Multiple-Function Digital Controller System for Active Flexible Wing Wind-Tunnel Model

A real-time multiple-function digital controller system was developed for the Active Flexible Wing program, which demonstrated through wind-tunnel tests that digital control can be used with great versatility to perform a multifunction task such as suppressing flutter and reducing loads during rolling maneuvers. The digital controller system (DCS) allowed simultaneous execution of two control laws: 1) flutter suppression and 2) either roll trim or a rolling maneuver load control. The DCS operated within, but independently of, a slower host operating system environment, at regulated speeds up to 200 Hz. It also coordinated the acquisition, storage, and transfer of data for near real-time controller performance evaluation and both open- and closed-loop plant estimation. It synchronized the operation of four different processing units, allowing flexibility in the number, form, functionality, and order of control laws, and variability in selection of sensors and actuators employed. Most importantly, the DCS enabled successful demonstration of active flutter suppression to conditions approximately 26% (in dynamic pressure) above the open-loop boundary in cases when the model was fixed-inroll, and up to 23% when it was free-to-roll. Aggressive roll maneuvers with load control were achieved above the flutter boundary. The purpose of this article is to present the development, validation, and wind-tunnel testing of this multiple-function digital controller system.