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Model 40 Tractor-biplane (1925)

Model 40 Tractor-biplane (1925)

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Model 40 Tractor-biplane (1925)

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Model 40 Tractor-biplane (1925)

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.

n 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.[1] 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.

Operational History

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.

The Contract Air Mail Act of 1925 set out the gradual privatization of the Post Office’s Air Mail routes. In late 1926, bids were requested for the main transcontinental trunk mail route, which was to be split into eastern and western sections, with Boeing bidding for the western section. Boeing revived the design for the tender, with the Model 40A replacing the Liberty engine with a 425 hp (317 kW) air-cooled Pratt & Whitney Wasp radial engine, which was 200 lb (91 kg) lighter than the Liberty, even ignoring the weight of the Liberty’s radiator and cooling water. The fuselage was redesigned to make more extensive use of welded steel tubing, and an enclosed cabin was fitted between the mail compartments, allowing two passengers to be carried as well as 1,200 lb (540 kg) of mail. Boeing’s bid of $3 per lb was much less than any of the competing bids, and Boeing was awarded the San Francisco to Chicago contract in January 1927, building 24 Model 40As for the route (with a further aircraft being used as a testbed by Pratt & Whitney)


Boeing Model 40 Mail

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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Boeing Model 40 (1925)


A Boeing Model 40 flying over mountains in Washington State, 1930s.
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.[10]
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.
Model 40B-4
Revised Model 40B with seating for four passengers and other improvements. Equipped with openable windows, plus seating for four passengers; 38 built


    • Crew: one
    • Capacity: two passengers and 1,200 lb (540 kg) mail
    • Length: 33 ft 2.25 in (10.12 m)
    • Wingspan: 44 ft 2.25 in (13.47 m)
    • Height: 12 ft 3.1 in (3.74 m)
    • Wing area: 547 sq ft (50.82 m2)
    • Empty weight: 3,531 lb (1,605 kg)
    • Max takeoff weight: 6,000 lb (2,727 kg)
    • Powerplant: 1 × Pratt & Whitney Wasp , 420 hp (313 kW)
  • Maximum speed: 128 mph (206 km/h, 111 kn)
  • Cruise speed: 105 mph (169 km/h, 91 kn)
  • Range: 650 mi (1,046 km, 565 nmi)
  • Service ceiling: 14,500 ft (4,420 m)
  • Rate of climb: 770 ft/min (3.9 m/s)

Ultimate encyclopedia


The B-29 was the progenitor of a series of Boeing-built bombers, transports, tankers, reconnaissance aircraft, and trainers. The re-engined B-50 Superfortress became the first aircraft to fly around the world non-stop during a 94-hour flight in 1949. The Boeing C-97 Stratofreighter airlifter, which was first flown in 1944, was followed in 1947 by its commercial airliner variant,

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