What is the meaning of V2?

[themoffster]

Firstly, I tried a search, but 'V2' is less than 3 characters long and isn't counted in any search results.

Anyhoo, I know V1 was decision speed (after this you take off), but I thought V2 was the speed you worked out beforehand that is the minimum to get you airborne - ie. at V2 you can pull back and you will take off.

Now the problem arises when it comes to VR. I'm now pretty certain this does the jjob I thought V2 did.

Do you call out V2 in take-off? What does it do nad how does this compare to VR?

Cheers!

[SquawkModeA]

V2 is the abbreviation for "takeoff safety speed" - the speed at which the takeoff and climb can be continued safely assuming an engine failure.

[In dis-sky's]

V2 is the so-called "Take Off safety speed". You will fly this speed in case of an N-1 situation during Take Off. It will provide best single engine climb performance during N-1. (Vx during N-1). As this speed is different for every weight, it is calculated together with V1 and Vr before departure.

V2 shall not be less than 1.2 Vs and 1.1 Vmca.

[Herp]

In our manuals, the definition of V2 is as follows:

The target speed to be attained at screen height with one engine inoperative and used to a point where acceleration to flap retraction speed is initiated.

V2 is the take-off safety speed, is not called out during the take-off, but the salmon bug on the ASI is set to V2 for the take-off. After take-off V2 is maintained (or slightly above usually) until the flap retraction altitide. In the event of an engine failure, the flight director will give pitch demands to maintain V2 to V2+15kts (depending on the speed at the time of the failure) until the speed bug is wound up for flap retraction.

Hope this makes sense to you.....757/767 by the way.

Cheers.

[themoffster]

thanks troops!
it does make sense a little.

[BOAC]

Searching for 'speeds' in Tech Log produced this (http://www.pprune.org/forums/showthread.php?s=&threadid=112277&highlight=speeds) which has links to previous threads.

[Tinstaafl]

Whilst V2 will enable at least the minimum climb gradient for obstacle clearance it won't necessarily be the greatest gradient. However, barring some unusual circumstance, the a/c is 'guaranteed' to achieve xyz gradient & the departure path vs obstacles is planned accordingly.

A deliberately increased V2 take off may be appropriate to clear some types of limiting obstacles ie increasing the time accelerating on the ground in order to achieve a faster V2 once airborne. Jets are usually on the back of the power curve during their initial climb so increasing V2 reduces drag with a resulting increase in climb performance. The catch is the longer runway needed to accelerate, V1 limits, brake limits etc etc.

[411A]

This all assumes that the aircraft is turbojet/turbofan powered...some turbopropellor types as well.

With older turboprops, and all large piston powered transport aircraft, V2 was achieved before liftoff...ie: the takeoff rotation was started at V2.
When jet transports came along, this was found to be impractical, as many of the early types (B707/DC8) had no/minimal leading edge devices, which required rather high V2 speeds...with resultant runway length/tire limit speed problems.
Having personally had takeoff runs approaching 12,000 feet in early model 707's, the idea of continuing to V2 before liftoff was not appealing, as in...up close and personal with the weeds at the end. :uhoh:

And that was with all four turning.:ooh: