Fixed-Time Observer-Based Bifunctional Control for Variable-Sweep Vehicle

This work presents a bifunctional anti-disturbance control architecture aimed at alleviating performance deterioration caused by strong morphing–flight interaction in variable-sweep aircraft. In contrast to traditional techniques that regard all morphing-induced couplings as detrimental disturbances, the proposed framework differentiates their effects in real time. Harmful couplings that negatively influence tracking accuracy are attenuated, while those that contribute positively are preserved. To achieve this, a fixed-time extended state observer is developed to promptly estimate lumped uncertainties within a bounded convergence time. Integrated into the longitudinal control loop, the complete scheme is evaluated through nonlinear simulations, demonstrating improved robustness and tracking precision compared with benchmark approaches.