Nonlinear Aeroelastic Response Analysis of Unmanned Multi-body Aircraft with Free Play

ifasd2024 Tracking Number 37

The unmanned multi-body aircraft (MBA) proposed in this paper represents a novel aircraft configuration connecting multiple independent aircraft at their wingtips through hinges. This design has attracted considerable research interest due to its effective resolution of issues such as poor wind resistance, challenges in low-altitude flight, and limited mission agility, which is commonly associated with high aspect ratio aircraft. The nonlinearity of the free play at flexible hinges between adjacent flight units is common existed, which can result in deviations in the aeroelastic stability boundaries of the aircraft. It is essential to conduct research that takes into account the free-play nonlinearity in the context of aeroelastic response analysis. In this study, the free play between the wing tips of the lead aircraft (mother aircraft) and the trailing aircraft (daughter aircraft) within an unmanned multi-body aircraft system is taken as the research object. To address the challenges posed by these free play, the fictitious mass method is used to linearize modal vibration patterns, establishing a modal array capable of expressing deformations across the entire response field. Additionally, the minimum state method is utilized to fit non-constant aeroelastic rational functions, in that case, how different design parameters for the gaps between aircraft wings affect the corresponding response characteristics of limit cycles is analysed. The results show that when there is a free play between the wings of an unmanned multi-body aircraft, nonlinear limit cycle oscillations occur within a specific region below the linear flutter threshold. Moreover, the parameters of free play will affect the amplitude of these limit cycle oscillations and the divergence critical dynamic pressure. The critical velocity of the limit cycle oscillation decreases with the increase of the gap and increases with the increase of the initial deviation of the gap; Besides, the free-play nonlinearity increases the amplitude of the system's limit cycle oscillation; as the flow rate increases, the system shows a complex response, with periodic and chaotic motions occurring intermittently. This study contributes valuable insights into the behaviour of unmanned multi-body aircraft, shedding light on the complex interplay of free play and their nonlinear effects on aeroelastic performance.