In-flight monitoring of aero engine health

1. A method for in-flight monitoring of health of an aero gas turbine engine comprising, in flow series, a compressor system including a low pressure compressor and a fan upstream of the low pressure compressor, a core gas generator including a combustor, a turbine, and a shaft system connecting the turbine to the compressor system and forming a torque path therebetween, the shaft system including a core shaft, a fan shaft and a gearbox, the core shaft receiving an input from the turbine and the gearbox receiving an input from the core shaft and outputting drive to the fan shaft so as to drive the fan shaft at a lower rotational speed than the core shaft, the fan shaft driving the fan, the method comprising:

measuring a first rotational speed of the fan shaft in a forward portion of the shaft system in front of the gearbox;

measuring a second rotational speed of the core shaft in a rear portion of the shaft system adjacent to or at the turbine;

measuring a third rotational speed of the core shaft in a portion of the shaft system adjacent to and behind the gearbox;

measuring other operational parameters of the engine, the operational parameters including at least one operational parameter associated with the core gas generator;

calculating power delivered by the torque path from the turbine to the compressor system from the measured rotational speeds;

calculating power delivered to the turbine by the core gas generator from the other measured operational parameters;

correlating the power delivered by the torque path at a given time with the power delivered to the turbine at that time;

calculating an amount of shaft twist in the shaft system across the gearbox from the first and third rotational speeds; and

identifying distress of the torque path in-flight that could potentially lead to a hazardous event when the correlation departs from an expected correlation of the power delivered by the torque path with the power delivered to the turbine when the amount of shaft twist departs from an expected amount of shaft twist in the shaft system across the gearbox.

2. The method of claim 1 , wherein the calculation of the power delivered by the torque path from the turbine to the compressor system from the measured rotational speeds is based on determining an amount of shaft system twist in the core shaft, and calculating the power delivered by the torque path from the amount of shaft twist in the core shaft.

3. The method of claim 1 , further including:

identifying periods of shaft system torsional vibration from the measured rotational speeds;

calculating torsional vibrational characteristics of the shaft system from the measured rotational speeds for the identified periods; and

identifying a possible unhealthy condition of the torque path when the calculated torsional vibrational characteristics depart from expected torsional vibrational characteristics of the shaft system.

4. The method of claim 1 , wherein the rotational speeds are measured by magnetic reluctance probe and phonic wheel sets and/or microwave sensors.

5. The method of claim 1 , wherein the other measured operational parameters of the engine include one or more operational pressures, and one or more operational temperatures.

6. The method of claim 1 , wherein the hazardous event is a failure in at least one of a shaft, the gearbox, a drive arm, an inter-stage drive arm, and a blade.

7. An in-flight health monitoring system of an aero gas turbine engine comprising in flow series a compressor system including a low pressure compressor and a fan upstream of the low pressure compressor, a core gas generator including a combustor, and a turbine, and further comprising a shaft system connecting the turbine to the compressor system and forming a torque path therebetween, the shaft system including a core shaft, a fan shaft and a gearbox, the core shaft receiving an input from the turbine and the gearbox receiving an input from the core shaft and outputting drive to the fan shaft so as to drive the fan shaft at a lower rotational speed than the core shaft, the fan shaft driving the fan, the control system comprising:

a first speed sensor configured to measure a first rotational speed of the fan shaft in a forward portion of the shaft system in front of the gearbox;

a second speed sensor configured to measure a second rotational speed of the core shaft in a rear portion of the shaft system adjacent to or at the turbine;

a third speed sensor configured to measure a third rotational speed of the core shaft in a portion of the shaft system adjacent to and behind the gearbox;

plural other sensors configured to measure other operational parameters of the engine, the operational parameters including at least one operational parameter associated with the core gas generator; and a processor configured to:

calculate a power delivered by the torque path from the turbine to the compressor system from the measured rotational speeds;

calculate a power delivered to the turbine by the core gas generator from the other measured operational parameters;

correlate the power delivered by the torque path at a given time with the power delivered to the turbine at that time;

calculate an amount of shaft twist in the shaft system across the gearbox from the first and third rotational speeds; and

identify distress of the torque path in-flight that could potentially lead to a hazardous event when the correlation departs from an expected correlation of the power delivered by the torque path with the power delivered to the turbine when the amount of shaft twist departs from an expected amount of shaft twist in the shaft system across the gearbox.

8. The system of claim 7 , wherein the calculation by the processor from the measured rotational speeds of the power delivered by the torque path from the turbine to the compressor system is based on an amount of shaft twist in the core shaft, and calculating the power delivered by the torque path from the angular deflection the amount of shaft twist in the core shaft.

9. The system of claim 7 , wherein the processor is further configured to:

identify periods of shaft system torsional vibration from the measured rotational speeds;

calculate torsional vibrational characteristics of the shaft system from the measured rotational speeds for the identified periods; and

identify a possible unhealthy condition of the torque path when the calculated torsional vibrational characteristics depart from expected torsional vibrational characteristics of the shaft system.

10. The system of claim 7 , wherein the speed sensors are magnetic reluctance probes and phonic wheel sets and/or microwave sensors.

11. The system of claim 7 , wherein the other measured operational parameters of the engine include one or more operational pressures, and one or more operational temperatures.

12. An aero gas turbine engine comprising in flow series a compressor system, a core gas generator including a combustor, and a turbine, and further comprising a shaft system connecting the turbine to the compressor system and forming a torque path therebetween, and the in-flight health monitoring system of claim 7 .

13. The aero gas turbine engine according to claim 12 , wherein the compressor system includes a low pressure compressor and a fan located upstream of the low pressure compressor, and the shaft system includes a core shaft and a gearbox, the core shaft receiving an input from the turbine and the gearbox receiving an input from the core shaft and outputting drive to the fan so as to drive the fan at a lower rotational speed than the core shaft.

14. The system of claim 7 , wherein the hazardous event is a failure in at least one of a shaft, the gearbox, a drive arm, an inter-stage drive arm, and a blade.