# Design, Manufacture and Wind Tunnel Test of a Modular FishBAC Wing with Novel 3D Printed Skins
## 1 Introduction  
Compliance-based camber morphing wings have the potential to improve aerodynamic performance in both fixed and rotary wings. This aerodynamic improvement is due to their ability to actively vary airfoil camber in a smooth and continuous way so that the airfoil geometry can adapt to the continuous changes in operating conditions (e.g., changes in altitude, speed, weight, weather conditions). Unsurprisingly, camber morphing has been a popular research topic in the past few decades [1, 2] due to its potential to significantly contribute to reducing the environmental impact of the aviation sector by reducing fuel consumption [3, 4]. Advancements in smart materials and lightweight structures, which have led to lighter and less complex morphing mechanisms. For example, developments in piezoelectric materials [5, 6] and Shape-Memory Alloys (SMA) [7, 8] have focused on exploring alternative actuation mechanisms, whereas the further understanding of composite laminates has led to exploiting structural instabilities for shape changing [9, 10, 11]. Furthermore, some concepts achieved variable camber by embedding actuators within the wing skin [5, 12], whereas others focused on active actuation of the internal load-bearing structural members [8, 13, 14, 15]. Despite the actuation mechanisms, a common aspect among the majority of these morphing concepts is that the change in shape does not occur across the entire aerofoil section but is mainly localised on the trailing edge, where the aerodynamic loads are relatively low. However, there are concepts that have developed morphing leading-edge devices, such as a compliant 'droop-nose' morphing leading edge using superelastic materials [16], whereas others have combined both leading and trailing-edge morphing devices [17]. Similarly,Werter et al. [18] proposed leading and trailing-edge morphing devices that combined skin warping and bending to induce shape change. This research effort focused on developing a morphing mechanism that could be retrofitted to an existing aircraft using as many off-the-shelf components as possible. In general, it can be said that compliance-based camber morphing devices can achieve continuous and smooth shape adaptation as they are designed to be compliant along the direction where shape change occurs. This compliance is normally achieved by a combination of both geometric design (i.e., carefully considering where to allocate geometric stiffness) and an adequate material selection [6]. Thus, these devices normally have multiple structural elements and material types that must be combined in a'seamless' way. Therefore, one main challenge in camber morphing research is how to manufacture these multi-element and multi-material devices so that the following goals can be achieved: _(a)_ the inclusion of aerospace-grade materials, _(b)_ the reduction in part count and manufacturing steps and _(c)_ the ability to easily remove or replace components for maintenance purposes. One camber morphing concept that has shown promising aerodynamic results and has made good progress in terms of manufacturability is the Fish Bone Active Camber (FishBAC) device. The FishBAC is a morphing device that achieves its compliance through both geometry and material choice. It consists of a central bending spine made from a thin composite plate placed at the trailing edge of the aerofoil. Onto this flexible spine are placed a series of spanwise stringers that support the aerodynamic skin and add additional spanwise rigidity without significantly adding stiffness in the direction of shape change. An elastomeric outer skin membrane is stretched over the stringers, and a series of tendon spooling actuation mechanisms are placed along the span to drive the shape change. Initially introduced by Woods and Friswell in 2013 [19], the FishBAC has significantly evolved in terms of the manufacturing and material selection process since its introduction. The first generation of FishBAC devices was mainly manufactured by 3D printing (Figure 1).