Lift-to-Drag Ratio - with wetted aspect ratio


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. A higher or more favorable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft’s required lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy, climb performance, and glide ratio.
The term is calculated for any particular airspeed by measuring the lift generated, then dividing by the drag at that speed. These vary with speed, so the results are typically plotted on a 2D graph. In almost all cases the graph forms a U-shape, due to the two main components of drag.
Most importantly, the maximum lift-to-drag ratio is independent of the weight of the aircraft, the area of the wing, or the wing loading.
This equation demonstrates the importance of wetted aspect ratio in achieving an aerodynamically efficient design.

Related formulas


Llift (N/m2)
Ddrag (N/m2)
ϵspan efficiency factor, a number less than but close to unity for long, straight edged wings (dimensionless)
Cfeequivalent skin friction coefficient (dimensionless)
bwingspan (m)
Swetwetted area (m2)