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Fly-by-wire control laws for a business jet were developed and a handling qualities assessment flight test was conducted on the Calspan Variable Stability System Learjet-25. The control laws, which provide an nzu-command response type in the longitudinal axis and a p-β-command response type in the lateral/directional axes, were optimized to meet Level 1 requirements for a comprehensive set of stability, handling qualities, and performance specifications. The control laws were evaluated in flight by USAF Test Pilot School and Textron Aviation test pilots using a series of handling qualities demonstration maneuvers. These included pitch and roll capture and tracking tasks and an offset landing task. Quantitative performance metrics were collected, in addition to pilot handling qualities ratings and comments. Several modifications were made to the control laws based on initial pilot comments and ratings. The final results show that the optimized fly-by-wire control laws provided assigned Level 1 handling qualities for discrete tracking and offset landing tasks.

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This paper provides an overview of flight-test system identification methods applied in the Virginia Tech Nonlinear Systems Laboratory that focus on modeling small, inexpensive, fixed-wing aircraft controlled by a ground-based pilot. The general aircraft system identification approach is outlined with details provided on the flight-test facilities, experiment design methods, instrumentation systems, flight-test operations, data processing techniques, and model identification methods enabling small aircraft flight dynamics model development. Specific small aircraft system identification challenges are overcome, including low-cost control surface servo-actuators and instrumentation systems, as well as a greater sensitivity to atmospheric disturbances and limited piloting cues. Four recent system identification research advancements using the general system identification process are featured, including application of uncorrelated pilot inputs for remotely piloted aircraft, aero-propulsive model development for propeller aircraft, spin aerodynamic model development, and nonlinear dynamic modeling without mass properties information. Although this paper provides a summary of several research efforts, the core system identification approach is presented with sufficient detail to allow the methods to be readily adapted to other research efforts leveraging small, low-cost aircraft.

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