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Aviation History
1996
1996 - 2459.PDF
A set of 24 airspray injectors is used in the combustor, each with increased air swirling for better combustion. Air is swirled by a set of inner swirl vanes and by two sets of outer swirl vanes. To avoid "thermal distress", the combus tor is also built with a mechanically isolated burner heatshield and external heat transfer ribs on the flame tube itself. TURBINE TECHNOLOGY The single-crystal HP turbine blades are made from CMSX4tnaterial and fitted to a single- stage disc, which is connected to a mini disc to the rear of the HP compressor drum. The flow of cooling air to the blades is controlled by two sets of seal fins, which are attached to the front face of the disc. Like all RB.211s, the turbine blades are shrouded — a tradition which differentiates the R-R engine from the unshrouded turbine blades of die GE and P&W products almost as much as the three- versus two-shaft arrangement. R-R has stuck to the shrouded blades because it believes that they offer better performance retention, although they are heavier and cannot spin as fast. Unlike previous engines and Trent 700, however, the shroud interlocks have been deleted. This was possible because the inclined root dampers'at the base of each blade produce a much lower vibration level. Another contrib utor to the reduced vibration level is the redesigned nozzle guide vanes. "As on the Trent 700 there are 40 NGVs compared with 36 on the othfer engines. We've changed to a 'wake-off 3-D.design which cuts the impact of the vane wake on the blades and moves the vane/blade resonance out of the operating range," says lerrett. "With the.interlock in place, we'd need to keep cool, but by not having to rely on the inter lock we can operate at higher temperatures. As a result, the HP turbine will never be a temper ature limiting factor on the Trent," he adds. One major benefit of the three-shaft design, says R-R, is the simplicity of an un-cooled IP turbine. TruS-single-stage unit rotates at 70% of the speed;of the HPT, "...so it's running at only half the stress and at cooler temperatures," says Terrett. The blade is made of single crystal RR3000 and a new short chord IP vane is pro tected with an advanced plasma vapour deposit ed aerofoil thermal barrier coating. At an early stage R-R also changed the material used for the HP/IP bearing structure between the two shafts from steel to nimonic. In a similar way to the - 524 and - 5 3 5, the annulus running between the HP turbine and the large diameter LP turbine also rises steeply. An IP turbine case cooling system, controlled by the Lucas-made full -authority digital engine- control (FADEC) system, maintains optimum rip clearance for the IP and LP blades. At take-off, flow from the cooling manifold is reduced to pre vent excessive tip rubs. At cruise, flow is increased to achieve the smallestclearances. Reflecting the higher thrust levels of the Trent 800, the LP turbine has a fifth stage, one more than the Trent 700 and two more than the RB .211. The first stage of the LPT is made from higher-temperature-resistantMarM 002 mate rial, which used to make up the IPT and HPT blades in earlier RB.211s. "It's like a tide of materials technology moving back through the engine," comments Terrett. The solid cast blades are welded in pairs to control vibration and, reflecting their 3-D com putational fluid dynamics (CFD) origins, are highly curved, thin and almost boomerang- looking. "We are looking at improving this even further using CFD, possibly by taking a few aerofoils out," Terrett says. The LPT vanes are also solid cast and R-R claims that this method makes both blades and vanes cheaper to produce than the previous hol low RB.211 designs. SYSTEMS CHANGES R-R has been able to benefit from the combined Trent 700/800 effort particularly in systems design. The benefits have been twofold. Firstly, the majority of systems are common, with sig nificant changes to only four line-replace- • These Legends i Are True*- ILLUMINATOR 2000 BETTER 4 WEEK LOWER MEET PRODUCT DELIVERY COST MIL SPEC Pay less and get better product quality in as little as 4 weeks. That's the bottom line in the decision to buy our annunciator switches and indicators or go with our competitors. And once you compare our product to theirs, the only real choice to be made is whether to phone br fax your order in to us. That's because Aerospace Avionics has superior quality legends in the popular 5/3 inch, as well as other sizes, for every application. For control rooms, communication consoles, on-board caution panels or anywhere you need an #•1 in 4i i £3 r n annunciated switch or indicator. Not! only do we have them for less, we will enable you to easily specify your requirements as well as guarantee timely delivery. AAI annunciators are available in a variety of switch configurations and colors (including NVIS) and are stringently tested to ^M^H applicable MIL Specs. •' i I F°r information on our ' " I Illuminator 2000 switches, ^^"^^ see us at the Night Vision Conference Aug. 29-30 (Booth 38) and at the Farnborough Air Show Sept.-2-8 (Booth H4/2) in the American Aerospace Industries Pavilion. Aerospace Avionics, Inc., 1000 MacArthur Memorial Highway, P.O. Box 1000, Bohemia, NY 11716 Phone: (516)467-5500 • Fax: (516)467-5939 FLIGHT INTERNATIONAL 11 -17 September 1996 55
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