# Aerodynamic Study of the NASA's X-43A Hypersonic Aircraft
## 1 Introduction  
NASA X-43A, also known as a Hyper-X Research Vehicle (HXRV), was one of the different NASA's uncrewed hypersonic aircraft designed with the innovative scramjet propulsion technology to fly at high speeds and high altitudes. Hyper-X was also the experimental hypersonic flight research program of X-43A managed by NASA whose main objective was to demonstrate, validate and implement the technology, the experimental techniques and the computational methods and tools for design and performance predictions of a hypersonic aircraft with an airframe-integrated, scramjet propulsion system. In order to obtain the required data, NASA designed and fabricated three similar X-43A vehicles; two of them were designed to fly at Mach 7 and the other one at Mach 10. All of them measured around 3.66 m in length and weighted roughly 1361 kg. Since the aerospace industry that is focused on hypersonic flight vehicles such as X-43A is very demanding in terms of high performance, a large amount of profound studies based on experimental techniques or computational algorithms on each technological part of those aircraft are extremely necessary. Among the first studies undertaken on such hypersonic flight vehicles, it is interesting to highlight the one carried out by French [1], where three-dimensional inviscid CFD results in support of the Hyper-X vehicle aerodynamic database were presented. French considered two geometricconfigurations of the aircraft and focused on the effects of Mach number, sideslip and angle of attack disturbances on the vehicle stability and control. A prediction of integrated vehicle aero-propulsive performance including an integration of aerodynamic and propulsion flow fields was introduced by [PERSON] et al. [2]. They used CFD simulations supported by ground test data. [PERSON] et al. [3] described the use of several computational methods for investigating the aerodynamics of the research and launch vehicles in close proximity under the hypothesis of unsteady effects. Aerodynamic database extrapolation and differences between wind-tunnel and flight environments were evaluated. [PERSON] and [PERSON] [4] developed a study focusing on the optimisation of the internal engine flow channel using genetic algorithms based on the decoupling and addition via explicit formulations, the viscous, thermal, species-transport and combustion physics into the implicitly solved Euler formulations of fluid flow. A CFD-based steady state and an unsteady solution initiations approach were implemented by [PERSON] and [PERSON] [5] in order to analyse the aeroelasticity of X-43A. [PERSON] et al. also presented an aerothermoelastic-acoustics simulation process of a cantilever wing with a NACA 002 airfoil and the X-43A aircraft in [6]. The pressure distribution over this particular aircraft was numerically determined by [PERSON] and [PERSON] [7], where they created an algorithm based on the quasi-gas dynamic system of equations with the objective of introducing artificial dissipation coefficients. They also illustrated the level lines of density and streamlines in the computational domain in which a vortex at the trailing edge of the aircraft was identified. [PERSON] and [PERSON] [8; 9] obtained the lift and drag coefficients and the lift-drag ratio for several angles of attack by solving the three-dimensional Navier-Stokes equations. The comparison between these parameters and different experimental measurements gave a relatively good agreement. Furthermore, the Mach, temperature and pressure fields in the central axial section of X-43A for different Mach numbers and a zero angle of attack and the variation of the flow structure around the aircraft with the increase in the Mach number for different angles of attack were provided. The flight dynamics affecting a CFD-based two-dimensional air-breathing generic hypersonic flight vehicle resembling the X-43A aircraft were described by [PERSON] et al.