Gas turbine engine drive system health monitor

1. A drive system of a gas turbine engine, the drive system comprising:

a first drive shaft and a second drive shaft operable to rotate within the gas turbine engine;

a first sensor operable to detect rotation of the first drive shaft;

a second sensor operable to detect rotation of the second drive shaft;

a drive gear system coupled to the first drive shaft and the second drive shaft; and

a processing system coupled to the first sensor and the second sensor, the processing system operable to:

determine a timing variation based on output of the first sensor and output of the second sensor;

determine a torsional deflection between the first drive shaft and the second drive shaft based on the timing variation; and

detect a health status of the drive system based on the torsional deflection, wherein the health status identifies whether a fault condition of the drive gear system is detected based on the torsional deflection.

2. The drive system of claim 1 , wherein the processing system is operable to track the timing variation between a first position indicator associated with the first drive shaft and a second position indicator associated with the second drive shaft.

3. The drive system of claim 1 , wherein the processing system is operable to perform a frequency domain analysis based on output of the second sensor and identify a dominant mode as a shaft frequency of the second drive shaft and a lower amplitude frequency domain component as a torsional mode of the second drive shaft.

4. The drive system of claim 3 , wherein the shaft frequency is used to identify an operating mode of the gas turbine engine, and trending of the torsional mode is determined based on the operating mode of the gas turbine engine.

5. The drive system of claim 1 , wherein the processing system is operable to perform a frequency domain analysis based on output of the first sensor.

6. The drive system of claim 5 , wherein the processing system is operable to identify a dominant mode as a shaft frequency of the first drive shaft and a lower amplitude frequency domain component as a torsional mode of the first drive shaft.

7. The drive system of claim 6 , wherein the shaft frequency is used to identify an operating mode of the gas turbine engine, and trending of the torsional mode is determined based on the operating mode of the gas turbine engine.

8. A gas turbine engine comprising:

a drive system comprising:

a first drive shaft operable to drive a fan of the gas turbine engine; and

a second drive shaft operable to be driven by a turbine of the gas turbine engine;

a first sensor operable to detect rotation of the first drive shaft;

a second sensor operable to detect rotation of the second drive shaft; and

a processing system coupled to the first and second sensors, the processing system operable to:

identify an operating mode of the gas turbine engine, wherein a shaft frequency is used to identify the operating mode of the gas turbine engine;

determine a trend of a torsional mode of the drive system based on the operating mode of the gas turbine engine; and

detect a health status of the gas turbine engine based on the torsional mode.

9. The gas turbine engine of claim 8 , wherein the processing system is operable to perform a frequency domain analysis based on output of the first sensor and identify a dominant mode as the shaft frequency of the first drive shaft and a lower amplitude frequency domain component as a torsional mode of the first drive shaft.

10. The gas turbine engine of claim 8 , wherein the processing system is operable to perform a frequency domain analysis based on output of the second sensor and identify a dominant mode as the shaft frequency of the second drive shaft and a lower amplitude frequency domain component as a torsional mode of the second drive shaft.

11. The gas turbine engine of claim 8 , wherein a drive gear system is coupled between the first drive shaft and the second drive shaft, and the health status identifies whether a fault condition of the drive gear system is detected.

12. A method of monitoring a drive system in a gas turbine engine, the method comprising:

detecting rotation of a first drive shaft via a first sensor operably coupled to a processing system;

detecting rotation of a second drive shaft via a second sensor operably coupled to the processing system;

identifying an operating mode of the gas turbine engine, wherein a shaft frequency is used to identify the operating mode of the gas turbine engine;

determining, by the processing system, a trend of a torsional mode of the drive system based on the operating mode of the gas turbine engine; and

detecting a health status of the drive system based on the torsional mode.

13. The method of claim 12 , further comprising:

performing a frequency domain analysis based on output of the second sensor and identify a dominant mode as the shaft frequency of the second drive shaft and a lower amplitude frequency domain component as a torsional mode of the second drive shaft.

14. The method of claim 12 , wherein a timing variation is tracked based on a first position indicator associated with the first drive shaft and a second position indicator associated with the second drive shaft.

15. The method of claim 12 , wherein a drive gear system is coupled between the first drive shaft and the second drive shaft, and the health status identifies whether a fault condition of the drive gear system is detected.

16. The method of claim 12 , further comprising:

performing, by the processing system, a frequency domain analysis based on output of the first sensor.

17. The method of claim 16 , further comprising:

identifying a dominant mode as the shaft frequency and a lower amplitude frequency domain component as a torsional mode of the first drive shaft, wherein the shaft frequency is used to identify the operating mode of the gas turbine engine.