V speeds

航空

V speeds (aircraft) are speeds that define certain performance and limiting characteristics of an aircraft and the "V" stands for velocity. They are established by the manufacturer during design and testing, and are specific to the aircraft model, and in many cases (V₁, V₂, V_ref, and several others) based on the current weight and balance characteristics of the individual aircraft, as described below. Usually "V speeds" are relative to the air through which the aircraft is moving and are thus airspeeds. In many cases, they are defined by reference to the standard atmosphere or other specific conditions, and/or at the aircraft's maximum gross weight, and the pilot is responsible for calculating the effective value based on the actual weight and air density. In other cases the indicated airspeed, the value uncorrected for atmospheric pressure differences (height and temperature), is useful directly by the pilot. For example, the indicated stall speed V_S remains essentially constant for all heights and temperatures while the true stall speed increases as pressure lessens.

In the U.S., V speeds are stated in knots or, for older aircraft models, miles per hour. For faster aircraft, some speeds are also defined by Mach number. Typically, V speeds are given for an aircraft at maximum gross weight, and are adjusted for lighter weights, the scheduled figures being given in the aircraft Flight Manual and Performance Manual.

Contents [hide] 1 Speeds frequently used in General Aviation 2 Other reference speeds 3 Non-regulatory speeds 4 Speeds indicated on Airspeed Indicator

Speeds frequently used in General Aviation

V_A

design maneuvering speed (stalling speed at the maximum legal G-force, and hence the maximum speed at which abrupt, full deflection, elevator control input will not cause the aircraft to exceed its G-force limit). The aircraft will stall prior to any structual damage occuring. Maneuvering speed is adjusted based on the weight of the aircraft. As the weight increases, Maneuvering speed increases. This is because the aircraft is less subject to rapid acceleration at the higher weight.

V_FE

maximum flap extended speed (a different maximum speed may be specified for partial flap extension).

V_LE

maximum landing gear extended speed. The maximum speed at which the aircraft may be flown with the landing gear extended. V_LE is typically higher than V_LO

V_LO

maximum landing gear operating speed. The maximum speed at which the aircraft may be flying while raising or lowering the gear. Although V_LO is designated as one speed, in most cases it will have both an extension and retraction speed. Many aircraft can extend the gear at V_LE, but (because of possible G-loading in climbout) must retract the gear at a lower speed. For example the Piper Seminole can extend the gear at its V_LE of 140 but must be below 109 to retract the gear, thus V_LO is read as 109,140 instead of a single airspeed. Another factor to consider is the direction of drop of the nose-wheel. In aircraft where the nosewheel retracts forward into the fuselage, the V_le can actually be higher than V_lo.

V_MC or V_MCA

minimum control speed with the critical engine inoperative. The speed below which control will be lost, normally due to roll or yaw divergence. In initial aircraft type testing and certification, this is tested at a safe height above ground and, when established, is factored in to V₂ (refer below) that by regulation has a set margin over Vmca and also over Vs.

V_NE

The V_NE, or never exceed speed, is the V speed which refers to the velocity that should never be exceeded because of the risk of structural failure, due for example to wing or tail deformation, or aeroelastic flutter. On many airspeed indicators the V_NE is marked with a red line. This speed is specific to each aircraft model, and represents the edge of its performance envelope in terms of speed.

V_NO

The V_NO of an aircraft is known as the maximum structural cruising speed (the maximum speed to be used in turbulent conditions) or can refer to the velocity of normal operation. V_NO is specified as the upper limit of the green arc on many airspeed indicators. This speed is specific to the aircraft model. The range above V_NO is marked on the airspeed indicator as a yellow arc from V_NO to the V_NE.

V_R

rotation speed. The speed of an aircraft at which the pilot initiates rotation to obtain the scheduled takeoff performance. It must be greater or equal to the V₁ speed.

V_REF

reference landing approach speed; speed (in calm air) at the landing screen height of 50 ft. Often used by pilots as a base from which to calculate speeds to be used during landing, and calculated as a margin over the stall speed - usually 1.3×V_S0.

V_S

the stalling speed or the minimum steady flight speed at which the aircraft is controllable. Usually synonymous with V_S1. This speed is specific to the aircraft model and depends upon the weight and balance of the aircraft. The true stall speed increases as atmospheric pressure decreases. (i.e. as temperature increases and/or as altitude increases.) The indicated stall speed, i.e. the speed indicated by the airspeed indicator, remains essentially unchanged with air pressure.

V_S0

the stalling speed or the minimum steady flight speed in the landing configuration.

V_S1

the stalling speed or the minimum steady flight speed obtained in a specific configuration (usually a "clean" configuration without flaps, landing gear and other sources of drag).

V_X

speed for best angle of climb. This provides the best altitude gain per unit of horizontal distance, and is usually used for clearing obstacles during takeoff.

V_Y

speed for best rate of climb. This provides the best altitude gain per unit of time.

Other reference speeds

V_B

design speed for maximum gust intensity.

V_C

The VC of an aircraft is the V speed which refers to the velocity of cruising. VC is within the green arc on many airspeed indicators. This speed is different for each aircraft model.

VC is also called the design cruising speed or the optimum cruise speed – the latter being the speed giving the most velocity (i.e. greatest distance/time) from a litre of fuel, usually utilising 75% power at Maximum Take-Off Weight (MTOW) and about 1.3 times the maximum lift-to-drag ratio (L/D) speed – Vbr above. The speed and power required decrease as the aircraft weight decreases from MTOW.

For normal category aircraft FAR Part 23 specifies a minimum design cruising speed (in knots) based on the wing loading of (weight in pounds divided by wing area in square feet). For the utility category, the minimum design cruising speed is . Many ultralight aeroplanes are unable to comply with the FAR part 23 requirement for a minimum design cruising speed.

V_D

design diving speed. Usually 1.4×V_NO.

V_DF/M_DF

demonstrated flight diving speed.

V_EF

the speed at which the critical engine is assumed to fail during takeoff.

V_F

design flap speed.

V_FC/M_FC

maximum speed for stability characteristics.

V_FTO

final takeoff speed

V_H

maximum speed in level flight with maximum continuous power.

V_LOF

lift-off speed.

V_MO/M_MO

maximum operating limit speed.

V_MU

minimum unstick speed.

V_SR

reference stall speed.

V_SR0

reference stall speed in the landing configuration.

V_SR1

reference stall speed in a specific configuration.

V_SW

speed at which onset of natural or artificial stall warning occurs.

V_TOSS

takeoff safety speed for Category A rotorcraft.

V_WW

maximum speed for windshield wiper operation.

V₁

critical engine failure recognition speed. V₁ is the minimum speed in the takeoff, following a failure of the critical engine at V_EF, at which the pilot can continue the takeoff with only the remaining engines. Any problems after V₁ are treated as in-flight emergencies. In the case of a balanced field takeoff, V₁ is 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 aircraft within the accelerate-stop distance and the minimum speed at which the takeoff can be continued and achieve the required height above the takeoff surface within the takeoff distance. In this context, V₁ is the takeoff decision speed.

V₂

the minimum safe speed in the second segment of a climb following an engine failure. Also called takeoff screen speed and sometimes, takeoff safety speed, although as the second climb segment indicates, V2 is an after takeoff speed frequently achieved shortly after rotate (Vr) as the aircraft accelerates. The engine failure case that is taken in the calculation of V2 is that of the "most adverse engine" because the effects of different engines when failed, differ. The calculation of V2 also includes set margins over the stall and other safety factors are built in as well.

V_2min

minimum safe speed in the second segment of a climb following an engine failure.

Non-regulatory speeds

These values are not defined by FAA regulations.

V_BE

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.

V_BG

best power-off glide speed; the speed that provides maximum lift-to-drag ratio and thus the greatest gliding distance available.

V_XSE

speed for best angle climb with the critical engine inoperative.

V_YSE

speed for best rate of climb with the critical engine inoperative.

V₂

t/o safety speed

V₃

steady initial climb speed with all engines operating

V₄

steady climb speed with all engines operating to be achieved by 400 ft gross height

V_a

design maneuvering speed

V_c

design cruising speed.

V_clmax

max coefficient of lift speed.

V_d

design diving speed

V_dmin

minimum drag

V_df

demonstrated flight diving speed

V_ef

the CAS at which the critical engine is assumed to fail

V_f

design flap speed

V_fe

max flap extended speed

V_fto

final t/o speed

V_imd

minimum drag

V_imp

minimum power

V_h

max speed in level flight with max continuous power.

V_le

max landing gear extended speed

V_lo

max landing gear operating speed

V_lof

lift-off speed

V_mbe

max brake energy speed

V_md

minimum drag

V_mc

minimum control speed with critical engine inoperative

V_mca

minimum control speed, air

Air minimum control speed is the minimum flight speed at which the aircraft is directionally controllable as determined in accordance with applicable aviation regulations. Aircraft certification conditions include one engine becoming inoperative and windmilling, not more than a 5 degree bank towards the operative engine, takeoff power on the operative engine, landing gear up, flaps in takeoff position, and most rearward C of G.

V_mcg

minimum control speed, ground, with nose wheel steering assumed inoperative

V_mcl

minimum control speed, approach and landing

V_me

max endurance

V_mini

minimum IFR speed for helicopters

V_mo

max operating limit speed

V_mp

minimum power

V_mr

max range

V_mu

minimum unstick speed

V_nd

max structural cruising speed

V_p

aquaplaning speed.

V_ra

rough air speed

V_ref

reference landing speed

V_s

V-stall

V_s0

stall speed in landing configuration

V_s1

stall speed in a specified configuration

V_s1g

one g stall speed

V_sr

reference stall speed

V_sse

safe single engine speed

V_t

threshold speed

V_tmax

max threshold speed

V_x

best angle of climb

V_xe

best angle of climb, single engine

V_y

best rate of climb

V_yse

best rate of climb single engine

Speeds indicated on Airspeed Indicator

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Airspeed Indicator

Several V speeds are denoted on the color-coded Airspeed Indicator, to give pilots an immediate reference, as follows:

• V_S0

bottom of white arc

• V_S1

bottom of green arc

• V_FE

top of white arc.

• V_NO

top of green and bottom of yellow arcs. The yellow arc is a caution, as speeds in this region may add dangerous stress to the aircraft, and are only to be used in smooth air when no turbulence or abrupt control inputs are expected.

• V_NE

red line and top of yellow arc.

• In addition, on light multi-engine aircraft, V_YSE is indicated by a blue line, and V_MC is indicated by a red line near the bottom of the green arc.nl:V-snelheden

sv:V2 (hastighet)

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