| M-1/M-2/M-3/M-4 | |
|---|---|
 | |
| General information | |
| Type | Single-seat mailplanes |
| Manufacturer | Douglas Aircraft |
| Primary users | United States Post Office |
| Number built | 57 |
| History | |
| Introduction date | 1926 |
| First flight | 1925 |
TheDouglas mailplanes are a family of 1920sAmerican single-seatmail planes designed and built by theDouglas Aircraft Company. 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.
The United States Post Office had been running the air mail service since 1918 mainly using variants of thede Havilland DH.4 biplane. In 1925, it decided to modernize and placed an order with Douglas for a replacement aircraft based on theDouglas O-2 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 theDAM-1 (Douglas Air-Mail-One) but this was soon shortened toM-1. The M-1 used the sameLiberty 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 theContract Air Mail (CAM) routes were introduced, the newly formedWestern Air Express Company (laterWestern Airlines) ordered six mailplanes with the designationM-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 designatedM-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 theM-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 theM-4A.
When the CAM-3 (Chicago-Dallas) route was passed toNational Air Transport Inc (NAT) in October 1925, the airline originally used theCurtiss 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 aPratt & Whitney Hornet 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.
Data from McDonnell Douglas aircraft since 1920 : Volume I,[1] The Illustrated Encyclopedia of Aircraft[2]
General characteristics
Performance
Media related toDouglas M-2 at Wikimedia Commons
