Synthesis of and Experiment on a Morphing Nose Cone Driven by a Biomimetic 4-3R1U&3R Parallel Mechanism

Abstract

Aircraft have received much attention because of their capability to adapt to various flight environments and complex missions. The nose cone is one of the key elements in optimising the aerodynamic shape of aircraft. A morphing nose cone (MNC) driven by a biomimetic 4-3R1U&3R parallel mechanism is proposed in this study. Based on screw theory, the parallel mechanism’s configuration is determined, and the structure’s full-cycle degrees of freedom are concurrently confirmed. Examples in the paper demonstrate the viability of the structure by configuration synthesis, and diagrams also show the chains. This MNC is modelled after the structural design of the cicada’s abdomen and can be extended, contracted and bent. It can actively adjust its shape in response to change in the flight environments, thereby aerodynamic performance and enhancing the aircraft’s multi-mission capabilities. A scaled-down prototype is created to verify the deformation capacity of the MNC meeting the engineering requirements. Results show that the extension ratio is 36.7%, and the bending angle is 21.7°, which is better than expected. The relative error value is within a reasonable range and the extension process is incredibly stable. This research proposes new perspectives for the design of MNCs.

1. Introduction

Traditional spaceplanes predominantly adhere to a fixed aircraft configuration, and the leading nations in this domain include the United States and Germany. The United States has achieved remarkable advancements in spacecraft technology through the successful launch of Lockheed Research’s hypersonic technology vehicle and the Falcon Program [1]. Similarly, Germany has provided notable contributions to the field through its advanced spaceplane design, known as the Sanger Plan. These innovations aim to address the inherent challenges associated with conventional single-stage orbit entry technology [2]. However, fixed-shape aircraft do not possess universal adaptability to all flight conditions. At supersonic velocities, the shock waves generated by these aircraft augment aerodynamic drag and the thermal load [3]. Morphing aircraft have emerged as a viable solution to address this challenge, and they have been extensively studied and evaluated from all performance aspects. These aircraft can dynamically modify the configuration of critical components, such as wings and nose cones, to optimise their functionality [4]. By adapting to prevailing flight conditions, these aircraft can effectively achieve substantial reduction in drag and enhance cooling effects. Such an innovative approach not only enhances the aircraft’s adaptability but also serves as a valuable theoretical and technical reference for the design of future morphing aircraft and morphing-wing UAVs [5].

The design of wing structures exemplifies an application of deformable technology. The aerodynamic profile of an aircraft can be precisely customised and optimised for various flight phases by continuously improving the wing shape through in-plane, out-of-plane and movable surface deformations [6–10]. This adjustment not only optimises performance but also enhances efficiency under different flight conditions, thereby reducing costs [11]. The design proposed by Yang et al. [12] utilises shape memory alloy (SMA) wire actuators to drive the wing tail, and has the potential to enhance aerodynamic efficiency by reducing noise and delaying flow separation. These advantages have led to the growing popularity of SMA actuators in deformable aircraft applications. Cao et al. [13] proposed a curved deformable wing design on the basis of a deformable truss structure. This deformable wing is easy to manufacture and implement in engineering applications and exhibits multi-cavity freedom characteristics. Moreover, the design demonstrates sufficient load-bearing capacity to meet practical requirements. Li et al. [14] designed a flexible, curved-wing leading edge.