Definition
The ratio of the lift produced by an airfoil or aircraft to the drag generated at the same angle of attack and airspeed, expressed as L/D. The maximum value of this ratio (L/Dmax) represents the most aerodynamically efficient operating point, where the wing produces the greatest amount of lift for the least amount of drag.
Plain English
A number showing how much lift a wing makes compared to how much drag it has to overcome. A higher number means the wing is working more efficiently — getting more useful force for less resistance.
Context Anchor
Seen in discussions of aircraft performance, gliding, configuration changes, and learner explanations of how an aircraft flies.
Derivation
Lift comes from an old word meaning to raise. Drag comes from a word meaning to pull or draw along. In aviation, those everyday ideas become specific forces: one helps support the aircraft, and the other holds it back as it moves through the air.
Why Pilots Care
The ratio directly determines best glide speed, maximum range, and how far an aircraft can travel after an engine failure.
Analogy
Think of it like miles per gallon for a wing. A higher L/D means more 'flight' for less 'cost' in drag.
Intuition Check
Lift is not just something being picked up by hand, and drag is not just something being pulled along the ground. Here, both are forces created by airflow around the aircraft: lift supports flight, and drag resists motion.
Example Sentence 1
After the engine quit, the pilot pitched for best glide speed, which is the airspeed that gives the highest lift-to-drag ratio.
Example Sentence 2
Knowing the aircraft's maximum lift/drag speed helps the pilot plan the longest possible distance after an engine failure.