Chaotic Behavior of Helicopter Servo-Flap Vibratory Data during Different Flight Conditions

This paper presents a preliminary study of the chaotic behavior of servo-flap mid-span bending of a four-blade helicopter during hover, low and high-speed forward flights. The servo-flap vibratory measurement was used to create state vectors in a multidimensional space through time-delay embedding, and the trajectory of state vectors in the reconstruction state space was quantified using the correlation dimension to provide a measure of the dimensionality or the number of active degrees of freedom of servo-flap bending. We found that, while the vibratory magnitude of servo-flap mid-span bending increases from hover to low-speed and high-speed flights, the estimated correlation dimension, however, decreases in dimensionality from 1.42 during hover to 1.3 at low-speed and 1.15 at high-speed flight. This observation is consistent with the waveform complexity of servo-flap bending measurements; it too sheds a light to better understand the control mechanism of servo-flap rotor through nonlinear dynamics.