Monitoring the Dynamics of an Operating Helicopter Rotor using 3D Digital Stereophotogrammetry

In this paper, stereophotogrammetry is investigated as an alternative to conventional sensors for measuring the vibration of a rotating helicopter rotor. Dynamic point tracking is used to measure displacements at numerous points distributed along a 10.1-meter diameter rotor blade of a Robinson R44 helicopter. A pair of high speed cameras was installed on a long camera bar that was calibrated by using an array of coded targets placed on the ground. The displacement of 22 optical targets mounted to the blades was measured while the helicopter rotor was spinning with the helicopter on the ground and hovering. Operational modal analysis of the measured data was performed revealing the dominant contribution of the structural modes to the operating deflection shapes. The helicopter rotor motion was dominated by harmonics of the blade passage frequency, however some non-harmonic operating deflection shapes were also observed. This paper provides a description of the experiment performed along with lessons learned while performing the test. This study reveals that stereophotogrammetry has significant potential as a robust non-contacting measurement technique for monitoring dynamic behavior of rotating helicopter rotors or wind turbine blades.