,700 ft (4,480.5 m)
See also 
- Aircraft of comparable role, configuration and era
- Boeing History - Boeing Monomail Transport Retrieved June 17, 2006.
- Taylor, Michael J. H. (1989). Jane's Encyclopedia of Aviation. London: Studio Editions.
- World Aircraft Information Files. London: Bright Star Publishing.
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