The accompanying diagram shows a drag polar for a typical light aircraft.Such diagrams identify a minimum C D point at the left-most point on the plot, where the drag is locally independent of lift; to the right, the drag is lift related. The line which is the tangent to the polar curve represents the best lift/drag ratio. Xfoil. In this example the best lift/drag ratio is 13, that is; the lift is 13 x the drag. There is also a graph of lift coefficient (Cl) against drag coefficient (Cd) which gives the theoretical glide angle of the airfoil. All the polar diagrams currently available have been produced using Xfoil, an application created by Mark Drela and Harold Youngren for the design and analysis of subsonic airfoils. The coefficients CL and CD are simply dimensionless numbers that when multiplied by the square of the velocity, the density of air and the wing area give the result in Lift or Drag … The best lift/ drag ratio for normal light aircraft is typically between 15 … In aerodynamics, 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. It provides the largest gliding distance. This will produce an aircraft with an optimized lift-to-drag ratio which is the minimum drag configuration. One component here is the induced drag of the wing, an unavoidable companion of the wing's lift, though one that can be reduced by increasing the aspect ratio. The trick when designing and specifying an airfoil profile for an aircraft is to try and ensure that the operating lift coefficient (usually the lift coefficient at cruise) corresponds to an angle of attack where the drag is at a minimum. The third curve is the ratio of lift coefficient to the drag coefficient. PF 4.5. Because wind turbine and fan airfoils have finite lengths, model equations must contain explicit adjustments for the effects of aspect ratio (length to chord width) on lift and drag.

Also, it is the Least thrust required however does not mean least fuel consumed which is why "Best Endurance" is a different value. a lift/drag ratio of 13.
This curve is labeled L/D. ~7: Largest Lift to Drag Ratio - Also known as the Gliding Angle of Attack, and on some aircraft, Best Climb Rate Angle of Attack. minimum of test data, because often only a limited number of lift and drag data points in just the pre-stall regime are available. the drag coefficient. Fig.