Definition
The minimum airspeed at which an airplane can maintain controlled flight in a specified configuration with the wing flaps fully retracted. It is higher than the stall speed with flaps extended, because retracted flaps produce less lift at a given angle of attack, requiring more airspeed to keep the wing flying.
Plain English
The slowest speed the airplane can fly without stalling when the flaps are all the way up. With the flaps up, the wing needs more speed to keep producing enough lift, so this stall speed is faster than it would be with flaps down.
Context Anchor
Seen in airplane handling discussions, performance data, and abnormal situations such as an asymmetric or split-flap condition.
Derivation
“Stall” originally carries the idea of stopping. In aviation, it means the wing has stopped making smooth, usable lift. “Flaps-up” is pilot shorthand for the flaps being retracted, not extended for extra lift.
Why Pilots Care
This higher stall speed must be known when flaps cannot be lowered, so the pilot selects appropriate maneuvering and approach speeds to avoid inadvertent stall.
Grounding Statement
With the flaps retracted, the wing usually needs more speed to keep producing enough lift.
Intuition Check
“Flaps-up” does not mean the flaps are pointing upward; it means they are retracted. Also, stall speed is not one fixed number—it changes with conditions such as weight and bank angle.
Example Sentence 1
After the right flap failed to extend, the pilot flew the approach well above the flaps-up stall speed and planned for a longer landing roll.
Example Sentence 2
The checklist directed the crew to use flaps-up stall speed plus 15 knots for the approach after the flap system malfunction.