In 1945, Pan American World Airways requested a DC-7 or a civilian version of the Douglas C-74 Globemaster military transport. Pan Am soon canceled their order. That proposed DC-7 was unrelated to the later DC-6 derived airliner. The DC-7 was the last major piston engine powered transport aircraft developed by Douglas as jet aircraft were beginning to come to the forefront of future aircraft development.
American Airlines revived the designation when they requested an aircraft that could fly across the USA coast-to-coast nonstop in about eight hours. Civil Air Regulations then limited domestic flight crews to 8 hours of flight time in any 24 hours. Douglas was reluctant to build the aircraft until American Airlines president C. R. Smith ordered 25 aircraft at a total price of $40 million, thus covering Douglas' development costs.
The DC-7’s wing was based on that of the DC-4 and DC-6, with the same span; the fuselage was 40 inches (100 cm) longer than the DC-6B. Four eighteen-cylinder Wright R-3350 Duplex-Cyclone Turbo-Compound engines provided power. The prototype first flew in May of 1953, and American received their first DC-7 in November, inaugurating the first nonstop East-to-West-coast service in the country (unrealistically scheduled just under the eight-hour limit for one crew) and forcing rival TWA to offer a similar service with its Lockheed Super Constellations. Both aircraft frequently experienced inflight engine failures, causing many flights to be diverted. Some blamed this on the need for high-power settings to meet the national schedules, causing overheating and failure of the engines' power recovery turbines.
The DC-7 was followed by the DC-7B with slightly more power, and on some DC-7Bs (Pan Am and South African Airways), fuel tanks over the wing in the rear of the engine nacelles, each carrying 220 U.S. gallons (183 imp gal; 833 L). South African Airways used this variant to fly from Johannesburg to London with one stop. Pan Am's DC-7Bs started flying transatlantic flights in the summer of 1955, scheduled 1hr 45min faster than the Super Stratocruiser from New York to London or Paris.
Early DC-7s were purchased only by U.S. carriers. European carriers could not take advantage of the slight range increase of the early DC-7, so Douglas released an extended-range variant, the DC-7C (Seven Seas), in 1956. Two 5 ft (1.5 m) wing root inserts added fuel capacity, reduced interference drag, and made the cabin quieter by moving the engines farther outboard; all DC-7Cs had the nacelle fuel tanks previously seen on Pan American and South African DC-7Bs. The fuselage, which had been extended over the DC-6Bs with a 40-inch (100 cm) plug behind the wing for the DC-7 and DC-7B, was lengthened again with a 40-inch plug ahead of the wing to give the DC-7Cs a total length of 112ft 3in (34.21 m).
Since the late 1940s, Pan Am and other airlines had scheduled a few nonstop flights from New York to Europe, but westward non-stops against the prevailing winds were rarely possible even with an economic payload. The L-1049Gs and DC-7Bs that appeared in 1955 could occasionally make the westward trip, but by the summer of 1956, Pan Am's DC-7C finally started doing it fairly reliably. BOAC was forced to respond by purchasing DC-7Cs rather than wait for the delivery of the Bristol Britannia. The DC-7C found its way into several overseas airlines' fleets, including SAS, which used them on cross-polar flights to North America and Asia. The DC-7C sold better than its rival, the Lockheed L-1649A Starliner, which entered service only a year later, but sales were cut short by the arrival of new jet powered aircraft like the Boeing 707 and Douglas DC-8 in 1958–60.
Starting in 1959, Douglas began converting DC-7s and DC-7Cs into DC-7F freighters to extend their service lives. The airframes were fitted with large forward and rear freight doors, and some cabin windows were removed. The predecessor DC-6, especially the DC-6B, established a reputation for straightforward engineering and reliability. Pratt & Whitney, the manufacturer of the DC-6s Double Wasp engines, didn’t offer an effective larger engine aside from the Wasp Major, which had a reputation for poor reliability. Douglas turned to Wright Aeronautical for a more powerful engine. The Duplex-Cyclone had reliability issues of its own, and this affected the DC-7's service record. Airlines with both DC-6s and DC-7s in their fleets usually replaced the newer DC-7s first once jets started arriving. Some airlines retired their DC-7s after more than five years of service, whereas most of the DC-6s lasted a while longer and were sold more readily on the secondhand markets.
This DC-7B, N51701, has had quite the career. She was built in 1955 and delivered to Pan American-Grace Airways (aka Panagra) in July of that year until being retired from service in favor of jets in 1964. She would be sold in December of that year to Argonaut Airways. Argonaut operated her for eight years until being sold again in November of 1972 to Maricopa Dust and Spray. In July of 1973, the aircraft was sold once more to Air Tankers Inc. and would fly with them until mid-1974. In May of 1974, she would be sold yet again, this time being handed over to the U.S. Forest Service.
Her career wouldn’t end there, however. She would be sold one more time in June of 1980 to T & G Aviation Inc. in Chandler, AZ, to be used as a water bomber against wildfires and became known as Tanker 31 until 1984, when she was grounded. After that, she remained derelict and in poor shape for nearly a decade when she was donated to the Pima Air and Space Museum in 1993. Today, most of the 338 DC-7s that were built have been scrapped, but there are at least eight examples that survive in museums today, making the type a rarity among piston-powered airliners. The last three operational DC-7s in the world were retired by Erickson Aero Tanker in 2020 and have since been parked at Madras Municipal Airport in Oregon. One of them, N838D (Tanker 60), is planned to join the Erickson Aircraft Collection; the fate of the other two DC-7s remains unknown.
