Trim State Discovery for an Adaptive Flight Planner

Automatic trajectory planners require knowledge of an aircraft’s flight envelope to ensure their solution is feasible. Existing flight management systems presume a nominal performance envelope, requiring online identification or characterization of any performance degradation. Given predictable failures such as a control surface jam, we can evaluate stability and controllability offline to establish a stablilizable trim state database that can be used in real-time to plan a feasible landing trajectory. In less-predictable cases, such as structural damage, performance can only be determined online. Given capable system identification and adaptive control capabilities, post-failure stability is achieved, and the attraction region can be safely explored in the neighborhood around the identified trim state. We propose a novel trim state discovery (TSD) strategy to automatically explore the operating envelope of an aircraft with appreciable but unknown damage or failures. We presume a system identification process identifies regions of attraction guaranteed locally, and that further damage or uncontrollable descent can result from excursion outside these regions. With the goal of identifying a sufficient flight envelope for landing, output from the TSD process feeds into an adaptive flight planner (AFP) that constructs safe landing flight plans as sequences of feasible trim states. We adopt a modified artificial potential field method to traverse the flight envelope space rather than physical space, incorporating envelope constraints as “obstacles” and desirable approach trim states as “attractors”. An F-16 aileron jam scenario is presented to illustrate the utility of TSD for damage-resilient flight planning and guidance.