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Chapter VII
Lateral and Directional Stability
§ 83. Introductory.—Lateral and directional stability relate to the equilibrium of the aerodone in respect of its three degrees of freedom involved by motions other than those in the phugoid plane.[1] Thus lateral stability is concerned primarily with rotation about the axis of flight; that is, a motion resembling the
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Fig. 75.
rolling of a ship; if such a motion does not give rise to a restoring couple an aerodone may turn over, otherwise "capsize," and so lose its equilibrium. Directional stability involves rotation about a vertical axis and motion of translation at right angles to the phugoid plane, these two kinds of motion being associated in any change of course.
- ↑ The vertical plane containing the flight path: see Chap. II.
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