Boeing Model 40


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Boeing Model 40

To meet the requirements of the Air Mail Department of the US Post Office, which needed a new mailplane to replace its ageing DH-4s, Boeing designed in 1925 a large biplane transport under the designation Boeing Model 40. It was required to compete against the submissions of other manufacturers, and the Post Office specification had stipulated the use of a Liberty engine, plus an ability to carry 454kg of air mail. A fairly conventional biplane of that period, with tailskid landing gear and a Liberty engine, the Model 40 had a mail . compartment in the forward fuselage, with the pilot seated well aft in an open cockpit. First flown on 7 July 1925, the Model 40 was unsuccessful in the competition, the Douglas entry being declared winner. This was to result in Boeing's design gathering factory dust for some 18 months until, in early 1927, the US Post Office began the process of turning the government air mail service over to private enterprise.

Requiring an aircraft to operate on any of the routes for which it might bid, Boeing dusted off the Model 40, and began a process of redesign and conversion to make it suitable for the sort of operation the company had in mind. The resulting Model 40A had three major changes by comparison with the original Model 40 prototype: the Liberty engine was replaced by a Pratt & Whitney Wasp radial; its composite structure fuselage gave place to one of steel tube with fabric covering; and better use was made of fuselage capacity. The pilot's position remained unchanged, but an enclosed cabin for two passengers was provided more or less directly over the lower wing, with cargo/mail compartments between the pilot's cockpit and the cabin, and between the cabin and the engine firewall.

Boeing was successful in its bid, being allocated the San Francisco-Chicago route, and was equally successful in gaining approval for its new aircraft. Following tests .for certification, the Model 40A gained Approved Type Certificate No. 2, issued by the US Department of Commerce. A total of 25 was built, 24 for service with the new Boeing Air Transport Corporation, and one as an engine test-bed for Pratt & Whitney. The first example of the Model 40A was flown initially on 20 May 1927, and all 24 for Boeing Air Transport had been delivered in time for inauguration of the company's first air mail service on 1 July 1927.

 MODELBoeing Model 40A
 ENGINE1 x 313kW Pratt & Whitney Wasp radial piston engine
  Take-off weight2722 kg6001 lb
  Empty weight1602 kg3532 lb
  Wingspan13.47 m44 ft 2 in
  Length10.12 m33 ft 2 in
  Height3.73 m12 ft 3 in
  Wing area50.82 m2547.02 sq ft
  Max. speed206 km/h128 mph
  Cruise speed169 km/h105 mph
  Ceiling4420 m14500 ft
  Range1046 km650 miles

Joe Buko, e-mail, 27.07.2014 07:56

July 2014- I am just beginning to build a flying model of the Boeing 40C with a wingspan of 89".It'll have a 1.20cu in. Saito glow engine. It's modeled after Addison Pemberton's 40C.


John Cummings, e-mail, 02.03.2011 06:44

There was a beatiful 40 at the Cottage Grove, Oregon fly in August 2009. I believe the pilot was the owner, and there is a fantastic web site. He took some VIP's for a ride. The skies over Cottage Grove was filled with the sound of that radial with long exaust pipes. Classy Classic Airplane.


ron schmidt, e-mail, 12.01.2009 22:50

do you know where i could find a set of construction drawings for the 40c plane to make a model?


stephen winkler, e-mail, 27.03.2007 00:53

There was a Boeing Model 40B with the new Pratt and Whitney Hornet engines at 525 horsepower. However, that was the most horsepower that could be expected from a single row of nine cylinders and increasing the number of cylinders did not always result in the increase of horsepower. For example, the Siddeley Jaguars were two rows of seven cylinders or fourteen cylinders and their horsepower was 385. So Boeing decided to increase the number of engines and this led to the Boeing 80 with three Hornets instead of one.


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