Allison Model 250
| Model 250 / T63 | |
|---|---|
_250_C20B.jpg) MTU-built Allison 250-C20B | |
| Type | Turboshaft/Turboprop |
| National origin | United States |
| Manufacturer | |
| Major applications | |
| Number built | >30,000 |
| Developed into | Rolls-Royce RR500 |
| Variants | Rolls-Royce RR300 |
The Allison Model 250 – now known as the Rolls-Royce M250 and designated the T63/T703 in US military service – is a successful turboshaft engine family, originally developed by the Allison Engine Company in the early 1960s. Rolls-Royce has produced the Model 250 since it acquired Allison in 1995.
Development
[edit]In 1958, the Detroit Diesel Allison division of General Motors was chosen by the US Army to develop a new light turbine engine to power a "Light Observation Aircraft" (LOA); the goal was to replace the Cessna O-1A Bird Dog aircraft. At this stage, the US Army was unsure whether to use a fixed- or rotary-wing aircraft, so Allison was instructed to consider both applications. The design studies that were undertaken considered a range of possible mechanical configurations for the turboprop/turboshaft. These studies culminated in testing the prototype engine, designated YT63-A-3, in April 1959.[1] In 1960, the US Army settled on a rotary-wing platform. The YT63-A-3 first flew in a variant of the Bell 47 helicopter in 1961. A modified version of the engine (the YT63-A-5) – with the exhaust pointing upward (to avoid grass fires) – soon followed. This version, rated at 250 hp, passed the Model Qualification Test in September 1962. The Hughes OH-6 design, powered by the T63, was selected for the US Army Light Observation Helicopter (LOH) in May 1965.
The Model 250 powers many helicopters, small aircraft, and a motorcycle (the MTT Turbine Superbike).[2] As a result, nearly 30,000 Model 250 engines have been produced, of which approximately 16,000 remain in service; thus, the Model 250 is one of the best-selling engines made by Rolls-Royce.
Design
[edit] |
Allison adopted a reverse-airflow engine configuration for the Model 250: although air enters the intake/compression system conventionally, the compressed air leaving the centrifugal compressor diffuser is ported rearwards via two transfer pipes – which go around the outside of the turbine system – before the air is turned 180 degrees upon entry to the combustor. The combustion products expand axially forward through the two-stage (single-stage on early engines) high-pressure turbine section, which is connected to the compressor via the HP shaft. The combustion products continue to expand through the two-stage power turbine, which generates shaft horsepower for the aircraft. A coaxial stub shaft connects the power turbine to a compact reduction gearbox, located inboard, between the centrifugal compressor and the exhaust/power turbine system. The exhaust stream then turns 90 degrees to exit the engine radially through twin exhaust ducts, which form a V-shape visible in front elevation.
An important design feature of the Model 250 engine is its modular construction, which significantly simplifies maintenance and repair activities. The unique reverse-flow design also facilitates hot-section maintenance. The engine has four modules:
- a compressor module at the front of the engine
- a gearbox module (including accessory drives)
- a turbine module (including V-shaped exhaust ports)
- a combustion module (including twin compressed air transfer ducts) at the rear
Earlier versions of the engine have seven axial compressor stages mounted on the HP shaft to supercharge a relatively low-pressure-ratio centrifugal compressor. The -C20B version is typical, with an overall pressure ratio of 7.2:1 and an airflow of 3.45 lb/s (1.56 kg/s), and a shaft power output of 420 hp (310 kW).
One of the latest versions of the Model 250 is the -C40, which has only a centrifugal compressor producing a pressure ratio of 9.2:1, at an airflow of 6.1 lb/s (2.8 kg/s), developing 715 hp (533 kW) at the shaft.
Variants
[edit] | This section may require copy editing for spelling, grammar, style, cohesion, or tone. (September 2025) |
- 250-B15
- 250-B15A
- 250-B15C
- 250-B15G
- 250-B17
- 250-B17B
- 250-B17C
- 250-B17D
- 250-B17Fg
- 250-B17F/1
- 250-B17F/2
- 250-C10D
- 250-C18
- 317 hp (236 kW)
- 250-C18A
- 317 hp (236 kW)
- 250-C20
- 250-C20B
- 250-C20F
- 250-C20J
- 420 hp (310 kW)
- 250-C20R
- 250-C20R/1
- 250-C20R/2
- 250-C20R/4
- 250-C20S
- 250-C20W
- 250-C22B
- 250-C28
- 250-C28B
- 250-C28C
- 250-C30
- Purpose-built for use with the Sikorsky S-76. Featured a single-stage centrifugal compressor instead of the multi-stage axial/centrifugal compressor of earlier models[3]
- 250-C30G
- 250-C30G/2
- 250-C30M
- 250-C30P
- 250-C30R
- 250-C30R/3
- 250-C30R/3M
- 250-C30S
- 250-C30U
- 250-C34
- 250-C40B
- 250-C47B
- 250-C47E[4]
- 250-C47M
- 250-E3
- Experimental engine containing a regenerative heat exchanger. First regenerative engine to fully power a vertical take-off and landing (VTOL) aircraft in flight. Ran on a Hughes YOH-6A Light Observation Helicopter in 1967. 185 lb (84 kg) engine delivering 280 hp (210 kW).[5]
- 250-KS4
- Used aboard marine ships as a starter system for larger gas turbines. Redundant Independent Mechanical Start System (RIMSS).
- T63-A-5
- T63-A-5A
- T63-A-700
- 317 hp (236 kW)
- T63-A-720
- 420 hp (310 kW)
- T703-AD-700
- Soloy Turbine-Pac
- Typically 2x 250-C20S driving a single propeller via a combining gearbox, able to operate individually.
- Mitsubishi CT63
- Licenced production for Kawasaki-Hughes 500 / OH-6A helicopters.
Applications
[edit]Fixed-wing
[edit]- Aermacchi M-290 RediGO
- BAE Systems Mantis
- Beechcraft Bonanza (prop-jet conversions)
- Britten-Norman BN-2T Turbine Islander
- Cessna P210 Silver Eagle (conversion)
- Extra EA-500
- Fuji T-5
- Fuji T-7
- GAF Nomad
- Gippsland GA10
- Grob G 120TP
- Partenavia AP.68TP variants - Spartacus & Viator
- RFB Fantrainer
- SIAI-Marchetti SF.260TP
- SIAI-Marchetti SM.1019
- Soloy Cessna 206 turbine conversion
- Stoddard-Hamilton T-9 Stalker
- Valmet L-90 Redigo
Rotary-wing
[edit]- Agusta A109A
- Bell 206
- Bell 407
- Bell 222SP
- Bell 230
- Bell 430
- Bell OH-58 Kiowa
- Bell YOH-4
- Boeing AH-6
- Cicaré CH-14
- Enstrom 480
- Eurocopter AS355F
- Fairchild Hiller FH-1100
- HESA Shahed 285
- Hughes OH-6 Cayuse
- Kamov Ka-226
- MBB Bo 105
- MBB Bo 108
- MD Helicopters MD 500
- MD Helicopters MD 600
- MD Helicopters MH-6 Little Bird
- Northrop Grumman MQ-8 Fire Scout
- PZL Kania
- PZL SW-4
- Schweizer 330/330SP
- Schweizer S-333
- Sikorsky S-76
Other applications
[edit]- Gerhardt 66 – USAC IndyCar racing car
- Loral GZ-22 – non-rigid airship
- MTT Turbine Superbike – motorcycle
- Redundant Independent Mechanical Start System (RIMSS) (used on gas turbine ships)
Engines on display
[edit]- A partially sectioned Allison 250-C20B is on public display at the City of Norwich Aviation Museum in Horsham St Faith, Norfolk, England.[6]
Specifications Model 250-C18 (T63-A-700)
[edit]Data from The Instrumentation Design And Control of a T63-A-700 Gas Turbine Engine[7]
General characteristics
- Type: turboshaft
- Length: 40.5 in (1,029 mm)
- Diameter: 22.5 in (572 mm)
- Dry weight: 138.5 lb (63 kg) dry
Components
- Compressor: 6-stage axial + 1-stage centrifugal
- Combustors: single-can combustion chamber
- Turbine: 2-stage axial gas generator power turbine + 2-stage axial free-power output turbine
- Fuel type: JP-4 aviation kerosene (alternatively JP-1 or JP-5)
- Oil system: pressure spray/splash, dry sump
Performance
- Maximum power output: 317 hp (236 kW) for take-off (Sea Level 59 °F (15 °C); 51,600 rpm NH, 35,000 rpm NL, 6,000 rpm Nout)
- Overall pressure ratio: 6.2:1
- Air mass flow: 3.3 lb/s (1.5 kg/s)
- Turbine inlet temperature: 1,380 °F (750 °C) at power turbine inlet
- Specific fuel consumption: 0.697 lb/hp·h (0.424 kg/kW·h)
- Power-to-weight ratio: 2.289 hp/lb (3.765 kW/kg)
See also
[edit]Related development
References
[edit]- ↑ "A look back at development of the Model 250 Turbine Engine" (PDF). Archived from the original (PDF) on 4 October 2016. Retrieved 14 March 2016.
- ↑ "Atlas Aviation - rolls royce allison model 250 application". Archived from the original on 24 August 2006. Retrieved 9 November 2016.
- ↑ "The Spirit of Sikorsky". Air International. Vol. 18, no. 3. March 1980. pp. 111–116, 142–144. ISSN 0306-5634. OCLC 907842170.
- ↑ "Press releases". rolls-royce.com. Retrieved 1 June 2018.
- ↑ McCardle, John J., ed. (20 October 1967). "Allison regenerative engine first to 'go it alone' in flight". AllisoNews. Vol. 27, no. 8. p. 1. OCLC 42343144.
- ↑ "Engines List". City of Norwich Aviation Museum. Retrieved 27 August 2023.[dead link]
- ↑ Haas, David William (1996). The Instrumentation Design And Control of a T63-A-700 Gas Turbine Engine. Monterey, California: Naval Postgraduate School.
External links
[edit]
