The
Allison Model 250 (US military designations
T63 and
T703) is a highly successful
turboshaft engine family, originally developed by the
Allison Engine Company 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 trombone-style 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 2-stage HP turbine, which is connected, via the HP shaft, to the compression system, before expanding through the 2-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 hi-tech centrifugal compressor pulling a pressure ratio of 9.2:1, at an airflow 6.1 lb/s (2.8 kg/s), and developing 715 shp (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 of 450 shp (336 kW).
The Model 250 propels a large number of helicopters and small aircraft. 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.
Variants
250-C18250-C18A250-C20250-C20B250-C20F250-C20J250-C20R250-C20R/1250-C20R/2250-C20R/4250-C20S250-C20W250-C22B250-C28250-C28B
250-C28C250-C30250-C30G250-C30G/2250-C30M250-C30P250-C30R250-C30R/3250-C30R/3M250-C30S250-C30U250-C34250-C40B250-C47B250-C47M
250-B15250-B15A250-B15C250-B17250-B17B250-B17C250-B17D250-B17F250-B17F/1250-B17F/2T63A-5T63A-5AT63A-700T63A-720T703AD-700
Applications
See also
