A Method for Compensation of Interactions Between Second-Order Actuators and Control Allocators

Typically, actuator dynamics are ignored when designing flight control allocators for aircraft because the bandwidths of actuators are normally much larger than the frequencies of the vehicle´s rigid body modes. Unfortunately, this in not always the case, particularly when dealing with non-aerodynamic surface actuators. Ignoring the interactions between constrained control allocators and actuator dynamics can have serious consequences. In this work, a method, which post-processes the output of a control allocation algorithm, is developed to compensate for actuator dynamics. The actuators can have dynamics which are either first-order, second-order with no zeros, or second-order with a single zero. The method developed here solves for a gain, which multiplies the commanded change in control effector setting as computed by the control allocator. This approach is not computationally intensive and thus has the added benefit of being an algorithm which can operate in real-time on a typical flight computer. Likewise, this approach is applicable to both the saturated and unsaturated control effector cases. The basic premise of this method is to post-process the output of the control allocation algorithm to overdrive the actuators so that at the end of a sampling interval, the actual actuator positions are equivalent to the desired actuator positions