V speeds

V speeds (aircraft) are speeds that define certain performance and limiting characteristics of an aircraft and the "V" stands for velocity. They are established by the manufacturer during design and testing, and are specific to the aircraft model, and in many cases (V1, V2, Vref, and several others) based on the current weight and balance characteristics of the individual aircraft, as described below. Usually "V speeds" are relative to the air through which the aircraft is moving and are thus airspeeds. In many cases, they are defined by reference to the standard atmosphere or other specific conditions, and/or at the aircraft's maximum gross weight, and the pilot is responsible for calculating the effective value based on the actual weight and air density. In other cases the indicated airspeed, the value uncorrected for atmospheric pressure differences (height and temperature), is useful directly by the pilot. For example, the indicated stall speed VS remains essentially constant for all heights and temperatures while the true stall speed increases as pressure lessens.

In the U.S., V speeds are stated in knots or, for older aircraft models, miles per hour. For faster aircraft, some speeds are also defined by Mach number. Typically, V speeds are given for an aircraft at maximum gross weight, and are adjusted for lighter weights, the scheduled figures being given in the aircraft Flight Manual and Performance Manual.