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DC-9

The twin-engine McDonnell Douglas DC-9, in its many versions, generally has a smaller passenger capacity, shorter range, and shorter field length capability than the Boeing 727. It has been produced In six major versions and is now in operation on airlines all over the world. The six versions now in operation vary in (1) passenger capacity from 90 to 172, (2) length from 104 to 147 feet, and (3) gross weight from 80 000 to 148 000 pounds. Perhaps more than any other aircraft type, the DC-9 represents an entire family of aircraft. The prototype of the DC-9 first flew in February 1965, and nearly 1100 examples have been produced by the early 1980s.

Basic configuration of the aircraft is similar to that of the Caravelle in that the two engines are mounted in the aft-fuselage position. The T-tail arrangement employed by the DC-9, however, is different from that of the Caravelle. The engines that power the aircraft are the same basic Pratt & Whitney JT81) turbofans as are employed on the Boeing 727. For this particular version of the DC-9-30, the two engines have 15 500 pounds of thrust each.

The sweptback wing of the DC-9 has a somewhat smaller sweep angle than that of the 727, and the cruising speeds for the aircraft are correspondingly lower than those of the 727. The lower cruising speed of the DC-9 results from tailoring the characteristics of the aircraft to relatively short range segments and small airports for which it was intended. The high-lift system on most versions of the DC-9 consists of trailing-edge double-slotted flaps and leading-edge slats (the DC-9-10 had no slats). The lateral control system utilizes inboard and outboard ailerons, with the outboard ailerons being used only at low speeds as in the DC-8. Speed brakes are mounted on the upper surface of the wing. With the exception of the elevators, all the control surfaces are hydraulically actuated. As in the DC-8, the elevators of the DC-9 are manually controlled through aerodynamic servotabs.

The gross weight of the DC-9-30 is 109 000 pounds, which is about half that of the 727-200, and the 115 tourist-class passengers are seated in a 5-abreast configuration. The higher thrust loading and lower wing loading of the DC-9, as compared with the 727, result in a much lower takeoff field length for the Douglas aircraft; the landing field lengths for the two aircraft, however, are about the same. The range at maximum payload for the DC-9-30 is 1812 miles, which is about half that of the Boeing 727. Clearly, the DC-9 and 727 are intended for different types of airline-route structures and passenger-load requirements. Both highly successful aircraft complement each other in airline operation, and both seem destined to fly on together for many years.



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