Definition
A flight condition for a glider or unpowered aircraft in which the airspeed is set to give the lowest possible rate of descent, allowing the aircraft to remain airborne for the maximum amount of time. This speed is slower than the best glide speed (which gives the greatest distance) and corresponds to the minimum sink point on the aircraft's power-required or sink-rate curve.
Plain English
The forward speed at which a glider loses altitude most slowly. Flying at this speed keeps the aircraft in the air longer, but it does not cover the most ground.
Context Anchor
Seen in aircraft performance, glide, descent, and helicopter autorotation discussions.
Why Pilots Care
Determines how far a pilot can glide to reach a suitable landing site after power loss.
Grounding Statement
Picture the aircraft moving ahead across the sky while its altitude changes only slowly.
Intuition Check
Do not read “least vertical speed” as “no vertical movement.” It means the smallest rate of altitude change for that flight condition, not necessarily level flight or the best distance-covered speed.
Example Sentence 1
When the pilot found a weak thermal, he slowed the glider to its minimum sink speed to stay aloft as long as possible while circling.
Example Sentence 2
The student practiced adjusting pitch to achieve forward speed and the least vertical speed during simulated emergencies.