Yoshimasa Ochi

Design of restructurable flight control systems using feedback linearization

In this paper, a design method is presented for restructurable flight control systems based on the feedback linearization method. Failures are identified indirectly by estimating parameters of the nonlinear aircraft model using the recursive least square algorithm. The aircraft is assumed to have many control surfaces that can be driven independently. In the design, actuator dynamics are taken into account and the Control distributor, which reduces real inputs to generic inputs, is used. The imaginary actuators for generic inputs are introduced to generate input signals used in parameter identification. Pitch and roll angles are controlled indirectly by controlling pitch and roll rates, respectively, which is an approximate way but makes the control system simpler than applying the feedback linearization method straight to the control of the angles. To evaluate the performance of the restructurable flight control system, two failure cases are simulated on the six-degree-of-freedom nonlinear aircraft model.

APPLICATION OF FEEDBACK LINEARIZATION METHOD IN A DIGITAL RESTRUCTURABLE FLIGHT CONTROL SYSTEM

The feedback I inearization method is appl ied to odation of aircraft failures occuring at the control effectors or the airframe. The failures are identified as parameter changes in the six-degree-offreedom nonlinear equations of motion by the recursive least square algorithm. The control parameters are updated using the latest estimated system parameters. In order to allow one to use digital computer in implementation, a discrete time servo controller is designed for the surface actuators and the engine, where the reference inputs are given by the continuous time control law. The performance of the RFCS is demonstrated through computer simulation using the nonlinear model of an aircraft which has half o f the right wing broken off.

Modeling of Aerodynamic Uncertainties and Introduction of Dynamic Pressure Compensation to Robust Flight Control Systems.

This paper first describes a modeling method for the uncertainty of aerodynamic coefficients in a linear state-space aircraft model. Second, a design method of robust flight control systems based on the model is also presented. The proposed method is applied to the structure of the uncertainty for the μ-analysis and has the following characteristics: 1) the variations of the altitude and the velocity are explicitly treated as real repeated scalar perturbations since all dimensional derivatives are the function of the altitude and the velocity, and as a result 2) a gain-scheduled controller using the dynamic pressure compensation which satisfies the robust performance for a comparatively wider flight envelope can be designed. Simulation study is carried out to indicate that the proposed method is less conservative and satisfies the robust performance for a wider flight envelope than those of the H∞ design and the μ-synthesis where all aerodynamic coefficients are assumed to be individually perturbed.