What the V-n diagram shows
A flight envelope, plotted as a V-n diagram, maps an aircraft's safe operating region with airspeed (V) on the horizontal axis and load factor (n, the ratio of lift to weight, measured in g) on the vertical axis. Every point inside the closed boundary is a combination of speed and g-loading the aircraft can sustain without stalling or structural damage.
The boundary is formed by distinct limits. On the low-speed side, curved stall lines mark where the wing can no longer generate the lift required for a given load factor. On the high side, horizontal lines mark the maximum positive and negative structural load factors the airframe is certified to withstand.
Key speeds on the envelope
Two reference speeds anchor the diagram. The maneuvering speed (Va) is where the stall limit meets the maximum load factor; below it the wing stalls before structural limits are exceeded, so full control deflection cannot overstress the airframe. The never-exceed speed (Vne) caps the high-speed side, beyond which flutter or structural failure becomes a risk.
Gust load lines are often overlaid to show how turbulence adds load factor at a given speed. The diagram is a core tool in aircraft structural design and certification, defining the limits pilots must respect.