| Section A | A index | 231-239 of 917 terms |
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aerodrome meteorological minima—Limiting meteorological conditions prescribed for determining the usability of an aerodrome for a particular aviation operation (e.g., IFR takeoff or landing)
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aerodynamic balance—An instrument used for the measurement of the forces exerted on the surfaces of instruments exposed to flowing air. It is frequently used in tests made on models in wind tunnels. Compare aerostatic balance.
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aerodynamic force—The force exerted by a moving fluid (especially air) on a body immersed in it. The component of the aerodynamic force parallel to the direction of flow is called the drag.
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aerodynamic resistance—(Also called drag or aerodynamic drag.) The component of force exerted by the air on a liquid or solid object (such as a raindrop or airplane) that is parallel and opposite to the direction of flow relative to the object. See aerodynamic force.
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aerodynamic roughness length—(Also called the roughness length, z0.) The height above the displacement plane at which the mean wind becomes zero when extrapolating the logarithmic wind- speed profile downward through the surface layer. It is a theoretical height that must be determined from the wind-speed profile, although there has been some success at relating this height to the arrangement, spacing, and physical height of individual roughness elements such as trees or houses. The average wind speed  in the surface layer can be written using Monin–Obukhov similarity theory as  where z is height above ground, d is height of the displacement plane above ground, L is the Monin–Obukhov length scale, k is von Kármán's constant, ψ is a stability correction factor (= 0 for statically neutral conditions), and u* is the friction velocity. To determine aerodynamic roughness, most experimentalists prefer to make wind profile measurements during statically neutral conditions (windy, overcast, negligible temperature advection) so that ψ = 0 in the equation above. Compare Charnock's relation.
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aerodynamic—Pertaining to a body moving in a fluid, especially air. Sometimes the term aerodynamic is applied to a dynamically stable body (e.g., aircraft or automobile) with a low drag coefficient.
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