Aeroservoelastic Modeling and Analysis of Aircraft with Multiple Control Surface Freeplay Nonlinearity

A new aeroservoelastic modeling and analysis methodology is presented for an aircraft with multiple control surface freeplay nonlinearities using the fictitious mass approach. The model incorporates freeplay in the right and left ailerons and the elevator, and is developed by combining linear aeroelastic models in an external simulation environment. State-space, time-domain simulations are performed to investigate both single and multiple freeplay configurations and their effects on limit cycle oscillation (LCO) characteristics, while a flight control algorithm maintains overall stability of the aircraft. The results show that, for elevator dynamics, LCO boundary decreases when combined aileron–elevator freeplay is present compared to the case with elevator freeplay alone. In contrast, for the same combined configuration, the aileron LCO onset occurs at a lower speed, while the flutter boundary shifts to a higher velocity relative to the aileron-only freeplay case. These findings demonstrate the strong coupling between longitudinal and lateral dynamics in the presence of multiple freeplay nonlinearities. The results further suggest that multiple freeplay can alter the dominant instability mode and delay the onset of sustained oscillations.