# THE AERODYNAMIC ANGLES

The linear motion V of the vehicle relative to the atmosphere can be given either by its three orthogonal components (и, v, w) in a body-axis system (see examples in Figs. 4.4 to 4.7), or alternatively by the magnitude V and two suitably defined angles. These angles, which are of fundamental importance in determining the aerodynamic forces that act on the vehicle, are defined thus:

Angle of attack (see Fig. 4.4):

otx = tan 1 – — я – < аж < 7Г (4.3,2)

и

Sideslip angle (see Fig. 4.5):

It is most important to note that oq. as here defined will be the same as that commonly used in aerodynamic theory and in wind-tunnel testing only if the body axis Gx is parallel to the basic aerodynamic reference direction, i. e. the mean aerodynamic chord or the zero-lift line. f Otherwise it differs by a constant. When the body axes used are stability axes Fs, the latter will normally be the case. It follows that the velocity components in the body axes are

(4.3,4)

It will be observed that, in the sense of Euler angles, the aerodynamic angles relate the two frames Fw and FB by the rotation sequence (—/3, oq, 0) which carry the former into the latter.

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