Lattice structures have shown great potential in that mechanical properties are customizable without changing the material itself. Lattice materials could be light and highly stiff as well. With this flexibility of designing structures without raw material processing, lattice structures have been widely used in various applications such as smart and functional structures in aerospace and computational mechanics. Conventional methodologies for understanding behaviors of lattice materials take numerical approaches such as FEA (finite element analysis) and high-fidelity computational tools including ANSYS and ABAQUS. However, they demand a high computational load in each geometry run. Among many other methodologies, homogenization is another numerical approach but that enables to model behaviors of bulk lattice materials by analyzing either a small portion of them using numerical regression for rapid processing. In this paper, we provide a comprehensive survey of representative homogenization methodologies and their status and challenges in lattice materials with their fundamentals.

The existing methods for analyzing the behaviors of lattice materials require high computational power. The homogenization method is the alternative way to overcome this issue. Homogenization is an analysis to understand the behavior of an area of lattice material from a small portion for rapid analysis and precise approximation. This paper provides a summary of some representative methodologies in homogenization.

This paper aims to numerically validate the aerodynamic performance and benefits of variable camber rate morphing wings, by comparing them to conventional ones with plain flaps, when deflection angles vary, assessing their D reduction or L/D improvement. Many morphing-related research works mainly focus on the design of morphing mechanisms using smart materials, and innovative mechanism designs through materials and structure advancements. However, the foundational work that establishes the motivation of morphing technology development has been overlooked in most research works. All things considered, this paper starts with the verification of the numerical model used for the aerodynamic performance analysis and then conducts the aerodynamic performance analysis of (1) variable camber rate in morphing wings and (2) variable deflection angles in conventional wings. Finally, we find matching pairs for a direct comparison to validate the effectiveness of morphing wings. As a result, we validate that variable camber morphing wings, equivalent to conventional wings with varying flap deflection angles, are improved by at least 1.7% in their L/D ratio, and up to 18.7% in their angle of attack, with α = 8° at a 3% camber morphing rate. Overall, in the entire range of α, which conceptualizes aircrafts mission planning for operation, camber morphing wings are superior in D, L/D, and their improvement rate over conventional ones. By providing the improvement rates in L/D, this paper numerically evaluates and validates the efficiency of camber morphing aircraft, the most important aspect of aircraft operation, as well as the agility and manoeuvrability, compared to conventional wing aircraft.

In this paper, the authors analyze an important but overlooked area, the aerodynamics of the variable camber morphing wing in transition, where 6% camber changes from 2% to 8% using the two airfoil configurations: NACA2410 and NACA8410. Many morphing works focus on analyzing the aerodynamics of a particular airfoil geometry or already morphed case. The authors mainly address "transitional" or "in-between" aerodynamics to understand the semantics of morphing in-flight and explore the linearity in the relationship when the camber rate is gradually changed. In general, morphing technologies are considered a new paradigm for next-generation aircraft designs with highly agile flight and control and a multidisciplinary optimal design process that enables aircraft to perform substantially better than current ones. Morphing aircraft adjust wing shapes conformally, promoting an enlarged flight envelope, enhanced performance, and higher energy sustainability. Whereas the recent advancement in manufacturing and material processing, composite and Smart materials has enabled the implementation of morphing wings, designing a morphing wing aircraft is more challenging than modern aircraft in terms of reliable numerical modeling and aerodynamic analysis. Hence, it is interesting to investigate modeling the transitional aerodynamics of morphing airfoils using a numerical analysis such as computational fluid dynamics. The result shows that the SST k-ω model with transition/curvature correction computes a reasonably accurate value than an analytical solution. Additionally, the $C_L$ is less sensitive to transition near the leading edge in airfoils. Therefore, as the camber rate changes or gradually increases, the aerodynamic behavior correspondingly changes linearly.

Flight range, endurance, maneuverability, and agility are the key elements that determine an aircraft’s performance. Both conventional and morphing wing aircraft have been well studied and estimated in all aspects of performance. When considering the performance of morphing aircraft, most works address aspects of the aerodynamical performance such as $L$ and $D$ as well as flight envelopes for flight dynamics and control perspectives. However, the actual benefits of adopting morphing technologies in practical aspects such as aircraft operation, mission planning, and sustainability have not been addressed so far. Thus, this paper addresses the practical aspect of the benefits when adopting a camber morphing wing aircraft. Identical geometrical and computational conditions were applied to an already-existing aircraft: the RQ-7a Shadow. The wing structure was switched between a fixed wing and a camber morphing wing to generate conventional and morphing wing geometries. The fixed-wing cases had varying flap deflection angles, and the camber morphing wing cases had varying camber rates from 4% to 8%. Once the $C_L$ values of the fixed and morphing wing cases were matched up to two significant figures, the $C_D$ and $C_L/C_D$ were analyzed for these matching cases to calculate the flight endurance, range, and improvement. When NACA 6410 is adopted, a 17% improvement in flight range and endurance average was expected. In the case of NACA 8410, an average 60% improvement was expected.

This paper presents state-of-the-art technologies of camber morphing mechanisms from the perspectives of design and implementation. Wing morphing technologies are aimed at making the aircraft more energy or aerodynamically efficient during flight by actively adjusting the wing shape, but their mechanism designs and implementation aspects are often overlooked from practical sense in many technical articles. Thus, it is of our interest that we thoroughly investigate morphing mechanisms and their nature of design principles and methodologies from the implementation and test flight aspects, navigate the trends, and evaluate progress for researchers’ methodology selection that possibly turns to design and build stages. This paper categorizes the camber morphing mechanisms from a wide collection of literature on morphing wings and their mechanisms, and the defined classifications are based on mechanism’s design features and synthesis methodology, i.e., by the tools and methods used to solve the design problem. The categories are (1) structure-based, (2) material-based, and (3) hybrid. Most of the structure-based camber morphing mechanisms have distinctive structural features; however, the material-based camber morphing mechanisms make use of material properties and tools to enhance the elastic nature of its structures. Lastly, the hybrid morphing mechanisms are a combination of both the aforementioned categories. In summary, this review provides researchers in the field of morphing mechanisms and wings with choices of materials, actuators, internal and external structure design for wings, and overarching process and design methodologies for implementation with futuristic and practical aspects of flight performance and applications. Moreover, through this critical review of morphing mechanism, selective design criteria for appropriate morphing mechanisms are discussed.