Allison Model 250

Le propulseur Allison 250 du Bell 206, entre autres, vu par Wikipedia.en

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The Allison Model 250, now known as the Rolls-Royce M250, (US military designations T63 and T703) is a highly successful [Vous devez être inscrit et connecté pour voir ce lien] engine family, originally developed by the [Vous devez être inscrit et connecté pour voir ce lien] in the early 1960s.

The Model 250 has been produced by Rolls-Royce since it acquired Allison in 1995.

Design and development

Allison adopted a reverse airflow engine configuration for the Model 250: although air enters the intake/compression system in the conventional fashion, the compressed air leaving the centrifugal compressor diffuser is ducted rearwards around the turbine system, before being turned through 180 degrees at entry to the combustor; the combustion products expand through the two stage HP turbine, which is connected,
via the HP shaft, to the compression system, before expanding
through the two stage power turbine; the exhaust gases then turn though 90 degrees to exit the engine in a radial direction; a stub shaft connects the power turbine to a compact reduction gearbox, located inboard, between the centrifugal compressor and the exhaust/power turbine system.

One of the latest versions of the Model 250 is the -C40, which has a centrifugal compressor pulling a pressure ratio of 9.2:1, at an airflow 6.1 lb/s (2.8 kg/s), and developing, at the shaft, 715 hp (533 kW).

Some of the earlier versions have axial compressor stages mounted on the HP shaft to supercharge a relatively low pressure ratio centrifugal compressor.

The -C20R is typical, pulling an overall pressure ratio of 8.0:1, at an airflow of 4.0 lb/s (1.8 kg/s), with a power output, at the shaft, of 450 hp (340 kW).

The Model 250 propels a large number of helicopters, small aircraft and even a motorcycle.^{[Vous devez être inscrit et connecté pour voir ce lien]
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As a result, nearly 30,000 Model 250 engines have been produced.

Of these, approximately 16,000 remain in service.

The Model 250 is one of the highest-selling engines made by Rolls-Royce.