V-speed designator[PDF]

Introduction

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.

V-speed in airspeed indicator

Light single-engine aircrafts

Anemometer Speed Definition.jpg

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:

  • the lower ends of the green arc is the stalling speed with wing flaps retracted : VS1
  • the lower ends of the white arc is the stalling speed with wing flaps fully extended : VS0
  • the upper end of the green arc is the maximum speed for normal operations : VNO
  • the upper end of the white arc is the maximum flap extended speed : VFE
  • the red line is the never exceed speed : VNE


Light twin-engine aircrafts

FAA-8083-3A Fig 12-1.PNG


Two more information appear on light twin-engine aircrafts:
  • Single engine best climb airspeed (VYSE): The airspeed which must be used for any climb whenever the aircraft is flown with one engine inoperative. This is marked with a blue pointer on the airspeed indicator.
  • Minimum Airborne Control Speed (VMCA): The lowest airspeed at which the aircraft stalls on the yaw axis whenever the aircraft is flown with one engine inoperative. This is marked with a red pointer on the airspeed indicator.

V-speed designator and definition

V-speed designator Description
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.
VLOF Lift-off speed.
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 or threshold 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.

Conditions affecting V-speeds

There are some conditions which can affect the value of V-speeds:

  • V-speeds change relative to aerodrome conditions, aircraft weight and configuration.
  • Gross take-off weight, pressure altitude, and temperature all affect aircraft performance.
  • Weight, altitude, temperature.
  • Aircraft configuration affects V-speeds (flap setting, slat setting, bleeds, anti-ice, a/c off/on, anti-skid inoperable), and can be used to improve performance.
  • Runway conditions also affect V-speeds (contaminated runway).

Relation between 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

V1 must always be:

  • V1 > VMCG
  • V1 < VMBE
  • V1 ≤ VR
  • V1 < V2

VR

VR must always be:

  • VR ≥ V1
  • VR > VMCA
  • V2 > VR

VLO

VLO must always be:

  • VLO ≥ VR
  • VLO > VMCA
  • VLO > VS
  • VLO > VMU

V2

V2 must always be:

  • V2 > VR
  • V2 > VMCA
  • V2 > VS
  • V2 > V1

See also

  • None

Reference

  • None

Author

  • VID 150259 - Creation
  • VID 200696 - Wiki integration
  • VID 200696 - Update

DATE OF SUBMISSION

  • 02:18, 14 May 2021

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.