The Douglas mailplanes were a family of 1920s

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

single-seat

mail plane A mail plane is an aircraft used for carrying mail. Aircraft that were purely mail planes existed almost exclusively prior to World War II. Because early aircraft were too underpowered to carry cargoes, and too costly to run any "economy class" ...

s designed and built by the

Douglas Aircraft Company The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated a ...

. The aircraft were used to run the main routes of the United States Air Mail service until the introduction of three-engined aircraft in 1928.

Development

The United States Post Office had been running the air mail service since 1918 mainly using variants of the de Havilland DH.4 biplane. In 1925, it decided to modernize and placed an order with Douglas for a replacement aircraft based on the

Douglas O-2 The Douglas O-2 was a 1920s American observation aircraft built by the Douglas Aircraft Company. Development The important family of Douglas observation aircraft sprang from two XO-2 prototypes, the first of which was powered by the 420 hp ...

observation biplane. The company modified an O-2 by covering over the forward cockpit to make a mail compartment and moving the pilot into what had been the observer's cockpit. The aircraft was designated the DAM-1 (Douglas Air-Mail-One) but this was soon shortened to M-1. The M-1 used the same

Liberty Liberty is the ability to do as one pleases, or a right or immunity enjoyed by prescription or by grant (i.e. privilege). It is a synonym for the word freedom. In modern politics, liberty is understood as the state of being free within society fr ...

engine as the DH.4, which was available in large numbers. Small modifications were made to the exhaust system to keep fumes away from the pilot and the design was considered a success, but was not ordered into production. When the

Contract Air Mail A contract is a legally enforceable agreement between two or more parties that creates, defines, and governs mutual rights and obligations between them. A contract typically involves the transfer of goods, services, money, or a promise to tra ...

(CAM) routes were introduced, the newly formed

Western Air Express Western Airlines was a major airline based in California, operating in the Western United States including Alaska and Hawaii, and western Canada, as well as to New York City, Boston, Washington, D.C., and Miami and to Mexico City, London and ...

Company (later

Western Airlines Western Airlines was a major airline based in California, operating in the Western United States including Alaska and Hawaii, and western Canada, as well as to New York City, Boston, Washington, D.C., and Miami and to Mexico City, London and ...

) ordered six mailplanes with the designation M-2. The main change from the M-1 was that the tunnel radiator was replaced with a frontal type. It also had the provision to carry a passenger instead of mail in the front cockpit. Just before Western Air Express introduced the aircraft into service (in April 1926 from Los Angeles to Salt Lake City), the Post Office ordered 50 aircraft designated M-3 for its major route network. The M-3 had only detailed differences from the M-2. Douglas then redesigned the M-3 to try to increase the payload, and the new aircraft was designated the M-4. The M-4 had a new longer span wing and the Post Office converted some of the M-3s order to be built as M-4s. One M-4 was also bought by Western Air Express and this was designated the M-4A. When the CAM-3 (Chicago-Dallas) route was passed to National Air Transport Inc (NAT) in October 1925, the airline originally used the Curtiss Carrier Pigeon. When the Post Office retired its aircraft in July 1926 after all the routes had been privatized, NAT bought ten M-3s and eight M-4s at auction. NAT bought other aircraft and at one point had a fleet of 24 Douglas mailplanes in use. Some of the NAT M-3s were modified by them with longer-span wings from 1928 onwards. One M-4 was re-engined by NAT with a

Pratt & Whitney Hornet The Pratt & Whitney R-1690 Hornet was a widely used American aircraft engine. Developed by Pratt & Whitney, 2,944 were produced from 1926 through 1942. It first flew in 1927. It was a single-row, 9-cylinder air-cooled radial design. Displacemen ...

radial engine. With the introduction of three-engined aircraft types beginning in 1928, the Douglas mailplanes were withdrawn from service; some were sold but most were scrapped.

Variants

;M-1 :Prototype mailplane modified from the

;M-2 :Production mailplane for Western Air Express EL-1999-00369

;M-3 :Production mailplane for United States Post Office ;M-4 : Douglas_M-4_L'Année_aéronautique_1926

Modified mailplane with stretched wing for United States Post Office. ;M-4A :One M-4 for Western Air Express ;MO-2B :A three-seat general purpose biplane developed directly from the ''M'' series of mailplanes, despite the O-2 designation.

Operators

; * National Air Transport *

United States Post Office The United States Postal Service (USPS), also known as the Post Office, U.S. Mail, or Postal Service, is an independent agency of the executive branch of the United States federal government responsible for providing postal service in the ...

Specifications (M-4)

References

* The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985), 1985, Orbis Publishing, Page 1574 *Francillon, René J. ''McDonnell Douglas Aircraft since 1920''. London:Putnam, 1979. .

External links

{{Douglas airliners 1920s United States mailplanes M-1 Single-engined tractor aircraft Biplanes Aircraft first flown in 1925