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Lift and drag are the two components of the total aerodynamic force acting on an aerofoil or aircraft.. 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.
The power is equal to the drag force times velocity. For aircraft in cruise flight the lift is equal to the weight (L=mg) and the engine thrust is equal to the drag (T=D). Hence, ϵ = P / ( m g v ) = D / L = 1 / f {\displaystyle \epsilon =P/(mgv)=D/L=1/f} , with f=L/D the lift-to-drag ratio , so the specific resistance of airplanes is roughly ...
Drag and lift coefficients for the NACA 63 3 618 airfoil. Full curves are lift, dashed drag; red curves have R e = 3·10 6, blue 9·10 6. Coefficients of lift and drag against angle of attack. Curve showing induced drag, parasitic drag and total drag as a function of airspeed. Drag curve for the NACA 63 3 618 airfoil, colour-coded as opposite plot.
L/DMAX occurs at minimum Total Drag (e.g. Parasite plus Induced) Coefficients of Drag and Lift vs Angle of Attack. Stall speed corresponds to the Angle of Attack at the Maximum Coefficient of Lift. The lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air ...
For many applications the Clark Y has been an adequate airfoil section; it gives reasonable overall performance in respect of its lift-to-drag ratio, and has gentle and relatively benign stall characteristics. The flat lower surface is not optimal from an aerodynamic perspective, and it is rarely used in modern designs.
In reference to the above diagrams relating lift and drag, Garrett explains that for a maximum speed made good to windward, the sail must be trimmed to an angle of attack that is greater than the maximum lift/drag ratio (more lift), while the hull is operated in a manner that is lower than its maximum lift/drag ratio (more drag). [33]
The thrust-to-weight ratio and lift-to-drag ratio are the two most important parameters in determining the performance of an aircraft. The thrust-to-weight ratio varies continually during a flight. Thrust varies with throttle setting, airspeed, altitude, air temperature, etc. Weight varies with fuel burn and payload changes.
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 ′, the lift force per unit span of the wing. The ...