Ihab Salloum[ad_1]
The McDonnell-Douglas MD-11, the next generation aircraft following the DC-10, and the third widebody tri-jet after the DC-10 and the L-1011 TriStar, has its roots in the competition between General Electric and Pratt and Whitney to provide engines for the Lockheed C-5A Galaxy military transport. This competition led to the development of the first high bypass ratio turbofan. The DC-10, which was originally designed to meet American Airlines’ needs for a transcontinental airliner in 1966, had five different versions, including the KC-10 Extender military variant. Despite facing cost overruns, the merger between Douglas Aircraft Company and McDonnell ensured the survival of both the company and its aircraft.
Douglas began designing potential successors to the DC-10 in the late 1970s. These designs included narrow and widebody options powered by high bypass ratio turbofans and capable of carrying 150 passengers. Although no definitive aircraft program was launched at that time, the market analysis and technological research conducted during this period proved valuable for future designs. The decision to develop the KC-10 military transport helped Douglas maintain the basic DC-10 production line longer, which delayed the need for a replacement. This provided an advantage over the competing Airbus A-340 and Boeing 777, allowing the MD-11 to enter the market earlier and tap into an existing DC-10 customer base for potential sales.
Unlike the DC-10, the projected successor in 1979 featured a 40-foot fuselage stretch and the capacity to carry 340 mixed-class passengers. It was powered by three General Electric CF6-50J turbofans, had a strengthened wing, and a gross weight of 630,000 pounds. This new design, known as the DC-10-60, offered a 24% fuel reduction compared to the DC-10 and lower seat-mile costs.
The launch of the DC-10-60 program in 1979 was delayed due to further definition of its versions. These versions, designated as the DC-10-61, DC-10-62, and DC-10-63, closely mirrored the DC-8-61, DC-8-62, and DC-8-63 nomenclatures. The DC-10-61 was a domestic variant with a 40-foot fuselage stretch and a capacity of 390 passengers. The DC-10-62 had a reduced, 26.7-foot fuselage insertion and was designed for very long-range operations. The DC-10-63 combined the features of both versions to create a high-capacity, long-range variant.
Various factors, including intermittent accidents involving the DC-10 and an economic recession, prevented further development of the Super DC-10 at that time. However, winglets were tested on a Continental Airlines DC-10-10 in August 1981. These winglets, which extended above and below the wingtip, resulted in a three-percent fuel reduction due to decreased drag.
During the recession, Douglas focused on selling MD-80 aircraft. In 1984, they proposed a DC-10 replacement called the MD-11X-10, which offered significant advancements over the Super 60 series. It was based on the DC-10-30, had a maximum takeoff weight of 580,000 pounds, a range of 6,500 nautical miles with a full payload, and was powered by either three General Electric CF6-80C2 or Pratt and Whitney PW4000 engines. A higher-capacity version with a 22.3-foot fuselage stretch and a gross weight of 590,000 pounds was also proposed. American, Delta, Lufthansa, and Toa Domestic Airlines provided feedback that helped refine the design.
By the following year, the MD-11 received authorization for order solicitations. Both versions had the same fuselage length, with the medium-range variant offering a range of 4,781 miles and the long-range variant offering a range of 6,900 miles. They featured composite construction, a two-person cockpit, and an advanced electronic flight system.
The official program launch took place on December 30, 1986, with 92 orders and options already placed by various airlines. The first MD-11 rolled out three years later in September 1989, bearing the logos of the 29 customers that had ordered or optioned the aircraft by that time. The MD-11 featured an 18.6-foot fuselage stretch, an elongated tailcone for reduced drag, and measured 201.4 feet in length when fitted with General Electric engines.
The MD-11 wings had a span of 169.6 feet, with low-speed lift augmented by full-span leading edge slats and redesigned trailing edge flaps. Roll control was provided by inboard and outboard ailerons, and each wing had five spoiler panels. The fuel was carried in wing integral tanks, totaling 40,183 US gallons.
The wingtips of the MD-11 featured winglets, which helped reduce drag by utilizing the vortex created by wingtip pressure differential. These winglets were made of aluminum alloy and carbon fiber.
The horizontal tail of the MD-11 was 30% smaller than that of the DC-10 and featured a trim tank that increased range and optimized the center of gravity. The tail had an advanced airfoil shape, a reduced sweepback, and was equipped with two-section elevators.
The MD-11 was powered by three high bypass ratio turbofans, either General Electric CF6-80C2 or Pratt and Whitney PW4462 engines. These engines provided a significant increase in thrust compared to earlier models. The CF6-80C2 had a bypass ratio of 5.05 and was linked to a full authority digital engine control system.
Overall, the MD-11 was a technologically advanced aircraft that built upon the success of its predecessor, the DC-10. Its development was influenced by market analysis, technological advancements, and customer feedback, leading to a highly capable and efficient aircraft.
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