Patent ID: 8892366

Claim:
A method of measuring torque at a drive shaft of a helicopter drive having at least a main gear in a main gearbox and at least a tail gear in a tail gearbox, said drive shaft being arranged for transmitting torque between said main gear and the tail gear, said method comprising the following steps: providing at least first and second vibration sensors with said vibration sensors being respectively attached to each of said main gearbox and said tail gearbox, applying torque to said drive shaft, detecting main gearbox vibrations related to gear mesh vibrations resulting from interaction of said drive shaft with said main gear by the first vibration sensor attached to said main gearbox vibrating in response to the main gearbox vibrating, detecting tail gearbox vibrations related to gear mesh vibrations resulting from interaction of said drive shaft with said tail gear by the second vibration sensor attached to said tail gearbox vibrating in response to the tail gearbox vibrating, communicating the main gearbox vibrations detected by the first vibration sensor to an evaluation unit, communicating the tail gearbox vibrations detected by the second vibration sensor to the evaluation unit, acquiring data related to the main gearbox vibrations related to the gear mesh vibrations communicated from the first vibration sensor to the evaluation unit, acquiring data related the tail gearbox vibrations related to the gear mesh vibrations communicated from the second vibration sensor to the evaluation unit, bandpass filtering said acquired data for each of said first and second vibration sensors separately, extracting separate phase information from said data filtered separately for each of said first and second vibration sensors, detecting the phase difference from the separately extracted phase information from each of said first and second vibration sensors, computing the rotations per minute for the drive shaft from the extracted phase information from said data filtered separately for each of said first and second vibration sensors, and computing the torque applied to the drive shaft from the phase difference computed from the separately extracted phase information for each of said first and second vibration sensors.