Douglas DC-7

Design and development of the Douglas DC-7 were prompted by American Airlines, which was seeking an aircraft superior in performance to the Lockheed Super Constellation being used by TWA. To meet the requirement of American Airlines it was decided to develop an improved version of the DC-6B using Wright Turbo-Compound engines, each of which had three exhaust-driven turbochargers giving some 20 per cent more output than the standard unit powerplant.
Originally assigned to the civilian version of the C-74 Globemaster (which did not proceed) ‘DC-7’ was later used for Wright R-3350-powered derivatives of the DC-6, but those were completely different airplanes.

American Airlines produced up-front funding for 25 new airliners, enabling Douglas to invest in its own Wright R-3350 Turbo Compound-powered airliner, the DC-7. The initial DC-7 was a direct development of the DC-6B, with the fuselage lengthened by 3 ft 4in to permit the inclusion of one additional row of seats. With the 2424kW R-3350 Turbo Compounds, gross weight went up to 15,200lb / 6895kg and required some strengthening of the landing gear structure. There were also some minor changes in detail, but externally the DC-7 appeared little different from the DC-6B.

One hundred and five DC-7s were built, followed by 112 DC-7Bs, the latter having only minor improvements. In the DC-7B, the engine nacelles were extended further aft to permit the installation of saddle tanks within the rear of the nacelles, made of the new metal titanium. The additional fuel capacity enabled Pan American Airlines to initiate non-stop London-New York service with the DC-7B on 13 June 1955.

The fuel capacity was marginal for North Atlantic services. With a full load and normal headwinds, DC-7Bs which were used to operate the east-to-west service, frequently had to divert for a refuelling stop. Douglas set about the task of developing a version of the DC-7B with greater range.

The third version was designated DC-7C and had, therefore, increased span to provide for greater fuel capacity. This was achieved by inserting a new parallel-chord wing section between the fuselage and the inboard engine nacelles, which had the added advantage of improving the cabin environment by reducing engine noise. During the development of the DC-7C, Curtiss-Wright was able to offer a further increase in engine power up to 3,700 hp and, as a result, the fuselage was lengthened by the insertion of a 1.02m plug to provide accommodation for up to 105 passengers.

 

Production of DC-7Cs totalled 120. Not only were they used on North Atlantic and Pacific Ocean services, but they also made possible non-stop scheduled operations across the continental USA, and were used also by SAS to inaugurate a Europe to Far East route over the North Pole. An improved DC-7D was planned, to be powered by four 4273kW Rolls-Royce Tyne turboprop engines, but the emergence of the Boeing 707 and the Douglas Company's purpose-built DC-8 jetliner meant that this remained only as an unfulfilled project.

Gallery

DC-7
Engines: 4 x Wright R-3350 Turbo-Compound, 3250 hp.
Max wt: 152,000 lb.
Maximum speed: 406 mph at 21,700ft.
Normal cruising speed: 355mph.
Range max payload: 4,605 miles.
Service ceiling: 21,700 ft.
Wing span: 127ft 6in.
Length 112ft 3in.
Height: 3lft l0in.
Wing area: 1,637 sq.ft.

DC-7C
Engines: 4 x Wright R-3350 Turbo-Compound, 2500kW.
Maximum speed: 406 mph / 650 km/h at 21,700ft.
Normal cruising speed: 355mph.
Range max payload: 7400 km / 4,605 miles.
Service ceiling: 21,700 ft.
Wing span: 38.8 m / 127ft 6in.
Length: 34.2 m / 112ft 3in.
Height: 9.7 m / 3lft l0in.
Wing area: 152.0 sq.m / 1,637 sq.ft.
Empty weight: 35785 kg / 78893 lb
Max take-off: 143,000 lb / 64865 kg.
Crew: 3-5
Passengers: 48-105