Measurement of twist deflection in active twist rotor

Abstract

Since the early days of rotary wing aircrafts the unsteady flow conditions in the rotor disk and unbalanced masses are causing intense vibratory loads and noise. Even modern helicopters still suffer from these drawbacks. This diminishes the ride quality as well as the public acceptance of rotary wing aircrafts. Further on the vibrations present a physical load for the pilot which reduces his concentration and can therefore not be neglected. Hence in the past there were numerous attempts to overcome these drawbacks. One of the most promising approaches evolved from a secondary control of the swash plate to an additional pitch angle of individual rotor blades applied at the blade root and further on to the control of the individual deformation of blades. The last step in this evolution became an option when smart materials like piezoceramics were used as actuators in the passive structure of traditional rotor blades. Since the actuators and their field of application are quite new, their capability to perform under strong centrifugal loads has to be proven. Within this work one concept for the active deformation of rotor blades will be presented. The evaluation of active twist blades under centrifugal loads is quite a challenge. Ether the data has to be acquired in the rotating frame and transmitted outside or the data has to be captured from outside, which demands a great deal of the sensors due to the high speed of the rotation. This investigation focuses on the design and evaluation of different measuring concepts to deliver reliable data of the blade actuation in the rotating system under full centrifugal loads. Most interesting is the determination of the blade tip twist angle.