Originally Posted by
john_tullamarine
That's not what is taken into the calculations, Vr is the MINIMUM speed to START the action that results in rotating, you must stay on the rwy till the A/C is under control then rotate.
Now, that's a tad different to what the design stuff has to say on the matter .. can you cite some authoritative references for your statement ? Alternatively, one could run with the more standard thought that Vr is chosen to achieve V2 for the OEI failure case. If you delay the rotation, you will exceed V2 and the numbers game gets a bit messy. (Irrelevant for the FAR 23 case).
You seem to miss the point. ALL the numbers are minimums, V1 is the only exact number because it's known as a decision speed, clear cut, Vr & V2 do NOT have to be adhered to as long as they are not acted upon or flown LESS than calculated. If perf allows a healthy climb greater than minimum V2 (you can remain at the current speed if an engine failure occurred above the min V2 speed during initial climb out) then there is no law to state you must be at V2 but usually is V2 + 10/20 in order to achieve the required climb gradient. Anyway I've always been shown during all my type endo's that stay on the Rwy till the A/C is tracking straight even if this means going beyond the MINIMIN Vr speed, its worked for all the 20.7.1B A/C I have been involved with. An Eg when NOT to rotate at Vr if V1 & Vr are the same. You have an engine failure just as you get to V1 (& you go) & the A/C heads bush momentarily (due the startle factor) say off Rwy Hdg by 15 degs towards the grass, are you going to rotate as soon as you heard Vr from the PNF if they are both the same numbers? No bloody way!