![]() ![]() These definitions and nomenclature will be given with reference to Figure 3.1.Īngle of Attack (a): The angle between the relative wind and the chord line.Īerodynamic Center: The point on the chord of an airfoil about which the moment coefficient is practically constant for all angles of attack. Before we proceed with the present discussion, some of the fundamental concepts and definitions of aerodynamics will be reviewed. Thus, any set of axes fixed in a rigid body is a body-fixed reference frame. The reference axis system standardized in guided weapons is centered on the cg and fixed in the body. These forces can be resolved along the missile's body-axis system (Xb, Yb, Zb) and fixed to the missile's center of gravity (cg). As discussed in Section 2.2, the forces acting on a missile in flight consist of aerodynamic, propulsive (i.e., thrust), and gravitational forces. In essence, the motion of the air around an aircraft or missile produces pressure and velocity variations, which produce the aerodynamic forces and moments. In practice, however, flow phenomena such as boundary-layer separation, shock-wave/boundary-layer interaction, and compressibility effects limit the range of flow conditions over which the dimensionless force and moment coefficients remain constant. In order to correlate the data for various stream conditions and configurations, the measurements are usually presented in dimensionless form. Briefly, the parameters that govern the magnitude of aerodynamic forces and moments include the following: (1) configuration geometry, (2) angle of attack, (3) vehicle size, (4) free-stream velocity, (5) density of the undisturbed air, (6) Reynolds number (i.e., as it relates to viscous effects), and (7) Mach number (i.e., as it relates to compressibility effects). Generally, the magnitude of the forces and moments that act on an air vehicle depend on the combined effects of many different variables. ![]() For a more in-depth discussion of these forces the reader is referred to, , and. However, the reader should be cautioned that both the aerodynamics and rigid-body dynamics are highly nonlinear. In particular, and unless otherwise specified, we will assume a skid-to-turn missile because this technique is used in the majority of both surface-to-air and air-to-air missile applications (for more details see Section 3.3.2). In this section we will discuss briefly the aerodynamic forces acting on a missile. 3.1 Aerodynamic Forces Relative to the Wind Axis System ![]()
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