In aviation, V-speeds (from velocity) 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's indicated 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.
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.
These V-speeds are defined by regulations
|V1||The speed beyond which the takeoff can no longer be safely aborted. (See V1 definitions below)|
|V2||Takeoff safety speed. The speed at which the aircraft may safely become airborne 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 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||See V1; generally used in documentation of military aircraft performance.|
|VD||Design diving speed.|
|VDF||Demonstrated flight diving speed.|
|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 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 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 aircraft's nosewheel leaves the ground. Also see note on Vref below.|
|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.|
Some of these V-speeds are specific to particular types of aircraft and are not defined by regulations.
|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.|
|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|
|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|
|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|
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".
V1 is defined differently in different jurisdictions:
- The US Federal Aviation Administration defines it as: "the maximum speed in the takeoff 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 takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance."
- Transport Canada defines it as: "Critical engine failure recognition speed" and adds: "This definition is not restrictive. An operator may adopt any other definition outlined in the aircraft flight manual (AFM) of TC type-approved aircraft as long as such definition does not compromise operational safety of the aircraft."
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V1. [...](1) The maximum speed by which a rejected takeoff must be initiated to assure that a safe stop can be completed within the remaining runway, or runway and stopway;