Everything about V Speeds Explained | Flying Magazine

Everything about V Speeds Explained

Part one.

v speeds

FAA regulations could change at any time. Please refer to current FARs to ensure you are legal.

Illustration by Tim Barker

V — From the French word vitesse, meaning “speed.”

V1 — Maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speedbrakes) 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 surface within the takeoff distance.

V2 — Takeoff safety speed for jets, turboprops or transport-category aircraft. Best climb gradient speed (i.e., best altitude increase per mile with the most critical engine inop). Twin-engine aircraft with an engine inop are guaranteed a 2.4 percent climb gradient (24 feet up per 1,000 feet forward). Minimum speed to be maintained to at least 400 feet agl.

V2MIN — Minimum takeoff safety speed. Usually 1.2 times the stall speed in takeoff configuration.

VA — Design maneuvering speed. The highest safe airspeed for abrupt control deflection or for operation in turbulence or severe gusts. It does not allow for multiple large control inputs. If only one speed is published it is usually determined at max landing weight. This speed decreases as weight decreases.

Formula for determining VA at less than max landing weight: VA2 equals VA multiplied by current weight divided by max landing weight.

VABE — Maximum speed for airbrake extension.

VABO — Maximum speed for airbrake operation.

VAC — Missed-approach climb speed for flap configuration with critical engine inop (2.1 percent climb gradient).

VAP — Approach target speed. VREF plus configuration (flaps/slats setting) and wind factor.

Typically add (to VREF) half the headwind component plus all the gust factor (to a max of 20 knots).

VB — Design speed for maximum gust intensity for transport-category aircraft or other aircraft certified under Part 25. Turbulent-air penetration speed that protects the structure in 66 fps gusts.

VC — Design cruising speed. Speed at which the aircraft was designed to cruise. The completed aircraft may actually cruise slower or faster than VC. It is the highest speed at which the structure must withstand the FAA’s hypothetical “standard 50 fps gust.”

VD — Design diving speed. The aircraft is designed to be capable of diving to this speed (in very smooth air) and be free of flutter, control reversal or buffeting. Control surfaces have a natural vibration frequency where they begin to “flutter” like a flag in a stiff breeze. If flutter begins, it can become catastrophic in a matter of seconds. It can worsen until the aircraft is destroyed, even if airspeed is reduced as soon as flutter begins.

VDEC — Accelerate/stop decision speed for multiengine piston and light multiengine turboprops.

VDF/MDF — Demonstrated flight diving speed. VDF is in knots. MDF is a percentage of Mach number. Some aircraft are incapable of reaching VD because of a lack of power or excess drag. When this is the case, the test pilot dives to the maximum speed possible — the demonstrated flight diving speed.

VEF — Speed at which the critical engine is assumed to fail during takeoff (used in certification tests).

VENR — En route climb speed with critical engine inop. Jets accelerate to VENR above 1,500 feet agl.

VF — Design flap speed. The flaps are designed to be operated at this maximum speed. If the engineers did a good job, the actual flap speed, or VFE, will be the same.

VFC/MFC — Maximum speed for undesirable flight characteristics. It must be regarded with the same respect as VNE: redline. Instability could develop beyond the pilot’s ability to recover. VFC is expressed in knots; MFC is expressed in percentage of Mach.

VFE — Maximum flap-extended speed. Top of white arc. The highest speed permissible with wing flaps in a prescribed extended position. Many aircraft allow the use of approach flaps at speeds higher than VFE. Positive load for Normal category airplanes is usually reduced from 3.8 Gs to 2 Gs with the flaps down, and negative load is reduced from minus 1.52 Gs to zero. The purpose of flaps during landing is to enable steeper approaches without increasing the airspeed.

VFR — Flap retract speed. The minimum speed required for flap retraction after takeoff.

VFS — Final segment speed (jet takeoff) with critical engine inop. Accelerate to VFS at 400 feet agl.

VFTO — Final takeoff speed. End of the takeoff path. En route configuration. One engine inoperative.

VG — Best glide speed. This speed decreases as weight decreases.

VH — Maximum speed in level flight with maximum continuous power. Mainly used for aircraft advertising. Ultralights are limited by Part 103 to a VH of 55 knots.

VLE — Maximum landing gear extended speed. Maximum speed at which an airplane can be safely flown with the landing gear extended.

VLLE — Maximum landing light extended speed.

VLLO — Maximum landing light operating speed.

VLO — Maximum landing gear operating speed. Maximum speed at which the landing gear can be safely extended or retracted. Usually limited by air loads on the wheel-well doors. On some aircraft, the doors close after extension, allowing acceleration to VLE. In an emergency involving loss of control — when the ground is getting close and the airspeed is quickly approaching redline — forget about this speed. Throw the gear out! As a now famous Flying magazine writer once said, you might lose a gear door, but it’s far better than losing a wing.

Next month: Part Two.


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