Douglas DC-7

Design and development

In 1945, Pan American World Airways requested a DC-7, a civil 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.

American Airlines revived the designation when they requested an aircraft that could fly across the United States coast-to-coast non-stop in about eight hours. (Civil Air Regulations then limited domestic flight crews to 8 hours' flight time in any 24-hour period.) Douglas was reluctant to build the aircraft until American Airlines president C. R. Smith ordered 25 at a total price of $40 million, thus covering Douglas' development costs.

The DC-7 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 flew in May 1953 and American received their first DC-7 in November, inaugurating the first non-stop east-coast-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 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.

DC-7B

The DC-7 was followed by the DC-7B with slightly more power and optional fuel tanks over the wing in the rear of the engine nacelles (selected by Pan Am and South African Airways), each carrying 220 US gallons (833 L; 183 imp gal). South African Airways used this variant to fly Johannesburg to London with one stop. Pan Am's DC-7Bs started flying transatlantic in summer 1955, scheduled 1 hr 45 min faster than the Super Stratocruiser from New York to London or Paris.

DC-7C

Early DC-7s were purchased only by U.S. carriers. European carriers could not take advantage of the small 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) wingroot inserts added fuel capacity, reduced interference drag and made the cabin quieter by moving the engines farther outboard; the optional nacelle fuel tanks previously seen on Pan American's and South African's DC-7Bs were made standard. 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-7C a total length of 112 ft 3 in (34.21 m).

Operational history

Since the late 1940s Pan Am and other airlines had scheduled a few non-stop flights from New York to Europe, but westward non-stops against the prevailing wind were rarely possible with an economic payload. The Lockheed Super Constellation and DC-7B that appeared in 1955 could occasionally make the westward trip, but in summer 1956 Pan Am's DC-7C finally started doing it 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 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 a year later, but sales were cut short by the arrival of Boeing 707 and Douglas DC-8 jets in 1958-60.

Starting in 1959 Douglas began converting DC-7s and DC-7Cs into DC-7F freighters to extend their useful 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, manufacturer of the DC-6s Double Wasp engines, did not offer an effective larger engine apart 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. Carriers who had both DC-6s and DC-7s in their fleets usually replaced the newer DC-7s first once jets started to arrive. Some airlines retired their DC-7s after little more than five years of service, whereas most DC-6s lasted longer and sold more readily on the secondhand market.

Morten Beyer, an airline executive who participated in the decision to buy second-hand DC-7s at Riddle Airlines (later known as Airlift International), said Riddle became comfortable with buying the DC-7, notwithstanding known engine problems, after seeing its success with carriers like Swissair that made an effort to "baby" the Wright engine. According to Beyer, many passenger carriers had competed on speed and operated the engine at its limits, where it tended to break down.