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Aviation History
1994
1994 - 1658.PDF
PW206A DESCRIBED tinued to meet an MDHS requirement for more power and the PW206A was re-certifi cated in November 1993 at a take-off ther modynamic rating of 475kW. The PW206B is a derated PW206A with a different reduction gearbox to match the EC. 135 transmission. Production is under way and 24 engines had been delivered to MDHS by mid-June, when the first flight of the fourth Explorer was imminent. MHDS had logged some l.OOOh on the PW206A by mid-June. Certification of the Explorer is planned for September and the first two helicopters are scheduled for delivery to US launch customer Petroleum Helicopters by the end of 1994. P&WCs agreement with MDHS guarantees the Canadian company exclusiv ity of the first 128 Explorers, after which customers will be able to choose between the PW206A and Turbo- meca's TM319 Arrius 2. Buyers of Eurocopter's EC. 135 will be able to choose from the outset between the PW206B and the French Arrius 2. Both engines have been flown, the PW206B powering the sec ond EC. 135 prototype which was flown for the first time in Germany in April. Certification of the PW206B is planned to coin cide with that of the heli copter in the fourth quarter of 1995. At Eurocopter's request, P&WC is working to bring certification forward to the third quarter, presumably to allow helicopter deliveries before the end of 1995. P&WC is talking to other helicopter manufacturers about the PW200, notably Bell, which is developing the Model 407 — a successor the 206 JetRanger/LongRanger which would be available in both single- and twin-turbine configurations. To meet expected requirements, the company has embarked on a growth pro gramme to take the PW200 to 630kW — closing the gap with the PT6. Under a demonstrator effort begun in December 1993, P&WC is testing increased-capacity compressor designs and a cooled compres sor turbine. One factor behind the growth pro gramme is the possibility of amended certi fication regulations allowing heavier light helicopters. US FAR Part 27 certification is now limited to helicopters of up to 2,700kg gross weight. Above that limit, more-oner ous FAR Part 29 rules apply. The Explorer is already bumping the 2,700kg limit and growth versions will require re-certifica tion to Part 29 — unless the rules are amended to raise the Part 27 limit to 3,600kg, as has been proposed. The PW200 will eventually cover the 410kW-630kW range, competing with Allison's latest Model 250-C40 turboshaft at the upper end. As befits a stablemate of Rear-bearing support structure provides power-turbine containment the PT6 (which spawned turboprop, tur boshaft, turbofan and auxiliary power-unit derivatives), the PW200 core has been studied as the basis of a family of engines. So far, turboprop and auxiliary-power derivatives have yet to be launched. FREE-TURBINE TURBOSHAFT The PW206 is a free-turbine turboshaft engine, with a single-stage centrifugal com pressor, reverse-flow annular combustor, single-stage compressor turbine with sin gle-crystal blades, and a single-stage power turbine. The power turbine drives a com bined accessory and reduction gearbox mounted at the front of the PW206 via a shaft which runs through the centre of the engine. Major features include single-chan nel full-authority digital engine control (FADEC) with hydromechanical backup. The PW206A weighs 130kg and has a take-off rating of 460kW and a 475kW one-engine-inoperative emergency rating. The engine comprises two modules: gear box and power section. The PW206B uses the same power section, mated to a new gearbox with an angled output shaft. Most of the design changes from the PW205B which was flown in the BO 105 to the PW206A have been made in the gear box, which is now considerably more com pact and lighter. The gearbox casings were changed from magnesium to aluminium for corrosion resistance and durability. An integral oil tank was added between the gearbox and the annular engine intake. While the 6.63:1 two-stage reduction geartrain is driven by the power turbine, the accessories are driven by the contra-rotating compressor- turbine rotor. Accessory drive- pads are provided for the per manent-magnet alternator, starter-generator, and fuel, oil and hydraulic pumps. An optional Freon pump is driven by the reduction geartrain. Compared with the reverse- flow PT6, the PW206 is "the right way round," says Mike Scanlon, project manager PW200 engines. Air is drawn in through an annular inlet at the front of the engine, pro tected by a wire-mesh screen. There is no integral inlet parti cle-separator. Instead, the heli copter manufacturers will offer airframe-mounted Centrisep inertial separators as options. The compressor is a single- stage forged-titanium centrifu gal impeller with an 8:1 com pression ratio — the same as that achieved by the PT6 with three axial and one centrifugal stages. The impeller rotates counter-clockwise at 58,000RPM. A port in the compressor shroud provides optional bleed air for cabin conditioning. Compressed air from the impeller is ducted via 22 stainless-steel diffuser pipes to the reverse-flow annular combustor. This features a two-piece heat-resistant alloy liner, two hybrid primary-secondary fuel nozzles and ten air-blast nozzles. The single-stage compressor turbine is a forged waspaloy disc with 32 insertable, uncooled, single-crystal blades. The blades are supplied by Pratt & Whitney's large- engine plant in Hartford, Connecticut. The compressor-turbine vane ring is integrally cast and internally cooled. The single-stage power turbine is a forged waspaloy disc with 48 insertable, uncooled Inconel 100 blades. The turbine spins clockwise at 39,800RPM, driving the front-mounted gearbox via shaft running through the engine. The power-turbine vane ring is integrally cast and surface cooled. The engine has five bearings: one pair either side of the reduction geartrain; another pair either side of the centrifugal impeller; and the fifth at the rear of the 32 FLIGHT INTERNATIONAL 13-19 July, 1994
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