Douglas DC-6

Design and development

The United States Army Air Forces (USAAF) commissioned the DC-6 project as the XC-112 in 1944. The USAAF wanted a lengthened, pressurized version of the DC-4-based C-54 Skymaster transport with more-powerful engines. By the time the prototype XC-112A flew on 15 February 1946, the war was over, the USAAF had rescinded its requirement, and the aircraft was converted to YC-112A, being sold in 1955.

Douglas Aircraft modified the design into a civilian transport 80 inches (2.0 m) longer than the DC-4, with a notable feature being the use of the Pratt & Whitney Double Wasp 18-cylinder radial engine, a powerplant that had seen considerable refinement and usage in World War II combat aircraft. The civilian DC-6 first flew on 29 June 1946, being retained by Douglas for testing. The first airline deliveries were to American Airlines and United Airlines on 24 November 1946. A series of inflight fires, one of which resulted in the fatal crash of United Airlines Flight 608, grounded the DC-6 fleet in 1947. The cause was found to be a fuel tank vent next to the cabin cooling turbine intake; all DC-6s were modified, and the fleet was back in service after four months on the ground.

Operational history

In April 1949, United, American, Delta, National, and Braniff were flying DC-6s in the United States. United flew them to Hawaii, Braniff flew them to Rio de Janeiro, and Panagra flew Miami-Buenos Aires; KLM, SAS, and Sabena flew DC-6s across the Atlantic. BCPA DC-6s flew Sydney to Vancouver, and Philippine flew Manila to London and Manila to San Francisco.

Pan Am used DC-6Bs to start transatlantic tourist-class flights in 1952. These were the first DC-6Bs that could gross 107,000 lb (49,000 kg), with CB-17 engines rated at 2,500 hp (1,900 kW) on 108/135 octane fuel. Several European airlines followed with transatlantic services. The DC-6B and -6C subtypes could often fly nonstop from the eastern US to Europe, but needed to refuel in Goose Bay, Labrador, or Gander, Newfoundland, when flying westbound into prevailing westerly winds.

Douglas designed four variants of the DC-6 - the basic DC-6, and the longer-fuselage [60 in (150 cm)], higher-gross-weight, longer-range versions—the DC-6A with cargo doors forward and aft of the wing on the left side, with a cargo floor; the DC-6B for passenger work, with passenger doors only and a lighter floor; and the DC-6C convertible, with the two cargo doors and removable passenger seats.

The DC-6B, originally powered by Double Wasp engines with Hamilton Standard 43E60 constant-speed, reversing propellers, was regarded as the ultimate piston-engined airliner from the standpoint of ruggedness, reliability, economical operation, and handling qualities.

Similar to the DC-6A, the military version was the USAF C-118 Liftmaster; the USN R6D version used the more powerful R-2800-CB-17 engines. These were later used on the commercial DC-6B to allow international flights. The R6D Navy version (in the late 1950s and early 1960s) had Curtiss Electric constant-speed, reversing propellers.

The U.S. Air Force (USAF) and U.S. Navy (USN) renewed their interest in the DC-6 during the Korean War and ordered 167 C-118/R6D aircraft, some of which later found their way to civilian airlines. Harry Truman's first presidential aircraft was a USAF short-fuselage DC-6, which was designated VC-118 and named The Independence. It is preserved in the National Museum of the United States Air Force at Dayton, Ohio.

Total production of the DC-6 series was 704, including military versions.

In the 1960s, two DC-6s were used as transmitter platforms for educational television, based at Purdue University, in a program called the Midwest Program on Airborne Television Instruction.

Many older DC-6s were replaced in airline passenger service from the mid-1950s by the Douglas DC-7, but the simpler, more economical engines in the DC-6 have meant the type has outlived the DC-7, particularly for cargo operations. DC-6/7s surviving into the jet age were replaced in frontline intercontinental passenger service by the Boeing 707 and Douglas DC-8.

Basic prices of a new DC-6 in 1946–47 were around £210,000–£230,000 and had risen to £310,000 by 1951. By 1960, used prices were around £175,000 per aircraft. Prices for the DC-6A in 1957–58 were £460,000–£480,000. By 1960, used prices were around £296,000. Equivalent prices for the DC-6B in 1958 were around £500,000. Used prices in 1960 were around £227,000.

From 1977 to 1990, five yellow-painted Douglas DC-6Bs were used as water bombers in France by the Sécurité Civile. They were registered as F-ZBAC, F-ZBAD, F-ZBAE, F-ZBAP, and F-ZBBU.