Definition
A graph showing how the total drag acting on an aircraft in steady, level flight changes with airspeed. It is formed by adding parasite drag (which rises with speed) and induced drag (which falls with speed) at every airspeed. The lowest point on the curve identifies the speed at which total drag is minimum, which corresponds to the aircraft's best lift-to-drag ratio (L/Dmax).
Plain English
A line on a chart that shows how much total drag the aircraft is fighting at each airspeed. It dips in the middle because drag is high at very slow speeds and high at very fast speeds, with a sweet spot in between where drag is least.
Context Anchor
Seen in aerodynamics and performance discussions when explaining why an airplane has a most efficient speed range for flight or glide.
Why Pilots Care
The curve reveals the single airspeed at which total drag is lowest, which is also the speed for best glide and maximum endurance.
Grounding Statement
Picture slowing the airplane down: at first drag may decrease, but if you keep slowing, the airplane must work harder to keep flying and total drag rises again.
Intuition Check
Do not assume drag only increases as speed increases. On the total drag curve, total drag is high at very low speeds, lowest at one middle point, and high again at higher speeds.
Example Sentence 1
The instructor used the total drag curve to show why flying below best glide speed in an engine-out scenario actually increases the rate of descent.
Example Sentence 2
At the bottom of the total drag curve the airplane uses the least power to stay level.