The Volvo RM12 is a Swedish turbofan engine developed from the General Electric F404J in the late 1980's to be the power plant of the Saab JAS 39 Gripen combat aircraft. In order to obtain a more efficient, reliable, and cheaper-to-maintain machine, the American engine was greatly improved as several changes were made to the original design to obtain a dependable power plant, such as a new flameholder, a thrust vectoring nozzle, and a more effective and stronger fan. For example, the RM12 fuel consumption at full throttle is 9:3 lb/sec (4.2 kg/sec) compared to the 18.1 lb/sec (8.2 kg/sec) of the original GE F404J. Engine reliability and easy maintenance are perhaps the two most important features of an aircraft engine.
Technical Description
The Volvo RM12 is a 4.1-m long, low-bypass turbofan engine. It consists of two spools, a 3-stage low-pressure compressor, a 7-stage axial high-pressure compressor, an annular combustion chamber, and a 1-stage high-pressure and a 1-stage low-pressure turbine. Downstream of both turbines, there is an afterburner and a hydraulically variable, convergent and divergent exhaust nozzle. The dry weight of the engine is 1,050 kg, with a 0.88-m diameter. Temperature in the afterburner can reach 2,000 degrees Celcius, which required the use of special heat-resistant materials.
The modification to the original F404J included a new and more efficient fan to allow more flow for higher thrust, a new flameholder in the combustion chamber to allow better performance for less weight, and a stronger variable stator inlet vanes. Another feature that makes maintenance cheaper is the fact that the RM12 is made in seven sections or modules, each of which can be changed separately. All these new technical innovations allowed the Swedish Gripen aircraft to lift heavier payloads for longer-range, attack missions.
Specifications
Type: low-bypass turbofan engine for supersonic speed
Fuel Type: MC-75
Dry Weight: 1,050 kg (2,310 lb)
Length: 4.1 m (13 feet, 4 inches)
Diameter: 0.88 m (2 feet, 10 inches)
Low-Pressure Compressor: 3 stages
High-Pressure Compressor: 7 stages
High-Pressure Turbine: 1 stage
Low-Pressure Turbine: 1 stage
Combustor Type: annular
Maximum Thrust: 12,100 pounds of thrust (54 kN)
Pressure Ratio: 27.5:1
Bypass Ration: 0.3:1
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| Above, the RM12 turbofan engine on the assembly line. |
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| Cut-away drawing of the Swedish engine, showing internal parts. |
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| Two technicians working on the RM12 in a Volvo Flygmotor factory in Sweden. |