05 Sep The McDonnell Aircraft Corporation – Douglas MD-80 Twin Aircraft Engine
The McDonnell Aircraft Corporation
Fuselage stretchability, inherently incorporated in the basic DC-9 design, had characterized its program, resulting in four dimensionally divergent, higher-capacity versions, including the initially-elongated DC-9-30 over the baseline series -10/14/15, the subsequent DC-9-40, and the final DC-9-50, the latter accommodating 49 more passengers than the twin-jet’s original maximum.
The DC-9 itself, founded upon the four design tenets of ruggedness, simplicity, reliability, and low-cost, had been McDonnell-Douglas’s best-selling commercial aircraft-so much so, in fact, that it took off or landed somewhere in the world every seven seconds, serving more than 570 cities with some 6,050 daily flights, and by 1979, the collective fleet had carried more than one billion passengers and logged more than 18 million hours with an almost 99-percent dispatch reliability rate.
Its Pratt and Whitney JT8D engine, the most widely used powerplant and numbering in excess of 12,000 units, had not only provided propulsive thrust for all versions of the DC-9, but had also powered the Boeing 727, the Sud-Aviation SE.210 Super Caravelle, the Boeing 737, and the Dassault-Breguet Mercure 100.
Both the DC-9’s basic design and its JT8D turbofan therefore offered the most optimum, cost-effective platform on which to base a larger-capacity successor, which needed to equal the DC-9-30’s range capability, yet exceed the DC-9-50’s economics.
Its fuselage, not having reached its limit of stretchability, lent itself to still higher-capacity accommodation, but its obstacle had been a powerplant of sufficient thrust to maintain acceptable payload, range, and performance parameters for its operators.
Based upon the earlier, two-stage JT3D, which had powered both the 707 and the DC-8, the JT8D, a low, one-to-one bypass ratio turbofan, had first run on April 7, 1961, taking to the skies for the first time on May 1 of the following year mounted to a 707. Receiving FAA certification on February 9, 1963, as the 14,000 thrust-pound JT8D-1, it had powered the 727-100 before being employed by the DC-9-10 and was subsequently offered in several successively higher-thrust versions, the last of which had been the 17,400 thrust-pound JT8D-17R.
A new-generation variant, providing application for an ultimate DC-9 stretch and designated JT8D-109, had been one of six demonstration powerplants incorporating larger, single-stage fans developed for NASA’s Quiet Engine Program, which had run between 1972 and 1975, and two of its versions had logged more than 50 hours retrofitted to a modified DC-9-32. Design of a further development, the 18,500 thrust-pound JT8D-209, began in 1974 and first ran two years later, test flown on a McDonnell-Douglas Advanced Medium STOL Transport (AMST) in March of 1977.
Although a new, supercritical wing had also initially been considered, the aircraft, intended for short- to medium-range sectors which entailed higher ratios of climb-and-descent to actual cruise profiles, could not fully exploit such a new design, its benefits resultantly unable to justify its higher development costs. The existing DC-9 wing, incorporating root and tip extensions and modified high-lift devices, would provide the required performance, economy, and range parameters.
Several initial iterations, mostly based upon the DC-9-50 and all featuring fuselage stretches for higher capacities, larger-area wings, and two refanned turbofans, had included the refan-stretched DC-9-50RS, the refan-super stretched DC-9-50RSS, the DC-9-55, and the DC-9-60, while a DC-9QSF, intended for Japanese operators as an NAMC YS-11 twin turboprop replacement, mated a DC-9-40 airframe with two 18,000 thrust-pound JT8D-209 engines and a two-foot larger wing, enabling the 114,000-pound aircraft to operate from 4,000-foot runways with 120 passengers.
However, cost constraints and design complexities dictated a simpler, more straightforward version which incorporated the longer fuselage, increased-area wings, and JT8D-209 turbofans, yet retained cockpit commonality with all previous DC-9 variants.
Skipping both the DC-9-60 and DC-9-70 sequences, the definitive aircraft, designated DC-9-80-or DC-9 Super 80, to more accurately reflect the intended year of service inauguration-had been launched on October 20, 1977 with the receipt of 27 firm and 13 optioned orders from Swissair, Austrian Airlines, and Southern Airways, along with a letter of intent from LAV Lineas Aeropostal Venezolanas, all of which had been previous DC-9 operators.
Envisioned as a higher-capacity complement to its DC-9 airframe and a replacement for higher-cost tri-jets, it intended to provide service in maturing markets whose environmental and noise restrictions had precluded larger-capacity equipment substitution, the aircraft offering a significantly smaller noise footprint, greater range and capacity, and the lowest seat-mile costs of any comparable twin-jet.
According to then-President of the Douglas Aircraft Company, John C. Brizendine, “In recent years…we have become acutely aware of the need to conserve energy, to protect the environment, and to produce more and more economically efficient aircraft. (The DC-9 Super 80) is specifically designed to meet the requirements of our industry for years to come. These include environmental compatibility, energy efficiency, economical operation, and a spacious, comfortable interior.”
McDonnell-Douglas boasted of the aircraft, “The DC-9 Super 80 is a blend of proven design with available low-risk technology for enhanced effectiveness, (but) the remarkable DC-9 reliability and lower operating costs are maintained.”
Although it had been based upon this earlier-generation twin, it nevertheless introduced several advanced features.
A fuselage stretch, attained by means of an eight-frame plug forward of the wing and a single-frame insertion aft of it, resulted in a 147.10-foot overall length, increasing maximum capacity to 172, or 33 more than the DC-9-50 and a staggering 82 more than the initial DC-9-10, and producing the most massively stretched commercial airliner up to that time.
The forward, left, and aft, ventral, exits, both equipped with extendible airstairs, had been retained, but an aft, left servicing door, located only feet from the engine, had been introduced. Aeritalia of Naples, Italy, manufactured its fuselage panels.
A new, 10.6-foot center section and two-foot parallel-chord tip extensions, resulting in the third dimensionally divergent DC-9 wing, yielded a 28-percent area, 57-percent fuel capacity, and 11-percent efficiency increase.
Measuring 107 feet, 10 1/4 inches, the airfoil, with a 24-degree sweep back at its quarter chord, a 9.62 aspect ratio, three degrees of dihedral, and a 1,239 square-foot area, had been comprised of four per-wing precision-machined skin panels which had been transformed from 14,000-pound ingots measuring 60 inches wide, 15 inches long, and 30 inches thick by the Reynolds Metal Company of McCook, Illinois.
The all-metal, two-spar structure, with riveted spanwise stringers, featured full-span, three-position leading edge slats with a new, intermediate setting to decrease take off drag and improve climb performance at higher gross weights; larger, doubled-slotted, trailing edge flaps which covered 67 percent of the span and lowered the aircraft’s stalling speed; three spoiler panels, the outer two of which were employable as both flight and ground lift dumpers; and ailerons.
All but the latter were hydraulically actuated, while the ailerons themselves were manually operated. An underwing vortillon fence ensured proper airflow. Providing 1,520 US gallons of additional fuel tankage, it also offered an increased-area main undercarriage bay.
The variable-incidence, electrically-actuated horizontal tail, spanning 40.2 feet, or 3.6 feet more than that of the DC-9-50, retained the design’s characteristic t-tail configuration and sported assister tab-equipped elevators, while the vertical fin, rendering an overall aircraft height of 30.2 feet, featured a hydraulically-actuated rudder. It had been 1.4 feet higher than the DC-9-50’s.
Its Pratt and Whitney JT8D-209 turbofan, mounted on either side of the aft fuselage and retaining the original target-type thrust reversers, was based upon the core of the earlier JT8D-9, but introduced a 49-inch wider fan and an advanced, low-pressure compressor, producing 18,500 pounds of thrust along with an additional 750 pounds of automatic power reserve (APR), generated during engine-loss conditions.
The larger-diameter, single-stage fan, driving a larger mass of hot core section-bypassing air, coupled with more efficient hot and cold exit duct intermixing air, and increased sound absorption material in its nacelle and surrounding casing, yielded numerous improvements, inclusive of increased thrust capability; a higher bypass ratio-of 1:1.78 as opposed to the earlier JT8D’s 1:1; a lower exit velocity; an 11-percent decrease in specific fuel consumption; and a significantly smaller noise footprint than that of the medium-range tri-jets it had been intended to replace.
Employing weight-reducing Kevlar-reinforced aluminum honeycomb stiffeners with graphite tape caps in the outer barrel of its nose cowl and its upper and two lower cowl doors, the nacelle, 21.1 feet long, was 4.5 feet longer than the JT8D-9’s and therefore presented engineering challenges relative to its mounting on the DC-9’s, albeit longer, body.
The DC-9 Super 80 retained the hydraulically-retractable, tricycle, dual-wheeled, Cleveland Pneumatic undercarriage, fitted with Goodyear wheels, tires, and disc brakes; Hydro-Aire Mk IIIA antiskid units; and Douglas ran air brake cooling. The nose wheel was steerable to 27 degrees to either side.
Although the Super 80 retained a common pilot type rating with the DC-9, it nevertheless offered several cockpit advancements, including a digital and flight guidance control system designed by the Sperry Flight Systems Division of Sperry Rand Corporation, which integrated the performance of seven flight control subsystems into two identical digital computers; cathode ray tube (CRT) displays; a digital fuel quantity gauge system; a dial-a-flap system.
And Category IIIA autoland capability of 50-foot decision height (DH) and 700 feet of runway visual range (RVR). A later introduced Electronic Performance Management System provided automatic pitch and thrust to effectuate optimum speed and fuel burn during the aircraft’s climb, cruise, and descent profiles.
The 101-foot-long, “wide look” cabin, featured a broad, contoured, and sculpted acoustically-treated ceiling which blended in with the enclosable overhead storage compartments; aluminum sidewall panels sculpted round the windows; fluorescent lighting; a 19-inch aisle; and five-abreast, two-three or three-two, configured economy class seating, which reduced by half the number of middle seats traditionally associated with six-abreast arrangements.
Interior decor, which varied from conservative, business-oriented appointment to bold patterns and bright colors, was determined by the operator and custom-designed by McDonnell-Douglas whose interior design teams often made trips to airline home countries in order to absorb local culture and customs and then convert that experience into area- or country-reflective motifs. Wool and wool synthetic blends were standardly used for seat covers and carpets.
Class and seating configuration equally varied according to operator. A 137-passenger, dual-class arrangement, for instance, entailed 12 four-abreast first class seats at a 38-inch pitch and 125 five-abreast economy class seats at a 34-inch pitch, while single-class densities included 155 passengers at a 32/33-inch pitch, 167 charter seats at a 30-inch pitch, or a maximum of 172 high-density passengers, the latter accommodatable with a single galley installation.
Interior noise reduction was attained by means of an insulating blanket of fabric-reinforced Mylar over fiberglass.
The elongated DC-9 introduced a new pressurization and air circulation system, which replaced cabin air at greater frequencies, and its potable water system featured in-line heaters in all of its water lines. An increased-capacity auxiliary power unit (APU) ran its environmental control system on the ground.
The aircraft’s longer fuselage significantly increased its lower-deck baggage and cargo compartment volume, whose forward, center, and aft holds respectively encompassed 434, 376, and 443 cubic feet.
The DC-9-80 retained 80 percent of the DC-9-50’s key maintenance features.
Like all of its earlier, shorter-fuselage predecessors, the aircraft had been designed for short-sector, rapid-turnaround, self-sufficient operations from short, limited-facility airfields, with its increased thrust, larger-area wings, self-contained airstairs, auxiliary power unit for environmental conditioning and engine starts, low-to-ground profile to facilitate servicing, loading, and maintenance, and ability to operate two or more sectors without the need for refueling. Most turnarounds required little more than baggage carts.
With a maximum structural payload of 40,112 pounds, the DC-9-81, as designated in its initial variant, had a 147,000-pound gross weight, although this had been later increased to 149,500 pounds with uprated engines, and a maximum landing weight of 128,000 pounds. Its normal and maximum cruise speeds were, respectively, Mach 0.76 and 0.80. Range, with 155 single-class passengers and domestic reserves, was 1,564 nautical miles.
Piloted by Douglas Chief Engineering Pilot H. H. “Knick” Knickerbocker, Project Pilot John P. Laine, and Flight Test Engineer Virginia “Ginny” A. Claire, the first DC-9 Super 80 and the 909th twin-jet to roll off the Long Beach assembly line, made its maiden flight from Long Beach Municipal Airport’s Runway 30 on October 18, 1979 with call sign DACO 80-for “Douglas Aircraft Company 80.”
Following a 25-mile circular, overwater pattern, the long, slender-fuselage aircraft, accommodating 13,100 pounds of test equipment, completed a successful two-hour, 50-minute basic-maneuvers test sortie before landing at McDonnell-Douglas’s Flight Operations Facility in Yuma, Arizona, where the Chief Engineering Pilot concluded, “The ground handling of the Super 80 is even better than the other DC-9s. It also seemed quite stable in flight…The new engines were faultless, and the reverse thrust was very effective on landing…I believe the Super 80 is a great airplane and will live up to all our expectations.”
The 1,085-hour, $36 million, three-aircraft flight test program, which entailed first flights of prototype N1002G on December 6, 1979 and N1002W on February 29, 1980, led to FAA certification seven months later, on August 26, under an amendment to the DC-9’s original type certificate.
First delivered to launch customer Swissair on September 12, which had operated earlier DC-9-15, -30, and -50 series, it was inaugurated into scheduled service on October 5 from Zurich to Frankfurt, becoming the quietest commercial pure-jet. Co-launch customer Austrian Airlines, which had equally operated a fleet of DC-9-30s and -50s, inaugurated its first revenue service 21 days later, on October 26, from Vienna to Zurich.
In order to adopt the McDonnell-Douglas designation scheme, the DC-9-80, or DC-9 Super 80, was rebranded the “MD-80” in 1983, its initial version dubbed “MD-81.”
Douglas MD-80 Twin Aircraft Engine
Development of the baseline Pratt and Whitney JT8D-209 engine, resulting in the uprated, 20,000 thrust-pound -217, augmented additional versions, the origin of which had been the 1979 requirement for a short take off and landing (STOL) aircraft to operate within the Japanese domestic market. A then-projected iteration, designated DC-9 Super 80SF, would have mated the DC-9-40’s fuselage with the DC-9-80’s wing and engines, but the higher-thrust JT8D-217, applied to existing fuselage dimensions, would have provided most of the desired performance.
Resultantly, a second variant, designated MD-82 and first announced on April 16, 1979, featured the uprated, 20,000 thrust-pound turbofans with 850 pounds of automatic power reserve, a 44,024-pound payload, and a 2,050-mile range with 155 passengers. First flying on January 8, 1981, it received its FAA type certification six months later, on July 31, at an initial 147,000-pound maximum take off weight, although the 1982 option of JT8D-217A engines further increased this to 149,500 pounds, resulting in still-higher payload and range capabilities.
Republic Airlines, the July 1, 1978 amalgamation of North Central and Southern Airways, had been the version’s launch customer, having been the world’s largest DC-9 operator with series -10s, -30s, and -50s, to which its eight MD-82s were eventually added.
The variant had been involved in two unique programs. The first of these, occurring in October of 1982, entailed the innovative lease of 20 MD-82s to American Airlines, for which McDonnell-Douglas agreed to bear the maintenance and training costs.
This let to the February 1984 purchase of 67 aircraft, at attractive prices and with low cancellation penalties, to be delivered in blocks of ten to 25 airframes, each block of which had been confirmable 24 months before the targeted delivery date. Becoming the mainstay of American’s short- to medium-range fleet to facilitate hub connections in Chicago and Dallas, the aircraft, configured for 142 first and economy class passengers, ultimately numbered 234, the world’s largest, single-type total outside of the former USSR.
The second innovative transaction occurred on April 12, 1985, when the Shanghai Aviation Industrial Corporation agreed to license-build 25 MD-82s in the People’s Republic of China.
An extended-range successor, designated MD-83 and first announced on January 31, 1982, introduced still higher-rated engines. The JT8D-219, rated at 21,000 pounds of thrust, featured a redesigned low-pressure turbine, a new high-pressure turbine, aerodynamically improved airfoils, a five-percent increase in thrust, and a two-percent reduction in fuel burn.
First flying on December 17, 1984, the twin-jet, with a 160,000-pound maximum take off weight, offered a 2,502-nautical mile range, attained by means of 1,160 US gallons of additional, lower deck hold-installed supplementary fuel tanks.
Finnair, which had operated the DC-9-14/15, -40, and -50, served as the version’s launch customer, operating the longest, nonstop MD-80 flight on November 14, 1985, when it covered the 3,406-mile distance between Montreal and Helsinki in seven hours, 26 minutes. Transwede, of Sweden, inaugurated the first revenue-earning trans-Atlantic flight from Stockholm to Ft. Lauderdale with intermediate stops in Oslo and Gander.
In order to offer a lower-capacity counterpart more suitable to reduced-demand sectors, and to more effectively compete with the 737-300 Boeing designed for this market, McDonnell-Douglas offered the first, and only, dimensionally-divergent variant, the MD-87, which had evolved from its earlier, DC-9 Super XX studies for a 100- to 120-passenger aircraft powered either by Pratt and Whitney JT8D-200 series or CFM International CFM56-3 turbofans and offering a 110,000- to 120,000-pound gross weight. The variant, with a 16.5-foot shorter fuselage, featured a new, 130.5-foot overall length and had a 38,726-pound maximum payload, or the same as the DC-9-50’s.
Because of the decreased moment-arm of the shorter fuselage, vertical axis control required a larger-area, ten-inch taller fin, visible by the extension above its traditional t-tail mating point and resulting in a new, 31.2-foot overall height. It also introduced low-drag flap hinges and fairings, a fillet fairing between the fuselage and the engine pylon, and a reduced-drag, blade-shaped tailcone.
Initially powered by the 20,000 thrust-pound JT8D-217B, but later retrofitted with the lower fuel consumption -217C version, the MD-87 had a 2,372-nautical mile range with 130 passengers and domestic reserves, although additional, MD-83 type fuel tankage in the lower holds increased this to 2,833 miles.
First taking to the skies on December 4, 1986, it received its FAA type certificate on October 21 of the following year, and was inaugurated into service on December 17 with Austrian Airlines from Vienna to Zagreb.
The last, and most advanced, of the five versions, the MD-88, reintroduced the original fuselage dimensions and was announced on January 23, 1986 after launch customer Delta Air Lines placed an initial order to 80 of the type. Offered with 21,000 thrust-pound JT8D-219 turbofans, the version, most closely based on the MD-82, featured increased composite material to reduce structure weight, a new passenger cabin with a wider aisle and modernized overhead storage compartments, and an advanced, glass cockpit, the latter comprised of an electronic flight instrument system (EFIS), a flight management system (FMS), and an inertial reference system (IRS). It retained the MD-87’s blade-shaped tailcone.
First flying on August 15, 1987 and FAA-certified four months later on December 9, the MD-88 entered scheduled service with Delta on January 5, or just over 22 years after it had operated the world’s first passenger-carrying service with the -14 series on December 8, 1965. It had also operated the stretched DC-9-30 and the MD-82.
The 1,000th MD-80 had been delivered on March 29, 1992, and by December of 1997, 1,150 of the type had been in service with 60 worldwide airlines. The design, partially succeeded by its advanced, re-engined MD-90 counterpart and Boeing’s own Next Generation 737 family after that manufacturer’s acquisition of McDonnell-Douglas, nevertheless became its best-selling pure-jet commercial airliner, exceeding sales of the DC-8, the Super DC-8, the DC-9 itself, the DC-10, the MD-11, the MD-90, and the MD-95/717, the last delivery of which had occurred on December 21, 1999, when an MD-83 had been handed over to TWA, ending two decades of production. Combined with the 976 sales of the original, short-fuselage DC-9, it became the third best-selling twin-jet after Boeing’s 737 and Airbus Industrie’s A-320 family, with a collective 2,167 airframes having been built.