Life extending control for helicopter using robust dynamic inversion

The goal of life extending control is to trade off the handling qualities of UH-60 Black Hawk helicopter and the service life of main rotor shaft. An increase in the service life results in enhanced safety and reduction in maintenance costs. Different from simply minimizing the amplitude of rotor shaft bending stress cycles, a real-time nonlinear fatigue crack growth model is included in the analysis, which serves as an indicator of service life. The explicit dynamic inversion control scheme is designed to regulate roll attitude, pitch attitude, vertical velocity and yaw rate. The controllers are gain scheduled with total airspeed and damage reduction as parameters. For the problem that dynamic inversion control needs for exact availability of the system dynamics, so its robustness is difficult to be ensured. The dynamic inversion method is used as inner loop of robust multivariable control, which is to compensate for bounded uncertainty. Nonlinear system simulation results show that the responses can meet the requirements on bandwidth and axes decoupling in relation to ADS-33 Level 1 handling qualities with no damage mitigation. As the damage increases, the bandwidth of system is slightly degraded, which results in smaller transients in bending moment response. Besides satisfying the requirement of robust stability in the face of uncertainty, ? analysis shows that robust performance level of robust dynamic inversion controller is much better than that of dynamic inversion-PID controller.