Definition
The airspeed at which total drag on the airplane is at its lowest value. It is the point on the drag curve where induced drag (drag produced by lift) and parasite drag (drag produced by the airplane moving through the air) are equal. Flying slower than this speed increases induced drag sharply; flying faster increases parasite drag. Minimum drag speed also corresponds to the speed for maximum lift-to-drag ratio (L/D max), which gives the best glide range and the most efficient cruise from a drag standpoint.
Plain English
The speed at which the airplane is slipping through the air with the least total resistance. Go slower or faster than this speed and drag goes up.
Context Anchor
You encounter this term in slow flight and power-required discussions, especially when learning why slower flight can sometimes need more power, not less.
Derivation
Minimum comes from Latin words meaning smaller or least. Drag comes from an old word meaning to pull or draw something along. Together, the phrase points to the speed where the air’s pulling-back force on the airplane is least.
Why Pilots Care
It is the speed that yields maximum glide distance after an engine failure and marks the point below which drag rises rapidly.
Grounding Statement
Below this speed, the wing is working hard to stay flying and induced drag dominates. Above it, the airplane is pushing harder against the air and parasite drag dominates. Right at it, the two are balanced and total drag is at its smallest.
Intuition Check
Do not read “minimum” as “slowest safe speed.” Here it means the speed with the least total drag.
Example Sentence 1
After the engine quit, he pitched for minimum drag speed to stretch the glide as far as possible toward the field.
Example Sentence 2
During slow-flight practice the instructor asked the student to identify minimum drag speed on the airspeed indicator before demonstrating the rising drag curve.