Powering wireless sensors for rotorcraft HUMS

Wireless sensors have been widely suggested as a technology to extend the capability of Health and Usage Monitoring Systems (HUMS) on rotorcraft. Free from the constraints of hard wiring, wireless systems not only appear to offer a cost-effective solution, but in cases of instrumenting rotating or hard to reach parts, sometimes the only solution. Wireless data connections can be implemented using a range of mature technologies, however to be a truly wireless system, power cabling must be also be eliminated. This requires either local energy storage in a battery, energy harvesting (where power is generated from the ambient conditions of the sensor node), or a form of wireless power transfer. Of these solutions, only batteries can be considered mature. In this paper the power requirements of a wireless HUMS sensor node, designed to be mounted directly on the rotor head, are described and the possible power solutions considered. The very best energy-dense batteries currently available could power this node for many 100's of flight hours (for a reasonable battery volume) but it is unlikely these chemistries would be acceptable in the high stress rotating environment; battery technologies that are proven for high g environments would power this node for just a few 10's of flight hours. A vibration-powered generator is described which can produce up to 50mW average power during flight, potentially providing the 1000+ flight hours desirable for whole lifetime monitoring of rotor head parts.