Rolls-Royce Model 250

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MTU build Allison 250-C20B

The Rolls-Royce Model 250 (US military designation T63) is a highly successful turboshaft/turboprop engine family, originally started by a General Motors offshoot, the Allison Engine Company, in the early 60's.

Allison adopted a rather unusual "trombone" style of 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 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. The engine configuration is shown clearly in http://helicopterflight.net/engine1.jpg.

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).

As the following site shows (http://www.atlasaviation.com/powerplant/aircraftapp.htm), 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.

Older retired units have also had a second life as theatrical props as engines for Colonial Vipers that are being worked on in the background of the port Hangar bay on the Sci FI channel remake of Battlestar Galactica.

[edit] Subtypes of the Model 250

250-C18

Bell 206A JetRanger

250-C20

MTT Turbine SUPERBIKE

250-C20B

Bell 206B JetRanger II and early model JetRanger III
BO 105 CBS
BO 105 Super Five
Cicaré CH-14
Hughes/MD 500E
PZL Kania
Hiller FH-1100

250-C20F

Eurocopter AS355F

250-C20J

Bell 206B JetRanger III (later models)

250-C20R

MD520N
Bell 206L LongRanger

250-C20R-1

Agusta A109C
Bell 206 JetRanger

250-C20R-2

PZL SW-4

250-C20S

Soloy Turbine-Pac conversion kit for Cessna 206/207 Stationair

250-C20W

Enstrom 480
Schweizer 330, 330SP, 333

250-C28

Bell 206L-1 LongRanger II
BO 105 LSA-3

250-C30

Hughes/MD 530F
Sikorsky S76A

250-C30P

Bell 206L.4 LongRanger

250-C40

Bell 430

250-C47

Bell 407
MD600N

250-B17F/2

Tradewind Turbines Propjet Bonanza (A36)
Extra EA-500

[edit] Applications of the Model 250

AgustaWestland
- Agusta A109A
Bell Helicopters
- Bell 206 JetRanger
- Bell 206 LongRanger
- Bell 206LT TwinRanger
- Bell 407
- Bell 430
Cicare Helicopteros S.A.
- Cicaré CH-14
Enstrom Helicopters
- Enstrom 480
Eurocopter / MBB
- AS355F
- BO 105
Hughes Helicopters, later MD Helicopters
- Hughes 369HE/369HS/369HM / Model 500C
- Hughes 369D / 500D
- Hughes 369E / 500E - later the MD369E
- Hughes 369F / 530F - later the MD369F
- MD520N
- MD600N
Schweizer Helicopters
- Schweizer 330, 330SP, 333
Sikorsky Helicopters
- Sikorsky S-76
Soloy Conversions
- Bell 47G Soloy
- Hiller 12E Soloy
- A36 Bonanza (STC now owned by Tradewind Turbines)
- Cessna 206/207 Stationair
Extra Aircraft, LLC
- EA-500