THE MCDONNELL DOUGLAS MD-11

The McDonnell-Douglas MD-11, intended successor to its earlier DC-10 and the third widebody tri-jet after the DC-10 itself and the Lockheed L-1011 TriStar, traces its origins to the General Electric and Pratt and Whitney engine competition to provide a suitable powerplant for the Lockheed C-5A Galaxy military transport, resulting in the first high bypass ratio turbofan, while the DC-10, the result of American Airlines' 1966 requirements for a 250-pasenger transcontinental airliner, had been built in five basic versions, inclusive of the DC-10-10, the DC-10-15, the DC-10-30, the DC-10-40, and the KC-10 Extender, achieving an ultimate production run of 446. Program cost overruns had intermittently necessitated the Douglas Aircraft Company's merger with McDonnell, hitherto a military aircraft manufacturer, in order to ensure survival of both the company and its aircraft.

Douglas design studies for both narrow and widebody successors, powered by high bypass ratio turbofans and accommodating 150 passengers, had been initiated as far back as the late-1970s. Although no definitive aircraft program had, in the event, been Commercial gas engineer launched, detailed market analysis, along with new technological research, would later prove valuable to the eventual design. The 60 orders for the KC-10 had enabled Douglas to maintain the basic DC-10 production line longer than it would have if it had only relied on commercial orders, thus delaying the need for a replacement. Yet, because it would be based upon its earlier-generation counterpart, it could proceed through its definition and design phase far more rapidly than the later, competing Airbus A-340 and Boeing 777, entering the market earlier than these aircraft and tapping into an existing DC-10 customer base for potential sales.

Unlike that aircraft, however--whose five basic versions had shared the same fuselage length and cross-section--the projected successor of 1979 had featured a 40-foot fuselage stretch capable of accommodating 340 mixed-class passengers, three General Electric CF6-50J turbofans producing 54,000 pounds of thrust each, a strengthened wing, and a 630,000-pound gross weight.

The resultant DC-10-60, paralleling the earlier, stretched, long-range DC-8-60 series, had offered a 75-passenger increase over the DC-10s of Air New Zealand and Swissair who had been targeted as potential launch customers, but use of the existing wing had severely eroded performance, and five-foot extensions, coupled with a new wing fillet and active ailerons to reduce gust loads, had considerably improved it. Indeed, revised trailing edge flaps and a larger tailcone had resulted in a 24-percent fuel reduction over that of the DC-10 and its seat-mile costs had been lower than those of the four-engined Boeing 747.

Program launch, intended for 1979, had been usurped by Douglas's further definition of its versions, which, designated "DC-10-61," "DC-10-62," and "DC-10-63," had even more closely reflected the DC-8-61, DC-8-62, and DC-8-63 nomenclatures. The DC-10-61, for instance, had been intended as a domestic variant with the 40-foot fuselage stretch and a 390-passenger capacity, and had been powered by 60,000 thrust-pound engines. The DC-10-62, with a reduced, 26.7-foot fuselage insertion, had been intended for very long-range operations, with a 14-foot wingspan increase, active ailerons, and a four-wheeled centerline main undercarriage unit. It had been intended to carry some 40 fewer passengers than the -61, while the -63 had combined the design features of both, resulting in a high-capacity, long-range variant.

A series of intermittent DC-10 accidents, none of which had been traced to an inherent design flaw, along with the prevailing economic recession, had precluded further Super DC-10 development at this time, although one of its features, eventually incorporated in its successor, had been flight-tested on a Continental Airlines DC-10-10 in August of 1981. Winglets, extending both above and below the wing tip, and varying in size, had resulted in a three-percent fuel reduction because of an equal decrease in generated drag.

Thus buoyed only by MD-80 sales, the Douglas Aircraft Company rode the recession. A projected DC-10 replacement, bearing an MD-11X-10 designation in 1984 and offering considerably more advancement than the original Super 60 series had, had been most closely based on the DC-10-30 with a 580,000-pound maximum take off weight, a 6,500-nautical mile range with a full payload, and either three General Electric CF6-80C2 or Pratt and Whitney PW4000 engines. A higher-capacity version, to be offered in parallel with the basic airframe, had featured a 22.3-foot fuselage stretch, to permit 331 mixed-class passengers to be carried over 6,000-mile ranges and had a corresponding 590,000-pound gross weight. American, Delta, Lufthansa, and Toa Domestic Airlines, considering this iteration, had suggested refinements which had later been incorporated in the definitive aircraft.

By the following year, the board authorized order solicitations, although both versions had, by this time, featured the same fuselage length, the medium-range variant, at a 500,000-pound gross weight, offering a 4,781-mile range, and the long-range counterpart, at a 590,000-pound gross weight, offering a 6,900-mile range. Accommodating some 335 passengers in a typically mixed arrangement, they introduced composite construction, a two-person cockpit, and an advanced electronic flight system.

At the time of official program launch, which had occurred on December 30, 1986, 92 orders and options had been placed by Alitalia, British Caledonian, Federal Express, Korean Air, SAS, Swissair, Thai Airways International, and Varig.

The MD-11, which had rolled out for the first time some three years later in September of 1989 in Long Beach, California, and had been registered N111MD, had been devoid of its engines, winglets, vertical stabilizer, and paint scheme, but displayed the logos of the 29 customers which had ordered or optioned the type by this time. As these surfaces had subsequently been added, however, it bore a close similarity to the DC-10-30 from which it had been derived.

Featuring an 18.6-foot stretch over that aircraft, attained by means of two fuselage plugs, it retained its nose and cockpit sections, but introduced an elongated, drag-reducing, chisel-shaped tailcone, and offered a 201.4-foot overall length when fitted with General Electric engines, or a 200.11-foot overall length with Pratt and Whitney powerplants.

The two-spar Douglas airfoil, built up of chordwise ribs and skins and spanwise stiffeners, featured a 169.6-foot span, a 35-degree sweepback at the quarter chord, and six degrees of dihedral, rendering a 7.9 aspect ratio and a 3,648-square-foot area. Low-speed lift was augmented by new, full-span leading edge slats and redesigned, double-slotted trailing edge flaps, while roll control was provided by inboard, all-speed ailerons made of metal with composite skins, and outboard, low-speed ailerons which drooped with the trailing edge flaps during take off and were entirely constructed of composite material. Each wing also contained five spoiler panels.

Fuel, carried in wing integral tanks, totaled 40,183 US gallons.

Up- and downward-extending winglets, installed on the wingtips themselves, had provided the greatest distinction to the DC-10. Harnessing the drag-producing vortex otherwise created by wingtip pressure differential intermixing, they had been comprised of a seven-foot, upward-angled section made of a conventional rib and spar, but covered with an aluminum alloy skin and completed by a carbonfibre trailing edge, and a 2.5-foot, downward-angled section made entirely of carbonfibre, collectively encompassing a 40-square-foot area.

Because of the increased moment-arm and computer-controlled longitudinal stability augmentation software, the MD-11's horizontal tail had been 30 percent smaller than that of the DC-10 and featured a 2,000 US gallon integral trim tank which increased range and facilitated in-flight center-of-gravity optimization. Its advanced, cambered airfoil, and reduced, 33-degree Commercial gas engineer sweepback, coupled with an electromechanically-activated variable incidence tailplane fitted with two-section, slotted, composite trailing edge elevators on either side, resulted in a 1,900-pound structural weight reduction and decreased in-flight drag.

Power had been provided by three 62,000 thrust-pound General Electric CF6-80C2 or 60,000 thrust-pound Pratt and Whitney PW4462 high bypass ratio turbofans, two of which had been pylon-attached to the wing leading edge underside and one of which had been installed in the vertical tail aft of the fin torsion box. Tracing its origins to the 41,000 thrust-pound TF39 engine originally developed for the Lockheed C-5A galaxy, the former had evolved into the quieter, more advanced CF-6 intended for commercial operation, and its 40,000 thrust-pound CF6-6D had powered the domestic DC-10-10, while its 48,000 thrust-pound CF6-50C had powered the intercontinental DC-10-30, along with the Airbus A-300 and some versions of the Boeing 747. The even more advanced CF6-80A had also been chosen to power the A-310 and the 767.

Incorporating the CF-6's core, with a larger, 93-inch, two-shaft fan, the CF6-80C2 powering the MD-11 had offered 17-percent more thrust and had a bypass ratio of 5.05. Linked to a full authority digital engine control system, which itself had provided electronic autothrottle and flight management system interface, the turbofan had offered reduced fuel burn.