Adaptive Morphing Rotors: A Variable Twist Mechanism for Enhanced UAS Performance

Abstract

Propellers and rotors, while similar in operation, are optimized for different environments— propellers excel in axial flow conditions, while rotors perform best in hover with low incoming flow. This polarity underscores the need for variable geometry blades that combine the strengths of both for UAS configurations such as tilt-rotor and tail-sitter, where the role of propulsion and lift generation is assigned to the same set of rotors for weight saving. This study explores a novel rotor blade morphing mechanism for UAS, integrating a variable twist system to optimize aerodynamic performance across hover and forward flight modes. The proposed design incorporates a simple actuation mechanism, enabling dynamic and continuous twist adjustments at the rotor hub while maintaining a rigid blade tip. The baseline configuration, featuring a 34◦ pitch angle at the hub and a 14◦ pitch angle at the tip, is optimized for forward flight. During hover, the mechanism untwists the blade to achieve a 24◦ pitch angle at hub, while tip pitch remaining the same, tailoring the blade geometry for efficient vertical lift. The blade construction was done with Thermoplastic polyurethane (TPU) for its flexibility and durability under dynamic loads. Finite element analysis conducted using ANSYS Static Structural validated the structural integrity and performance of the rotor under varying operational loads. The results demonstrated a linear relationship between applied forces on the actuating shaft and the resulting pitch angle variations, confirming the precision and controllability of the mechanism. This adaptable rotor design will ensure smooth transitions between flight modes, enhancing the efficiency and versatility of VTOL systems. © 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.