In 1935, a consortium of major carriers, led by United Air Lines, collated their requirements for an advanced airliner and negotiated a contract with Douglas Aircraft to build a very large, long-range transport with four engines. Douglas decided to produce a four-engine transport about twice the size of the DC-3 and, in 1938, developed the single DC-4E to carry 42 passengers by day or 30 by night. It had complete sleeping accommodations, including a private bridal room. The DC-4E made big headlines during an inaugural tour in 1938-1939. It proved too expensive to maintain, so airlines agreed to suspend development in favor of the less complex DC-4, but it was not put into commercial service until 1946. The DC-4E, as Arthur Raymond dryly observed, "It was an example of design by committee [and] took so long to build it that technology had advanced in the meantime." Consequently, Douglas engineers "took a fresh sheet of paper" and came up with the classic DC-4.
Tricycle landing gear had appeared on some planes before WWII, but the DC-4E, the DC-4, and their successors made this feature standard on postwar American airliners. Boarding various "tail draggers" like the DC-3 required passengers to scramble up a steep aisle and necessitated some alacrity to settle into their seats; planes with tricycle gear allowed customers to board and stow their gear with everything comfortably horizontal. For ground crews, tasks of handling luggage, cargo, and various service requirements also went more smoothly. Pilots appreciated a steerable nose gear that enhanced taxiing around on the ground, the cockpit position afforded pilots a far better view of busy airport activities, and tricycle gear automatically positioned wings for the big airliners at a more efficient attitude to enhance takeoff performance.
The Douglas DC-4 also introduced power-boosted controls, along with advanced engineering details like flush-riveted skin. With Pratt & Whitney R-2000 Twin Wasp engines, each generating some 1,450 horsepower, the DC-4 carried an impressive load of 42 (or more) passengers and could cruise at more than 200 mph over ranges of more than 2,000 miles. And its tubular fuselage and stoutly engineered wings lent themselves to stretching the basic DC-4 into bigger and better airplanes.
On Feb 14, 1942 the Douglas DC-4 Skymaster made its initial flight, thereafter becoming prominent in a generation of four-engine U.S. transports that advanced long-haul air travel. The plane was a scaled-down version of a prototype developed in 1939. The DC-4 carried a crew of six and up to forty-two passengers. Unlike the Boeing 307 and 307B, it did not have a pressurized cabin. Its military derivative was the C-54 "Skymaster" transport, ordered by the U.S. Army Air Forces in 1942.
When the DC-4 reached flying status early in 1942, military requirements took precedence, and they went directly into service with the USAAF as C-54 transports. Douglas built 1,241 of the DC-4s and its military counterparts. During the war, C-54s flew a million miles a month over the rugged North Atlantic - more than 20 round trips a day. A special C-54C, nicknamed the "Sacred Cow" by the White House press corps, became the first presidential aircraft, ordered for Franklin D. Roosevelt. After World War II, commercial airlines placed more than 300 civilian DC-4 transports into service.
On October 24, 1945 a DC-4 operated by American Export Airlines landed at Hurn Airfield, England, after a flight from New York, inaugurating the first scheduled landplane commercial service between North America and Europe. (Pan American had earlier begun the first regular seaplane transatlantic service on June 28, 1939.) After beginning the new service, American Export adopted the name American Overseas Airlines on Nov 10, 1945. In the years immediately following the war, new DC-4s and used C-54s carried more passengers than any other four-engine transport. Some were still flying through 1998.
The C-69 Constellation had two advantages over the DC-4. One was that it was pressurized, which allowed passengers to be taken comfortably higher in the air, and it was about 100 mph faster. The DC-4, however, won the first round against the Constellation as a commercial airliner because there were many more DC-4s available to use. There were about 1,100 DC-4s built during the war whereas only a few hundred C-69s were built. Eventually, the DC-4 was used by nearly every large airline, including foreign carriers. When the supply of "cheap" surplus DC-4s ran out and the airlines had to start buying new airplanes, the Constellation became the top-selling airliner.
On June 15, 1947 President Harry S Truman appointed a Special Board of Inquiry on Air Safety, headed by CAB Chairman James M. Landis. The action followed a series of three DC-4 airline accidents that claimed the unpredecented total of 145 lives between May 29 and Jun 13, 1947. On Aug 15, Landis suggested that the Civil Aeronautics Board immediately hold hearings on airline crew complement to determine whether a flight engineer was required on all four-engine air transports in scheduled domestic passenger service. Between Oct 6-8, CAB held such hearings, and as a result, in April, 1948, adopted the so-called 80,000-pound rule. Effective Dec 2, 1948, (subsequently extended to Mar 31, 1949), all airplanes certificated for a maximum takeoff weight of more than 80,000 pounds were required to carry an airman holding a flight engineer's certificate.
The DC-4 was followed by the DC-6, DC-6B, DC-7, DC-7B and DC-7C. The Douglas aircraft grew from 44 seats (DC-4) to 105 seats (DC-7C). The DC-7 can be distinguished from the DC-4 and DC-6 models by square windows, with three being forward of the wing (DC-4 has round windows), and four-blade propellers (DC-4 & DC-6 have three-blade propellers). The DC-6 is similar to the DC-7 as it has the same wingspan and square windows but is about 1 foot shorter in length and has smaller engines. The DC-6 has three-blade propellers (DC-7 has four-blade propellers) and may or may not have windows (1 or 2) ahead of the wing. The DC-4 has the same wingspan as the DC-6 and DC-7 models but is considerably shorter in length. It can be identified by the round windows and three-blade propellers. The "Super" DC-4 is a stock model that has been converted to operate with larger engines.
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