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Aviation History
1986
1986 - 0009.PDF
DEFENCE display, flat screen liquid- crystal eye-level display collimated at infinity to avoid refocussing the eyes from the Hud presentation, two lateral colour multifunction shadow- mask CRTs, and a head-down flat display. Active voice control will be used exten sively to change displays or call up information. Rafale will also demon strate the general integration of all flight systems. In addi tion to the flight control system, all aircraft systems and circuits—fuel, electrics, hydraulics, air conditioning, engine controls, navigation, and communications—are broadly based on digital tech nology. All information from, and orders to, these systems will be transmitted and exchanged through two centralised digibus lines. Health monitoring The pilot will not have to bother with monitoring these systems in normal operation. He will be aurally warned (but only if strictly necessary) about a system failure. The pilot will then automatically be provided with the informa tion he needs to rectify a system fault. Systems per formance is automatically recorded for subsequent replay by groundcrew to identify any shortfalls. Rafale's construction uses a high proportion of new materials and new manu facturing techniques. Com posites of carbon, boron, Kev- lar, or mixes of these, allow weight to be reduced by about 20 per cent from similar all- metal structures. Composites are used to form the front fuselage section (cockpit and equipment bay), the fuselage centre section, and its integral fuel tank, and the rear-lower fuselage. The wings, canards, rudder, elevons, and leading- edge flaps are also of com posite construction, as are the gear doors and numerous access panels. The radome and wing-to-fuselage fillets and fairings are of Kevlar. Overall, composite materials account for about a quarter of Rafale's weight. To this weight saving must be added the savings from using aluminium-lithium alloys. On Rafale allithium, or "alii", is used for the fin and wing to fuselage attachment frames, fuselage skinning, and fuel tank walls. Alii offers a 7-8 per cent weight reduction over conventional aluminium alloys and could eventually replace 60-70 per cent of conventional alloys in future aircraft. Lithium is a low- ,density metal with a mass of 0 • 6gm/cm3 compared with Left View to the rear is good and the all-moving canards are unobtrusive to the pilot's downward field of view. Below Basic structure of Rafale lgm/cm3 for water and alumi nium's 2-7gm/cm3. Added to aluminium, lithium decreases the metal's density and, unusually, increases its stiff ness while the strength stays the same and fatigue behavi our is better. A typical alii alloy would have 2 • 5 per cent lithium by weight (10 per cent by volume). Superplastic metals When conventional materi als and metals remain the best solution for some specific parts, Dassault has progressed in the manufacturing tech niques used with these materials. An example with Rafale is the use of super- plastic forming and diffusion bonding of titanium pieces. Superplasticity is the prop erty of some metals to become highly ductile at high temperature and thus be stretched into most intricate shapes. With most of today's alloys a stretch of 20 per cent is possible before the metal tears. With superplastic alloys the stretch factor can be as high as 1,000 per cent. Dass ault has used titanium sheet ing tack welded into a mould which is then heated and has pressure applied to form it into the shapes required. The Rafale programme has allowed the company to fine- tune this technique for reduced-cost fabrication of complex parts. Rafale's fly-by-wire system draws heavily on company experience gleaned from the neutral-stability Mirage 2000 programme, but has much higher performance because of increased computer power, complete digitalisation of the system and more functions. In addition, the unstable Rafale's flying canards offer more inherent manoeuvra bility, approaching control- configured vehicle standards. Rafale's flight control surfaces consist of the rudder, three elevons on each trailing edge, which can be moved identically or differentially, plus automatic leading-edge flaps which can be combined with elevon droop to alter wing camber and provide high lift. The active canards allow the introduction of direct-lift control principles. For instance, it will be possible to increase or decrease lift at will, by using the canards and elevons together, without changing aircraft attitude or angle-of-attack. At present Rafale has an electronically signalled fly-by- wire system, but ACT/ACM will use fibreoptics for data transmission; a fly-by-light system is currently being test flown in a Mirage 2000. FLIGHT INTERNATIONAL. 4 January 1986
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