Integrated System Identification and Flight Control Optimization in S-92 Handling-Qualities Development

摘要

System identification modeling and control law optimization techniques are being integrated in the development of handling-qualities and flight control systems for the S-92 dual-use helicopter. This paper discusses the unique aspects of control law design for a limited-authority civil helicopter. Dedicated flight tests were conducted to provide a data set that spanned the critical flight conditions. Accurate linear state-space models, which include the coupled dynamics of the fuselage, flapping, coning, dynamic inflow, lead-lag, and engine degrees-of-freedom were extracted. Comparison of the S-92 nonlinear blade-element simulation with the flight data shows that the simulation predicts the on-axis responses and a low-frequency instability typical of helicopers, with reasonable accuracy, but the off-axis response comparison shows the sign error characteristic of analytical simulation models. The incorporation of aerodynamic phase lag improved the off-axis agreement considerably. The control law gains were tuned in an automated design environment to meet the relevant civil and military design requirements. A fundamental tradeoff is apparent between increased feedback gain to stabilize the low frequency dynamic modes and reduced feedback gain to improve the short period damping ratio. Closed-loop flight test results validated the accuracy of the integrated design tools and showed that the desired dynamic response characteristics can be achieved.