DC-10

The Lockheed L-1011 and the McDonnell Douglas DC-10 are wide-body transports in a weight class between that of the 707 and the very heavy 747. Both aircraft are powered by three high-bypass-ratio turbofan engines located in a new configuration arrangement; one engine is mounted under each wing, and the third engine is mounted at the rear of the aircraft. The L-1011 and the DC-10 were initially designed to an airline requirement for a high-capacity transport with transcontinental range, but growth versions of each are presently available with intercontinental capability.

Initial flights of' both aircraft occurred in 1970. An early version of the DC-10 entered airline operation in 1971, and the L-1011 began service in 1972. Both aircraft are in wide Use throughout the world. The three-engine configuration employed on both aircraft, in which two of the engines are located near the aircraft center of gravity, offers ail advantage in aircraft balance over an arrangement in which all three engines are mounted at the rear of the fuselage (Boeing 727, for example). Placement of two of the engines under the wing also allows the horizontal tall to be mounted in the highly desirable low position, as contrasted with the T-tall arrangement. The large lateral distance between the wing-mounted engines, however, causes larger yawing moments following loss of' power of one of these engines as compared with a similar power loss in the rear-mounted engine arrangement.

The method of mounting the rear engine is seen to be quite different on the L- 1011 and the DC-10. The L-1011 utilizes a mounting arrangement similar to that of the Boeing 727. The center engine is mounted in the aft end of the fuselage and is connected through an S-shaped duct to the large inlet mounted on top of the fuselage. In contrast, the center engine of the DC-10, including inlet and exhaust nozzle, is integrated with the fin above the fuselage. The engine efficiency resulting from this straight inlet-engine-nozzle configuration, as compared with the S-shaped duct arrangement, was thought to more than offset the structural complexity (and probable weight increase) of integrating the engine with the fin. The high performance of both aircraft, however, suggests that either method of engine installation can be made to operate successfully.

The Lockheed L-1011-200 is powered with three Rolls-Royce RB.211-524 engines of 48 000 pounds thrust each. The McDonnell Douglas DC-10-30 is powered by three General Electric CF6-50CI engines of 52 500 pounds thrust each but is also available with a version of the Pratt & Whitney JT9D engines.

The main landing gear of the L-1011 has two struts to which are attached four-wheel bogies. Early versions of the DC-10 employed a similar arrangement. The heavier DC-10-30, however, employs a third strut, equipped with a two-wheel bogie mounted on the fuselage centerline between the other two main landing-gear struts. This arrangement helps to distribute the weight of the aircraft on the runway and thus keeps the runway-bearing stress within acceptable limits.

The aerodynamic design of both of the three-engine jet transports is conventional. The wings of both aircraft have about 35° of sweepback with aspect ratios in the range of 7.0 to 7.5 and feature transonic airfoils of advanced design. The wings have double-slotted trailing edge flaps and leading-edge slats. Lateral control is provided by a combination of ailerons and spoilers. The spoilers are also used to control lift and drag when deployed symmetrically. Longitudinal control of the L-1011 is provided by a variable incidence stabilizer to which the elevator is mechanically linked. The DC-10 employs separately actuated elevators and stabilizers. Neither aircraft employs longitudinal trim tabs. The maximum lift-drag ratio of the two aircraft is estimated to lie in the range between 17.0 and 17.5.