jueves, 27 de octubre de 2016

V speeds

A single-engine Cessna 150L's airspeed indicator indicating its V speeds.
A flight envelope diagram showing VS (stall speed at 1G), VC (corner/maneuvering speed) and VD (dive speed)
In aviationV-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 designatorDescription
V1The speed beyond which the takeoff should no longer be aborted. 
V2Takeoff safety speed. The speed at which the aircraft may safely be climbed with one engine inoperative.
V2minMinimum takeoff safety speed.
V3Flap retraction speed.
V4Steady 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.
VADesign 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.
VatIndicated 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".
VBDesign speed for maximum gust intensity.
VCDesign cruise speed, used to show compliance with gust intensity loading.
VcefSee V1; generally used in documentation of military aircraft performance.
VDDesign diving speed, the highest speed planned to be achieved in testing.
VDFDemonstrated flight diving speed, the highest actual speed achieved in testing.
VEFThe speed at which the critical engine is assumed to fail during takeoff.
VFDesigned flap speed.
VFCMaximum speed for stability characteristics.
VFEMaximum flap extended speed.
VFTOFinal takeoff speed.
VHMaximum speed in level flight at maximum continuous power.
VLEMaximum landing gear extended speed. This is the maximum speed at which a retractable gear aircraft should be flown with the landing gear extended.
VLOMaximum landing gear operating speed. This is the maximum speed at which the landing gear on a retractable gear aircraft should be extended or retracted.
VLOFLift-off speed.
VMCMinimum 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.
VMCAMinimum 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.
VMCGMinimum 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.
VMCLMinimum control speed in the landing configuration with one engine inoperative.
VMOMaximum operating limit speed.
VMUMinimum unstick speed.
VNENever exceed speed.
VNOMaximum structural cruising speed or maximum speed for normal operations.
VOMaximum operating maneuvering speed.
VRRotation 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.
VrotUsed instead of VR (in discussions of the takeoff performance of military aircraft) to denote rotation speed in conjunction with the term Vref (refusal speed).
VRefLanding 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."
VSStall speed or minimum steady flight speed for which the aircraft is still controllable.
VS0Stall speed or minimum flight speed in landing configuration.
VS1Stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration.
VSRReference stall speed.
VSR0Reference stall speed in landing configuration.
VSR1Reference stall speed in a specific configuration.
VSWSpeed at which the stall warning will occur.
VTOSSCategory A rotorcraft takeoff safety speed.
VXSpeed that will allow for best angle of climb.
VYSpeed 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 designatorDescription
VBEBest endurance speed – the speed that gives the greatest airborne time for fuel consumed.
VBGBest power-off glide speed – the speed that provides maximum lift-to-drag ratio and thus the greatest gliding distance available.
VBRBest range speed – the speed that gives the greatest range for fuel consumed – often identical to Vmd.
VFSFinal segment of a departure with one powerplant failed.
VimdMinimum drag
VimpMinimum power
VLLOMaximum landing light operating speed – for aircraft with retractable landing lights.
VmbeMaximum brake energy speed
VmdMinimum drag (per lift) – often identical to VBR. (alternatively same as Vimd
VminMinimum speed for instrument flight (IFR) for helicopters
VmpMinimum power
VmsMinimum 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.
VpAquaplaning speed
VPDMaximum speed at which whole-aircraft parachute deployment has been demonstrated
VraRough air speed (turbulence penetration speed).
VSLStall speed in a specific configuration
Vs1gStall speed at 1g load factor
VsseSafe single engine speed
VtThreshold speed
VTDTouchdown speed
VTGTTarget speed
VTOTake-off speed. (see also VLOF)
VtocsTake-off climbout speed (helicopters)
VtosMinimum speed for a positive rate of climb with one engine inoperative
VtmaxMax threshold speed
VwoMaximum window or canopy open operating speed
VXSEBest 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.
VYSEBest 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.
VZRCZero 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. VMO: Maximum operating speed, MMO: 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".

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