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In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under given flight conditions. The L/D ratio for any given body will vary according to these flight conditions.
Automotive aerodynamics differs from aircraft aerodynamics in several ways: The characteristic shape of a road vehicle is much less streamlined compared to an aircraft. The vehicle operates very close to the ground, rather than in free air. The operating speeds are lower (and aerodynamic drag varies as the square of speed).
The total aerodynamic force acting on a body is usually thought of as having two components, lift and drag. By definition, the component of force parallel to the oncoming flow is called drag; and the component perpendicular to the oncoming flow is called lift. [7] [4]: Section 5.3 At practical angles of attack the lift greatly exceeds the drag. [8]
Spoilers are added to cars primarily for styling and either have little aerodynamic benefit or worsen the aerodynamics. The term "spoiler" is often mistakenly used interchangeably with "wing". An automotive wing is a device designed to generate downforce as air passes around it, not simply disrupt existing airflow patterns.
The term drag area derives from aerodynamics, where it is the product of some reference area (such as cross-sectional area, total surface area, or similar) and the drag coefficient. In 2003, Car and Driver magazine adopted this metric as a more intuitive way to compare the aerodynamic efficiency of various automobiles.
For comparison: the top ten most aerodynamic production cars in 2014/2015 were in the range 0.26 down to 0.19. [ 3 ] [ 4 ] The Fiat Balilla of the mid-1930s, by contrast, was rated at 0.60. [ 5 ] To enable the car's aerodynamic shape, the Tropfenwagen also featured the world's first (single plane) curved windows in a production car.
The Lanchester-Prandtl lifting-line theory [1] is a mathematical model in aerodynamics that predicts lift distribution over a three-dimensional wing from the wing's geometry. [2] The theory was expressed independently [ 3 ] by Frederick W. Lanchester in 1907, [ 4 ] and by Ludwig Prandtl in 1918–1919 [ 5 ] after working with Albert Betz and ...
Foils of similar function designed with water as the working fluid are called hydrofoils. When oriented at a suitable angle, a solid body moving through a fluid deflects the oncoming fluid (for fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the deflection.