Transport and Supply Aircraft

Transport and Supply Aircraft. The U.S. Army Air Corps' interest in transport airplanes started in 1925 by acquiring the Douglas C‐1, a single engine biplane with a maximum takeoff weight (Mtow) of 7400 pounds. In an airplane the figure for Mtow is similar to that of displacement tonnage for an oceangoing ship; it is the one figure that provides a definite measure of size and probable productivity. An airplane's payload is typically about 20 percent of its Mtow.

Built to Air Corps specifications, a C‐1 had seats for eight passengers; alternatively, it could carry 2000 lbs of cargo. A C‐1's range was 380 miles; its cruising speed 85 mph. This was the last transport prepared to an Air Corps specification for more than 15 years. Prior to World War II transport planes served the Air Corps' internal needs and rarely the Army at large so it was expedient to buy transports that had been designed for civilian airlines.

The demonstrated success of Nazi Germany's use of airborne troops in lightning conquests of Norway, Belgium, and the Netherlands in early 1940 moved the Air Corps to create an increasingly large transport force. The backbone of this force was the immediately available Douglas DC‐3 and the Curtiss CW.20 then under development. Both were twin‐engine civil airliners. The DC‐3, 28,000 lb Mtow, became the military C‐47 or C‐53, the former being the cargo version, the latter a troop carrier. More than 10,000 C‐47/C‐53s were procured during World War II. The CW.20, 40,000 lb Mtow, became the C‐46; more than 3,000 were procured.

A shortcoming of both types was that they had been designed in the mid‐1930s, too soon to take advantage of the innovation of tricycle landing gear. The C‐47, C‐53, and C‐46 were “taildraggers”; on the ground they sat on a tailwheel with their noses up at an angle. This made the loading of heavy cargo difficult and unloading awkward. The Douglas DC‐4 airliner which became available after 1942 as the C‐54, 62,000 lb Mtow, was a versatile airplane but left something to be desired as a military transport. It sat up on tricycle gear which provided a level cabin on the ground, but like most airliners it was a low wing airplane. This required a tall landing gear to maintain propeller clearance with the ground, a result being an airplane that was so high off the ground that forklifts, elevated platforms, and other devices were necessary to gain access to its cabin for loading and unloading.

In 1947 the U.S. Air Force was established as a separate service. Although the Air Force continues to adapt airline equipment to its transport needs, these airplanes only indirectly meet the Army's combat airlift requirements. Ideally, a military transport plane is a high wing airplane, its fuselage slung beneath the wing resulting in minimum clearance between its cabin floor and the ground. This facilitates loading and unloading, including roll‐on and roll‐off of wheeled vehicles with a bare minimum of auxiliary equipment. In 1941 a specification was prepared for such an airplane. This was the Fairchild C‐82 known as the “Flying Boxcar,” a twin engine airplane, 54,000 lb Mtow, but the prototype did not fly until late 1944; more than 200 were produced but they were too late for World War II.

The C‐82 was redesigned in a larger and more powerful version, the C‐119, 72,700 lb Mtow, more than 900 built. Both types were used in the Korean War and in Vietnam. After 1954, however, they were gradually supplanted by the ubiquitous 4‐engine Lockheed C‐130 Hercules. Whereas the C‐82 and C‐119 were powered by piston engines, the C‐130 has turbine driven propellers. And the main element of the C‐130's tricycle landing gear consists of four wheels “nested” into the sides of the fuselage. This distributes the airplane's weight across a broader “footprint,” facilitating operations from unimproved airfields.

Initially 124,200 lb Mtow, with increases in engine power the C‐130 has grown to more than 155,000 lb and built in more than four dozen variants for the U.S. Air Force, Navy, Marines, and Coast Guard, and more than 60 of the world's air forces. More than 2100 C‐130s have been built, and by the year 2004 it will have been in production for a half century.

By the late 1950s there was clearly a requirement for a high‐speed transatlantic trooplift capability to reinforce NATO and it produced the Lockheed C‐141A which flew in 1963. The C‐141A was a 4‐engine turbojet of 323,000 lb Mtow capable of lifting 138 equipped troops or 62,000 lb of cargo across 4100 miles. A total of 285 were built. In 1976 the fuselages of C‐141As were “stretched” by some 23 feet to increase hull volume, were modified to be receivers of inflight refueling, and redesignated C‐141Bs. In 1995 most C‐141Bs were 30 years old; by the year 2005 it is expected that C‐141Bs will have been replaced by the new McDonnell Douglas C‐17A.

Although the C‐141 met the requirements for trooplift and most cargo, it could not carry heavy tanks and other less heavy but bulky loads, such as Army troop‐carrying helicopters, all of which would be required in a reinforcement of NATO. The result was the Lockheed C‐5A, 769,000 lb Mtow, which flew in 1968. Whereas the cabin cross‐section of C‐141B is 124 inches, that of a C‐5A is 228 inches; usable cubic volumes of cargo spaces are 11,399 and 34,796 cubic feet, respectively. A versatile aspect of the C‐5A is cargo doors in both the nose and tail permitting straight‐through loading and unloading. An upper deck has seats for 75 troops who may be necessary to handle the cargo at terminal points.

The C‐5A is the first U.S. military transport equipped to receive inflight refueling, a feature that proved invaluable in the resupply of Israel in the Arab‐Israeli War of 1973. A specification for a transoceanic transport airplane usually described a range of 4000 miles, roughly the distance from bases in northeastern United States to bases in West Germany. It could be assumed that if operations were to be extended to the Eastern Mediterranean they could be staged through Western Europe. But the distance from the U.S. to Israel is about 6000 miles and during the 1973 War the Arabs pressured the nations of Western Europe to deny refueling services to the U.S. airlift to Israel. Although a C‐5A could fly 6000 miles nonstop it could do so only with a reduced payload. However, refueled in flight by Boeing KC‐135 tankers based in Spain and the Azores, C‐5As were able to fly full loads from North America to Israel nonstop.

Flight operations revealed a flaw in the C‐5A's wing structure that limited the wing's fatigue lift to less than expectations and in the 1980s all C‐5As were re‐winged. Concurrently, 50 C‐5Bs were procured. Built with the new wing, they are essentially the same as the C‐5A and increase the C‐5 fleet to more than 120 airplanes.

With the C‐141 fleet more than 30 years old and approaching the end of their fatigue lives, they are being replaced by the McDonnell Douglas C‐17, a 4‐engine jet transport of 580,000 lbs Mtow that is equipped for inflight refueling. The C‐17 was first flown in 1991 and in 1995 it started to equip its first squadrons. At the turn of the century the backbone Air Force's Air Mobility Command will consist of C‐5s, C‐17s, and C‐130s, served by some 500 KC‐135 and 50 KC‐10 tankers which provide the force with global range.
[See also Air Force, U.S.: Overview; Air Force, U.S.: Predecessors of, 1907 to 1946; Air Force, U.S.: Since 1947.]

Richard K. Smith