Update — McDonnell Douglas MD-11/12

Perhaps the most obvious external difference to the MD-11 is the addition of Whitcomb-style winglets which have surfaces both above and below the wing. The winglets-which were first tested on a Continental Airlines DC-10-30 during the mid eighties has cut the total cruise drag over the DC-10-30 by more than 4%. As well as reducing drag, the winglets provide an increased lift capability which helps raise the economical cruise speed of the aircraft.

The rest of the wing is basically the same as that of the DC-10-30, though there have been some modifications that improve not only performance but safety. One important feature of the MD-11 is its two stage leading edge slats which, in the case of hydraulic failure, automatically lock in position. Should a rupture of hydraulic lines in one wing occur (as in the Chicago DC-10 crash) the wing slats in the opposite wing will automatically shut off, preventing a dangerous asymmetric flight condition.

Also acting to reduce drag in the MD-11 is the smaller horizontal tail that MDC was able to incorporate in the airframe. This was reduced from 1,338sq ft (408m) to just 920sq ft (280. 6m) and could be done by introducing leading edge anti-icing and a longitudinal stability augmentation system (LSAS). The reduction decreases drag by 2%, gives a weight saving of 1,900lb (862kg) and an overall fuel burn saving of 3%. The redesigned tail also has reduced sweep and a cambered leading edge to increase its effectiveness at high angles of attack.

The LSAS system, which is an essential element of the re- designed tail area, acts in the same way as a conventional yaw damper, deflecting the elevator by up to 5 degrees countering sudden changes in pitch attitude. It also helps provide an extra level of stall protection when used in conjunction with the auto-throttle for a nose down/throttle up response when close to stalling.

The tail itself holds some 2,000lb (908kg) of fuel which is pumped forward to the main wing tanks during flight. In the event of fuel line rupture or fuel pump failure, fuel from the tail tank will be fed directly to the tail engine. The tail cone has been extended and reshaped, and even this relatively minor modification provides about 0. 5% in fuel savings by eliminating a small area of afterbody flow separation present on the DC-10 tail cone’s upper surface.

Less discernable on the MD-11 airframe are the fuselage plugs that have added 18. 6ft (5. 7m) to the fuselage length. This extra length enables the MD-11 to carry 293 passengers in a typical three class configuration, compared to 247 in the DC-10-30. It also provides more space for the passenger luggage and reve- nue cargo, which is becoming increasingly important to airlines. The MD-11 in a standard passenger configuration can in fact carry some 34% more revenue cargo than its predecessor and, surprisingly, some 41% more than the Boeing 747 (in which most storage space is taken up by passenger luggage. ) Besides modifications to the basic airframe, an important difference in the MD-11 is the use of modern, higher performance engines. McDonnell Douglas is offering a choice of three engines. to power the MD-11: the General Electric CF6-80C2, Pratt & Whitney 4460 or the Rolls-Royce Trent 650. Testing of the General Electric and Pratt & Whitney powered aircraft will be completed by the time the new airliner is fully certified later this year. Certification of the Rolls-Royce Trent 650, however, is not expected until 1993.

The use of these engines is another a factor in the aircraft’s superior performance over the DC-10. Not only are they more reliable engines, they also offer increased thrust which, when combined with the effects of the reduced drag and increased lift created by the winglets, produce a longer ranged and faster cruising airliner. For example, an MD-11 operating out of Los Angeles with a full load of 293 passengers will be able to fly non stop to Australia, whereas the DC-10-30 has to be refuelled enroute. Travel time will be reduced not only because the need for a refuelling stop is eliminated, but actual flight time is reduced because of a higher long-ange cruise speed.

The cockpit layout of the MD-11 has, like the airframe, benefitted from technological advances. From the cockpit door forward the MD-11 is all new, bearing little resemblance to the DC-10. It has benefitted from the availability of new cockpit technology which has not only radically altered cockpit displays and layout, but has removed the need for the third flight crew member, the flight engineer.

Functions that would previously have been performed by the flight engineer have been automated to decrease cockpit work-load. Automatic system controllers (ASC) have been introduced to replace the third crew member. These are contained in an overhead panel which are viewable and reachable by either of the two flight crew. The pre-flight check list is fully automated to -eliminate a manual task previously performed by three flight crew. This reduces crew workload, eliminates human error in the checks and, because the automated checklists are completed simultaneously, reduces check time.

The most obvious difference in the new cockpit layout is the use of six 20cm2 cathode ray tubes (CRTs) to display primary flight deck information. Two CRTs are programmed to provide primary flight display information, two provide navigation displays, while an engine/alert display and a systems display complete the cockpit layout. The use of CRTs has cut the number of flight instruments needed in the cockpit with, for instance, no less than fifteen pin-programmable display options being offered on the primary flight display.

The actual MD-11 flight deck operates on the ‘dark cockpit’ philosophy in which all lights for switches, warnings and other devices are off most of the time. A light goes on only as an alert to ensure pilot attention should trouble arise. Once a problem is revealed, the engine/alert display indicates the actual fault. This ensures prompt corrective action because only the primary malfunction is displayed, so deciding priorities among all the malfunctions resulting from a major systems failure is not a problem. After the systems failure has been identified and the emergency drill completed, the system display can be checked by the crew to ascertain current configuration.

The MD-11 will also have wind shear avoidance and protection as a standard feature. Provisions for TCAS II collision avoidance system will also be made, with TCAS II symbology being readily accepted by the cockpit CRTs where the system be fitted. TCAS and other systems such as satellite communications (SATCOM) and maintenance data transmission (ACARS) will not be available as standard equipment until such time as the industry is ready to fully accept and utilise these functions.

MDC has incorporated a fair degree of fly-by-wire control in the MD-11. Both the full authority digital control (FADEC) of the engines and LSAS can be overridden by the pilots, and the engine fire handles are connected to conventional cables which control the airliners fuel, hydraulics and oil cutoff. Fire extinguishers bottles are also triggered by conventional cables.

The standard MD-11 is available in three models-passenger, freighter, and combi with both passengers and freight carried on the main deck. The biggest seller will no doubt be the passenger versions in which considerable interior changes have been. made in the cabin. These include enlarged overhead stowage compartments (providing one third more carry-on baggage space for passengers) and better cabin lighting. The cabin layout is very flexible and will enable airlines to reconfigure the interior of their airliners in a relatively short period of time. This feature was primarily made necessary by European demands for a flexible interior which can be altered to make allowance for seasonal passenger variations. Thus the aircraft can be changed by the airline from a typical three class configuration to that of an economy class only airliner, ideal for charter operation.

As a freighter, the MD-11 can carry a maximum payload of 205,700lb (93,304kg) with a range of 3,542nm (6,560km). The MD-11 Combi can typically seat 176 passengers in a three class configuration, and carry six pallets of cargo on the main deck. Additionally, 14 LD3 containers and six pallets can be accommodated below deck.

Flight testing of the MD-11 for FAA certification is progressing well, albeit nearly a year behind the original launch schedule, as are sales of this important new airliner. Development of the DC-10 airframe is not, however, expected to end with the MD-11. Already being discussed – but not yet formally announced – is the MD-12X, previously known as the MD-11 Stretch. The MD-12X is perhaps the first airliner which could conceivably provide direct competition for the 747. With a stretch of 35ft (10. 7m)-20ft (6. 1m) forward of the wing and 15ft (4. 6m) aft-pas- senger capacity in a typical three class configuration is increased from 293 in the MD-11 to 372 in the MD-12X; in an all-economy configured aircraft for high density operations (such as in Japan) 520 passengers could conceivably be seated.

A ‘Panorama deck’ is also considered to be a possible option for the MD-12X. Similar in concept to the upper deck of the 747, the new passenger cabin would be located forward of the wing but below the main deck. Space for passengers in the Panorama deck compares favourably to the 747 upper deck, providing a projected 62 business class seats (four abreast) or up to 99 economy class seats (five abreast). Present projections for the MD-12X also include an all economy high-density short range airliner which could seat an unprecedented 619 passengers! It is firmly believed that the MD-12X will become a reality, with MDC only waiting to have the MD-11 development program completed before a formal announcement is made. Already financing for the project has been discussed with Japanese companies, while JAL has secured conversion rights with its recent MD-11 (10+10)order for the MD-12X when the project is formally launched. JAL is, along with British Airways, being targeted as a for- mal MD-12X launch customer.

The MD-11 flight test program is currently underway with five aircraft being used in the test program so MDC can make up for time lost during development. The first MD-11 was slightly over-weight on first flight, but efforts are being made to lighten the aircraft; the added weight is not expected to greatly affect the air-liner’s overall performance. Delivery of the first new build MD-11 is expected by year’s end (although Federal Express will receive first delivery when it accepts its first GE powered MD-11 freighter which is currently the lead aircraft in the flight test program. ) At time of writing, orders and commitments for the MD-11 stood at 381; it is anticipated that initially the production rate will be four per month (equal to the maximum DC-10 delivery rate) to ensure a reasonable rate of delivery, although it is planned to raise this to five per month by 1992.

By all accounts the MD-11 and MD-12X will be formidable competitors in the airline industry. Already sales of the MD-11 are fast approaching in number the 506 DC-10/KC-10 airframes built and no doubt production will surpass this figure. The new airliner will certainly be seen on air routes to and from Australia with American Airlines expected to commence MD-11 Pacific flights to Australia in 1991. At least eight airlines in the Asian region – including Garuda, JAL, Singapore Airlines, Korean Air and Thai International which service Australia— have placed orders for the MD-11. It could, conceibably, even fulfil future Qantas requirements for an airliner to service new routes to be established in the mid to late 1990s.