The Douglas DC-7 was an American transport aircraft built by the Douglas Aircraft Company from 1953 to 1958. It was the last major piston engine powered transport made by Douglas, coming just a few years before the advent of jet aircraft such as the Boeing 707 and Douglas DC-8.
The early DC-7s were only sold to U.S. carriers. European carriers could not take advantage of the small range increase in the early DC-7, so Douglas released an extended-range variant, the DC-7C (Seven Seas) in 1956. A 10 feet (3.0 m) wing-root insert added fuel capacity, reduced interference drag, and made the cabin quieter by moving the engines further outboard; all DC-7C's had the nacelle fuel tanks previously seen on Pan American's and South African's DC-7Bs. The fuselage, which had been extended over the DC-6B's by a 40 inches (100 cm) plug behind the wing for the DC-7 and -7B, was lengthened by a similar plug ahead of the wing to give the DC-7C a total length of 112 feet 3 inches (34.21 m).
Since the late 1940s Pan Am and other airlines had scheduled a few nonstop flights to Europe, but westward nonstops against the wind were rarely possible with an economic payload. The 1049G and DC-7B that appeared in 1955 could make the trip if the headwinds weren't bad, but in summer 1956 Pan Am's DC-7C finally started making the westward trip fairly reliably. BOAC was forced to respond by purchasing DC-7Cs rather than wait on the delivery of the Bristol Britannia. The DC-7C found its way into several other overseas airlines' fleets, including SAS, which used them for cross-polar service to North America and Asia. The DC-7C sold better than its rival, the Lockheed L-1649A Starliner, which entered service a year later, but sales were cut short by the arrival of Boeing 707 and DC-8 jet aircraft in 1958-60.
Starting in 1959, Douglas began converting DC-7 and DC-7C aircraft into DC-7F freighters, which extended the life of the aircraft past its viability as a passenger transport.
The predecessor DC-6, especially the DC-6B model, had established, for its time, a reputation for straightforward engineering and reliability. Pratt & Whitney, the DC-6's R-2800 engine manufacturer, did not offer an effective larger engine apart from the R-4360, a very large and overly-complex engine with a poor reliability reputation. Therefore Douglas turned to Wright Aeronautical for a more powerful engine. The Wright R-3350 however had reliability issues of its own and this affected the DC-7's service record and usage. It was noticeable that carriers which had both DC-6s and DC-7s in their fleets, usually replaced the newer DC-7s first once jets started to arrive. Some airlines had to scrap their DC-7s after little more than five years of service, whereas the vast majority of DC-6s lasted longer and then sold more readily on the secondhand market.