L/D max is defined as which of the following?

L/D max is defined as which of the following?

• A. The airspeed at which lift equals drag.
• B. The airspeed at which the difference between lift and drag is greatest.
• C. Maximum endurance speed.
• D. Maximum engine-out glide speed.

Answer: (B)

In aerodynamics, the idea behind L/D max is aerodynamic efficiency: the speed where the aircraft has the greatest lift-to-drag ratio, meaning it gets the most lift for the least amount of drag. That point corresponds to the best glide performance—a condition where the aircraft can cover the most horizontal distance for a given loss of altitude. The statement describing the airspeed at which the difference between lift and drag is greatest aligns with that efficiency idea. When lift is large relative to drag, the net effect is a more favorable balance for forward travel, which translates into the longest glide range for a given altitude. The other options describe different flight concepts: lift equaling drag is not the efficiency criterion for L/D max; maximum endurance relates to power and time aloft rather than glide efficiency; and engine-out glide speed is a practical application of best glide, but the formal definition centers on the lift-to-drag ratio.

In aerodynamics, the idea behind L/D max is aerodynamic efficiency: the speed where the aircraft has the greatest lift-to-drag ratio, meaning it gets the most lift for the least amount of drag. That point corresponds to the best glide performance—a condition where the aircraft can cover the most horizontal distance for a given loss of altitude.

The statement describing the airspeed at which the difference between lift and drag is greatest aligns with that efficiency idea. When lift is large relative to drag, the net effect is a more favorable balance for forward travel, which translates into the longest glide range for a given altitude. The other options describe different flight concepts: lift equaling drag is not the efficiency criterion for L/D max; maximum endurance relates to power and time aloft rather than glide efficiency; and engine-out glide speed is a practical application of best glide, but the formal definition centers on the lift-to-drag ratio.