Bioinspired Control of Rudderless Morphing UAVs

Abstract

Morphing to seamlessly alter aircraft geometry for either multi-mission or adaptive fly-by-feel flight has recently become an emerging field of research. With the added benefits of tailored aerodynamics, an aircraft no longer needs to be designed to suit a single cruise flight condition. This is particularly useful for small Unmanned Aerial Vehicles (UAVs) which, like birds and insects, tend to operate at lower altitudes and even in urban environments where the flow can frequently change drastically.

The primary objective of this research is to investigate morphing applications for rudderless UAVs, which have seldom been studied prior to this point, through bioinspiration. As natural fliers undergo multi-scale low-altitude morphing to adapt to changes in either flight objective or aerodynamic conditions, they are prime subjects for investigation. This is accomplished through both analytical aerodynamic modeling, and experimental design and investigation of novel morphing actuators using Macro Fiber Composites (MFCs). Using these smart material actuators, complex shape change such as spanwise camber morphing and three-dimensional bending-twisting coupling is achieved.

This dissertation presents three main contributions to the field of morphing aircraft. The first contribution is an analytical derivation that assesses the impact of scale and altitude on flight. This is aimed at justifying the need for morphing technologies particularly at the UAV scale by assessing the impact of winds on flight velocity and direction. More specifically, both a steady wind and a quasi-steady sharp-edge cross wind were assessed to characterize the response, and showed that low-altitude fliers are prone to drastic changes in flight path, acceleration, and sensitivity with respect to winds.

A nonlinear Lifting Line Theory (LLT) model was also developed specifically for spanwise morphing aircraft. With this model, the spanwise geometry of a morphing wing can be tailored and optimized to achieve a desired aerodynamic outcome. As this model is capable of characterizing nonlinear aerodynamics, the spanwise wing geometry is tailored to recover from stall. A comprehensive analysis of possible adaptation scenarios is also conducted to characterize the limitations of the system and demonstrated excellent recovery capabilities of the spanwise morphing wing.

Lastly, a novel bioinspired tail actuator is developed for multifunctional pitch and yaw control using MFCs. Two Finite Element Method (FEM) models are compared to determine both an appropriate method of modeling MFC actuators with custom non-rectangular geometries and fiber orientations, and the optimal fiber orientation to obtain adequate transverse and out-of-plane displacements. The optimized actuator was integrated into a bioinspired aircraft for wind tunnel testing. Experimental investigation was geared towards quantifying both pitch and yaw response of the actuator with respect to both changes in angle of attack and sideslip.