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Aviation History
1990
1990 - 2793.PDF
The LCDs are only half as deep as the CRTs they replace, consume only half the power, require only passive cooling and should be many times more reliable. Boeing is evaluating flat panels from two suppliers in the laboratory. Much greater use of datalink information is planned for the 777 and communications messages will be displayed on the engine instrument and crew alerting system (EICAS) screens. Boeing admits there is a potential to flood the cockpit with informa tion—datalink will be used for both air traffic control and airline communications and by the cabin staff and passengers. Another cockpit innovation planned is the electronic checklist, and attempt "to get rid of paper in the cockpit", says Boeing. This will duplicate the paper checklist and use the lower EICAS multifunction display. The aim is to automate a large part of the checklist. Although the 777's flight management and guidance systems are based on those of the 747-400 (flight management software will be identical to the -400 Package B to be released in 1993-4 and also retrofitted to the 757 and 767) the hardware implementation will prob ably be different—for two reasons. First because the 777 will use the Boeing- developed ARINC 629 DATAC multiplex digital databus and, second, because Boeing plans to use card files instead of line-replace able units (LRUs) for at least some of the 777 avionics. Thirdly, Boeing may select a suppli er different to that used on the 747-400. The 777 flight management system control display unit (CDU) will include a touchpad or trackerball control to drive a cursor on the navigation display, or upper or lower EICAS screen. This can be used with the electronic checklist or for en route flight planning. To avoid the degree of customisation that plagued, and ultimately delayed, the 747- 400, Boeing will provide as standard most of the features airlines are likely to want. The basic 777 will have around 60 more standard features than the basic 767-300ER and a further 120 "standard options" will be offered in packages to keep variability under control. Standard features will include satellite communication, global position and micro wave landing systems. A single integrated air data and inertial reference unit will replace two inertial reference systems (IRSs). The avionics architecture is based around the DATAC databus developed by Boeing and modelled on the military 1553B data high way. The 777 will have two DATAC net works, one for systems and the other, isolated and clean, for fly-by-wire. The 777 will be Boeing's first fly-by-wire airliner. There will be three digital flight control computers and no mechanical rever sion. The computers, to be supplied by GEC Avionics, will use dissimilar processors to provide a degree of redundancy that would otherwise require several more computers. Boeing has not opted for A320-type flight- path vector control but stayed instead with conventional pitch/roll control. It has also stayed with a conventional control wheel believing that, with a sidestick, the visual and tactile cues between pilots are lost. Boeing has gone for envelope protection and not envelope limiting, describing the former as a soft limit the pilot can, and the latter as a hard limit the pilot, cannot over ride. In pitch the 777 fly-by-wire system will provide stall, overspeed, tailstrike, load factor and windsheer protection. Stall protection will be provided by a stick-force gradient and a soft load-factor limit of around 2.5g will be applied. In roll there will be bank-angle protection and in yaw engine-out compensa tion to lead the pilot in the correct direction. The fly-by-wire system will also provide gust- load alleviation. With the electronic cockpit and computer ised flight controls, integrity of power supply is essential, particularly as the 777 is a twinjet intended for long overwater routes. The electrical system is therefore comprehensive: three 120kVA generators, two engine-driven and one on the auxiliary power unit; two engine-driven 20kVA variable-speed/con stant-frequency (VSCF) generators; standby rarrr-air-turbine/battery power; plus separate power supplies for the fly-by-wire system— three permanent-magnet generators on each engine (two for each channel). The 777 will also be the first Boeing airliner with composite primary structure, reveals John Roundhill, 767-X chief project engineer, airline requirements. The company believes the latest toughened carbonfibre- reinforced plastics are now suitable for use in airliners and will use them for the fin and tailplane. The company will not use light weight aluminium-lithium, however, but will use "advanced" aluminium alloys. The all-new wing is designed for a Mach 0.83 cruise speed, slightly higher than that of the competing A330/A340, Boeing believes. The long span reduces fuel burn but could pose parking difficulties so Boeing is propos ing to fold the tips to fit DC-10 gates. The fold mechnpm will be based on that developed by Boei.ig for the A-6 Intruder composite wing. Refining the fold design has reduced the drag penalty associated with the hinge to only 0.2% although the weight premium remains at around 1,360kg. The fold can be deleted, saving 360kg. Other 777 features include a six-wheel main-gear truck which Boeing says is lighter " than having a third, centrepost, main gear. Although Boeing has yet to secure a launch customer for the 777, it is working to protect a May 1995 delivery deadline. Two engineer ing simulators are planned, one to begin operating in January 1991, the other late in 1992, plus a systems integration laboratory and Boeing 757 fly-by-wire and avionics testbed to fly early in 1992—all part of the biggest airliner test programme Boeing has ever undertaken. ^ FLIGHT INTERNATIONAL U.-IB itpiembcr 1990
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