Definition
VX is the airspeed that produces the greatest gain in altitude per unit of horizontal distance traveled. At VX, the airplane climbs at the steepest angle relative to the ground, making it the speed used when maximum altitude must be gained over the shortest possible distance — for example, to clear an obstacle shortly after takeoff.
Plain English
VX is the speed that lets the airplane climb at the steepest angle. You travel less ground distance for each foot of altitude gained, so you go up more sharply. It's the speed to use when you need to clear something ahead, like trees at the end of a short runway.
Context Anchor
Seen in takeoff and climb procedures, especially when discussing how to clear obstacles near the departure end of a runway.
Derivation
The 'V' comes from the aviation convention of using V (for velocity) followed by a letter to label specific airspeeds. The 'X' is simply the assigned letter for this particular speed and does not stand for a word.
Why Pilots Care
VX is used after takeoff when nearby obstacles must be cleared in the shortest distance.
Analogy
VX is like choosing the steepest safe path up a hill when there is a fence close ahead. The goal is not to cover ground quickly; the goal is to gain height before reaching the obstacle.
Intuition Check
Best angle of climb does not mean the highest nose-up attitude. It means the speed that gives the most altitude gained for the least forward distance traveled.
Example Sentence 1
After lifting off from the short strip with trees at the departure end, the pilot pitched up and held VX until clear of the obstacle.
Example Sentence 2
The POH shows VX decreasing as aircraft weight increases.