Douglas DC-6 DC-6A

Douglas designed four versions of the DC-6: the basic aircraft and three with the fuselage stretched by 60 inches (150 cm), higher weights and longer range. The DC-6A is the freighter of that trio: it has cargo doors fore and aft of the wing on the left side and a strengthened cargo floor. Some aircraft kept their cabin windows and could be fitted with seats; on others the windows were omitted and the aircraft were used purely for freight.

The rear cargo door came as standard with a built-in 4,000 lb (1,800 kg) lift elevator and — at first — a Jeep, a public relations stunt that was dropped shortly afterwards. Slick Airways was the first airline to operate the freighter version, in April 1951. The Liftmaster name, later attached to the USAF aircraft, started here.

Its figures: 32.2 m long, 35.8 m in span, 20,803 kg empty, 48,626 kg maximum take-off weight, 507 km/h cruise, a 6,675 m ceiling and 28,188 lb of cargo, with 2,948 nautical miles (5,460 km) of range at maximum payload and 4,317 (7,995 km) at maximum fuel.

The DC-6A is also the pattern for the military versions: the USAF C-118 Liftmaster and the Navy R6D derive directly from it, the latter with the more powerful R-2800-CB-17 engines that would later go into the commercial DC-6B to allow international flights.