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V1 And V2 During Take Off At Roll  
User currently offlineAlphasierra From Australia, joined Aug 2001, 34 posts, RR: 0
Posted (10 years 6 months 2 weeks 4 days 15 hours ago) and read 27341 times:

Can someone help with the definition of V1 and 2.

Be as technical as you like.

Many thanks a.netters

A.S.

16 replies: All unread, jump to last
 
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 1, posted (10 years 6 months 2 weeks 4 days 11 hours ago) and read 27183 times:

Please do a search of the forums. This must get answered every couple weeks.


09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 2, posted (10 years 6 months 2 weeks 4 days 9 hours ago) and read 27134 times:

Because the guy above cant seem to type more than a few sentances...

V1 = The speed at which the aircraft will HAVE to takeoff no matter what happens... Its a descision speed, the Non-Pilot In Command (PIC) will shout V1. And then the PIC will decide to continue the takoff or abort and bring the aircraft to a halt. Then at the rotation speed, Rotate is called... Vr. V2 is simply the safe flight speed. A minimum speed that the aircraft must fly at to acheive safe flight. The aircraft will continue climb and retract the gear as specified in the Climb out check list.

Hope that helps



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineN243NW From United States of America, joined Jul 2003, 1641 posts, RR: 20
Reply 3, posted (10 years 6 months 2 weeks 4 days 9 hours ago) and read 27121 times:

HI Alphasierra:

V1 is defined as the "decision speed" during the takeoff roll. At or above this speed the aircraft must take off due to the fact that there is not enough runway left to safely abort the takeoff. The V1 speed varies according to the aircraft weight, runway length, altitude, temperature, engine de-rating, etc. I always think of Cornelius Brothers and Sister Rose when this term comes up; "It's too late to turn back now." Laugh out loud

Vr is the rotation speed, the speed at which the PNF calls "Rotate" or "Vr" and the PF raises the nose to actually take off. Again, this speed varies due to many factors and is usually calculated by the FMS/FMC, if there is one on board.

V2 is the minimum speed on climbout. It is the highest V-speed mentioned here, usually 5-10kts greater than Vr. On the initial climbout, the pilots usually adjust their pitch attitude to hold a certain speed, such as V2+10, instead of maintaining a constant VVI. If you have ever seen any threads about typical airliner VVI on takeoff, the replies tend to be very ambiguous, because it is not constant and depends on many factors.

Cheers!
-N243NW  Big thumbs up



B-52s don't take off. They scare the ground away.
User currently offlineRduBE90Pilot From United States of America, joined Jun 2004, 63 posts, RR: 0
Reply 4, posted (10 years 6 months 2 weeks 4 days 7 hours ago) and read 26997 times:

"the aircraft must take off due to the fact that there is not enough runway left to safely abort the takeoff"

Not necessarily true..........As an example,when I operate our CJ or King Air out of a 10,000' runway, there is more than enough to safely abort. V1 by itself has nothing to do with how long the runway is. Rather, it correlates to how much runway is needed.


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 5, posted (10 years 6 months 2 weeks 4 days 1 hour ago) and read 26844 times:

V1 is not a decision speed. This is a common error.

V1 is--

The maximum speed at which the first pilot action occurs with regard to a rejected takeoff.
With most jet transport aircraft, these actions by the pilot would be:

Apply maximum wheel braking
Close the throttles
Ensure deployment of auto ground spoilers. If auto spoilers are not fitted,
deploy manual ground spoilers.
Select reverse thrust on operating engines, as required.

Note that scheduled stopping distances are not predicated on the use of reverse thrust, under FAA regulations. Other regulatory authorties have other ideas, in the regard.

V2 is,

JET transport aircraft:

The minimum speed that must be reached at a height of 35 feet.
This 35 foot height is called the screen height.

PISTON transport aircraft:
The minimum airborne speed at takeoff.


V2 is called the safety takeoff speed.


User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 6, posted (10 years 6 months 2 weeks 4 days ago) and read 26827 times:

G'day 411A

My understanding is that V1 is the speed at which the decision to reject the takeoff must be made and that action must be taken to reject the takeoff within 2 seconds following V1.

The recognition time on the other hand is the time between the engine failure (Vef) and V1 and varies from aircraft to aircraft based on engine location and other factors...

Is this incorrect?

Cheers  Smile


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 7, posted (10 years 6 months 2 weeks 4 days ago) and read 26810 times:

Liamksa,
No, you are not incorrect.
Recognition times are indeed taken into account.
The older standard was one second.
The newer thinking is two seconds.

However, the newer definition of V1 is as I have described.



User currently offlineNudelhirsch From Germany, joined Oct 2003, 1438 posts, RR: 18
Reply 8, posted (10 years 6 months 2 weeks 3 days 19 hours ago) and read 26775 times:

I read this:

V1! No aborted TakeOff possible any linger, we will be going...
Vr! normal rotating speed
V2! Safe operation speed, minimum safe flying speed



Putana da Seatbeltz!
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (10 years 6 months 2 weeks 3 days 11 hours ago) and read 26736 times:

In a 'round about way, yes.

In the early days of jet transport flying, rejected takeoffs were planned to be done more or less as in piston transport aircraft.
Max wheel braking.
Close throttles.
Spoilers up (jets only).
Reverse selected.
Originally, this seemed a good idea, but a series of nasty overrun accidents showed that the rules that applied to piston transport aircraft just would not be suitable for jet transport aircraft, so certification regulations were amended to take into account the much higher energy involved in stopping a heavy jet transport, in the event that the takeoff needed to be rejected for whatever reason.
Engine failure recognition times were built in to account for the slower reaction times demonstrated with normal line pilots (certification pilots do takeoffs with failed engines every day, line pilots do not) and, in one country, Australia, takeoff distances available were reduced by the amount of runway required to actually line up the aircraft from a right angle taxiway (in the case of the Boeing 707, 150 feet).

Further, Vr was added for jet transport aircraft, as it was demonstrated that jets, quite unlike piston engine transport aircraft, needed a definate larger pitch attitude for liftoff.
If certification regulations had not been changed, and jet aircraft flown like a piston (ie: takeoff at V2), massive amounts of runway would be reguired, and tire limit speeds would be exceeded at heavy weights.

In addition, pilot training was changed to indicate the problems associated with trying to reject a takeoff in a heavy transport jet, which is much more demanding than in piston transport aircraft.
A high energy stop in a heavy transport jet is a very difficult maneuver to do successfully in most conditions, and overruns can be rather unpleasant.


User currently offlinePhilsquares From , joined Dec 1969, posts, RR:
Reply 10, posted (10 years 6 months 2 weeks 3 days 10 hours ago) and read 26714 times:

Just a point of clarification on V1. There is no reverse thrust taken into account for the computation of V1. Theoretically, the aircraft should be able to stop at V1 using spoilers and wheel brakes alone.

User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 11, posted (10 years 6 months 2 weeks 3 days 3 hours ago) and read 26643 times:

Yes, that certainly is the case with FAA certification.
However, the UK ARB (now UK CAA) required runway distances to be increased for rejected takeoffs with transport jet aircraft, if all engines reverse was not available, on runways classified as WET.
These were the older regulations that applied to B707 and L1011 aircraft.
I have no idea about newer types.


User currently offlineGunFighter 6 From Netherlands, joined Jan 2001, 404 posts, RR: 0
Reply 12, posted (10 years 6 months 2 weeks 1 day 10 hours ago) and read 26434 times:

V1 and V2 according to the JAR ATPL study guides. (cant be more accurate then that).

And i am sorry 411A, V1 is definately a decision speed

V1:
The decision speed V1 is a speed from which a/c in performance class A, following failure of the critical engine, shall be able to either come to a stop on the remaining rwy, or continue the take off and achieve 35 feet and V2 within the remaining rwy including any clearway.

V2 take off safety speed:
the target speed to be attained at the screen height with one engine inoperative, and used to the point where acceleration to flap retraction speed is initiated.

Well hope it clears all up
Cheers
G.


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 13, posted (10 years 6 months 2 weeks 1 day 1 hour ago) and read 26375 times:

All very well, GF6, however your thinking does not agree with the latest from the FAA.
Which, is what makes aviation so very interesting.
Oddly enough, until very recently, even European member states could not agree on aircraft certification and pilot licensing requirements...and even now there are differences with certain national authorities, JAA or no JAA.

Oh yes, food for thought, for you in particular.
The aircraft does not know what your 'decision' is, it only 'knows' what actually is working/not working, from a performance standpoint.
You could 'decide' for example to reject at 100 knots, but if you were slow to act, and the speed increased, the performance would be vastly different.


User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 14, posted (10 years 6 months 2 weeks 8 hours ago) and read 26294 times:

Suppose an MD-80 has a failure on one of its engines, before V1, if the pilot uses reverse thrust, would the aircraft sway significantly because of asymetricla thrust?

User currently offlineNightFlyer From United States of America, joined Sep 2001, 95 posts, RR: 3
Reply 15, posted (10 years 6 months 2 weeks 3 hours ago) and read 26266 times:

Asymmetrical reverse thrust is not a big deal. I flown MD11's with deferred reversers on a wing mounted engine and even at max reverse thrust it's not very noticeable. The MD80 would be even less noticeable since the engines are mounted on the fuselage.


NightFlyer


User currently offlineWing From Turkey, joined Oct 2000, 1575 posts, RR: 23
Reply 16, posted (10 years 6 months 1 week 6 days 8 hours ago) and read 26214 times:

Whatever the definition you imply for V1,don't try to decide after you reach to it.My B737 training manuals teachs me that V1 marks the end of the decision process and the latest point you start taking action as 411A described above.

The training manuals also says there is 2 second time interval is given for unexpecting line pilot to decide so the PNF should call the V1 earlier than the aircraft actually reaches to that mark.Another interesting example given about it is on a calculated speed and runway if you start aborting 2 seconds after V1 you can leave the runway end with a speed of 20 to 40 kts.

You really would to look embaressed over the grass if you take V1 as a "decision speed"



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