GB2167865A

GB2167865A - Methods of calibrating helicopter power train torque monitoring systems

Info

Publication number: GB2167865A
Application number: GB08430506A
Authority: GB
Inventors: Alastair Cameron Gordon
Original assignee: Bristow Helicopters Ltd
Current assignee: Bristow Helicopters Ltd
Priority date: 1984-12-04
Filing date: 1984-12-04
Publication date: 1986-06-04
Also published as: GB8430506D0

Abstract

In a method of calibrating a torque monitoring system for a helicopter power gear train in which transmitted torque is monitored by means of strain gauges 11 on the shaft(s) 10 to respond to the torque in the shaft(s) and connected to transmitting devices 18 on the shaft(s) to transmit a signal to receiving means 16 encircling shaft(s), The receiving means 16 is connected to a torque display instrument. In order to calibrate the system, a pre-calibrated shaft is installed in the helicopter power train in place of the standard shaft and subjected to a torque to enable the display instrument to be calibrated. The standard shaft is then reinstalled in the power train and its torque monitored utilising the nearly calibrated monitoring system. <IMAGE>

Description

SPECIFICATION A method of calibrating helicopter power train torque monitoring systems This invention relates to methods of calibrating helicopter power train torque monitoring systems.

The invention provides a method of calibrating a helicopter power train torque monitoring system comprising the steps of incorporating a calibration shaft in the helicopter power train, the calibration shaft being provided with means responsive to application of torque to the shaft whilst rotating in the power train and means to transmit a corresponding signal determined by the torque being transmitted, receiving the signal and using it to give an indication of the torque being transmitted by the calibration shaft and calibrating the torque monitoring system of the helicopter in accordance with that indication.

The calibration shaft may be provided with strain gauges which are used to indicate the torque to which the shaft is subjected.

Preferably telemetry means are used to transmit the signal from the calibration shaft to the receiving means indicating the torque to which the shaft is subjected.

It is also preferred the calibration shaft is substituted for a shaft in the helicopter power train to perform the calibration operation.

In the case where the helicopter has twin engines and a power train from the engines to the rotor including a combining shaft for combining the output of the two engines to provide a single output to the rotor, the combining shaft may be replaced by the calibrating shaft for the calibration operation.

The invention also provides a calibration shaft for calibrating a helicoptor power train monitoring system comprising a shaft to be incorporated in the helicopter power train, the shaft having strain measurement means for responding to torque transmitted by the shaft and telemetry means for responding to torque transmitted by the shaft and telemetry means for transmitting a signal from the strain gauge means to a non-rotating receiving means, the receiving means being connected to the torque indicating means to display the torque to which the shaft is subjected.

The following is a description of a specific embodiment of the invention, reference being made to the accompanying drawing which shows two calibration shafts for use in helicopter power trains.

A conventional helicopter with a single or twin engines normally has a torque monitoring system and a torque indicator dial is usually included in the pilot's instrument panel to supply an instantaneous reading of the torque currently being transmitted by the power train for the helicopter. This information is required by the pilot so that he may control the power supply to the engine to avoid un-necessarily straining the power train. Indeed, in some helicopters automatic controls are provided for restricting or cutting off the fuel supply to the engine if an excessive torque is applied to the power train by the helicopter engine or engines.It is therefore extremely important that the instantaneouq value of the torque transmitted by the power train is accurately assessed since the engine power could be reduced automatically following an indication that the power train has been over torqued in an emergency situation and could cause the helicopter to crash.

Output torque in the power train from the engine or engines of the helicopter is usually determined by using oil pressure developed in the gear box for the or each engine as an indication of the torque being transmitted by the gearbox and providing a pressure responsive device to measure that pressure and to actuate the display instrument for the pilot.

Such devices have to be calibrated on installation of the engine and although experience shows that the datum drifts substantially within use, it is extremely difficult to re-calibrate the display instrument.

In accordance with the present invention, a calibration shaft 10 is provided for installation in the helicopter power train at an appropriate location. In the case where the helicopter has twin engines, the combining shaft for the two engines can readily be substituted for by the combining shaft.

The calibration shaft is provided with a number of sets of strain guages 11 bonded to the surface of the shaft at locations spaced around the circumference of the shaft to respond to twisting of the shaft when the latter is subjected to torque. The strain guages 11 have connecting leads indicated at 12 which connect the gauges to printed circuits 13, bonded around the shaft. Power supply packs are contained within a two part housing 15 clamped around the shaft to supply a suitable current to the strain gauges and the associated circuitry. A telemetry system for receiving signals from the strain gauges is indicated generally at 15 and comprises an annular ring 16 mounted on a stationary housing 17. The ring encircles a ring 18 mounted on the calibration shaft and carrying transmitting means for transmitting signals derived from the strain gauges to receiving means on the ring 16.

Circuitry is provided for interpolating the signal and a display instrument is provided for indicating the current torque being transmitted by the shaft. The calibration shaft is pre-calibrated in accordance with a known torque and the arrangement provides an accurate indication of the current torque being transmitted by the shaft. That information can be used to calibrate the display instrument for the conventional monitoring system of the helicopter as described above to compensate for a drift in reading since the system was installed.

Since the calibration shaft can be readily mounted in the helicopter power train without any significant amount of stripping down, the arrangement does provide a simple and convenient method for re-calibrating the helicopter torque monitoring system from time to time throughout the life of the helicopter.

Claims

1. A method of calibrating a helicopter power train torque monitoring system comprising the steps of incorporating a calibration shaft in the helicopter power train, the calibration shaft being provided with means responsive to application of torque to the shaft whilst rotating in the power train and means to transmit a corresponding signal determined by the torque being transmitted, receiving the signal and using it to give an indication of the torque being transmitted by the calibration shaft and calibrating the torque monitoring system of the helicopter in accordance with that indication.

2. A method as claimed in claim 1 wherein the calibration shaft is provided with strain gauges which are used to indicate the torque to which the shaft is subjected.

3. A method as claimed in claim 1 or claim 2 wherein telemetry means are used to transmit the signal from the calibration shaft to the receiving means indicating the torque to which the shaft is subjected.

4. A method as claimed in claim 3 wherein the calibration shaft is substituted for a shaft in the helicopter power train to perform the calibration operation.

5. A method as claimed in claim 4 and in the case where the helicopter has twin engines and a power train from the engines to the rotor including a combining shaft for combining the output of the two engines to provide a single output to the rotor wherein the combining shaft is replaced by the calibrating shaft for the calibration operation.

6. A calibration equipment for calibrating a helicopter power train monitoring system comprising a shaft to be incorporated in the heli copter power train, the shaft having strain measurement means for responding to torque transmitted by the shaft and telemetry means for transmitting a signal from the strain gauge means to a non-rotating receiving means, the receiving means being connected to the torque indicating means to display the torque to which the shaft is subjected.

7. A method of calibrating a helicopter power train torque measuring system substantially as described hereinbefore.

8. Calibration equipment for calibrating a helicopter power train monitoring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.