Anthony B. Page

Nonlinear adaptive and sliding mode flight path control of F/A-18 model

The question of inertial trajectory control of aircraft in the three-dimensional space is discussed. It is assumed that the nonlinear aircraft model has uncertain aerodynamic derivatives. The control system is decomposed into a variable structure outer loop and an adaptive inner loop. The outer-loop feedback control system accomplishes (x,y,z) position trajectory and sideslip angle control using the derivative of thrust and three angular velocity components (p,q,r) as virtual control inputs. Then an adaptive inner feedback loop is designed, which produces the desired angular rotations of aircraft using aileron, elevator, and rudder control surfaces to complete the maneuver. Simplification in the inner-loop design is obtained based on a two-time scale (singular perturbation) design approach by ignoring the derivative of the virtual angular velocity vector, which is a function of slow variables. These results are applied to a simplified F/A-18 model. Simulation results are presented which show that in the closed-loop system asymptotic trajectory control is accomplished in spite of uncertainties in the model at different flight conditions.

Effects of Control Allocation Algorithms on a Nonlinear Adaptive Design

Abstract : The effect of the choice of control allocation algorithm used in conjunction with a nonlinear adaptive control law is examined. In particular, an existing back stepping control law design is modified to allow the incorporation of various control allocation algorithms. Simulation results are presented for two separate adaptive control law designs and for a nonadaptive two-loop dynamic inversion controller. With the control law designs fixed, tracking maneuvers are simulated using four separate control allocation routines - Direct Allocation, Discrete Time Direct Allocation, Pseudo-inverse, and Weighted Pseudo-Inverse. System performance is then examined as a function of control allocation method. As expected, even though the remainder of the control law design remains fixed, system performance is directly impacted by the choice of control allocation algorithm. Further, some of the important control law/control allocation interactions are identified and their effects on overall system performance analyzed.

Nonlinear adaptive flight control with a backstepping design approach

Abstract : This paper examines the use of adaptive backstepping for multi-axis control of a high performance aircraft. The control law is demonstrated on a 6 Degree-of-Freedom simulation with nonlinear aerodynamic and engine models, actuator models with saturation, and turbulence. Simulation results are demonstrated for large pitch-roll maneuvers, and for maneuvers with failure of the right stabilator. There are substantial differences between the control law design and simulation models, which are used to demonstrate some robustness aspects of this control law. Actuator saturation is shown to be a considerable problem for this type of controller. However, the flexibility of the backstepping design provides opportunities for improvement. In particular, the Lyapunov function is modified so that the growth of integrated error and the rate of change of parameter growth are both reduced when the surface commands are growing at a rate that will likely saturate the actuators. In addition, the deadzone technique from robust linear adaptive control is applied to improve robustness to turbulence.

HIGH-FIDELITY SIMULATION TESTING OF CONTROL ALLOCATION METHODS

This paper describes high-fidelity simulation testing of some of the more popular advanced control allocation techniques integrated with two separate dynamic inversion control laws. The allocation methods include variations of quadratic programming, linear programming, direct allocation, cascaded generalized inverse, and weighted pseudo-inverse. Results are presented for single and multi-axis pitch and roll maneuvers with and without actuator failures. A velocity vector roll is also considered for the no failure case. Results show that a robust control law can mask differences in the various control allocation routines and lead to similar performance from both optimal and sub-optimal allocation methods. Furthermore, the current results illustrate that the closed-loop performance does not directly follow from the openloop measures that are widely used in the literature.

High-fidelity simulation testing of intelligent and adaptive aircraft control laws

This paper compares the robustness of seven popular adaptive and intelligent control approaches using a high fidelity aircraft simulation. The control laws were originally developed and tuned using a lower fidelity simulation of the same aircraft, which is significantly different from the high fidelity simulation used to generate all results in, this paper. The control law approaches examined are fuzzy logic, linearly and nonlinearly parameterized neural network approaches, an indirect adaptive version of dynamic inversion, variable structure, and a hybrid approach that combines direct and indirect adaptive elements. In addition, a conventional scheduled dynamic inversion controller is used as baseline. The approaches are demonstrated on a high fidelity six degree-of-freedom simulation with nonlinear aerodynamic and engine models, actuator models with position and rate saturations, and turbulence. Simulation results are given for single and multi-axis pitch and roll maneuvers in both nominal and failed cases.

A Comparison of Neural, Fuzzy, Evolutionary, and Adaptive Approaches for Carrier Landing

Abstract : This paper compares in simulation six control approaches for an automated carrier landing design problem. The key requirements of this problem are that the aircraft must remain within tight bounds on a three dimensional flight path while approaching the ship, and then touch down in a relatively small area with acceptable sink rate, angular attitudes and speed. Further, this must be accomplished with limited control authority for varying conditions of ship motion, air turbulence, radar tracking noise/data delays, and ship air wake. The control law approaches examined are: fuzzy logic, two neural network approaches, indirect adaptive and non-adaptive versions of dynamic inversion, and a hybrid approach that combines direct and indirect adaptive elements. In some of the cases, a genetic algorithm was used to optimize fixed parameters during design. The approaches were demonstrated on a 6 Degree-of-Freedom simulation with nonlinear aerodynamic and engine models, actuator models with position and rate saturations, and turbulence. Simulation results include statistics for landing with damage to both control and lifting surfaces in different environmental conditions.

Variable structure and nonlinear adaptive flight path control

Treats the question of inertial trajectory control of aircraft in the three-dimensional space. The control system is decomposed into a variable structure outer-loop and an adaptive inner-loop. The outer-loop feedback control system accomplishes (x, y, z) position trajectory and sideslip angle control using the derivative of thrust and three angular velocity components (p, q, r) as virtual control inputs. Then an adaptive inner feedback loop is designed, which produces the desired angular rotations of aircraft using aileron, elevator, and rudder control surfaces to complete the maneuver. These results are applied to a simplified FA-18 model. Simulation results are presented which show that in the closed-loop system asymptotic trajectory control is accomplished in spite of uncertainties in the model at different flight conditions.