No abstract

No abstract

In this paper, we examine the control of a scramjet-powered hypersonic vehicle with significant aeroelastic-propulsion interactions. Such vehicles are characterized by open loop unstable non-minimum phase dynamics, low frequency aero-elastic modes, significant coupling, and hard constraints (e.g. control surface deflection limits, thrust margin). Within this paper, attention is placed on maintaining acceptable closed loop performance (i.e. tracking of speed and flight path angle commands) while satisfying hard control surface deflection constraints as well as stoichiometrically normalized fuel-equivalency-ratio (FER) margin constraints. Control surface constraints are a consequence of maximum permissible aerodynamic loading. FER margin constraints are a consequence of thermal choking (i.e. unity combustor exit Mach number) and the fact that thrust loss may not be captured for FER greater than unity. Such limits are particularly important since the vehicle is open loop unstable and "saturation" can result in instability. To address these issues, one can design conservative (i.e. less aggressive or lower bandwidth) controllers that maintain operation below saturation levels for anticipated reference commands (and disturbances). Doing so, however, unnecessarily sacrifices performance -particularly when small reference commands are issued. Within this paper, the above issues are addressed using generalized predictive control (GPC). A 3DOF longitudinal model for a generic hypersonic vehicle, which includes aero-elastic-propulsion interactions, is used to illustrate the ideas.

This paper describes the implementation and evaluation of a trajectory prediction function. This function is a critical component of tactical flight management, a new concept that can increase the resiliency and robustness of trajectory based operations through a paradigm shift that improves Flight Management System (FMS) compatibility with tactical operations. The trajectory prediction function generates and continually updates the fourdimensional flight path that will be flown by the FMS. This motion-based trajectory represents an extension of the aircraft's current state, and incorporates control laws, mode transition logic, and drag estimation as part of the prediction. The predicted trajectory is then displayed on navigation and vertical situation displays in an effort to reduce mode confusion occurrences and increase situational awareness of what the automation is doing now and what it will do in the future. These display features were evaluated in the Advanced Concepts Flight Simulator at NASA Ames Research Center to investigate the impact on flight crew energy state awareness when operating in the highly constrained and dynamic environment of the Next Generation Air Transportation System. Commercial airline crews flew multiple optimized profile descents under two conditions. In one condition, crews were presented with standard navigation displays, including a Vertical Situation Display (VSD). In the second condition, trajectory predictions were added to both the lateral map display and the VSD. Results show that predictive trajectory displays have the potential to improve situational awareness of the future automation mode and energy state of the aircraft, and that prediction accuracy and computational times are sufficient to support more advanced use in tactical flight management.