Analysis of oversteer/understeer characteristics of aircraft ground steering

A lower-order equivalent aircraft steering system model with time-varying parameters was developed to analyze oversteer/understeer characteristics of aircraft steering and improve handling characteristics of nose wheel steering system after touchdown. Combining system stability analysis with flight data, it is found that the curve of oversteer/understeer characteristics rapidly approaches to the critical speed stability boundary in a certain speed range, which is caused by yaw rate command bandwidth decreasing nearly to zero. It results in a sharp deterioration in ground-handling characteristics. Then a stability augmentation design with self-tuning controllers was proposed, using a yaw-rate feedback as the cue of adjusting. The analysis and simulation indicate that the model proposed simplifies the related analysis which would be a complex problem in high-order models and it could be used as a complement to high-order, detailed model analysis. And the stability augmentation design could set yaw rate command bandwidth in a desired range and ameliorate the rudder pedal sensitivity, greatly improving the ground-handling characteristics.