No fewer than fifteen US combat planes, fighters, transport, cargo carriers, light, medium and heavy bombers have been afforded much publicity during the last three and a half years. Only now, however, is the Douglas C-54 combat transport beginning to get the merited acclaim that it has earned during its tour of active duty.
In service for over a year, the Skymaster has done a tremendous job in long range transport work, freeing many smaller craft for concentrated duties an the war zones. its job has been to carry airplane parts, blood plasma, medical supplies, food and munition to the fighting fronts; then doubling as a hospital plane and cargo ship on return flights, carrying fifty-four wounded men or vital war supplies to keep the factories here on the home front operating at top pitch.
The prototype of the plane that ultimately became the C-54 was the DC-4, designed and developed by the Douglas Aircraft Company in conjunction with the technical departments of five major airlines. It was their aim to give to the world a four-engined transport the like of which it had never seen. Work was begun at great research and engineering cost.
The first prototype received its Approved Type Certificate in May, 1939, as a commercial airliner capable of seating fifty-two passengers, It was powered by four Pratt and Whitney Twin Hornet 1150-hp engines. Known as the Douglas DC-4 Superliner, it was one of the greatest single factors in maintaining qualitative superiority for American air transport companies.
After undergoing extensive flight and engineering tests by United Air Lines, it was mutually decided that this first four-engined superluxury liner had fallen short of Douglas' aim because of the advancement in aviation during the period of its construction; it was declared unsuitable for airline operation in the United States at that time, and subsequently sold to Japan where it ultimately crashed.
Changes and progress in aerodynamics and engine construction which paralleled the final construction of the prototype resulted in the complete redrafting and redesigning of the original plans. The new designs called for a pressurized cabin airliner that would be more than twice as big and twenty-five per cent faster than the DC-3. It would be twenty per cent lighter and twenty per cent faster than the original DC-4; have approximately half the wing area and be aerodynamically much cleaner.
On the strength of the blue prints alone, five domestic airlines purchased a total of sixty-one of the prospective planes. Just recently in New York, United Air Lines and American Air Lines signed contracts with Douglas calling for more of these superliners for use after the war.
With the approach of the present world conflict, modifications were made in the new DC-4 to meet the specifications of the United States Army, redesignated the C-54, and taken over by the USAAF for use as troop carriers and cargo transports. The first C-54 flew from the production line only twelve weeks after our entry into the war.
Other uses were soon found for the huge Skymaster. The large accommodations, the ease and safety with which it was flown made the C-54 a natural for transporting high ranking government officials. In May, 1943, President Roosevelt used a C-54 for all of his overland hops on his trip to Casablanca. In November, 1943, the President and some 250 of his assistants used eleven Skymasters for overland transportation to their Cairo and Teheran conferences. Other governments of the United Nations have used C-54s to transport their own diplomats, and want still more when available.
The Skymaster is a four-engined, low-wing, tricycle landing geared transport. It carries a crew of six: pilot, co-pilot, radio operator, navigator and two extra crew- men. The weight of the C-54, empty, is 37,250 pounds, and has a gross (maximum allowable) of 65,000 pounds.
The fuselage of this huge plane is of the semi-skin-stressed all-metal, monocoque construction with transverse frames and longitudinal stiffeners. The width of the fuselage is ten feet five inches; height, eleven feet six inches; length over all is ninety-three feet eight inches. The outer skin covering is smooth sheet aluminum alloy material that is attached to the frames and longitudinals with flush type rivets.
The Skymaster's wing when fully assembled is composed of five sections, or panels, the over all span of which is 117 feet six inches. With the exception of the center sections, the other four components are completely interchangeable with a like panel on another plane of the same model.
The wing is of multi-cellular structure with flush- riveted stressed-skin covering. From the center line to the point where wing fillets meet the wing flaps, construction is of the split type. From this point to the aileron it is of the hinged aileron type.
The center section is permanently attached to the fuselage. It extends under the fuselage and serves as a mounting for the four huge engine nacelles. Two removable outer panels are bolted to the center section. In turn, two removable wing tips are bolted to the outer panels. An aileron is hinged to each outer panel, and a conventional type trim tab is attached to the right hand aileron. Two hydraulically operated wing flaps move aft and down on links that are attached to the structure of the center section.
Three spars extend the entire span of the center wing panel to the outer wing attachment points. Ribs interconnect the spars and reinforce the wing structure. Flush type rivets fasten the wing skin to the ribs, which contributes to smoother flow of air over the wing surface. Four compartments in the center wing, between the front and center spars, serve as fuel tanks.
Four engine nacelles are attached to the center wing section and give support and fairing for the demountable power plant units. Constructed of transverse frames and longitudinal stringers, the nacelles are covered with a smooth flush-riveted skin. Stainless steel firewalls form an integral part of the nacelles, and incorporate the engine mount fittings.
The tail group on the C-54 is of the cantilever monoplane type. Height of the vertical stablilizer is fourteen feet three inches; span of the horizontal stabilizer, thirty-nine feet six inches. The vertical fin is integral with the fuselage and is balanced both statically and dynamically by lead weights attached to the nose skin. It is mounted on two hinges and a torque tube. All fixed surfaces are metal with stressed skin covering. The elevators and rudder have metal frames and are fabric covered. There are combination trim and service tabs on the movable surfaces.
The landing gear is composed of three units: two fully retractable main gears and a nose gear. The main gears have dual wheels with hydraulically operated brakes, The nose gear has a steerable single wheel.
The empennage is protected by a faired non-retracting oleo-pneumatic shock strut supported tail skid. Fittings on the front and rear spar at each inboard engine nacelle furnish the attachment of the main landing gear.
Engines on the Skymaster are Pratt and Whitney Hornet, Model R-2000, and equipped with Hamilton Standard Hydromatic propellers. The P&W R-2000 is a 14-cycle, two-row radial, air-cooled engine. It develops 1350 hp at takeoff and 1100 hp at 7000 feet. Four of these engines give the Skymaster a cruising speed of from 180 to 190 miles per hour with a normal range of over 2000 miles. It can carry 40 to 45 troops and a six-man crew. The C-54 can reach 10,000 feet in thirteen and a half minutes, has a service ceiling of over 20,000 feet and a maximum speed of over 275 miles per hour.
The four engine units on the airplane are interchangeable, except for the exhaust collector rings, which are for either left or right engines. The hydraulic pumps, too, are for either left or right units.
Douglas can well be proud of the record that the C-54 has made under toughest conditions at best. It has proved itself by doing a job that must be done and by doing it well. By flying daily transoceanic schedules to all of the continents, it has charted postwar global air transportation possibilities, it has won distinction and recognition from those who have come in contact with it. And it will not stop with the end of the war.
The Skymaster's capabilities can only be fully realized when the big ship is flying hourly schedules from point to point, when the public, who, after all, is the final judge, entrusts to it their lives in safe, convenient, fast transportation in a thriving post war world .
This article was originally published in the December, 1944, issue of Air Tech magazine, vol 5, no 6, pp 17-25.