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V Speeds - What's VT Stand For?  
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Posted (11 years 1 month 1 week 2 days 22 hours ago) and read 17583 times:

Hi guys.

I have a quick question of curiousity about the photo below.

In the bottom left hand corner of this Challenger 604 bizjet's HUD (Heads Up Display), is an area where a set of 4 V-speeds can be displayed. They're V1, VR, V2, and VT. Unfortunately, the V numbers are not shown.  Sad

What does VT mean?

I've never heard of a VT speed before. On the HUD in the photo, the VT speed is located at the top of the V-speed sequence, which makes me think that the VT speed occurs after the jet has reached it's V2 speed at 35 ft AGL.


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Photo © Manuel Marín - IBERIAN SPOTTERS



PS, is VT a speed that only bizjets use, or do larger commercial airliners use this speed as well?

Thanks,

Chris  Smile



"Just a minute while I re-invent myself"
9 replies: All unread, jump to last
 
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 1, posted (11 years 1 month 1 week 2 days 21 hours ago) and read 17508 times:

Quite funny...XFSUGimpLB41X had the same question the other day, in regards to a CRJ. He asked me and I couldn't find the answer either. Can't wait to find out.

User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 2, posted (11 years 1 month 1 week 2 days 20 hours ago) and read 17492 times:


V Speeds: Various Aviation Authorities



This document is designed to be a compilation of V-speeds used by any agency/military/company of the world, including outdated speeds no longer used, to act as a general reference for anyone who is looking for a brief definition of an unfamiliar speed. 1999.



VA - design maneuvering speed. This is the recommended indicated speed in moderate turbulence or when throwing the aircraft about. At or below this speed the aircraft will stall, and thus reduce the aerodynamic force on the wings, before it encounters a vertical current imparting enough energy to exceed the design wing loading. VA is the maximum speed at which full control deflections can be made safely.



VAT - threshold crossing speed, usually 1.3 VS0



VAT0 - threshold crossing speed with all engines operating



VAT1 - threshold crossing speed with the critical engine inop



VAT max - maximum threshold crossing speed, above which a go-around should be initiated to prevent exceeding the scheduled landing distance (VAT0 + 15kts)



VAPP - target approach airspeed

VB - the design speed for maximum gust intensity. Whereas VA is a fixed calculation relative to VS1 for all aircraft within the same category, VB is developed as a recommended turbulence penetration speed for a light aircraft in severe turbulence with vertical gust components up to 50 feet/second.



VBR - best range - the speed that provides (L/D)max, thus minimum drag and minimum power required and consequently greatest distance per liter of fuel. Usually utilizes about 55% power and decreases as the aircraft weight decreases from MTOW. Rather boring to fly at that speed, wind conditions have to be taken into account and the fuel saving may not be that significant compared to say 60% power.



VBE - best endurance - the speed which gives the greatest airborne time per liter, usually around 75% of the speed for range and decreases as the aircraft weight decreases from MTOW. Might utilize about 40% power at MTOW. The speed that might be used when flying a search pattern allowing a proper area survey, but it is generally uncomfortable to fly at such a low speed. Also the low power setting may not be consistent with good engine handling.



VBG - best power-off glide - the speed that provides (L/D)MAX, or maximum glide ratio, consequently greatest flight distance available from the potential energy of height in a specified configuration. It is the same speed as that for best range and decreases as the aircraft weight decreases from MTOW.



VC - the design cruising speed or optimum cruise speed - the speed giving the most velocity (i.e greatest distance/time) from a liter of fuel, usually utilizing 75% power at MTOW. The speed and power required decrease as the aircraft weight decreases from MTOW. VC is sometimes indicated to be the normal level flight speed range for the aircraft as shown by the ASI green band.



VCL - clean configuration safety speed



VD - design diving speed



VDF - demonstrated flight diving speed (MDF)



VEF - the speed at which a critical engine is assumed to fail during takeoff for V1 calculations (assumes acceleration after the critical engine fails) >105% of VMC



VF - design flap speed



VF1 - design flap speed for procedure flight conditions



VFC - maximum speed for stability (flight controllability) characteristics (or: final climb speed**)



VFE - maximum flaps extended speed. The top end of the white arc on the ASI. Flight with flaps extended, or extending flaps, above this speed may result in distortion of the flaps or the extension mechanism. (MFC)



VFR - flap retraction safety speed, the lowest airspeed at at which the flaps should be retracted during climbout



VFTO - final take-off speed



VGA - go-around target airspeed



VH - the maximum level flight indicated speed attainable utilizing maximum continuous engine power -which, for some engines, may be less than full throttle power.



VHOLD - holding airspeed which gives best endurance for a specified configuration and altitude

VK - target velocity

VL/D max – speed which produces the greatest glide distance (max lift to drag ratio)




VLE - retractable undercarriage aircraft - the maximum indicated speed at which the landing-gear can remain extended without risking gear door damage.



VLO - the maximum indicated speed at which the landing gear system can be operated. Different limits may exist for extension and retraction



VLL - the maximum indicated speed for extending the landing lights



VLLO - the maximum indicated speed at which the landing gear can be extended (assigned only when extension and reatraction speeds are different)



VLOF - maximum lift off speed - for normal take-off (about 10% above VMU).



VLS - minimum selectable airspeed (VMIN)



VMAX - maximum attainable airspeed in level flight at a specified altitude, or maximum selectable airspeed



VMBE - maximum speed for brake energy absorbtion capability



VMC - minimum control speed with critical engine inoperative



VMCA - Minimum control speed in flight at which the a/c can be controlled with 5° of bank, in the case of failure of the critical engine with the other engine at takeoff power (takeoff flaps setting and gear retracted).



VMCG - Minimum control speed on the ground at which the a/c can be controlled with critical engine inop and the other engine at rated takeoff power.



VMCL - Minimum flight speed at which the a/c can be controlled after failure of the critical engine, in the landing configuration (landing flaps setting, gear extended) with go-around power set on the operating engine



VMD - minimum descent - the speed that results in the lowest sink rate in a power-off glide, providing the longest duration of flight from the potential energy of height; but less than maximum gliding range. Probably about 90% of the power-off glide speed - VBG.



VMIN - minimum selectable airspeed



VMO - maximum operating limit speed (MMO)



VMS - minimum speed in a stall



VMT - minimum threshold crossing speed (see VAT)



VMU - minimum unstick speed. An indicated speed used in take-off conditions where it is advisable to lift off at the lowest possible airspeed to get the tires off the surface (e.g. soft field, wet grass, asphalt w/ potholes) and safely fly in ground effect until VTOSS is attained to allow climb away. Acceleration after lift off at VMU is slow, due to the drag at the high AOA, and should not be used as an obstacle clearance technique.



VNE - never exceed speed. The speed which must not be exceeded in a glide or dive or other maneuvers in smooth air. The red line at the top end of the ASI yellow arc, usually 90% of the 'design diving speed' - VD - which latter is usually 1.4 times VNO.



VNO - maximum structural cruise speed. The top end of the ASI green arc. When cruising at, and below, VNO the aircraft should not be damaged by a 35-knot vertical gust; which is at the bottom end of the severe turbulence scale. Flight above VNO should only be conducted cautiously and in smooth air.



VP – pull-up speed. The maximum airspeed at which the aircraft may be pulled out of a dive with instantaneous full control deflection (or: hydroplaning speed**)



VR - rotation speed



VRA - rough air speed, must be less than VMO - 35kts (TAS) and less than or equal to VB



VREF - the reference indicated approach speed, usually 1.3 times VS0 plus 50% of the wind gust speed in excess of the mean wind speed.



VS - stalling speed or the minimum steady flight speed at which the aircraft is controllable



VS0 - stalling speed, or the minimum steady flight speed, in the landing configuration, (at MTOW and 1G wing loading with the cg at the most extreme position allowed, usually the most forward where backward movement of the control column may be limited). The bottom end of the ASI white arc, but it may be documented as IAS or CAS. VSO decreases as the aircraft weight decreases from MTOW.



VS1 - stalling speed, or the minimum steady flight speed, in a specified flight configuration. For a simple aircraft usually just flaps up, MTOW and 1G wing loading, engine idling and a slow deceleration to the minimum flight speed. The bottom end of the ASI green arc, but it may be documented as IAS or CAS. VS1 decreases as the aircraft weight decreases from MTOW, which also means that if the pilot can reduce the wing loading below 1G - by an 'unloading' maneuver - VS1 is decreased.



VS2g - stalling speed in a specified flight configuration under a 2G vertical load.



VS15 - stalling speed in the specified flap configuration (flaps xx°)



VSR - slat retraction safety speed, the lowest airspeed at which the slats should be retracted during climbout



VSS - stick shaker activation speed (notwithstanding AOA probe)



VSSE - safe single engine speed (about 10% above VMC ).



VSW - stall warning airpeed



VT - threshold crossing speed; target speed (after V2 has been reached); maximum aerotow speed (gliders) **



VTmax - maximum threshold crossing speed



VTD - touchdown speed



VTOSS - minimum take-off safety speed. An indicated speed chosen to ensure that adequate control will still exist during initial climb after take-off under conditions of turbulence - or even engine failure. After lift off the aircraft should not be allowed to climb away until VTOSS is attained. (rotorcraft)



VU - utility speed (military equivalent to VA?)



VX - indicated speed for best angle of climb. i.e. To attain height over the shortest ground distance. The initial climb speed used when there are obstructions off the runway end. VX decreases as the aircraft weight decreases from MTOW, refer rule of thumb 3 above, but the angle of attack is maintained at around 12º. VX stated in an operating handbook also has to be at least equal to VTOSS. However be aware that the angle of climb will also depend on the low level wind conditions at the airfield.



VXSE - best angle of climb with single engine operative (or assymetric power condition)



VY - indicated speed for best rate of climb. i.e. To attain height in the shortest time. VY decreases as the aircraft weight decreases from MTOW, but the angle of attack is maintained at around 8º. After reaching a safe height airspeed is usually increased to an appropriate 'en-route climb' speed. VY also decreases with altitude i.e. as TAS increases.



VYSE - best rate of climb with single engine operative (or assymetric power condition)



VW - maximum speed for winch launch (glider)

VWW - windshield wiper operation speed



VZF - minimum zero flaps speed



V1 - Decision speed. The maximum speed in the takeoff at which the pilot must take the first action to stop the aircraft within the accelerate-stop distance. This speed is adjustable based on many factors included ambient condtions and takeoff thrust used.



V1MIN - The slowest decision speed at which the takeoff may be continued and which will allow the aircraft to reach V2 (and 35ft) over the runway. (Aceclerate - Go)



V1BAL - The decision speed which allows the Accelerate - Stop distance to equal the Accelerate - Go distance



V1MAX - The fastest decision speed which will allow the aircraft to stop on the runway. (Accelerate - Stop)



V2 - Take-Off safety speed. The lowest speed at which the a/c complies with the handling criteria associated with the climb after T.O. following an engine failure.



V2MIN - minimum takeoff safety speed, not less than 1.2 VS1



V3 - initial steady climb speed at which the a/c is assumed to pass through the 35 ft screen height with all engines operating on takeoff (or: minimum flap retraction speed**)



V4 -all engines operating take-off climb speed with undercarriage up and flaps at t/o configuration; used to the point where acceleration to the flap retraction speed is initiated; it should be attained by 400 ft above field elevation (or: minimum slat retraction speed**)




**: not in conjunction with other given definition, usually the result of two authorities choosing different speeds for the same letter or my own lack of a definitive answer



hawke@antisocial.com




[Edited 2003-07-22 23:38:17]

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 3, posted (11 years 1 month 1 week 2 days 18 hours ago) and read 17435 times:

Hi guys.

> Aaron atp, WOW!!!  Wow! Thanks for your great info!

As soon as I saw your post, the first thing I did was click on PRINT.  Big thumbs up

OK, so the definition for VT is ...... threshold crossing speed; target speed (after V2 has been reached).

I had to think about this explanation for a moment because I normally associate a runway's threshold with the "begining" of the runway (for arrival), not the "end" of the runway (for departure), as is the case in the above definition of VT.

Now that my mind is un-twisted,  Nuts I understand that VT is another target airspeed that a flight crew wants to achieve by the time they're passing over the Departure Threshold.


PS. Flyf15, now we know ALL the V-speeds! Big grin


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 4, posted (11 years 1 month 1 week 2 days 18 hours ago) and read 17426 times:

First of all, great list Aaron!

I think the ";" in the definition of VT is imperative here though.

The way I read it, VT is either threshold crossing speed (also known as VTHR), or target speed (after V2 has been reached).

Threshold crossing speed is only relevant on landing, no-one really cares what speed we cross the "departure threshold" of the runway.

In this case therefore VT is the target initial climbout speed (a bit like V2 + 15 knots for a 757/767)



I used to love the smell of Jet-A in the morning...
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 5, posted (11 years 1 month 1 week 2 days 18 hours ago) and read 17432 times:

Mr Spaceman, I agree -- Aaron ATP, you rock.

User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 6, posted (11 years 1 month 1 week 2 days 17 hours ago) and read 17408 times:

Rick is indeed correct, those are indeed two separate definitions.

I'll edit that so it's clearer if I ever bother to revise that list again... and include VTHR.

If anyone has anything else to add (or corrections, I made this a long time ago and haven't read through the entire thing in several years), please let me know.

-aaron


User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 7, posted (11 years 1 month 1 week 2 days 17 hours ago) and read 17412 times:

As if you hadn't already figured this out, the VT you are looking for is not the VAT synonym, but the target speed for climbout, after V2. Hence the positions in sequence with V1 VR V2...

User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4195 posts, RR: 37
Reply 8, posted (11 years 1 month 1 week 2 days 14 hours ago) and read 17379 times:

Vt = Vfto, final takeoff speed.... it will give you your maximum climb angle.

From what I've seen..it is typically about V2+30....


fyi- was originally thinking it was something like the equivalenth to Vzf, or minimum clean speed. Apparently doesnt have anything to do with it.

[Edited 2003-07-23 06:35:58]


Chicks dig winglets.
User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 9, posted (11 years 1 month 1 week 1 day 4 hours ago) and read 17296 times:

The list of V speeds given by Aaron, is the official V speed list as found in airworthiness publications and regulatory agencies...
xxx
Then there are those "V speeds" which are inventions of each individual chief pilots of many airlines... I remember in my PanAm days, we had a V Thresh and a V Bug... and others I forget... Every airline tends to re-invent the wheel and redesign the airplanes of the Wright Bros.  Big grin
xxx
(s) Skipper


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