Chris, Danny, Parul, and Raghu arrived at the UMore Park Airfield around 9am for the seventh, eighth, and ninth flights of Baldr. Baldr is the UAV LabÕs newest UltraStick 120 airframe that will be used for aircraft reliability research. Baldr is a modified UltraStick 120 airframe that has split elevators and split rudders, each surface driven by a dedicated servo motor. Recently, efforts have been underway at the University of Minnesota to design fault tolerant control laws for UAVs. Specifically, researchers have been focusing on attempting to control Baldr using only the split elevators, with all other control surfaces locked into their respective trim positions. The key idea in this experiment is controlling a conventional aircraft with two coplanar control surfaces. There are two main motivations that drove this experiment: 1. Exploring the controllability of conventional aircraft (with an empennage) that have been severely handicapped with losses in multiple aerodynamic control channels, and 2. Drawing meaningful conclusions about the controllability of two-surface flying wing aircraft which are subject to faults in any one of the two aerodynamic control surfaces. For this experiment, the performance objectives were tracking phi and theta commands. Hence, only phi and theta tracking control loops were synthesized and implemented. It is important to note that each of the split elevators induce both longitudinal and lateral-directional motion in the aircraft. As a consequence, researchers were specifically interested in synthesizing multi-input, multi-output control laws (as opposed to the conventional loop-at-a-time designs). For this experiment, researchers synthesized an H-infinity controller, with the primary performance objective being output regulation. A secondary performance objective was tracking phi and theta commands. The H-infinity controller was designed in Simulink and subsequently autocoded using Simulink coder. In addition, updated input trim settings for all the control surfaces (estimated from Baldr flights 1, 2, and 3) were used in this flight. This experiment used ONLY the left elevator of Baldr to regulate outputs around trim and track phi and theta.
Baldr Flight 7.
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