The lift-to-drag ratio (L/D) is the amount of lift generated by a wing or airfoil compared to its drag. The L/D ratio indicates airfoil efficiency. Aircraft with higher L/D ratios are more efficient than those with lower L/D ratios. By plotting the induced and parasitic drag relative to speed, a ‘U’ shaped profile emerges as shown below. This profile is known as total drag and is simply the sum of the induced and parasitic drag.
An unbelievable feature of gliding performance is the effect of airplane gross weight. Since the maximum L/D ratio of a given airplane is an intrinsic property of the aerodynamic configuration, the gross weight will not affect the gliding performance.
For example, if an aircraft has an (L/D)MAX of 15, it can obtain a maximum of 15 miles horizontal distance for each mile of altitude. This would be true of this particular airplane at any gross weight if the airplane is flown at the angle of attack for (L/D)MAX. Of course, the gross weight would affect the glide airspeed necessary for this particular angle of attack but the glide ratio would be unaffected.