Recovery of desired flying characteristics with an l₁ adaptive control law: Flight test results on calspan’s vss learjet

This paper presents flight test results from a flying and handling qualities assessment of a stability augmentationf flight control law for Calspan’s variable-stability Learjet aircraft. The control law comprised a baseline stability augmentation system (SAS) designed to provide level 1 flying qualities, as defined in MIL-HDBK-1797A, and an L₁ adaptive control law. Details regarding the design of the baseline SAS and the L₁ flight control law are presented in the companion paper titled “A Flying and Handling Qualities Evaluation of an L₁ Adaptive Control Law on Calspan’s Variable-Stability Learjet.” The apparent dynamics of the Learjet were modified in flight using the aircraft’s variable stability system, allowing the validation of the L₁ flight control law against several off-nominal aircraft configurations, some of which had severe flying qualities deficiencies and aggressive tendencies toward adverse pilot-aircraft interaction. All off-nominal configurations were opaque to the control law, and no fault detection and isolation methods were employed. The flight test results demonstrate that the L₁ augmentation was able to significantly restore the dynamic characteristics of the desired baseline Learjet model, and provide consistent and safe handling qualities across all configurations. This flight test was conducted by the U.S. Air Force Test Pilot School at Edwards Air Force Base, CA, and builds on prior fight testing of L₁ adaptive control on Calspan’s Learjet.