A turboshaft engine comprising a gas generator and a free power turbine is selected to provide propulsive power for a helicopter. The helicopter is hovering in ISA conditions at an altitude of 4100 feet. The following data applies to this engine at this static max power operating point. Intake mass flow: 8.9 kg/s Compressor pressure ratio: 24.5 Compressor isentropic efficiency: 88% Mechanical efficiency: (HP & PT shaft) 99% Combustion chamber pressure loss Combustion chamber inlet pressure 4% Combustion efficiency 98.8% Combustion chamber exit temperature: 1585K Gas generator turbine isentropic efficiency: 92% Power turbine isentropic efficiency: 90% The effects of the intake and exhaust ducts may be ignored. It may be assumed that for: Air: Cp = 1.005 kJ/kg • K, y = 1.4, R = 0.287 kJ/kg • K Combustion gases: Cp = 1.148kJ/kg • K, y = 1.333, R = 0.287 kJ/kg • K A 6% direct bleed of air from the exit of the compressor is used to supply the aircraft environmental control system (ECS). 75kW of power is extracted from the gas generator shaft to satisfy the helicopter hydraulic and electrical power requirements. a) Calculate the power available from the power turbine shaft to drive the helicopter rotor at this operating condition.
A turboshaft engine comprising a gas generator and a free power turbine is selected to provide propulsive power for a helicopter. The helicopter is hovering in ISA conditions at an altitude of 4100 feet.
The following data applies to this engine at this static max power operating point.
|
Intake mass flow: |
8.9 kg/s |
|
Compressor pressure ratio: |
24.5 |
|
Compressor isentropic efficiency: |
88% |
|
|
99% |
|
Combustion chamber pressure loss Combustion chamber inlet pressure |
4% |
|
Combustion efficiency |
98.8% |
|
Combustion chamber exit temperature: |
1585K |
|
Gas generator turbine isentropic efficiency: |
92% |
|
Power turbine isentropic efficiency: |
90% |
The effects of the intake and exhaust ducts may be ignored.
It may be assumed that for:
Air:
Cp = 1.005 kJ/kg • K, y = 1.4, R = 0.287 kJ/kg • K
Combustion gases:
Cp = 1.148kJ/kg • K, y = 1.333, R = 0.287 kJ/kg • K
A 6% direct bleed of air from the exit of the compressor is used to supply the aircraft environmental control system (ECS). 75kW of power is extracted from the gas generator shaft to satisfy the helicopter hydraulic and electrical power requirements.
a) Calculate the power available from the power turbine shaft to drive the helicopter rotor at this operating condition.
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