16Juin
By: admin On: juin 16, 2017 In: Travel agency & Tour Comments: 0

             Commercial aircraft are the result of the airline requirements which shape them, attempting to fulfill, as completely and cost-effectively as possible, the particular combination of mission goals.  For airliner-type aircraft, these include two primary parameters: payload, comprised of passengers, baggage, cargo, and mail, and range, which enables a carrier to offer nonstop service between specific city pairs.

              Aircraft configurations are, in essence, design solutions to intended operating missions and hence vary according to fuselage length and width; wingspan, planform, and sweepback; engine type, thrust, and mounting; and horizontal and vertical tail location and size.

                The 777 traces its origins to 1986 when Boeing had first determined the need for a widebody design sandwiched, in capacity, between its existing 767-300 and 747-400 to replace the McDonnell-Douglas DC-10 and Lockheed L-1011 trijets.  Although initial configurations, all designed 767-X, had closely resembled its predecessor 767 with a larger capacity and winglets, it had quickly become apparent that an all-new design, the seventh in the Boeing Commercial Airplane Company line, would be needed after a last-ditch iteration had featured a winglet-equipped 767 with a 757 fuselage graphed on to its aft section, producing a semi-double decker.  Aside from the aerodynamic drag considerations, the existing underfloor baggage, cargo, and mail volume would have been inadequate for its projected capacity.  Because of increasingly more reliable and higher capacity turbofans, the new aircraft could, like the 767, be configured round two of them.

                Boeing Board of Director authority to offer the new design, still designated 767-X, had been granted on December 8, 1989 for an aircraft which had been 16 feet longer, 41 inches wider, and had sported a 14-foot greater wingspan than its predecessor, but initial feedback from All Nippon, American, British Airways, Cathay Pacific, Delta, Japan Air Lines, Qantas, and United had indicated that Boeing had not been innovative enough: they had all sought a still larger aircraft with state-of-the-art technology, such as fly-by-wire flight controls, and extended-range twin-engine operational capability.

                A further iteration, with a 20.3-foot wide, circular fuselage cross section, had resulted in a 747-like, twin-aisled passenger cabin, and its 199.11-foot, supercritical wing, with a 31.6-degree sweepback, had been able to  meet design goal cruise speeds, yet meet American Airliners’ DC-10-size gate compatibility requirements with innovative, foldable wingtips.  It would be the world’s largest twin-jet, of narrow or widebody dimensions, ever to be produced. Because of its relatively late design phase, it would equally offer the widest cabin among its competition.

               When United Airlines had placed its $3.5 billion launch order for 34 firm and 34 options on October 15, 1990 to replace its DC-10s, it had launched both Boeing’s seventh pure-jet design and a collaborative partnership with the manufacturer to produce an airframe of the highest quality.

                The aircraft which had subsequently rolled out three and a half years later on April 9, 1994, designated WA001, had been the first to have been digitally designed with three-dimensional computer graphics, and had exceeded its original design goal of reducing change, error, or rework by 50 percent.  Indeed, the aircraft’s first alignment had been off by a mere .023 of an inch.

                The airliner, the Boeing 777, had also been the first to have been designed round its fuselage.  In order to provide the carriers’ requests for large capacity, Boeing had, for the first time, deviated from its traditional ovoid fuselage cross section, employing one with a perfectly circular circumference, which had provided sufficient internal width and volume for 747-like, ten-abreast coach seating. and had resulted in a simpler, lighter, and cheaper structure.  Internal seating options had provided for twin-aisle configurations varying between six and ten abreast, in a variety of classes and densities, for a maximum capacity of 440, while flexibility zones had permitted rapid galley and lavatory reconfiguration, according to airline need.

                Unlike the preceding 767, the 777 had once again been able to accommodate the standard LD-3 containers on its lower deck, storing 18 (or six pallets) in its forward hold and 14 in its aft hold.

                A supercritical airfoil, with a 199.11-foot span, a 31.30-degree sweepback at its quarter chord, and an 8.68 aspect ratio, had optimized its take off and payload-range capability, yet had equally ensured high-altitude operation and low-speed handling.  Aft wing camber had resulted in considerably rear lift generation, while double-slotted inboard and single-slotted outboard trailing edge flaps had augmented low-speed lift.  The outer 21.3 feet of each, wing, connected to a hydraulically-actuated hinge, had facilitated gate compatibility on the ground, although American Airlines, for which it had been designed, had, in the event, never chosen this option, nor had any of the other carriers.

                Unlike that of the 767’s conical-shaped tail cone, the 777 had introduced a drag-reducing, blade-shaped one, facilitated by the auxiliary power unit’s side-facing exhaust.

                Employing the largest percentage of composite material construction of any previous Boeing design, particularly in the fixed wing leading edges, the wing root fairings, the spoiler panels, the wing trailing edge surfaces, the vertical fin, the engine nacelles, and the main undercarriage doors, the aircraft had featured a 2,600-pound weight reduction because of it.

                Its two high bypass ratio turbofans had been the most powerful and reliable ever to have been designed for a commercial airliner, their 123-inch diameter equal to that of a 737 fuselage which accommodates six-abreast coach seating.  Featuring all-composite, wide chord fan blades, they swallowed two million cubic feet of air per minute and had initial potential for 100,000 pounds of thrust. 

                Its 14-wheeled, tricycle undercarriage had included a twin-wheeled, steerable nose unit and two six-wheeled main gear units which had obviated the need for a third, DC-10-30-like strut and had featured an aft-axle, hydraulically-controlled steering system which had operated in alignment with the nose wheel.

                The first Boeing design to replace the older-technology cable-and-pulley flight control system with fly-by-wire electronic signaling, the aircraft had no longer been maneuvered by means of directly-linked pilot input commands.  Instead, computers had “translated” those commands into flight control-moving signals.

                First flying on June 12, 1994 from Everett, Washington, the Boeing 777, powered by Pratt and Whitney 4084 engines and shadowed by a T-38 chase plane, had completed a successful three-hour, 48-minute flight, and had sparked the type’s two-year, nine-aircraft test program which had entailed three engine types, 6,700 airborne hours, and 4,800 flight cycles.  Simultaneously certified by the FAA and the JAA on April 19, 1995, it had been the first commercial aircraft ever to have earned extended twin-engine operations of 180 minutes with the Pratt and Whitney engine from the first day of service entry, which had occurred two months later with United from London-Heathrow to Washington-Dulles.

                The basic design’s inherent flexibility, coupled with use of the previously dry center section fuel tank and successively higher-thrust engines, had optimized the type for increasingly larger route sectors, resulting in the initial A variant, a subsequent B version, and a final increased gross weight, or 777-200IGW, model, before the type had been collectively designated -200ER, for “extended range.”  Utilizing fuselage, wing, tailplane, engine pylon, and undercarriage structural strengthening, the aircraft, with a 14,220 US gallon fuel increase and a higher, 656,000-pound gross weight, had offered a 7,700-nautical mile range, but had otherwise been dimensionally identical to its -200 predecessor.  First flying on October 7, 1996 with General Electric GE90 engines, it had been certified the following January and had entered service with British Airways on February 9.

                Airline need dictating higher capacity, coupled with the basic airframe’s inherent stretchability, had resulted in the first dimensional modification and had followed the trend of previous Boeing jetliners, which had all been designed with the same growth capability. 

                The version, targeted as an early 747-100 and -200B replacement, would offer similar passenger capacities as these quad-engined wide bodies, but with far greater fuel efficiency, lower seat-mile costs, and advanced technology.

                Cathay Pacific had, coincidentally, identified the need for a very high capacity widebody on its intra-Asian routes where range capability had not been crucial, but the type’s twin-engine economy would render them more profitable.

                The stretched version, sharing the same pilot type rating as the baseline aircraft, would result in a 777 family, meeting several range and capacity needs.

                Officially announced at the 1995 Paris Air Show after receiving 31 orders from Cathay Pacific, Korean Air, Thai Airways International, and ANA, the elongated variant, designated 777-300, had featured a ten-frame forward and nine-frame aft fuselage insertion, to ensure an optimum balance and center of gravity and to continue to obtain required take off rotation angles with the existing 777-200 undercarriage, increasing its maximum, single-class passenger capacity to 550.  In order to be able to demonstrate evacuation speed with this number, two type A overwing exit doors had been inserted.  Fuselage section, inboard wing, and nose and main gear strengthening had catered to the increased structural weight, while a tailskid had protected the fuselage underside from excessive take off angles.

                Because of the unprecedentedly long wheelbase, a belly- and horizontal stabilizer-mounted “ground maneuvering camera system,” or “GMCS,” had provided electronic images to cockpit crew to facilitate taxiing and turning.

                The 777-300, with a 242.4-foot overall length, but the same 199.11-foot wingspan, had first flown on October 16, 1997 with 82,800-thrust-pound Rolls Royce Trent 892 engines, its test pilots reporting taxiing differences which had been augmented by its ground maneuvering camera system, but inflight characteristics which had been virtually the same as those of the –200 after its nearly four-hour inaugural flight.

                The 777-300’s certification program, which had involved five aircraft and 1,500 hours, had focused on the differences between the two versions.

                The type, inaugurated into service with Cathay Pacific on May 27, 1998, had eventually been powered by the 98,000 thrust-pound Pratt and Whitney 4098, the 90,000 thrust-pound Rolls Royce Trent 892, and the 93,700 thrust-pound General Electric 90-94B turbofan, and had a 660,000-pound maximum take off weight.  Its wing and fuselage center section fuel capacity of 45,220 US gallons had provided a typical, mixed-class range of 6,000 nautical miles, and the variant had become the first serious contender to Boeing’s own 747 in capacity.

                The -100 series 777, hitherto missing from the basic family and strongly supported by American Airlines, had been reserved for a smaller-capacity, ultra long-range version with a foreshortened fuselage which could connect any two points on the globe.  Because the engine manufacturers had been reluctant to develop a powerplant with a thrust capability higher than that employed by the 777-200ER, the fuselage shrink could still use existing engines, trading structural weight for fuel-producing range.

                As initially envisioned, a 777-100X, with a ten- to 12-frame decrease for a three-class complement of about 250, would have resulted in higher operating costs, since fewer passengers and less cargo would have reduced the aircraft’s overall revenue potential, although the desired range would have been achieved.  Key to such a design had therefore been use of at least the existing –200 length fuselage.

                The resultant version, the 777-200X, would store fuel in tanks beyond the never-used wing hinge and, with a 298-passenger, three-class capacity, would emerge as the world’s longest-range commercial aircraft capable of flying 8,600 nautical miles.  A comparable stretched-fuselage, 355-passenger 777-300X would offer a 6,600-nautical mile range.

                Although Malaysia Airlines had signed a memorandum of understanding for 15 -200Xs and Thai Airways International had also expressed strong interest, many Asian carriers had found the design’s range to have still been deficient, since it could not offer their desired Pacific-US West Coast capability.

                Battling strong competition from Airbus with it’s A-340-500, which Singapore Airlines itself had ordered in May of 1998, Boeing could only achieve the desired range with an expanded wing, more capable engines, and higher gross weights.

                Six-foot, five-inch wingtip extensions, sporting drag-reducing, raked wingtips, had extended the span and wingbox, and had increased integral fuel capacity, while a new, 750,000-pound gross weight had required considerable structural reinforcement of the fuselage and the vertical and horizontal tail.  The engine nacelles had been revised.  The main landing gear had incorporated new wheels, brakes, and tires, and had semi-lever capability on the stretched version in order to augment rotation angles.

                Internally, repositioned air conditioning ducts and parts of the secondary support structure had permitted installation of crew rest compartments configured with two to nine beds in the fuselage’s crown above the passenger overhead storage compartments, facilitating 19-hour inflight duty times.  Similar crown galley provision had increased main deck seating by four and lower deck container capacity by four on the shorter-fuselage version, and seven and six, respectively, on the longer fuselage variant.

                Because of competition from the A-340-500, the latter would be developed first.

                Officially announcing the program on February 29, 2000, Boeing had launched the world’s largest, longest-range, and most powerful twin-jet in the form of the 777-200LR “Longer Range” Worldliner and the 777-300ER “Extended Range.”  The latter, first flying on February 23, 2003, had featured 115,300 thrust-pound General Electric GE90-115B turbofans, a 212.7-foot wingspan, a 775,000-pound gross weight, a 47,800 US gallon fuel capacity, and a 7,930-nautical mile range, and had entered service with Air France the following May.  The 777-200LR, which had not first flown until March 8, 2005, had retained the -200’s overall length and the -300ER’s expanded wingspan, but with three optional, aft cargo hold fuel tanks, had a 53,515 US gallon capacity, giving it a 9,380-nautical mile range with 110,100 thrust-pound GE90-110B1 engines.  After an 886-hour test program, which had entailed two aircraft, 318 ground hours, and 328 cycles, the variant had entered service with Pakistan International one year later on March 3, 2006.

                Boeing had thus been able to offer a complete family of medium-, long-, and ultra long-range passenger aircraft with two baseline capacities.

                The type had quickly recorded several milestones.  After five years of service with 280 aircraft, the Boeing 777 had exceeded ten million hours and had flown more than 100,000 extended twin operations, mostly over the Atlantic.  Because United had been the launch customer, it had logged more 777 hours than any other carrier.  Lauda Air had recorded the type’s highest daily aircraft utilization rate, of 14.92 hours, on the Austria-Australia route.

                As the fastest-selling twin-aisle commercial airliner, it had notched up 500 deliveries by 2004.

                Its range capability had often resulted in many of these milestones.  On April 7, 1997, for example, it had attained an eastbound global circumnavigation record of 41 hours, 59 minutes with a single intermediate stop in Kuala Lumpur, Malaysia, before landing at Boeing Field.  Flying 10,823 nautical miles, it had set the “Great Circle Distance without Landing” record, and averaging 553 mph, it had also earned the “Speed Around the World, Eastbound” record.  And on November 10, 2005, the 777-200LR had captured the world distance record of 11,664 nautical miles in 22 hours, 42 minutes, a distance more than half way round the world.

                As a 747 replacement, the 777-300 had flown the same number of passengers on one-third the fuel and had required 40 percent less maintenance.

                The final version, a freighter devoid of either external passenger windows or internal amenities, had resulted from carrier need for a long-range, high-capacity, all-cargo aircraft and had been launched on May 24, 2005 when Air France had placed an initial order.  Based upon the 777-200LR Worldliner, it had been powered by 110,100 thrust-pound GE90-110B1L turbofans.  With a maximum fuel capacity of 47,890 US gallons, the 766,000-pound aircraft had a 4,886-nautical mile range.  Its 226,000-pound payload capability could be carried in an inner-fuselage, 23,051-cubic foot volume: of the 18,301 cubic feet on the main deck, it could accommodate 27 96-inch pallets and of the 4,150 cubic feet on the lower deck, it could carry ten 96-inch pallets.  Another 600 cubic feet of cargo could be carried in the bulk compartment.

                Having notched up some 1,000 sales of all versions in the 13-year period between 1995 and 2008, the versatile widebody, twin-engined Boeing 777 seemed poised to carry passengers and cargo well into the 21st century.



Source by Robert G. Waldvogel

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