Determination of the operational parameters values for Airbus A300-600ST Beluga aircraft on the basis of CFD tests

. The article presents a method for estimating the values of basic operational and aerodynamic parameters of an aircraft. It contains a multistage analysis of CFD test results for the Beluga Airbus A300-600ST model. The first step of the method is to determine the values of aerodynamic parameters such as lift coefficient, drag coefficient, lift force and drag force in specific flight conditions. A comparative analysis of the coefficients of lift and drag force depending on the angle of attack of the aircraft allowed the estimation of the optimal angle of attack of the Airbus A300-600ST Beluga. In the next step, the operational values and the maximum flight ceiling of the aircraft were determined. For this purpose, the results of CFD simulation tests for the optimal angle of attack of the aircraft were used. This article allowed determining the characteristics of the components of aerodynamic force of an airplane depending on the angle of attack, flight altitude and flight speed, determining the optimal angle of attack of the aircraft and calculation of the optimal and maximum flight ceiling values of the Airbus A300-600ST Beluga.


Introduction
Aircraft perfection is a parameter that can help determine the optimal angle of attack for an aircraft and its operating altitude. An airplane is aerodyne, which means it is heavier than air and aerodynamic force must be generated in order to start flight. The components of the aerodynamic force are the lift and drag force of the aircraft. To generate lift, the plane must move in relation to the surrounding medium. The force responsible for giving an airship speed is called the thrust [2]. It counteracts the drag force of the aircraft. The forces acting on an airplane during flight are shown in Fig. 1. [7,8]. total aerodynamic force, FLlift force, FD -drag force, αangle of attack [5].
The lift force is created as a result of the medium flowing around the airfoil. This flow accelerates the air stream over the profile and slows down the stream under the profile, which leads to the formation of a pressure difference between the top and bottom of the airfoil [1,9]. The generation of the lift is described by the equation (1) [3].
A drag force acts on a moving object in the opposite direction to its direction of movement. It affects the fuel consumption of the aircraft and its flight properties. The drag force can be described by the equation (2)

Methodology
The first step in the method for determining the operational parameters of the aircraft was to create a three-dimensional model of the Airbus A300-600ST Beluga in real dimensions, and then subject it to a series of numerical CFD simulations. The model was made with attention to the characteristic geometric features of the aircraft, including type of aviation profile, wing angle. This aviation profile is NACA 63-215. CFD numerical simulations were divided into two stages, the first of which was the stage of determining the optimal angle of attack for α.

Results
The performed CFD simulations allowed, using the dependencies (1) and (2), to determine the lift coefficient CL and the drag force coefficient CD ( Table 2). The optimal angle of attack is understood to be the angle at which the airplane generates the highest value of lift FL while generating the lowest value of drag FD. The analysis of the test results led to the conclusion that the optimal angle of attack for the Airbus A300-600ST Beluga is α = 18 o .   In the next step of the research, the maximum flight altitude of the considered aircraft was estimated. The values of the lift force FL, the drag force FD, the coefficients of the lift force and the drag CL and CDare presented in Table 3.  The data contained in Table 3 allowed for the determination of the aerodynamic perfection coefficient k. It is understood as the lift coefficient -to drag coefficient ratio. The maximum value of the k coefficient indicates that the airplane has reached the operating flight altitude. Analyzing the determined data, it can be concluded that the operational ceiling of the Airbus A300-600ST Beluga Hop=12,000 m.

Conclusions
The method of determining the value of the aerodynamic force, using CFD simulations, proposed in the article allowed for the determination of the optimal angle of attack, operating flight level and maximum altitude of the Airbus A300-600ST Beluga aircraft. The conducted research allowed to determine the optimal angle of attack for the aircraft at the level of α = 18 o . The second part of the research included numerical analyzes of the aircraft flow in flight conditions with an angle of attack α = 18o and a variable flight altitude in the range from 9000 to 15000 m. This allowed for the determination of the equation of the function describing the dependence of the generated lift force FL and drag force FD on the flight altitude. Knowing the function equation, the maximum flight altitude of the Airbus A300-600ST Beluga Hmax = 14665 m was determined. The analysis of the test results also led to the determination of the lift and drag coefficients for all tested flight altitudes, the quotient of which gives the value of the coefficient of aerodynamic excellence k. The highest k value was recorded for a flight altitude of 12,000 m, which means that it is the optimal operating altitude of the aircraft.