Lateral-Directional Static and Dynamic Stability Analysis at High Angles of Attack for the X-31 Configuration

摘要

Wind-tunnel and drop model flight data were analyzed to document the lateral-directional static and dynamic characteristics of the X-31 configuration at high angles of attack. Special emphasis was given to the analysis of the lateral-directional dynamic instabilities exhibited by this configuration, in particular, wing rock and high incidence kinematic roll (HIKR) departure. Results showed that wing rock for the X-31 configuration was triggered by the interaction of forebody flow with the forward fuselage and sustained by poor roll damping characteristics coupled with strong lateral static stability and nonlinear sideslip effect on rolling moment. A nonlinear simulation based on wind-tunnel data accurately predicted wing rock motions at high angles of attack. Without lateral-directional stability augmentation, as the angle of attack increased, the wing rock motions became divergent and the X-31 configuration exhibited a HIKR departure. Data analysis showed that a reversal from restoring to propelling rolling moment at sideslip angles larger than 30 deg was the cause for HIKR departure. A high-gain roll damper, implemented on the Drop model Flight Control System, demonstrated the viability of this control augmentation approach to suppress the wing rock and the HIKR departure.