V speeds

In aviation, V-speeds or Velocity-speeds are standard terms used to define airspeeds important or useful to the operation of aircraft, such as 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, aircraft performance or both. 
The actual speeds represented by these designators are true airspeeds 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.
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. 
Having V speeds properly displayed is an airworthiness requirement for type-certificated aircraft in most parts of the world. 
==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). 
==Regulatory V-speeds==
These V-speeds are defined by regulations.
V-speed designator	Description
V1 	Critical engine failure recognition speed. (See V1 definitions below)Peppler, I.L.: From The Ground Up, page 327. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996. ISBN 09690054-9-0
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, also known as the "Speed for maximum control deflection." 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. The heavier an aircraft is loaded the faster this speed.
VB 	Design speed for maximum gust intensity.
VC 	Design cruising speed, also known as the optimum cruise speed, is the most efficient speed in terms of distance, speed and fuel usage.
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.
VLOF 	Lift-off speed.
VMC 	Minimum control speed with Critical engine inoperative.
Vmca 	Minimum control speed in the take-off configuration – the minimum calibrated airspeed at which the aircraft is directionally controllable in flight with a sudden Critical engine failure and takeoff power on the operative engine(s).
Vmcg 	Minimum control speed on the ground - the minimum airspeed at which the aircraft is directionally controllable during acceleration along the runway with one engine inoperative, takeoff power on the operative engine(s), and with nose wheel steering assumed inoperative.
VMO 	Maximum operating limit speed.
VMU 	Minimum unstick speed.
VNE 	Never exceed speed.Bell Helicopter Textron: Bell Model 212 Rotorcraft Flight Manual, page II. Bell Helicopters Textron Publishers, Fort Worth, Texas, Revision 3, 01 may 1998. BHT-212IFR-FM-1
VNO 	Maximum structural cruising speed or maximum speed for normal operations.
VR 	Rotation speed. The speed at which the aircraft's nosewheel leaves the ground.
VRef 	Landing reference speed or threshold crossing speed.
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. This may be used when there is reason to remain aloft for an extended period, such as waiting for a forecast improvement in weather on the ground.
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 - 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- identical to VBR.
Vmcl 	Minimum control speed in the air in an approach or landing configuration with one engine inoperative.
Vmin 	Minimum speed for instrument flight (IFR) for helicopters
Vmp 	Minimum power
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 maximum lift coefficient
Vsse 	Safe single engine speed
Vt 	Threshold speed
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.
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.
VZRC 	Zero rate of climb speed in a twin-engine aircraft
==Mach Numbers==
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.
==V1 definitions==
V1 is the critical engine failure recognition speed or takeoff decision speed. It is the decision speed nominated by the pilot which satisfies all safety rules, and above which the takeoff will continue even if an engine fails. The speed will vary between aircraft types and also due to aircraft weight, runway length, wing flap setting, engine thrust used, runway surface contamination and other factors.
V1 is defined differently in different jurisdictions:
*The US Federal Aviation Administration defines it as: V1 means 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.
==References==
Category:Aircraft instruments
Category:Airspeed
Category:Aviation terminology
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