Boeing Commercial Airplanes
Model 40 Mail Plane

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General Info

Boeing
Model 40 Mail Plane

Role Mail plane
Manufacturer Boeing
First flight July 20, 1925
Introduction July 1, 1927
Primary users Boeing Air Transport Varney Air Lines
Pacific Air Transport
Number built ca. 80

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History Boeing Commercial Airplanes
Boeing Model 40 Mail Plane

The Boeing Model 40 was a United States mail plane of the 1920s. It was a single-engined biplane that was widely used for airmail services in the United States in the 1920s and 1930s, especially by airlines that later became part of United Airlines. It became the first aircraft built by the Boeing company to carry passengers.

In 1925, the US Post Office issued a requirement for a mailplane to replace the ex-military DH-4s then in use. The new aircraft was required to use the same water-cooled Liberty V12 engine as used by the DH-4, of which large stocks of war-built engines were available. The resultant aircraft, the Boeing Model 40, was a conventional tractor biplane, with the required Liberty engine housed in a streamlined cowling with an underslung radiator. The aircraft's fuselage had a steel tube structure, with an aluminum and laminated wood covering. Up to 1,000 lb (450 kg) of mail was carried in two compartments in the forward fuselage, while the single pilot sat in an open cockpit in the rear fuselage. The wings and tail were of wooden construction, and the Model 40 had a fixed conventional landing gear.

The Model 40 made its first flight on July 7, 1925. Although the prototype was purchased by the US Post Office, the production order went to the Douglas M-2.^[1]^[3]

Model 40C at Oshkosh 2008. Both passenger entry doors, one for each of the two-seat rows, are on the left side of the fuselage

Variants

Model 40: Original 1925 design with Liberty engine.
Model 40A: Revised 1927 design for BATC. the aircraft was powered by a Pratt & Whitney Wasp radial engine, plus seating for two passengers in an enclosed cabin; 25 built. Received Dept of Air Commerce Approved Type Certificate #2.
Model 40B: Model 40As re-engined with a 525 hp (391 kW) Pratt & Whitney Hornet radial piston engine. 19 Model 40A were converted. Redesignated Model 40B-2.