View Full Version : What are V-speeds?
Sprite
27th Jan 2005, 05:14
V speeds are speeds which are relevent various stages of flight.
V1...called "decision speed" or "commitment speed" depending on where you were trained. If you have an engine failure before v1 you stop. If it is after, you must continue the takeoff.
VR is the speed at which rotation is commenced
V2 is the speed at which you should climb after an engine failure to guarantee obstacle clearance.
Vref is the speed appropriate for landing. ie Vref(30) is the flaps 30 speed at which you should commence flare.
Then of course there is Vs (stall speed) VMCA (minimum control speed in the air with the critical engine out) VNE (never exceed speed) VMO (maximum operating speed) MMO (maximum operating mach) VMCG (maximum control speed on the ground with the critical engine out) Vfe (flap extend speed) VLO (landing gear operating speed)
Anyone willing to correct or add is welcome....
Hope that answers part of your question!
HotDog
27th Jan 2005, 06:21
VMCG (maximum control speed on the ground with the critical engine out) I think you meant to say minimum control speed.
Alex Whittingham
27th Jan 2005, 07:40
Do you mean 'Define the term "V speeds"' or 'List all known V speeds'?
Sprite
27th Jan 2005, 07:58
Errr.... yes sorry HotDog... minimum control speed :) oops.... must concentrate when posting (slap) :ouch:
I got the following in an email from a leading regional jet manufacturer... V speeds really mean vertical speeds
It surprised me, so i was just wondering what others thought.
Mutt.
Vref. "Handling the Big Jets" calls it Vat which is defined as the target threshold speed; the scheduled speed at the threshold for landing in relatively favourable conditions. Screen speed (and screen height) which are the speeds assumed at 35 ft above the runway after take-off and at 30 feet above the runway on approaching to land used in establishing the field performance of the aeroplane. Splitting hairs, maybe. Sorry!
Alex Whittingham
27th Jan 2005, 10:14
To paraphrase Beagle... 'it sounds like bolleux'. A bit more context?
JerryMaguire
27th Jan 2005, 12:25
Hey since this thread is talking abt the various V, lemme just throw some queries. I've no problem with the definitions as these can be found pretty easily in reference books but am interested in typical numbers.
For typical heavy jet (Boeing 747/Airbus 345) landings, what are the typical flight level versus ground speed profile? (assuming this is the speed usually referred to for landing in contrast to IAS/TAS/EAS) As for take off, what are the typical V1, Vr, Vs and V2 speeds for say the Boeing 747/Airbus 345? Also, what are the Take off Distance Required (TODR) and Landing Distance Required for a typical maximum loaded jet plane using maximum thrust takeoff. It'll also be ideal if someone can lemme know of the typical thrust settings and flaps deployments vis a vis the pitch of the aircraft (deploying of elevators?) during landing and take off.
I got the following in an email from a leading regional jet manufacturer... V speeds really mean vertical speeds - I'd be interested if you could reply and ask in which nomenclature HIS/HER company refer to various performance related speeds for aircraft (carefully contrived words to avoid using the letter 'V':D )
Old Smokey
27th Jan 2005, 14:40
Well Mutt, ya coulda fooled me (but then I'm easy to fool).
I'd always assumed that the V stood for Velocity.
Are you sure that your source was correct?
I'll bet a pint of your choosing that 99% of prooners had assumed the same as me.
Regards,
Old Smokey
BOAC, they use the term "Takeoff & Reference Speeds together with V1 etc"
Just to put this in context, we were discussing the FMS functions in relation to V-speeds and i got this....By V speeds I presume you mean "Takeoff & Reference Speeds" as V speeds really mean vertical speeds
Now where is Mad Flight Scientist when we need him :)
Old_smokey.... looking forward to collecting that pint..
Mutt.
they use the term "Takeoff & Reference Speeds together with V1 etc - how DARE they?:D :D
BEagle
27th Jan 2005, 21:09
Hmm - some of this is indeed bolleaux!
However, a V/S selector is included on many a/c Automatic Flight System panels and is used to set the desired Vertical Speed required (rate of climb or descent) during level changes.
Port Strobe
27th Jan 2005, 22:06
HSWL
Vref. "Handling the Big Jets" calls it Vat which is defined as the target threshold speed; the scheduled speed at the threshold for landing in relatively favourable conditions. Screen speed (and screen height) which are the speeds assumed at 35 ft above the runway after take-off and at 30 feet above the runway on approaching to land used in establishing the field performance of the aeroplane. Splitting hairs, maybe. Sorry!
The critical point missed out in this explaination given here is Vat is calculated for maximum landing weight whereas Vref changes from one approach to the next depending upon the actual landing weight and wx conditions etc so the two terms are not interchangeable. I believe Vat is used to define the performance category the a/c belongs in? This would be since all parameters are fixed and so it can only be a category C a/c or whatever. Please correct me if I'm wrong though.
Mad (Flt) Scientist
28th Jan 2005, 00:21
Did someone at my company actually say that?
:O
The only credible defence I can offer - other than innate stupidity, which is surprisingly common worldwide of course - is that they may have been a francophone and not been as familiar with English as they should be when responding to questions in that language.
If I caught anyone in our department calling V1 etc "vertical speeds" they'd get a good cuff round the ears, 1950s bobbies style.
Of course, if you were discussing FMS operation you may have been interacting with our more systems-oriented folks who can have a certain 'interesting' take on aviation terminology ..... ;)
Mad (Flt) Scientist.
It came from your marketing people :):):)
Mutt.
HotDog
28th Jan 2005, 06:07
Old_smokey.... looking forward to collecting that pint..
Not much chance of that Mutt, you better dig deep. V= velocity.
212man
28th Jan 2005, 06:37
Maybe if it's an FMS they're talking about, they're discussing
V NAV?
enicalyth
28th Jan 2005, 10:19
I seem to remember Universal UNS-1 FMS had mention of V speed in the V-NAV training literature and was an entry on the scratchpad called target v/speed. Tended to be in Dash-8, Learjet 25/35, Fokker 50 market. Never saw it anywhere else.
Ojuka
28th Jan 2005, 10:47
V for Velocity.
100%.
No argument.
VS is indeed a vertical speed mode in Flight Guidance Systems / autopilots. Nothing to do with V1/Vr/V2/Vmca etc.
I also agree that Vat is used to define aircraft Category (A,B or C etc.) for approach purposes. Vref changes with weight on the day but Vat, for PANS OPS purposes, remains a fixed max weight speed.
Mad (Flt) Scientist
28th Jan 2005, 22:31
marketing
No further comment required.
Charles Darwin
29th Jan 2005, 11:50
Well, reaching vertical one speed doing a horizontal run down the pavement clearly indicates runway slope...eh?:suspect:
effortless
29th Jan 2005, 12:38
Just to confuse even more, my PA28 pilots operating notes uses vat for vacate and taxi speed. What's Vo?
john_tullamarine
30th Jan 2005, 00:00
Vo -- operating manoeuvring speed. Similar to Va.
Current references to look at include
(a) FAR Final Rule Making - Small Airplane Airworthiness Review Program Amendment No. 4 (http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFinalRule.nsf/0/d9b03117bc05edd9862569030062b2b0!OpenDocument&ExpandSection=6,4.3,-1) (and search for Vo),
(b) FAR 23.1507 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=fd3fda730e86929ea55b58bd42b80cac&rgn=div8&view=text&node=14:1.0.1.3.9.7.105.3&idno=14) (which is where it is defined), and
(c) FAR 23.1583 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9cb30d3240ff95307ea558f2037409ae&rgn=div8&view=text&node=14:1.0.1.3.9.7.106.28&idno=14) (where it is required to be published if determined).
Just how relevant these references are to your particular POH I'm not sure .. but they give you a starting point to research the matter.
.. I gotta get a life ...
Snot Box
30th Jan 2005, 05:56
Okay let's see:
V1: The decision speed in the event of an engine failure during the takeoff roll at which it is possible to continue the takeoff and achieve the screen height within the normal takeoff distance available or to bring the aircraft to a full stop within the emergency distance available.
Thus, the takeoff must be abadoned with an engine failure below V1 and the takeoff must be continued with an engine failure above V1.
If the Takeoff Weight is limited by the Takeoff Distance Available (TODA), Takeoff Run Available (TORA), or Emergency Distance Available (EMDA), the V1 speed relates to a single point along the runway where the pilot will have the decision to continue or abort the takeoff in the event of an engine failure. V1 Cannot be less than VMCG; V1 cannot be greater than Vr or VMBE.
Vr: rotation speed where the speed at which the pilot initiates rotation during the takeoff to acheive V2 at the screen height even with an engine failuare. Vr cannot be less than 1.05 VMCA divide by 1.1 or 1.05 VMU.
V2: takeoff safety speed achieved by the screen height in the event of an engine failure that maintains adequate directional control and climb performance properties of the aircraft. To be more specific, V2 cannot be less than Vs x 1.20 and VMCA x 1.10.
V3: where the all-engine-operating takeoff climb speed the aircraft will achieve at the screen height.
V4: speed is the all-engine-operating takeoff climb speed the aircraft will achieve by 400' and is used as the lowest height where accleration to flap retraction speed is initiated.
VMU: minimum demonstrated unstick speed at which it is possible to get airborne on all engines and to climb out without hazard.
VMBE: maximum brake energy speed on the ground which a stop can be accomplished within the energy capabalities of the brakes.
I hope this will help!