# Modeling, Simulation, and Cruise Characteristics of Wingtip-Jointed Composite Aircraft
## 1 Introduction  
As aeronautical technologies develop, new-concept aircraft with better flight performance are created. Wingtip-jointed composite aircraft, representing a specific sort of new-concept aircraft, can form a composite aircraft system with wingtips jointed together when flying. As their aerodynamic performance is optimized by reduced induced drag force, such composite aircraft have the capacity for better range and endurance. The concept of wingtip-docking technology was originally proposed by Dr. [PERSON], a German scientist, during World War II [1]. The United States Air Force (USAF) carried out the Tom-Tom project [2], the FICON project [3], and several other projects and experiments [4] to validate this theory, utilizing varieties of conceptual wingtip-docking models. Professor [PERSON] of Draper Laboratory and Cornell University demonstrated the aerodynamic modification created by the combination of two separate wings using the vortex lattice method [5], and wind tunnel testing [6]. The FICON project conducted by the USAF designed a strategic bombing unit named a flying aircraft carrier with a B-29 bomber carrying two F-84 D/E fighters. After the verification of wind tunnel testing, ground effect experiments and several successful hookups were performed; one fighter was torn away from the right wingtip of the other due to insufficient collaboration among the aircrafts [7]. The F-84 immediately flipped over onto the wing of the B-29 and both crashed, with the loss of all onboard [8]. Since then, relevant research into this technology has focused on the dynamics of multibody systems with rotational hinge constraints. A multibody system refers to a mechanical system composed of multiple bodies interconnected in a certain way. Multibody dynamics is a new branch of the discipline based on classical mechanics. To deal with a multibody system, in principle, traditional classical mechanics methods are typically used, including the vector mechanics method represented by the Newton-Euler equation and the analytical mechanics method represented by the Lagrange principle. Based on this, the Roberson-Wittenburg method mainly uses graph theory and mathematical tools to describe the structure of a multibody system, using the relative displacement between adjacent rigid bodies as generalized co-ordinates to derive universal dynamics suitable for arbitrary multi-rigid body systems. [PERSON]'s augmented body concept was used to create a physical interpretation of the coefficient matrix A of the equation [9]. [PERSON] et al. analyzed the modeling and control method of an aeroelastic morphing UAV [10]. [PERSON] of Florida University analyzed the modeling method of a specific variable-sweep aircraft [11]. [PERSON] and [PERSON] have conducted dynamic characteristics analyses and flight control designs for Z-wing morphing aircraft [12; 13], oblique wing aircraft [14; 15], and variable-sweep morphing vehicles [16]. [PERSON] et al. [17; 18], [PERSON] et al. [19], [PERSON] [20], and [PERSON] [21] have developed different dynamic models for other similar multibody aircraft systems. For a wingtip-jointed composite aircraft system, [PERSON] and [PERSON] investigated a traditional Newton-Euler dynamic modeling method which adds constraints to a single aircraft. At the same time, the gain scheduling method was used to complete the control characteristics study, and the composite trajectory was discussed [22]. However, for a composite system composed of multiple aircraft based on the aerodynamic data and trim strategy of a single aircraft, a multi-aircraft composite method giving a multi-aircraft trim strategy was not established. The existing research studies mainly finish the composite aircraft study based on the aerodynamic data and trim strategy of a single aircraft, while the dynamic model establishment, aerodynamic database, and composite trimming strategy simulation of a composite system will help the aircraft cruise simulation results be more reasonable.