## 1 Introduction  
Performance is one of the most essential factors in the designing of aircraft. Traditional fixed-geometry aircraft cannot primely satisfy the aerodynamic performance requirements at different flight stages. As a new solution, morphing aircraft can change their aerodynamic configuration to ensure optimal performance under various environmental conditions and mission requirements [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. Since the wing is the main component of the aircraft to provide lift, the primary research object of the current morphing aircraft technology is the morphing wing [11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Specifically, the variable-camber airfoil technology that can be used on morphing wings has obvious advantages in improving the aerodynamic performance and enhancing the efficiency of the aircraft, which makes it attract extensive attention, and it has gradually become a research hotspot [21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]. Extensive investigations have been conducted on aerodynamic aspects of variable-camber airfoil technology, with the main focus on aerodynamic design and benefits analysis of trailing-edge variable-camber airfoil. Two famous trailing-edge variable-camber designs are the Adaptive Compliant Trailing Edge (ACTE) [32; 33; 34] and the Variable Camber Continuous Trailing Edge Flap (VCCTEF) [35; 36]. The ACTE technology, which is investigated by FlexSys and NASA, uses compliant structures to deform the trailing edge of the wing. This technology is relatively mature as a series of successful flights was tested on a testbed Gulfstream III airplane [33]. The VCCTEF technology investigated by Boeing and NASA has completed aerodynamic analysis and optimization design of different VCCTEF configurations using two-dimensional airfoil and three-dimensional wing/body on a Generic Transport Model (GTM) under cruise condition [29; 37; 38]. Aiming at the aerodynamic aspects, [PERSON] et al. [39], [PERSON] and [PERSON] [40], [PERSON] et al. [41], and [PERSON] et al. [30] utilize numerical simulation, experimental validation, and optimization design methodsto conduct a systematic study on trailing-edge variable-camber airfoil at low-speed flight stage, and the critical design parameters and fine morphing strategy are identified. Besides, [PERSON] et al. [26], [PERSON] and [PERSON] [42], [PERSON] and [PERSON] [43], [PERSON] et al. [44; 45; 46], [PERSON] et al. [47], [PERSON] and [PERSON] [48], [PERSON] et al. [49], and [PERSON] et al. [50] adopt drag reduction mechanism analysis, optimization design, and aerodynamic-performance benefits-quantification methods to perform series of trailing-edge variable-camber investigations under transonic cruise condition. Their research objects include airfoil, wing, and wing/body configuration, and the results show that variable-camber airfoil can achieve the largest drag reduction of 13.2% [44]. In addition to the above-mentioned aerodynamic research on trailing-edge variable-camber airfoils, some studies are also conducted on aerodynamic topics of the leading-edge variable-camber airfoil or both leading-edge and trailing-edge variable-camber airfoil. [PERSON] and [PERSON] [51] indicate that the main benefit of the morphing leading edge is a substantial drag reduction. [PERSON] et al. [28] studied the steady aerodynamic characteristics of the leading-edge variable-camber wing and unsteady aerodynamic characteristics under different leading-edge deflection frequencies. The design verification and optimization design research on aerodynamic aspects of Variable Camber Compliant Wing (VCCW) technology (both leading-edge and trailing-edge variable camber) undertaken by AFRL and others shows that VCCW is better than the flap-deflection method, and the benefits of increased lift under take-off stage and drag reduction under cruise condition are obvious [52; 53]. Aiming at the aerodynamic topics of the both leading-edge and trailing-edge variable-camber technology, [PERSON] et al. [54], [PERSON] et al.