in compressor, decrease in turbine) and the shaft power input (compressor) or output (turbine).

For a turbofan engine the number of turbine stages required to drive the fan increases with the bypass-ratio unless the turbine speed can be increased by adding a gearbox between the turbine and fan in which case fewer stages are required. The number of turbine stages can have a great effect on how the turbine blades are designed for each stage. Many gas turbine engines are twin-spool designs, meaning that