Definition
The airspeed at which an airplane, during the takeoff roll, generates enough lift to leave the runway and become airborne. Also called rotation speed in some aircraft, it is determined by aircraft weight, configuration, and manufacturer guidance, and is reached after sufficient acceleration along the runway.
Plain English
The speed the airplane needs to be going down the runway before the wings can lift it into the air.
Context Anchor
Seen in takeoff discussions and in power-on stall practice, where the airplane may be slowed to about the speed it would normally have as it leaves the runway.
Derivation
“Lift-off” is a plain English aviation phrase for the moment an aircraft lifts away from the surface. The useful point is that “lift-off speed” refers to that leaving-the-runway moment, not just to the general force called lift.
Why Pilots Care
Determines the point at which rotation must produce flight, affecting runway distance required and stall margin.
Intuition Check
Lift-off speed is not simply the speed where the pilot pulls back on the controls. It is the speed where the airplane can actually become airborne for its current weight and setup.
Example Sentence 1
As the airplane accelerated through lift-off speed, the pilot applied smooth back pressure and the main wheels left the runway.
Example Sentence 2
During a short-field takeoff the goal is to reach lift-off speed with the shortest possible ground roll.