Real-Time Adaptive Control Allocation applied to a High Performance Aircraft

This paper presents the development and application of one approach to the control of aircraft with large numbers of control effectors. This approach, referred to as real-time adaptive control allocation, combines a nonlinear method for control allocation with actuator failure detection and isolation. The control allocator maps moment (or angular acceleration) commands into physical control effector commands as functions of individual control effectiveness and availability. The actuator failure detection and isolation algorithm is a model-based approach that uses models of the actuators to predict actuator behavior and an adaptive decision threshold to achieve acceptable false alarm/missed detection rates. This integrated approach provides control reconfiguration when an aircraft is subjected to actuator failure, thereby improving maneuverability and survivability of the degraded aircraft. This method is demonstrated on a next generation military aircraft (Lockheed-Martin Innovative Control Effector) simulation that has been modified to include a novel nonlinear fluid flow control control effector based on passive porosity. Desktop and real-time piloted simulation results demonstrate the performance of this integrated adaptive control allocation approach. Introduction Future aircraft are being proposed with many more control effectors than the traditional elevator, aileron, and rudder. Innovative control effectors under study range from thrust vectoring to all-moving wing tips and actuated forebody surfaces to more exotic effectors such as shape-change materials and fluidflow devices (figure 1). For example, hundreds or even thousands of micro fluid-flow devices could be distributed in arrays across the upper and lower surface of a wing to allow direct control of the wing’s boundary layer. Optimal use of this large number of effectors will be challenging, but the potential control power and redundancy offers the flight controls designer freedom to maximize mission performance and enhance survivability. * Research Engineer † Senior Research Engineer No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. In particular, reconfigurable control approaches seek to take advantage of this control redundancy to mitigate the deleterious effects of control effector failure or battle damage [Buffington 1998, Brinker 1999, Tallant 1999]. A key element in these approaches is reconfigurable control allocation. The reconfigurable control allocator [Lallman 1985, Durham 1992, Buffington 1997, Enns 1998] maps moment (or angular acceleration) commands into physical control effector commands as a function of individual control effectiveness and availability. This paper presents the development of an integrated reconfigurable control allocation method which combines a nonlinear method for control allocation with actuator failure detection and isolation (FDI) (figure 2). This integrated approach provides control reconfiguration when an aircraft is subjected to actuator failure, thereby improving maneuverability and survivability of the degraded aircraft. Desktop and realtime piloted simulation are used to demonstrate the performance of this integrated adaptive control allocation approach. Real-Time Adaptive Control Allocation The adaptive control allocation is an integrated approach that combines two main elements: a nonlinear control allocation approach and actuator failure detection and isolation. These elements are discussed in more detail in the following sections. Control Allocation In general, the forces and moments generated by the control effectors are a function of vehicle flight condition and effector commands. In the case where, at a given flight condition, the control effectiveness is relatively linear with effector command and there is minimal control coupling, the system can be considered as a linear control allocation problem. The linear control allocation problem can be stated as follows. Given the system