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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.
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]
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.
Wings are defined by two shape characteristics, an airfoil section and a planform. Wing efficiency is expressed as lift-to-drag ratio, which compares the benefit of lift with the air resistance of a given wing shape, as it flies. Aerodynamics is the study of wing performance in air.
[37] [38] In this case, the aerodynamic advantages of the flying wing are not the primary reasons for the design's adoption. However, modern computer-controlled fly-by-wire systems allow for many of the aerodynamic drawbacks of the flying wing to be minimized, making for an efficient and effectively stable long-range bomber. [39] [40]
A fixed-wing aircraft increases or decreases the lift generated by the wings when it pitches nose up or down by increasing or decreasing the angle of attack (AOA). The roll angle is also known as bank angle on a fixed-wing aircraft, which usually "banks" to change the horizontal direction of flight.
An elliptical planform is the most efficient aerodynamic shape for an untwisted wing, leading to the lowest amount of induced drag. The semi-elliptical planform was skewed so that the centre of pressure, which occurs near the quarter-chord position at all but the highest speeds, was close to the main spar, preventing the wings from twisting ...
Nonplanar wings: results for the optimal aerodynamic efficiency ratio ε. The parameter ε is the optimal aerodynamic efficiency ratio [25] and represents the ratio between the aerodynamic efficiency of a given non-planar wing and the corresponding efficiency of a reference classical cantilevered wing with the same wing span and total lift ...