Definition
The specific angle of attack and airspeed at which an airplane produces the greatest amount of lift for the least amount of drag. At this point, the ratio of lift to drag is at its highest value, which corresponds to the most efficient flight condition aerodynamically. In a power-off glide, flying at L/DMAX produces the maximum glide distance for a given altitude.
Plain English
The single airspeed where the wing is working most efficiently — getting the most lift for the least drag. If the engine quits, this is the speed that lets the airplane glide the farthest.
Context Anchor
Seen in glide performance discussions, especially when learning best glide speed and how far the airplane can glide after a power loss.
Derivation
L/D is shorthand for the ratio of Lift divided by Drag — two of the four forces acting on an airplane. 'MAX' simply marks the highest point that ratio reaches. So L/DMAX is the peak of the lift-to-drag curve — the sweet spot where the wing gives you the most lift per unit of drag.
Why Pilots Care
Maintaining L/DMAX after an engine failure lets the pilot reach the farthest possible landing spot.
Analogy
Think of coasting a bicycle downhill. There is a speed where you roll the farthest before losing height; too slow or too fast wastes energy sooner. L/DMAX is the airplane’s version of that most efficient coasting point.
Grounding Statement
In a glide with no engine power, L/DMAX is the condition that gives the most forward travel for the altitude being lost.
Intuition Check
L/DMAX does not mean the airplane is making the most lift, and it does not mean drag is zero. It means lift and drag are in their best balance for glide distance.
Example Sentence 1
After the engine lost power, the pilot pitched for L/DMAX to stretch the glide toward the nearest field.
Example Sentence 2
The handbook lists the airspeed for L/DMAX as the target for maximum glide distance.