System identification of longitudinal channel of unmanned helicopter using conditional spectrum analysis

Longitudinal channel dynamic equations of the experimental unmanned helicopter, Raptor-90, was established in hovering flight. The relationship between the power spectrum density and the system transfer function was described, and the way to derive formulas used to identify parameters of the single-input single-output, double-input single-output and three-input single-output linear time-invariant system using the conditional spectrum analysis method was introduced. Using these formulas, we get the longitudinal channel dynamic model of the Raptor-90. The fitting results show that this model has high forecast accuracy, reflects the relationship between the inputs and the state variables. It provides a reference for the control system design.