V speeds

A single-engine Cessna 150L's airspeed indicator indicating its V speeds.

A flight envelope diagram showing V_S (stall speed at 1G), V_C (corner/maneuvering speed) and V_D (dive speed)

In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft. 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, aircraft performance or both.

The actual speeds represented by these designators are specific to a particular model of aircraft. They are expressed by the aircraft'sindicated airspeed (and not by, for example, the ground speed), so that pilots may use them directly, without having to apply correction factors, as aircraft instruments also show indicated airspeed.

In general aviation aircraft, the most commonly used and most safety-critical airspeeds are displayed as color-coded arcs and lines located on the face of an aircraft's airspeed indicator. The lower ends of the green arc and the white arc are the stalling speed with wing flaps retracted, and stalling speed with wing flaps fully extended, respectively. These are the stalling speeds for the aircraft at its maximum weight.The yellow range is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement, and the red line is the Vne, the never exceed speed.

Proper display of V speeds is an airworthiness requirement for type-certificated aircraft in most countries.Regulation

The most common V-speeds are often defined by a particular government's aviation regulations. In the United States, these are defined in title 14 of the United States Code of Federal Regulations, known as the Federal Aviation Regulations or FARs. In Canada, the regulatory body, Transport Canada, defines 26 commonly used V-speeds in their Aeronautical Information Manual (AIM).V-speed definitions in FAR 23, 25 and equivalent are for designing and certification of airplanes, not for their operational use. The descriptions below are for use by pilots.

Regulatory V-speeds

These V-speeds are defined by regulations. Some of the descriptions provided are simplified.

V-speed designator	Description
V1	The speed beyond which the takeoff should no longer be aborted.
V2	Takeoff safety speed. The speed at which the aircraft may safely be climbed with one engine inoperative.
V2min	Minimum takeoff safety speed.
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 maneuvering 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 usually 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, though some manufacturers apply different criteria. 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	See V1; generally used in documentation of military aircraft performance.
VD	Design diving speed, the highest speed planned to be achieved in testing.
VDF	Demonstrated flight diving speed, the highest actual speed achieved in testing.
VEF	The speed at which the critical engine is assumed to fail during takeoff.
VF	Designed flap speed.
VFC	Maximum speed for stability characteristics.
VFE	Maximum flap extended speed.
VFTO	Final takeoff speed.
VH	Maximum speed in level flight at maximum continuous power.
VLE	Maximum landing gear extended speed. This is the maximum speed at which a retractable gear aircraft should be flown with the landing gear extended.
VLO	Maximum landing gear operating speed. This is the maximum speed at which the landing gear on a retractable gear aircraft should be extended or retracted.
VLOF	Lift-off speed.
VMC	Minimum control speed. Mostly used as the minimum control speed for the takeoff configuration (takeoff flaps). Several VMCs 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). The minimum speed at which steady straight flight can be maintained 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 for VMCA to be valid should be provided by the manufacturer with VMC(A) data; any other bank angle results in a higher actual VMC(A). 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 takeoff may be safely continued following an engine failure during the takeoff 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.
VNE	Never exceed speed.
VNO	Maximum structural cruising speed or maximum speed for normal operations.
VO	Maximum operating maneuvering speed.
VR	Rotation speed. The speed at which the pilot begins to apply control inputs to cause the aircraft nose to pitch up, after which it will leave the ground.
Vrot	Used instead of VR (in discussions of the takeoff performance of military aircraft) to denote rotation speed in conjunction with the term Vref (refusal speed).
VRef	Landing reference speed or threshold crossing speed. (In discussions of the takeoff performance of military aircraft, the term Vref stands for refusal speed. Refusal speed is the maximum speed during takeoff from which the air vehicle can stop within the available remaining runway length for a specified altitude, weight, and configuration.) Incorrectly, or as an abbreviation, some documentation refers to Vref and/or Vrot speeds as "Vr."
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 takeoff safety speed.
VX	Speed that will allow for best angle of climb.
VY	Speed that will allow for the best rate of climb.

Other V-speeds

Some of these V-speeds are specific to particular types of aircraft and are not defined by regulations.

V-speed designator	Description
VBE	Best endurance speed – the speed that gives the greatest airborne time for fuel consumed.
VBG	Best power-off glide speed – the speed that provides maximum lift-to-drag ratio and thus the greatest gliding distance available.
VBR	Best range speed – the speed that gives the greatest range for fuel consumed – often identical to Vmd.
VFS	Final segment of a departure with one powerplant failed.
Vimd	Minimum drag
Vimp	Minimum power
VLLO	Maximum landing light operating speed – for aircraft with retractable landing lights.
Vmbe	Maximum brake energy speed
Vmd	Minimum drag (per lift) – often identical to VBR. (alternatively same as Vimd
Vmin	Minimum speed for instrument flight (IFR) for helicopters
Vmp	Minimum power
Vms	Minimum sink speed at median wing loading - the speed at which the minimum descent rate is obtained. In modern gliders, Vms and Vmc have evolved to the same value.
Vp	Aquaplaning speed
VPD	Maximum speed at which whole-aircraft parachute deployment has been demonstrated
Vra	Rough air speed (turbulence penetration speed).
VSL	Stall speed in a specific configuration
Vs1g	Stall speed at 1g load factor
Vsse	Safe single engine speed
Vt	Threshold speed
VTD	Touchdown speed
VTGT	Target speed
VTO	Take-off speed. (see also VLOF)
Vtocs	Take-off climbout speed (helicopters)
Vtos	Minimum speed for a positive rate of climb with one engine inoperative
Vtmax	Max threshold speed
Vwo	Maximum window or canopy open operating speed
VXSE	Best angle of climb speed with a single operating engine in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of horizontal distance following an engine failure, while maintaining a small bank angle that should be presented with the engine-out climb performance data.
VYSE	Best rate of climb speed with a single operating engine in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of time following an engine failure, while maintaining a small bank angle that should be presented with the engine-out climb performance data.
VZRC	Zero rate of climb speed in a twin-engine aircraft

Mach numbers

Whenever a limiting speed is expressed by a Mach number, it is expressed relative to the speed of sound, e.g. V_MO: Maximum operating speed, M_MO: Maximum operating Mach number.

V₁ definitions

V₁ is the critical engine failure recognition speed or takeoff decision speed. It is the speed above which the takeoff will continue even if an engine fails or another problem occurs, such as a blown tire.The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length, wing flap setting, engine thrust used and runway surface contamination, thus it must be determined by the pilot before takeoff. Aborting a takeoff after V₁ is strongly discouraged because the aircraft will by definition not be able to stop before the end of the runway, thus suffering a "runway overrun".