Helicopter flight dynamics using linear and nonlinear analyses

This paper compares measures derived from linear power spectral analysis and nonlinear chaotic analysis of helicopter vibratory data obtained during different flight tests. In particular, the strange attractor behavior of the trajectory of reconstructed state vectors in phase space was examined and quantified using the correlation dimension, which provides a fractal dimension measure in regards to the number of active degrees of freedom of helicopter vibration. We have examined the helicopter vibratory data collected from a well tuned four-blade servo-flap rotor system conducting hover, low-speed, and cruising-speed forward flights. In this paper, we examined servo-flap mid-span bending and rotor blade flat-wise bending. The results have shown that during helicopter hover, vibratory data of servo-flap bending and rotor flat-wise bending are more random than chaotic. On the other hand, the complexity (fractal dimension) of vibratory data increase when the helicopter switched from the minimum forward speed flight to cruising-speed forward flight.