How do you power a sensor system that rotates with the propeller?

SHM Electronics Power Requirements and Management activities under TorPropel leads to a development of a monitoring system that operates while the propeller turns, tracking how the composite structure behaves in real operating conditions. Strain sensors embedded in the blades are interrogated by embedded electronics installed in the nose cone that send their readings wirelessly to the aircraft, so no cables have to cross from the spinning propeller to the stationary side. 

Nonetheless, these electronics still need electricity, and on an aircraft propeller, both weight and reliability are of critical importance. The data acquisition system has been optimised for minimising electric power requirements, with our current estimate for the whole monitoring package sitting at around 1.7 watts, roughly the same as a small LED bulb. The wireless link and the sensors themselves account for most of it, as shown on attached chart.

Even with this minimal power consumption, it must be considered that a battery small and light enough to fit inside the nose cone will only run for a few hours before it needs recharging. Add to that the challenge of fitting the electronics into a compact compartment that has to stay balanced, cope with constant vibration and remain easy to reach for maintenance, and a simple question becomes an interesting engineering problem. This is where the rotation stops being an obstacle and starts being an opportunity. 

We are exploring small energy harvesting devices that capture a fraction of the propeller's own motion and turn it into electricity, topping up the battery as the aircraft flies. In effect, the propeller would help power the system that validates its safe operation. 

Self-powered monitoring is a step towards aircraft that can flag maintenance needs before problems appear, and towards sensing systems that fly with the aircraft rather than staying in the laboratory.