## 1 Introduction
Several other EU projects, including SADE [15] and SARISTU [16], targeted similar goals, focusing on the incorporation of morphing with standard features such as deicing, erosion and bird-strike protection. Among the morphing demonstrators released in SARISTU by integrated European teams, a full-scale Adaptive Trailing Edge was set up, aimed at compensating the weight variation of the aircraft along the flight [17]. A wide and structured assessment of the technology in that time frame (2017) is reported in [17]. In general, solutions based on kinematic systems, made of namely rigid elements, face common challenges associated with mechanical components and exhibit the drawbacks of having multiple assembled parts. Alternatively, compliant morphing architectures convert actuation inputs into desired motions or shape changes by driving an elastic deformation throughout the structure. Unlike rigid mechanisms, these layouts are designed as single units without joints, resulting in greater fatigue lifEM and enhanced reliability. Additionally, these structures do not require specific assembly tools and are free from issues related to friction or backlash. Furthermore, they are generally easier to manufacture, leading to significant time and cost efficiencies. Finally, they can combine good kinematic and load-bearing properties. Lack of hinges, whether flexible or rigid, reduces stress concentrations, ensuring gapless and smoothly deformable wing structures. Thus, compliant structures may substitute traditional high-lift systems and control surfaces, implementing morphing technology and simplifying current solutions based on kinematics. FlexSys Inc. carried out a relevant in-flight demonstration of this principle in partnership with the AFRL (US Air Force Research Laboratory) and NASA on a Gulfstream III equipped with the FlexFoil(tm) Adaptive Compliant Trailing Edge (ACTE) [18]. Such work was possible through the development of proper synthesis procedures [19] and dedicated topology multi-phase optimization algorithms to design the compliant structure aimed at driving the solution to extreme accuracy and surface refinements [20]. Over the past decade, the Italian Aerospace Research Centre (CIRA), in what follows, has developed original optimization design procedures for compliant morphing structures [21]. Such methodologies are applied in the EU-funded Clean Aviation HERWINGT project, where some morphing technologies applications (specifically for a droop nose, flaps and ailerons) are being fostered for a strut-braced, high aspect-ratio wing, suitable for next-generation Hybrid-Electric Regional Aircraft [22]. In detail, the Adaptive Structures Unit of CIRA drives the realization of a wing-integrated compliant morphing flap, with a specific focus on the full-size structural design of the integrated camber morphing flap. The device will undergo static, dynamic, and fatigue tests, which refer to classical standard production parameters. The workflow is synthetically and graphically represented in Figure 1.  
The paper is structured as follows: the approach for the design of the compliant adaptive component is introduced first, followed by the outcomes of the conceptual design in terms of system layout, actuation system, and finite element (FE) model description for two different configurations. Subsequently, the results obtained by applying the proprietary design procedure to the full-scale numerical models of the demonstrator (DEMO) are presented. Finally, the main conclusions and key lessons learned are discussed. Figure 1: HERWINGT CIRA activities at the project level, with a focus on the aim of this work.