Power harvesting using piezoelectric materials: applications in helicopter rotors

The blades of helicopters are heavily loaded and are critical components. Failure of any one blade will lead to loss of the aircraft. Currently, the technical lifespan of helicopter blades is calculated using a worst-case operation scenario. The consequence is that a blade that may be suitable for, for example, ten thousand flight hours is discarded after only three thousand hours. The costs associated with this practice are enormous. For heavily loaded military aircraft this practice may be a reasonable approach. On the other hand, light duty aircraft in civil aviation may only use the blades for half or one third of the total technical lifespan, incurring unnecessarily high costs. Although the blade life could be extended through more advanced materials, extensive inspection regimes and better design, the uncertainty concerning the blade loads and fatigue issues remains. These options are all very costly. Measuring systems are required within the blade in order to more accurately follow the actual loads that it is subjected to. In this manner it is possible to monitor the loads, calculate the actual fatigue within the blade and, finally, the end of life can be predicted far more accurately. This will result in blades being used longer, reducing maintenance costs for the operator and lowering the environmental impact of blade manufacturing. The main challenge is supplying the sensors with electric power. Large rotorcraft have slip rings within the rotor head, supplying power for de-icing systems on the leading edge of the blade. This power is unsuitable for sensing and data processing because it is high voltage, and is not a stable source of power. Additionally, slip rings are maintenance intensive. The idea proposed in this thesis is to generate the power needed for sensing within the blade itself. Many generation methods are available varying from traditional electromagnetic generators to solid state conversion mechanisms. In this work, piezoelectrics are considered as a candidate to harvest power. Piezoelectric material is a material which develops an electrical charge as it is mechanically stressed. It is shown in this thesis that a useful amount of power can be recovered from the blade when combined with the right electric circuit