Definition
The airspeed that produces the greatest gain in altitude per unit of horizontal distance traveled. At VX, the airplane climbs at the steepest possible angle relative to the ground, which is useful when terrain or obstacles must be cleared shortly after takeoff. VX is typically slower than VY (best rate of climb airspeed) at sea level, and the two speeds converge with increasing altitude until they meet at the airplane's absolute ceiling.
Plain English
The speed that gives you the most height gained for the least distance traveled forward. You use it when you need to climb steeply to clear something ahead.
Context Anchor
Seen in climb performance discussions, takeoff planning, and the airplane’s operating handbook.
Derivation
The 'V' in V-speeds comes from the French 'vitesse,' meaning speed. The 'X' is simply a label the FAA and ICAO use to distinguish this particular speed from others (VY, VS, VA, etc.). It does not stand for a word.
Why Pilots Care
Using VX after liftoff gives the shortest distance to reach a safe altitude when trees, power lines, or terrain lie just beyond the runway end.
Grounding Statement
VX is the speed for climbing over something ahead, not the speed for getting to altitude in the shortest time.
Intuition Check
Do not read “best angle” as “pull the nose up as high as possible.” VX is a specific airspeed, and pitching too high can slow the airplane too much.
Example Sentence 1
After rotation, the pilot held VX until clear of the trees at the end of the runway, then lowered the nose and accelerated to VY.
Example Sentence 2
At high density altitude the pilot still flew the published VX but recognized that the actual climb gradient would be shallower than on a standard day.