Definition
A graph that shows an aircraft's flight envelope by plotting load factor (g) on the vertical axis against airspeed (V) on the horizontal axis. The diagram defines the combinations of speed and load factor at which the aircraft can be operated safely, bounded by the aerodynamic stall limit, the structural limit load factors (positive and negative), and the never-exceed speed.
Plain English
A chart that shows how much g-force the airplane can handle at different airspeeds. The area inside the lines is safe; outside the lines, you either stall the wing or risk breaking the airplane.
Context Anchor
Seen in aerodynamics training, aircraft limitations discussions, and explanations of why abrupt control movements become more dangerous at higher airspeeds.
Derivation
The 'V' stands for velocity (airspeed) and the 'g' stands for the load factor expressed in multiples of gravity. So 'Vg' is simply velocity-versus-g — the two things the diagram plots against each other.
Why Pilots Care
It defines the boundaries pilots must respect to avoid overstressing the airframe in turbulence or during maneuvers.
Grounding Statement
The safe operating area is inside the boundary of the diagram; outside it, the aircraft is either stalled or being loaded too heavily.
Intuition Check
Do not read a Vg diagram as a chart of best performance speeds. It is a limits chart: it shows combinations of speed and loading that are safe, stalled, or structurally unsafe.
Example Sentence 1
The instructor pointed to the Vg diagram to show why pulling hard on the controls at cruise speed could exceed the airplane's structural limits.
Example Sentence 2
Designers use the Vg diagram to set the gust load lines that determine the airplane's certified flight envelope.