Definition
A graph that plots the total drag acting on an airplane against airspeed in level flight. Total drag is the sum of induced drag (which decreases as airspeed increases) and parasite drag (which increases as airspeed increases). The curve is U-shaped, and the lowest point on the curve identifies the airspeed at which total drag is at its minimum, known as L/D max.
Plain English
A chart showing how much the air pushes back on an airplane at different speeds. At very slow speeds drag is high, at very fast speeds drag is also high, and there is a sweet spot in the middle where drag is lowest.
Context Anchor
Seen in airplane performance, slow flight, glide, and power-required discussions.
Derivation
‘Drag’ comes from Old Norse ‘draga,’ meaning to pull or draw. ‘Curve’ comes from Latin ‘curvus,’ meaning bent. Together: a bent line on a graph showing how the pulling-back force changes with speed.
Why Pilots Care
It identifies the airspeed at which total drag is lowest, allowing the most efficient flight for range, endurance, or glide distance.
Grounding Statement
Drag is lowest somewhere in the middle of the speed range, not at the slowest speed as many people first assume.
Intuition Check
A drag curve is not the path the airplane flies through the air. It is a graph showing how much drag the airplane has at different airspeeds.
Example Sentence 1
The instructor pointed to the bottom of the drag curve to show where best glide speed comes from.
Example Sentence 2
The lowest point on the drag curve indicates the airspeed for minimum total drag during a glide.