Isn't V2 and VR the same thing?

Question

V2 is the lowest speed that you can takeoff and VR is the speed you rotate at. So, isn't it knid of the same? And also, which order do they come in? I would think V1, V2, VR right?

Answer 1

Not at all. You rotate at Vr so as to reach V2 at precisely 35 feet which believe it or not is the end of the takeoff run and beginning of the first segment climb, gear retraction. V1 may be equal to Vr but V2 is always greater than Vr. May not make sense to you but you are rotating as I said so you will be exactly fast enough, V2, at thirty five feet. Takes time for a transport to complete rotation and arrive at a height of 35 feet. Even with one flamed out she's going to continue to accelerate during that time. If Vr was not lower than V2 there is no way you could keep from exceeding V2 and that aint good. Sure makes sense to me.

Answer 2

No, you actually have it all wrong unfortunately

VR is the rotation speed or the speed at which the pilot starts to pull the nose gear off the runway, and V2 is the speed at which a pilot can still safely fly the plane in the event of an engine loss

The order is actually V1, the speed at which you can safely abort the takeoff if something to were occur during the takeoff roll. VR, is as i have said, the speed at which the pilot begins to pull the nose of the aircraft off the runway, and V2

Answer 3

No, sorry its V1 decision speed VR Rotation speed V2 positive rate of climb.

Don't forget to vote best answer.

Answer 4

Define these speeds first, then we'll get into a discussion of what they mean.

V1: Takeoff decision speed.  Below  V1 an engine failure results in an abort.  At or after V1, the pilot must continue.

Vr.  The speed at which rotation is begun and the nosewheel is lifted.

V2: Takeoff safety speed.  Its a complex definition, but essentially it boils down to something approximating Vxse.  It would the the speed at which the airplane should climb in order to maintain a required single-engine climb gradient.  Obviously the real definition is much more complicated than that, but we'll stick with what I've listed for now.

On a takeoff roll, after the power is set the aircraft accelerates down the runway.  At V1, an engine failure occurs.  The pilots continue the takeoff (because thats what V1 means) and begin a rotation at Vr.  As the aircraft continues to accelerate, it also begins to climb.  However, this is not the most aerodynamically efficient speed to be climbing at.  Vr can kind of be closely approximated as "minimum flying speed" or maybe as Minimum "unstuck" speed (Vmu).  However, this is not a speed that results in the best climb gradient.

Aircraft are certificated to meet certain climb gradient requirements (feet of altitude per nautical mile).  Vr simply means "get the airplane off the ground."  Built into the V speeds calculation is a little wiggle room that allows the pilots to pull the airplane off the ground early (At Vr) and continue to accelerate.  As the wheels come off the ground, there is significantly less friction slowing the airplane down, so it will accelerate.  The difference between Vr and V2 allows the aircraft to use that extra time to accelerate to V2 prior to reaching 35' above the runway elevation.  After 35', the airplane climbs out at V2, which is approximately best angle of climb on a single engine (best climb gradient) and the airplane meets all the required climb gradient requirements for that particular airport.

It is a very complex set of calculations that are done.  Most airlines send off to a company called AeroData in order to crunch all the numbers for them rather than doing it themselves.  Included on every dispatch release is a section known as Takeoff Data in which all these variables are accounted for and every available runway is accounted for.  The maximum weight available for each runway is the one variable that is directly under the control of the crew, so usually each runway will have a maximum weight allowed for takeoff at any specific temperature.

Answer 5

V2 isn't the slowest speed at whch you can take off.  The airplane is capable of taking off and flying slower than V2.   V2 is the takeoff safety speed.

Vr is the speed to begin rotating, according to the tables predicting takeoff performance.  

V1 is the takeoff decision speed.

The callout sequence if each is to be called out is V1, Vr, V2.  

In a shear to tailwind after V1 the pilot sometimes rotates before Vr (and climbs out slower than V2) in order to take off before reaching the departure threshold.

".....rotating before you're going fast enough"?  A gradual rotation doesn't keep the plane from accelerating.  It is still accelerating.

Answer 6

No hes not, John B is correct.  But isnt it like 15ft in the wet? and why is that?

Answer 7

no they're not, the sequence is V1, VR, V2.

VR by definition is your rotate speed. V2 is your take off safety speed which is the speed you fly with an engine out which takes into account VMCA, VS etc, it is not the lowest speed you can takeoff.

Answer 8

the first guy is spot on

Answer 9

Negative, Ghostrider.  V2 is not the lowest speed for takeoff.  It is your initial climb speed with an engine out.  By definition, it must be higher than VR.

It's hard to explain this without getting too deep into performance theory... Here's the abridged version.  V2 is only critical if there's an engine failure.  It's most important to what's considered the "second segment climb."

The following information assumes an engine failure at V1 with the takeoff continued.

[edited below for more accurate information]

The actual takeoff distance is calculated from brake release to the point the airplane reaches 35 feet above the runway.  It assumes a rotation in a manner that the airplane accelerates to achieve V2 right at 35 feet with the gear down or in transit.

Second segment climb starts at the point where the gear is up and locked with and performance calculated with the flaps in the takeoff position and a speed maintained at V2.

3rd and 4th (or final) segments are not as critical to answering your question... but if you're curious, the 3rd segment is a level-off at 400 feet so the airplane can accelerate to a safe speed to retract the flaps.  Larger planes with more power may not need to accomplish this level-off.  The smaller bizjets that I fly don't have enough power to accelerate without an intermediate level-off.  Once the airplane is in a clean configuration, it starts the final segment climb, which is an enroute climb at a higher speed (called Vfs) in a clean configuration.

[EDIT]

John, I cleaned it up a bit.  You're right, second segment climb begins at the point the gear is up and locked.  Both of the jets I fly defines the first segment climb from the point of liftoff to the point the gear is up and locked, although the first 35 feet are also included in the takeoff distance.  Variation in terminology between airplanes?

Answer 10

This one made me realize how much has changed in the 30 years I've been out of Aviation.  Our two Critical Speeds were, Vr, velocity refusal, now identified as V1.  Simply stated it was the point you were committed to takeoff, NO MATTER WHAT!

Vrot, Velocity Rotate was determined by weight, temperature, density, cg, etc.  At that point if you put slight negative pressure on the yoke, the aircraft would shed itself of the ground.

Now going past trivia, I researched V2 and don't believe we used it. It actually takes more into consideration in slope, wind direction, etc.  We either didn't use or it was calculated into Vr.  I really can't remember.

While trying to find the correct answer I found a great site you may enjoy, http://www.auf.asn.au/groundschool/umodu...  It really describes takeoff sequence in explicit detail.  It's from Ozie Land so don't trip up on terminology.

Cheers Mate!!

By the way, in out times, but using todays reference, V1 would be after Vr on a long runway.  When V1, refusal, came before VR, get unstuck, it added to the pucker factor cuz you could be taking off with a dead engine or fire warning.  So I don't think it's correct to say there is a given sequence for V1 & VR, it depends on the runway and conditions.