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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.
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]
The significant aerodynamic properties of aircraft wings are summarised by two dimensionless quantities, the lift and drag coefficients C L and C D. Like other such aerodynamic quantities, they are functions only of the angle of attack α, the Reynolds number R e and the Mach number M. C L and C D can be plotted against α, or can be plotted ...
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 aerodynamic center is the point at which the pitching moment coefficient for the airfoil does not vary with lift coefficient (i.e. angle of attack), making analysis simpler. [ 1 ] d C m d C L = 0 {\displaystyle {dC_{m} \over dC_{L}}=0} where C L {\displaystyle C_{L}} is the aircraft lift coefficient .
Aerodynamics – is the study of the motion of air, particularly with respect to its interaction with a solid object, such as an airplane wing. Aerodynamics is a sub-field of gas dynamics, which in turn is a sub-field of fluid dynamics. Many aspects and principles of aerodynamics theory are common to these three fields.