The 787 is Boeing's grand innovation, nose to tail, wingtip to wingtip. The aircraft's majority-composite design is at the heart of the airframer's leap in the use of new materials and systems. At 50% by weight, the higher strength-to-weight ratio of carbon fibre is intended to replace the traditional architecture of Boeing's metallic wings and fuselage on its earlier narrow and widebody commercial aircraft.
Of Boeing's three big leaps on the 787, its materials and its systems are the biggest game-changers for customers, requiring adaptation by the airlines that will put its technologies into use, with the goal of reducing fuel burn by 20% and operation cost by 10%. Of the 20% improvement in fuel burn, Boeing estimates 8% is engine-driven, 3% from the systems, 3% from the majority composite airframe, 3% from aerodynamics and a further 3% from the integration of all the technologies,
The seven monolithic carbon laminate fuselage barrels eliminate longitudinal joins on the majority of the aircraft, aiming to significantly increase its fatigue life and cut its heavy maintenance interval in half. The composite primary structure also allowed Boeing to significantly increase the size of the 787's windows to 48.3cm (19in) with electro-chromatic dimmable glass.
The composite manufacturing processes from one facility to another - with slight variations - remain uniform across the programme's primary structural suppliers - Spirit AeroSystems in the US, Alenia in Italy and Kawasaki, Fuji and Mitsubishi Heavy Industries in Japan. Carbon fibre tape is laid down on a mould or mandrel either by hand or automatic fibre placement (AFP) machines, cured in a high-temperature autoclave, trimmed, drilled, non-destructively inspected, painted with primer and then flowed to the assembly or build-up process.
There are significant differences, depending on the size and purpose of the parts, which range in size from floor beams all the way up to 19.4ft-wide (5.91m-wide) fuselage barrels and the 98ft-long wing skins. For lightning strike protection, Boeing has embedded a thin wire mesh into the carbon laminate, which in conjunction with an aircraft-wide current return network provides a return ground plane for all the equipment installed in the aircraft.
The aircraft's wings, manufactured and assembled by Mitsubishi in Nagoya, Japan, and also carbon laminate, are assembled with single-piece top and bottom wing skins and joined with aluminium ribs and composite spars. The structure of the aircraft's Alenia-built horizontal and Boeing-built vertical stabilisers also employs carbon laminate for primary structure, replicating Boeing's previous experience on the 777's composite empennage.
Carbon sandwich has a more limited implementation on the Goodrich laminar flow nacelles, and the aircraft's elevators, rudder, spoilers, raked winglets and inboard movable leading edge. Fibreglass sandwich accounts for the forward and leading and trailing edge structure of the horizontal and vertical stabilisers, along with the wing forward and trailing leading edges and the wing-to-body fairing.
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More-Electric Architecture
The biggest sea change under the 787 carbon fibre skin can be found in its more-electric bleedless systems architecture, aimed at reducing engine fuel burn by allowing the power extraction to work on demand, managing the pull of electricity as it is needed from the engine's generators rather than bleeding air from the engine when it is more efficiently used for propulsion.
As one of the programme's earliest systems suppliers, Hamilton Sundstrand was first selected in 2004 to supply nine systems for the 787, including the aircraft's environmental control system (ECS), auxiliary power system (APS), electrical power generating and start system (EPGSS) and ram air turbine (RAT).
Without a pneumatic system seen on all other Boeing aircraft, the airframer developed an electric engine start system with Hamilton Sundstrand anchored by two 250kVA variable frequency starter generators on each General Electric GEnx-1B or Rolls-Royce Trent 1000 engine and two 225kVA generators in the auxiliary power unit. The six generators provide up to 1.45MW of electricity fed through nine power panels that manage and distribute electrical power to a myriad of aircraft systems.
The hydraulic system's biggest difference from previous Boeing aircraft is the power source for its three independent systems, all electrically driven, supporting the primary flight control actuators, landing gear, nose gear steering, thrust reversers and leading and trailing edge flaps with 5,000 pounds per square inch (psi) pumps. Both left and right systems feature engine-mounted and driven pumps along with an electric motor pump, while the centre system has twin large electric motor pumps - one that runs throughout a flight and the other employed during takeoff and landing.
Rather than use the hydraulic actuation on the main landing gear brakes, Boeing would use an electrically driven carbon brake-by-wire system supplied by either Goodrich or Messier-Bugatti, while the GKN-supplied wing anti-ice system also follows Boeing's more-electric architecture, eliminating the use of hot bleed air to melt any forming ice on the wings, opting to use a heater mat technology instead.
The more-electric systems provide cabin pressurisation, run by electrically driven compressors on the ECS that provide a cabin altitude of 6,000ft (1,830m), compared with 8,000ft on previous Boeing aircraft.
The 787 is the world's first commercial jetliner to employ a required nitrogen generation system from its first day of operation, a certification requirement developed in the wake of the 1996 TWA Flight 800 disaster, caused by an explosion of fuel vapour in an unused fuel tank.
Aerodynamically, the Honeywell-supplied flight control system enables the 787's three-axis fly-by-wire, using the aircraft's ailerons for manoeuvre load alleviation and elevator for active gust load alleviation. The 787's wing also adapts to changing gross weight conditions, optimising the camber of the wing through the trailing edge variable camber (TEVC) system moving it up or down by 1.5e_SDgr from its neutral position.
Fourteen drooped spoilers also eliminate the need for fore flaps, bridging the gap between the wing and extended flaps, while also serving as traditional spoilers dumping lift on landing and providing slowing drag while in flight. Flaperons provide additional flight control functionality, drooped when acting with the high lift system, roll control as ailerons and upward deflection as spoilers on landing.
Reducing external drag further, Boeing has incorporated a passive laminar flow system on the engine nacelles by maintaining a smooth boundary layer of air, providing each pair of nacelles a white colour by default for customers to apply a universal paint thickness designed to preserve the flow over a larger area.
Common Core Brain
The heart of the 787's integrated systems architecture is founded on the GE Aviation Common Core System (CCS) aimed at increasing reliability, lowering aircraft weight and cost by implementing a common processing and data network to drive the aircraft's systems. The system is tied together through Rockwell Collins' fibre optic ethernet-based avionics full duplex (AFDX) command data network (CDN) allowing communication between modules with the AIRNC 664 standard.
The modular nature of the CCS, which is made up of twin Common Computing Resources that are housed in the forward electronics equipment (EE) bay below the flight deck and ahead of the forward cargo compartment, allows the system to be both scaled and upgraded without a comprehensive redesign for each change, allowing the aircraft to acquire new capabilities without major modifications.
Source: Flight International
