Model Following Control Allocation For The X-62A

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The United States Air Force Test Pilot School (USAF TPS) operates a uniquely modified F-16 for research and development of the world’s most advanced flight control systems. This aircraft is known as the Variable In-Flight Simulator Test Aircraft or VISTA. In the summer of 2021, VISTA was redesignated from an NF-16D to the X-62A to highlight its unique capabilities to perform advanced experimental flight tests and flight simulation of other aircraft. VISTA is able to achieve these flight tests through a simulation through a technique called Model Following. As part of a upgrade of the VISTA aircraft, known as GEN2020, Lockheed Martin’s Skunk Works® developed new capabilities of the Model Following Algorithm (MFA) that has provided for the ability to drive VISTA X-62A to simulate the dynamics of another aircraft through the control augmentation process of Non-Linear Dynamic Inversion. A critical centerpiece to the MFA is the Control Allocator. The MFA Control Allocator is designed to determine the control surface vector solution that allows VISTA to accurately yield any set of desired accelerations within VISTA’s attainable moment set. A critical performance requirement of the MFA is to enable VISTA to simulate the flight dynamics of any other air vehicle in 5 degrees of freedom across VISTA’s flight envelope. Such a challenge poses a demand to develop a robust architecture that enables VISTA to allocate both its aerodynamic and propulsive controls such that it maximizes VISTA’s attainable moment set. In order to meet such requirements, the Control Allocator architecture employs a cascading generalized inverse method similar to the “effector blender” method. The cascading generalized inverse control allocation architecture is designed to carefully consider the global and rate limitations of each of VISTA’s control effectors (aerodynamic and propulsive) to effectively redistribute available control effectors in the presence of a saturated control surface. A comprehensive frequency domain analysis procedure, otherwise know as 1/s analysis, was used to evaluate and maximize VISTA’s ability to meet its wide range of model following mission requirements.