# Design and Optimization of a Compliant Morphing Trailing Edge for High-Lift Generation
## 7 Results vs. Requirements  
In this section, the main achievements of the work are discussed against the requirements. The philosophy at the basis of the morphed trailing edge is compliant with the preservation of the laminar flow in cruise, with a consequent reduction in the aerodynamic drag. What is also significant is the placement of the actuation system, which is entirely housed within the available space of the wing box, contributing to a cleaner wing in cruise. All these aspects are in line with the first requirement at the A/C level (enhanced aerodynamic performance). Differently from a conventional flap, the actuation must bear not only the external aerodynamic loads but also the elastic reaction of the structure. This is a penalty that generally characterizes compliant devices. However, the optimization addressed in this work kept the maximum actuation load within a value of 1293 N for the 0.5 m spanned flap, which is lower than the requirement (1500 N). A rough estimate of the impact on the weight of the actuator can be obtained by the empiric formula that links the actuator force, \(F_{act}\), to its weight, \(W_{act}\)[54]:  
\[W_{act}=F_{act}^{0.5} \tag{7}\]  
As a result, a weight saving of over 7% with respect to the requirement was observed. Moreover, the optimization of the morphing device as a whole (actuation included) led to a total weight of 8.85 kg that, scaled to 1 m span, corresponds to 17.7 kg/m against the requirement of 22 kg/m, with a net saving of about 19.5%. The geometry and the materials of the parts were chosen to reduce as much as possible the integration and the maintenance efforts and improve the reliability level. The skin, made of aluminum alloy sheets, can be cut, milled, and bent by means of conventional  
Figure 17: First modal shape of the refined FE model (**a**) and second and third modal shapes (**b,c**); the displacements illustrated in these plots were suitably magnified to better highlight the details of the modal shapes. operations. The same is true for the web. The connection can be obtained by conventional riveting or structural bonding. The kinematic chain can be also easily built through conventional manufacturing operations, and its integration requires a simple assembly rig, given the small number of parts (the transmission arm and the flanges of connection to the bottom skin). This dramatically reduces the number of operations and the complexity of the required tools, with remarkable advantages with respect to a conventional flap characterized by a more complex architecture. However, the sliding part of the skin is worthy of particular attention; the driving tracks represent, in fact, a criticality not in terms of fabrication and material reliability but for the interface and based on bearings, whose inspection and replacement involves a region of the wing box. In this case, a dedicated procedure must be defined to have an easy access to the region, considering removable panels on the lower part of the wing box. This solution must obviously also encompass the replacement of the actuators. But, once again, despite the necessity of accessing the wing box, as the involved interfaces are fewer than in a conventional flap, maintenance advantages can still be conferred. Figure 18 illustrates the lift coefficient for different configurations computed in the assumption of flow 2D; the two highest ones were computed through the Eulerian hypothesis and thus do not take into account any separation. The highest of them refers to the target morphed shape and the other one to configuration 3. The cluster of the lowest curves was computed by means of the SU2 open-source RANS code [45]; this type of analysis cannot determine the exact maximum lift coefficient but provides the trend in the presence of separation. These lines, corresponding to configurations 1-5, were about 0.3 points below the mid-curve computed through the same method and referring to the target morphed shape.