Lift To Drag Ratio
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. A higher or more favourable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft's needed lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy and climb performance.
The effect of airspeed on the rate of descent can be depicted by a polar curve. These curves show the airspeed where minimum sink can be achieved and the airspeed with the best L/D ratio. The curve is an inverted U-shape. As speeds reduce the amount of lift falls rapidly around the stalling speed. The peak of the 'U' is at minimum drag.
As lift and drag are both proportional to the coefficient or Lift and Drag respectively multiplied by the same factor (1/2mv2S), the L/D ratio can be simplified to the Coefficient of lift divided by the coefficient of drag or Cl/Cd, and since both are proportional to the airspeed, the ratio of L/D or Cl/Cd is then typically plotted against angle of attack.
Read more about this topic: Gliding Flight
Famous quotes containing the words lift, drag and/or ratio:
“Men, forever tempted to lift the veil of the future—with the aid of computers or horoscopes or the intestines of sacrificial animals—have a worse record to show in these “sciences” than in almost any scientific endeavor.”
—Hannah Arendt (1906–1975)
“I know those little phrases that seem so innocuous and, once you let them in, pollute the whole of speech. Nothing is more real than nothing. They rise up out of the pit and know no rest until they drag you down into its dark.”
—Samuel Beckett (1906–1989)
“Official dignity tends to increase in inverse ratio to the importance of the country in which the office is held.”
—Aldous Huxley (1894–1963)