Magnitude Of Aerodynamic Forces Research Articles

СИЛА ТА МОМЕНТ СИЛИ МАГНУСА. ЇХ ВПЛИВ НА ДАЛЬНІСТЬ СТРІЛЬБИ 155-ММ СНАРЯДІВ

An important component of the main vector of aerodynamic forces and moments of the projectile is the force and moment from the Magnus force, which significantly affect the dynamics of the projectile flight. At the same time, the influence of the Magnus force and moment on the flight of projectiles has been studied relatively little, in addition, the leading scientists of Ballistic Research Laboratories (USA) published quantitative indicators achieved during its calculations, which do not fully meet the requirements for the accuracy of their determination. It is shown that the Magnus force and moment depend on the density of the air, the angular velocity of rotation and the velocity of the projectile, the lateral surface and diameter of the projectile, as well as the angle of its nutation. To evaluate the influence of the Magnus force and moment (their aerodynamic coefficients) on the range of the projectile, a difference method is used, which consists in solving the system of differential equations of spatial motion of a projectile so that changing the value of the aerodynamic coefficient results in a change in the value of the flight range. Numerical modeling of the dependence of the flight range of the 155-mm PF Assegai M2000 projectile and the 155-mm PF ERFB/BB projectile on the change in the magnitude of aerodynamic force and Magnus moment coefficients by 1 % was carried out. It is shown that the aerodynamic force coefficient of Magnus creates the largest errors in the range at the minimum charge, the deviation reaches – 0,005 %, the smallest at the maximum charge – 0,003 %. The largest error in the flight range of the projectile from the aerodynamic coefficient of the Magnus moment is observed at the minimum charge, the deviation reaches 0,6 % D; the effect on other charges leads to much smaller deviations, which are 1-3 orders of magnitude smaller compared to the minimum charge. The obtained results provide an opportunity to assess the required accuracy of determining the aerodynamic coefficients of the Magnus force and the moment of the Magnus force under different conditions of firing by artillery systems.

Динамика летательного аппарата с системой смещения центра масс

For modern aircraft of axisymmetric shape, including lander, aeroballistic vehicles, an important condition for regular operation is the absence of asymmetries of various kinds, provided that they were not intentionally introduced during the design and production of the structure. Asymmetries caused by changes in the shapes of the outer surface lead to changes in the massinertial characteristics of the vehicles, displacement of the center of mass, the appearance of centrifugal moments of inertia, the appearance of aerodynamic moments. All this can lead to a deviation of the flight path of the aircraft from the nominal trajectory, to an increase in the loads acting on the structure, due to an increase in the angle of attack, the magnitude of aerodynamic forces and overloads. In addition, asymmetries can lead to resonant phenomena in the process of movement. The paper presents a mathematical model of the motion of an aircraft in the atmosphere, which allows taking into account the displacement of the center of mass, dynamic imbalance and aerodynamic asymmetry. The influence of the displacement of the center of mass, the influence of aerodynamic moments leading to aerodynamic asymmetry on the movement of aircraft without spin stabilization and with spin stabilization has been studied. A law is proposed for displacement of the center of mass of an aircraft in order to create lifting force components, both for correcting disturbances caused by asymmetries, and for spatial maneuvering, which allows smoothly changing the angle of attack and setting the vehicle in the equilibrium position. By numerical simulation of the motion of an aircraft with spin stabilization, the effectiveness of using the displacement of the center of mass to reduce the components of accelerations, angular velocities of rotation and angle of attack is shown.

Effects of Bank Angle During Powered Aerogravity-Assist Maneuver

In a swing-by maneuver, the variation of energy of the spacecraft is controlled by the angle, velocity, and distance of approach. These parameters are defined by the incoming trajectory, when the spacecraft is far from the planetary atmosphere. The passage of the spacecraft by the atmosphere generates aerodynamic forces, affecting its trajectory and giving new forms of control, which are functions of the attitude of the spacecraft. This maneuver is called aerogravity-assist maneuver. This control can change the direction and magnitude of aerodynamic forces. Previous results showed the influence of the lift-to-drag ratio and the effects of the application of impulses in this maneuver. However, the variations of energy due to the control that can be given by the bank angle have not been studied before, and this study constitutes the main new aspect of the present paper. In this research, it is implemented the classical methodology to calculate the variations of energy to analyze the effects of the bank angle in aerogravity-assist maneuvers. This analysis can identify regions of collisions and the variations of energy as a function of the bank angle, giving new alternatives to this maneuver that are not available in the literature.

The effects of wing twist in slow-speed flapping flight of birds: trading brute force against efficiency

In aircraft propellers that are used to propel aircraft forward at some speed, propeller blade twist is important to make the individual propeller ‘wings’ operate at a relatively constant effective angle of attack over the full span. Wing twist is sometimes also assumed to be essential in flapping flight, especially in bird flight. For small insects, it has however been shown that wing twist has little effect on the forces generated by a flapping wing. The unimportance of twist was attributed to the prominent role of unsteady aerodynamic mechanisms. These were recently also shown to be important in bird flight. It has therefore become necessary to verify the role of wing twist in the flapping flight of birds.The aim of the study is to compare the efficiency and the aerodynamic forces of twisted and non-twisted wings that mimic the slow-speed flapping flight of birds. The analyses were performed by using physical models with different amounts of spanwise twist (0°, 10°, 40°). The flow was mapped in three-dimensions using digital particle image velocimetry. The spanwise circulation, the induced drag, the lift-to-drag ratio and the span efficiency were determined.Twist and Strouhal number (St) both determine the local effective angles of attack of the flapping wing. Wings with low average effective angles of attack (resulting from high twist and/or low St) are more efficient, but generate significantly lower aerodynamic forces. High average effective angles of attack result in lower efficiency and high aerodynamic forces. Efficiency and the magnitude of aerodynamic forces are competing parameters. Wing twist is beneficial only in the cases where efficiency is most important—e.g. in cruising flight. Take-off, landing and maneuvering, however, require large and robust aerodynamic forces to be generated. The additional force comes at the cost of efficiency, but it enables birds to perform extreme manoeuvres, increasing their overall fitness.