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Aviation History
1954
1954 - 2154.PDF
DOUGLAS DC-7 Of* Latest of the World-famous Line: Its Design, Performance and Passenger-appeal UNTIL recently, when the appearance of Britain's turbo prop and turbojet airliners began to alter the picture, the world's main source of transport aircraft was firmly established in the United States. And, in the U.S.A., it was to the Douglas Aircraft Company that a great many airlines went for their machines, since the introduction in 1933 of the DC-2, most significant aircraft of its time. Following the success of the K.L.M. DC-2 which, carrying a full load of passengers, came second only to the first D.H. Comet in theEngland-Australia Race of 1934, the interest of many of the world's operators was focussed for the first time on this Douglas product, which was already laying the foundations for a long record of reliability, versatility, and relative economy for domestic airlines in the .U.S. The subsequent success story of the DC-3 (some 1,500 of which are estimated to be still in use at present) is now well known, as is that of the four-engine DC-4 which followed it. .-; Successive processes of "stretching" through the DC-6, 6A and 6B have now resulted in the DC-7 which, with the same span as the DC-4, has a fuselage 15ft longer and a vastly improved performance. The appraisal which follows describes the main features of this aircraft and includes the first-hand impressions of the Editor when he recently flew in the machine and visited the Douglas factory at Santa Monica, California. Design.—The DC-7 is basically a development of the DC-6B, and a few details of this latter machine may be recalled with advantage before the "Seven" is considered. The DC-6B, passenger version of the DC-6A, is well known as an efficient, conventional transport aircraft in the American manner. It is of semi-monocoque all-metal construction with flush-riveted skin and, powered by four Pratt and Whitney F-2800 Double Wasps, can carry between 54 and 92 passengers according to the type of service. The span is117ft 6in and length 105ft 7in. Normally the empty, take-off, and landing weights of the DC-6B are 54,148 lb, 106,000 lb and 88,200 lb respectively; the improved Super Six" version of Pan American carries 82 passengers on transatlantic tourist-class operations and has been certificated for a gross take-off weight of 107,000 lb. Cruising speed is 307 m.p.h. at 22,400ft, normal range 3,860 miles (absolute range 4,910 miles), andwing loading 72.5 lb/sq ft. fhe main aims in the design of the DC-7 were to obtain a higher speed, increased range and a greater payload. These were made possible largely through the adoption of Wright Turbo-Compound engines,^ very extensively developed and used by the Armed Services | before being made available for commercial use. The Turbo-Compound consists of a basic R-3350 18-cylinder two-row radial engine, with, the addition of a "power-recovery" unit between the power section and the supercharger section. This comprises three blow-down turbines, each driven by the exhaust gases from six cylinders: power generated by the turbines (due to the exhaust gases passing through the turbine blades) is transmitted through a fluid |coupling to the main crankshaft, augmenting the engine's outpiit by some 600 h.p. In general the introduction |f the new power plants has caused Neat and businesslike, the cockpit'of the DC-7 is an improved version of that of the DC-6B. Improved con\rol-response has been built into the new machine.
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