208 DICTIONARY OF AVIATION
squall-cloud 'skiuci^ktaud n. the roll-cloud in front ef and above a squall of wind or in front of a thunder-storm cloud. squall-wind 'sku)c:l,wind n. a squally wind, such as the out- blowing wind due to the kick of a thundercloud. squally 'skiuc:-li adv. abounding with squalls or strong gusts
of wind; having the nature ot a squall; gusty. stability sta'bih-ti n. the state, condition, or property of being stable, stedy, or habitually well balanced in the air; the character of equilibrium; equipoise, balance, stableness, stediness.
automatic stability, stability or stediness maintaind in an air-craft by automatic means; balance by means of self* acting mechanism; automatic equilibrium or balance.
directional stability, stability or stediness of an aerodone or air-craft in respect of its direction or tjanslatory motion, or of the course of its flight; directional equilibrium.
dynamic stability, stability of an aerodone or air-craft due to the forces acting upon it so as to keep it in motion ; dynamic equilibrium : distinguisht from static stability.
equation of stability, the equation which expresses the mutual relations of the factors concernd in the stability of an aerodone or air-craft.
foretandzaft stability, longitudinal stability.
horizontal stability, the stability or stediness of an aero- done or air-craft in the right-and-left or transverse direc- tion ; lateral stability : distinguisht from longitudinal sta- bility.
lateral stability, stability or stediness in a side-to-side direction; transverse balance or equipoise; the quality or condition of net tipping sidewise or rolling from side to side during travel ; lateral equilibrium : distinguisht from longitudinal stability.
longitudinal stability, stability or stediness in the longitu- dinal or fore-and-aft direction ; fore-and-aft stability ; longitudinal equilibrium : distinguisht from lateral stability.
pendular stability, stability or equilibrium resembling that of a pendulum or free-siuinging hanging body: as, the
- pendular stability of a helicopter.
rotative stability, stability of an aerodone or air-craft in respect of its rotativ or rotary motion around a vertical axis, or an axis perpendicular to its flight-path, and result- ing from the interaction of the motions involvd in the maintenance of lateral and directional stability.
static stability, stability of a material object which is sta- tionary or motionless ; static equilibrium : distinguish! from dynamic stability.
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