V2 and Vy

[airmen]

I am looking for any link between Take off safety speed V2 and Best ROC speed Vy however cannot find it.
V2 being min 1.2 Vs1 and min 1.1 VMCA, the speed we are supposed to keep is min V2 and max V2+10 until MSA or MAA where we accelerate and do the clean-up.

Thank you

[Alex Whittingham]

There is no link. JAR 25 and FAR 25 specify a minimum value for V2, not an optimum rate of climb speed. VY for a clean jet would be a long way off scheduled V2, typically in excess of 400kt at sea level.

[PantLoad]

From the standpoint of the pilot, one can consider V2 as the one-engine-inoperative (OEI), best-angle-of-climb speed. In reality, V2 is actually not optimal, that is, it is usually somewhat below the OEI best-angle-of-climb speed. There are, also, certification issues involved in the computation of V2.

Airbus has a series called "Getting to Grips". One of their articles is entitled "Getting to Grips with Performance". You can download this and read for yourself how the various V speeds are derived. It's a rather lengthy paper...over 200 pages...but, it explains in simple terms and in detail all about performance.

PantLoad

[Old Smokey]

PantLoad speaks the truth. V2 is typically below Vmd, thus is less than optimum speed for best angle. The V2+10 reference puts you closer to best gradient speed, BUT (and it's a big BUT), only if you've ALREADY achieved the higher speed at the time of engine failure.

If engine failure occurs at or close to V2, don't accelerate to V2+10, even though the gradient achieved at V2+10 will be greater after having achieved it, the acceleration will mean 'ducking under' the required gradient to clear obstacles, thus your resultant flight path will be less than that required.

Example -

Failure at V2 = Maintain V2
Failure at V2+7 = Maintain V2+7
Failure at V2+10 = Maintain V2+10
Failure above V2+10 = Reduce to V2+10, then maintain V2+10

Regards,

Old Smokey

[Intruder]

VY for a clean jet would be a long way off scheduled V2, typically in excess of 400kt at sea level.
Nowhere near 400 kt for transport category jets. I don't think any current airliners have sea level Vmo that high!

Vy for the 747 ranges from about 280 to 335 KIAS, depending on weight.

[Alex Whittingham]

Thanks, my data was from a Hunter :}

[airmen]

Airbus has a series called "Getting to Grips"

Downloaded that one and find the doc very good. Thank you PantLoad

Thank you also Old Smokey

[High Wing Drifter]

Hi all,

You can find the document that PantLoad refers to at this most excellent of repositories: http://www.wingfiles.com/#Performance