Design and optimisation of SMA-activated landing gear door locking mechanism of an air vehicle

Abstract Landing gear door locking mechanisms are commonly actuated using hydraulic/pneumatic or electromechanical systems. However, due to their complex structures, these systems are prone to failure and are not efficient in terms of weight and cost. This study presents the design, optimisation and experimental evaluation of a novel locking mechanism unprecedented globally driven by shape memory alloy (SMA) elements, specifically developed for hook-type landing gear door locking systems used in unmanned aerial vehicles (UAVs). The unlocking action is achieved via a NiTi-based SMA spring heated through electrical resistance, while automatic locking is ensured by preloaded tension springs. Two-dimensional kinematic analysis was then conducted to determine the pin locations of the mechanism and optimise the stroke, guaranteeing stable locking/unlocking. Subsequently, a 3D model with a minimal number of components was created, and the force requirements were evaluated through dynamic performance analyses. In prototype tests conducted on a 3D-printed model, the austenite and martensitic phase forces of the SMA over a range of extensions were measured, and the activation–recovery times were refined through iterative testing, which enabled stable locking performance. The system demonstrated competitive activation times compared to conventional solutions, re-locked via assisted cooling, and exhibited reliable switching behaviour. The dynamic analysis results of the designed system aligned well with data obtained from physical testing, validating the stability of the design. Overall, the results indicate that SMA-based actuators offer a lighter, more compact and energy-efficient alternative to traditional actuation methods in aerospace applications.