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Aviation History
1985
1985 - 2879.PDF
Ranger and BO105LS, there is overseas competition from the Turbomeca TM319, which replaced the Allison 250 in the Aerospatiale AS.335 Ecureuil 2 for the French Air Force. The Model 400A and 440 TwinRanger will use the PW209T engine with is own TwinPac-style combining gearbox. Bell prefers the TwinPac type of design because it saves both weight and cost. The Model 440 will have improved useful load because it is to have a lightweight all- composite fuselage. The hot-and-high MBB BO105LS will have its two Allison 250-C28 turboshafts replaced by a pair of PW205B engines. The PW209T and PW205B are both to be certificated in 1988. Several helicopter manufacturers are looking at the PW200 series for new aircraft, including using the PW205B to replace a single Allison 250, says P&WC. Aerodynamic demonstrator Engineering development of the PW200 Is centred on Mississauga, near Toronto in Ontario, where new test facilities have seen built. The first run of the 8:1 jressure-ratio compressor in December 1984 was made at the 55,000 r.p.m. design ;peed in an aerodynamic demonstrator, fhe first run of a complete engine is !xpected before the end of 1985, with nstallation in a Bell 400A TwinRanger cheduled for autumn 1986, leading to a irst flight early in 1987. Designed to power Bell Helicopter Canada's Model 400A and 440 TwinRanger, below, Pratt & Whitney Canada's 1,000 s.h.p.-class PW209T, left, comprises two turboshafts driving a combining gearbox with a single output shaft to the helicopter transmission Seven engines are being built initially, five for ground testing and two for certifi cation testing. The first four experimental customer engines will be available in July 1986 for ground running, and the rest for flight testing by the end of that year. Special tests will be performed to cover such conditions as icing, high-altitude operation, and overhaul to meet the sched uled certification date of March 31, 1988. The PW209T will have a sea-level static standard-day uninstalled take-off power rating of 937 s.h.p. with both engines running; 523 s.h.p. for 2jmin with one engine running; and 510 s.h.p. for 30min with one engine running. Take-off specific fuel consumption (s.f.c.) is 0 • 557, rising to 0-579 at the 800 s.h.p. maximum continuous rating. Two-engine take-off power at 5,000ft, ISA plus 20°C, is 702 s.h.p. (s.f.c. 0-580), while maximum continuous power is 587 s.h.p. (s.f.c. of 0-611). A PW200 turboprop is projected, but details are not finalised. All technical solutions for such a configuration have been reviewed and evaluated, however. There are useful advantages in power/weight ratio relative to specific fuel consumption and initial cost trade-offs, but it is still too early to launch a new 500 s.h.p.-class turboprop while the general aviation market is depressed, although utility transport applications have consid erable promise, P&WC believes. Simplicity is evident in the PW200 configuration. Engine layout comprises a radial air intake, centrifugal compressor, pipe diffuser, reverse-flow annular combustion chamber, single-stage compressor turbine, single-stage power turbine, and front drive. Although rear- mounted gearboxes were evaluated, front drive was found to offer lower weight and a better e.g. location. Choice of front drive with a shaft passing through the engine core from power turbine to gearbox necessitated this shaft having whirling speeds well away from the engine's normal operating range. This was achieved by selecting appropriate stiffnesses and connections between the shaft and the gearbox input pinion, while minimising the corresponding energy in the driveshaft at these speeds. Front-drive turboshafts The PW209T has two front-drive turboshafts bolted to a combining gearbox incorporating accessory drives. There is one coupling at the front for the main- rotor driveshaft and another at the rear for the tail-rotor shaft. There are three separate oil systems to ensure isolation of each power section from the other and from the output section. Backed by extensive research, various centrifugal compressors were evaluated to ensure high efficiency and good surge margins. Initially, the combustion system used vapourisers and transpiration-cooled IGHT INTERNATIONAL, 19 October 1985 27
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