Vertical stability. Stability about an aircraft’s vertical axis. Also called yawing or directional stability. 

V$_{FE}$. The maximum speed with the flaps extended. The upper limit of the white arc. 

V$_{FO}$. The maximum speed that the flaps can be extended or retracted. 

VFR Terminal Area Charts (1:250,000). Depict Class B airspace which provides for the control or segregation of all the aircraft within the Class B airspace. The chart depicts topographic information and aeronautical information which includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and related data. 

V-G diagram. A chart that relates velocity to load factor. It is valid only for a specific weight, configuration, and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds. 

Visual approach slope indicator (VASI). The most common visual glidepath system in use. The VASI provides obstruction clearance within 10° of the extended runway centerline, and to 4 nautical miles (NM) from the runway threshold. 

Visual Flight Rules (VFR). Code of Federal Regulations that govern the procedures for conducting flight under visual conditions. 

V$_{LE}$. Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended. 

V$_{LOF}$. Lift-off speed. The speed at which the aircraft departs the runway during takeoff. 

V$_{LO}$. Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear. 

V$_{MC}$. Minimum control airspeed. This is the minimum flight speed at which a twin-engine airplane can be satisfactorily controlled when an engine suddenly becomes inoperative and the remaining engine is at takeoff power. 

V$_{MD}$. Minimum drag speed. 

V$_{MO}$. Maximum operating speed expressed in knots. 

V$_{NE}$. Never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator. 

V$_{NO}$. Maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc. 

V$_{P}$. Minimum dynamic hydroplaning speed. The minimum speed required to start dynamic hydroplaning. 

V$_{R}$. Rotation speed. The speed that the pilot begins rotating the aircraft prior to lift-off. 

V$_{S0}$. Stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc. 

V$_{S1}$. Stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc. 

V$_{SSE}$. Safe, intentional one-engine inoperative speed. The minimum speed to intentionally render the critical engine inoperative. 

V-tail. A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers. 

V$_{X}$. Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle. 

V$_{XSE}$. Best angle of climb speed with one engine inoperative. The airspeed at which an airplane gains the greatest amount of altitude in a given distance in a light, twin-engine airplane following an engine failure. 

V$_{Y}$. Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time. 

