Design of Flight Control Laws for Agile and Highly Swept Aircraft Configurations

Abstract

In the course of the FaUSST project scope, a versatile and flexible method for the synthesis of flight control laws (FCL) for agile and highly swept aircraft configurations was required in preparation for upcoming closed-loop assessments of these configurations within the succeeding MEPHISTO project. Therefore methods and tools were required to allow for the integration within the commonly applied, distributed workflow-driven integration environment tool RCE, project specific interfaces and defined aircraft datasets (such as aircraft geometry, aerodynamics, mass and propulsion) together with control synthesis parameters (tuners) as defined within the “Common Parametric Aircraft Configuration Scheme” (CPACS). The resulting control law design philosophy is characterized by the use of model based control strategies – namely the Nonlinear Dynamic Inversion (NDI) method for the inner control loops. This allows the respective outer control loops to be set up as a linear controller structure, as the non-linear control path (the actual aircraft) can be treated as a continuously linearized system – widely independent from the actual aircraft configuration. In addition to this behavior, the described approach allows the partial use of existent methods and tools, currently in use for the generation of open-loop 3-DOF and 6-DOF flight dynamics models – based on the Modelica physical equation language for the actual implementation of the flight dynamics model equations. Thus the respective inner control loops can be automatically derived (auto-coded) by the inversion of the overall model equation system. The outer control loop can then be optimized for a multitude of target functions and tuners as requested by closed-loop flight dynamics assessment capabilities within the project scope. This is achieved by using the DLR-SR optimization tool MOPS (Multi-Objective Parameter Synthesis) being controlled by externally applied control synthesis parameters within CPACS. In the context of the FaUSST project, a “Proof-of-Concept” setup – regarding the described inner/outer control law structure and methods – has been implemented. Ongoing tasks within the MEPHISTO project scope are the further investigation, overall automation and enhancement of the used methods and derived control laws in conjunction with the respective assessment applications.