Damage Detection Testing on a Helicopter Flexbeam

The main and tail rotor systems of a helicopter must be maintained in a damage-free condition to ensure the safety of the helicopter. The components of the rotor system require regular maintenance and inspection, and some of the components are difficult to inspect. Accordingly, an integrated sensor system that continuously monitors the structural integrity of the rotor system is needed to assure the safety of flight and reduce the cost of maintenance of the rotor system. This smart monitoring system could also provide immediate information on the dynamic loading in the rotor system. This information could define the performance limit of the helicopter based on the condition of the rotor system. The operator will then be able to adjust the flight condition and prevent damage from occurring or propagating. The challenges in designing this monitoring system are related to the operating conditions of the helicopter. These include significant aerodynamic and external damping in bending and torsion modes, moderate nonlinearities in the system, large dynamic loads, and difficulty in actuating pure interrogation signals in the airborne condition. In this paper, piezoceramic sensors and actuators and different techniques for damage detection that use symmetry properties of the structure and no structural model are tested in a static condition for health monitoring of a helicopter flexbeam. Testing under dynamic loading is needed as the next step in the development of the smart sensor system.