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The drag curve or drag polar is the relationship between the drag on an aircraft and other variables, such as lift, the coefficient of lift, angle-of-attack or speed. It may be described by an equation or displayed as a graph (sometimes called a "polar plot"). [ 1 ]
Drag vs Speed. L/DMAX occurs at minimum Total Drag (e.g. Parasite plus Induced) Coefficients of drag C D and lift C L vs angle of attack. Polar curve showing glide angle for the best glide speed (best L/D). It is the flattest possible glide angle through calm air, which will maximize the distance flown.
It is also useful to show the relationship between section lift coefficient and drag coefficient. The section lift coefficient is based on two-dimensional flow over a wing of infinite span and non-varying cross-section so the lift is independent of spanwise effects and is defined in terms of L ′ {\displaystyle L^{\prime }} , the lift force ...
Lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, in aerodynamics, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air ...
This increase can cause the drag coefficient to rise to more than ten times its low-speed value. The value of the drag-divergence Mach number is typically greater than 0.6; therefore it is a transonic effect. The drag-divergence Mach number is usually close to, and always greater than, the critical Mach number.
If speed decreases, drag decreases, and the aircraft will accelerate back to its equilibrium speed where thrust equals drag. However, in slow flight, due to lift-induced drag, as speed decreases, drag increases (and vice versa). This is known as the "back of the drag curve". The aircraft will be speed unstable, because a decrease in speed will ...
Drag polar is the name used by aerodynamicists to describe how Cl varies with Cd, whether by a diagram or an equation. Drag polars do not use angles of attack explicitly, though drag curves and lift curves do. This is covered in the opening para. I've reverted the title, since this sort of plot/ equation is the subject of the article.
In the examples for close-hauled and reach (left and right), the sail's angle of attack (α) is essentially constant, although the boom angle over the boat changes with point of sail to trim the sail close to the highest lift force on the polar curve. In these cases, lift and drag are the same, but the decomposition of total aerodynamic force ...