# Design and Optimization of a Compliant Morphing Trailing Edge for High-Lift Generation
## 2 Requirements and Specifications  
The top-level aircraft requirements (TLAR) for HERWINGT were identified by Leonardo Aircraft (LDO) with respect to a baseline configuration consisting of a conventional ATR72-like aircraft. The overall target is a reduction of 15% in fuel emission, broken down into a 12% improvement of the aerodynamic efficiency, 3% reduction in the weight, and 1% decrease in the off-take power. These requirements can be translated to the wing level in 12%, 20%, and 50%, respectively, as shown in Figure 1.  
In this scenario, two high aspect-ratio wings were designed. CIRA in particular created the aero-structural design of a cantilever wing [2], while a truss-braced wing architecture design and final MD optimization were created by Politecnico of Milan (PoliMi). Technical University of Delft (TUD) performed detailed wing aerodynamic and structural sizing. The wings were subject to a trade-off analysis by Leonardo Aircraft by comparing the aerodynamic performance in cruise and climb conditions as well as the structural analysis and weight. Finally, the truss-braced high-aspect ratio wing was selected as representative of the wing configuration investigated in HERWINGT. The requirements relevant to the high-lift system, comprising the combination of a morphing droop nose, an adaptive trailing edge, and an active flow control, were specified by Leonardo Aircraft and can be summarized as follows:  
1. Enhanced Aerodynamic Performance: The movable parts devoted to the high-lift generation, morphing trailing edge, and droop nose must assure a clean configuration in cruise condition, without any steps and gaps when retracted [43];
2. Weight Reduction in Actuation Systems: Due to the integration of the actuation system within the structure, constrained by a lack of deployment systems and external fairings, a weight reduction of approximately 10% is expected at the A/C level. This requirement, with specific reference to the morphing trailing edge, means a weight lower than 22 kg/m, including actuation;
3. Shorter Take-off Distances: The advanced high-lift system allows for a reduction in take-off distances of around 9%. This capability enables aircraft to operate from shorter runways, enhancing operational flexibility;
4. Improved Landing Roll Efficiency: The implementation of this system may result in a 6% reduction in landing roll distances, which not only enhances safety but also decreases wear on runway surfaces and brakes [44]. The high-lift flow is characterized by a velocity of 130 KTAS at zero altitude, resulting in a Mach number of 0.20 and Reynolds number per unit length of 4.58 \(\times\) 10\({}^{6}\) L/m. The requirements for high-lift performance, formulated at the aircraft level in the framework of the Clean Aviation HERA Project, are C\({}_{\text{L,MAX}}\) = 2.6 in take-off and 2.8 in landing conditions, respectively. Some numerical assessments based on engineering methods were performed in order to evaluate the 3D-to-2D scaling factor. The result was about 0.8 and was confirmed by lattice Boltzmann-based physics CFD simulations. These figures have a critical impact on the requirements of the take-off and landing distances and thus are used as standard of comparison in this work. This augmented high lift is produced by the aerodynamic configuration shown in Figure 2, suited for the truss-braced wing sketched in Figure 3 and aimed at significantly enhancing the lift capacity of an aircraft, particularly during critical phases of flight, such as  
Figure 1: Requirements at wing and aircraft level. take-off, landing, and low-speed maneuvering. It is achieved through advanced design features that optimize airflow, minimize drag, and adapt the aerodynamic profile dynamically. To this scope, the SU2 open-source RANS flow solver was used [45]. Two flaps contribute to generation of the high lift, namely the inner and outer flaps (Figure 3). The target morphed shape produces the lift coefficient illustrated in the plot of Figure 4 together with the one in the clean configuration.