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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.
It is a better measure of the aerodynamic efficiency of an aircraft than the wing aspect ratio. It is defined as: = where is span and is the wetted surface. Illustrative examples are provided by the Boeing B-47 and Avro Vulcan. Both aircraft have very similar performance although they are radically different.
A wing of infinite span and uniform airfoil segment (or a 2D wing) would experience no induced drag. [11] The drag characteristics of a wing with infinite span can be simulated using an airfoil segment the width of a wind tunnel. [12] An increase in wingspan or a solution with a similar effect is one way to reduce induced drag.
In two-dimensional flow around a uniform wing of infinite span, the slope of the lift curve is determined primarily by the trailing edge angle. The slope is greatest if the angle is zero; and decreases as the angle increases. [14] [15] For a wing of finite span, the aspect ratio of the wing also significantly influences the slope of the curve ...
For conventional fixed-wing aircraft with moderate aspect ratio and sweep, Oswald efficiency number with wing flaps retracted is typically between 0.7 and 0.85. At supersonic speeds, Oswald efficiency number decreases substantially. For example, at Mach 1.2 Oswald efficiency number is likely to be between 0.3 and 0.5. [1]
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 word "wing" from the Old Norse vængr [1] for many centuries referred mainly to the foremost limbs of birds (in addition to the architectural aisle). But in recent centuries the word's meaning has extended to include lift producing appendages of insects, bats, pterosaurs, boomerangs, some sail boats and aircraft, or the airfoil on a race 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 Max Munk ...