V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft (including fixed-wing aircraft, gliders, autogiros, helicopters, and dirigibles).
These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing and verified in most countries by government flight inspectors during aircraft type-certification testing.
Using them is considered a best practice to maximize aviation safety and aircraft performance.
The speeds are specific to a particular model of aircraft, and are expressed in terms of the aircraft's indicated airspeed, so that pilots may use them directly, without having to apply correction factors.
Proper display of V speeds is an airworthiness requirement for type-certificated aircraft in most countries.
In general aviation aircraft, the most commonly used and most safety-critical airspeeds are displayed as colour-coded arcs and lines located on the face of an aircraft's airspeed indicator:
Two more information appear on light twin-engine aircrafts:
|V1||Engine failure recognition speed or decision speed. It is the maximum speed in the take-off at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the take-off, following a failure of the critical engine at VEF, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the take-off distance. If an engine failure is detected after V1, the take-off must be continued. This implies that the aircraft must be controllable on ground. Therefore, V1 is always greater than VMCG.|
|V2||Take-off safety speed. It is the minimum speed that needs to be maintained up to acceleration altitude, in the event of an engine failure after V1. Flight at V2 ensures that the minimum required climb gradient is achieved, and that the aircraft is controllable.
V2 speed is always greater than VMCA, and facilitates control of the aircraft in flight.
In an all-engines operative take-off, V2+10 provides a better climb performance than V2.
|V3||Flap retraction speed|
|V4||Steady initial climb speed. The all engines operating take-off climb speed used to the point where acceleration to flap retraction speed is initiated. Should be attained by a gross height of 400 feet.|
|VA||Design manoeuvring speed. This is the speed above which it is unwise to make full application of any single flight control (or "pull to the stops") as it may generate a force greater than the aircraft's structural limitations.|
|Vat||Indicated airspeed at threshold, which is equal to the stall speed VS0 multiplied by 1.3 or stall speed VS1g multiplied by 1.23 in the landing configuration at the maximum certificated landing mass. If both VS0 and VS1g are available, the higher resulting Vat shall be applied.
Also called "approach speed".
|VB||Design speed for maximum gust intensity.|
|VC||Design cruise speed, used to show compliance with gust intensity loading.|
|Vcef||Generally used in documentation of military aircraft performance as V1.|
|VD||Design diving speed.|
|VDF||Demonstrated flight diving speed.|
|VEF||The speed at which the Critical engine is assumed to fail during take-off.|
|VF||Designed flap speed.|
|VFC||Maximum speed for stability characteristics.|
|VFE||Maximum flap extended speed.|
|VFTO||Final take-off speed|
|VH||Maximum speed in level flight at maximum continuous power.|
|VLE||Maximum landing gear extended speed. This is the maximum speed at which it is safe to fly a retractable gear aircraft with the landing gear extended.|
|VLO||Maximum landing gear operating speed. This is the maximum speed at which it is safe to extend or retract the landing gear on a retractable gear aircraft.|
|VMC||Minimum control speed. Mostly used as the minimum control speed for the take-off configuration (take-off flaps) in many publications. Several VMC's exist for different flight phases and airplane configurations: VMCG, VMCA, VMCA1, VMCA2, VMCL, VMCL1, VMCL2. Refer to the minimum control speed article for a thorough explanation.|
|VMCA||Minimum control speed in the air (or airborne) for maintaining steady straight flight when an engine fails or is inoperative and with the corresponding opposite engine set to provide maximum thrust, provided a small (3°) 5° bank angle is being maintained away from the inoperative engine and the rudder is used up to maximum to maintain straight flight. The exact required bank angle should be provided by the manufacturer with VMC(A) data. Refer to the minimum control speed article for a description of (pilot-induced) factors that have influence on VMCA. VMCA is also presented as VMC in many manuals.|
|VMCG||Minimum control speed on the ground is the lowest speed at which the take-off may be safely continued following an engine failure during the take-off run. Below VMCG, the throttles need to be closed at once when an engine fails, to avoid veering off the runway.|
|VMCL||Minimum control speed in the landing configuration with one engine inoperative|
|VMO||Maximum operating limit speed.|
|VMU||Minimum unstick speed. It is achieved by pitching the aircraft up to the maximum (tail on the runway, for aircraft that are geometrically-limited) during the take-off roll. The speed at which the aircraft first lifts off is VMU. Therefore, lift-off is not possible prior to VMU.|
|VNE||Never exceed speed.|
|VNO||Maximum structural cruising speed or maximum speed for normal operations.|
|VO||Maximum operating manoeuvring speed.|
|VR||Rotation speed. The speed at which the aircraft's nose wheel leaves the ground during take-off.|
|Vrot||Used instead of VR (in discussions of the take-off performance of military aircraft) to denote rotation speed in conjunction with the term VRef (refusal speed).|
|VRef||Landing reference speed orthreshold crossing speed.
VRef stands for refusal speed for military aircraft. Refusal speed is the maximum speed during take-off from which the air vehicle can stop within the available remaining runway length for a specified altitude, weight, and configuration.
|VS||Stall speed or minimum steady flight speed for which the aircraft is still controllable.|
|VS0||Stall speed or minimum flight speed in landing configuration|
|VS1||Stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration|
|VSR||Reference stall speed.|
|VSR0||Reference stall speed in landing configuration.|
|VSR1||Reference stall speed in a specific configuration|
|VSW||Speed at which the stall warning will occur.|
|VTOSS||Category A rotorcraft take-off safety speed.|
|VX||Speed that will allow for best angle of climb.|
|VY||Speed that will allow for the best rate of climb.|
|VYSE||One-engine inoperative best climb gradient speed for twin-engine aircrafts.|
Whenever a limiting speed is expressed in terms of Mach number, it is expressed as an "M speed", e.g. VMO: Maximum operating limit speed (in knots), MMO: Maximum operating limit Mach.
There are some conditions which can affect the value of V-speeds:
These relationships will always hold true, but the speeds themselves will change according to aircraft weight, atmospheric conditions, aircraft configuration, and runway conditions.
The specific speeds are obtained by consulting the performance charts or quick reference cards.
V1 must always be:
VR must always be:
VLO must always be:
V2 must always be: