V2+20 clean is my final segment climb speed and configuration.
I can climb at that for as long as I like.
However, I can also accelerate to my enroute climb speed and achieve a better climb rate though not necessarily a better gradient because of the increased forward speed. If there are no obstacles we should climb at Venr because of the increased climb rate.
Recap. These are all the same - retract the flaps on schedule and you can't go wrong.
If we have an engine failure at V1 up to V2+20 - can't retract the flaps because we can't accelerate and climb. So climb to 1500 feet, reduce pitch to level flight and retract the flaps accelerating through V2+20. Keep accelerating to Venr, climb away.
If we manage to get to V2+20 with both engines running we can now retract the flaps WITHOUT a level segment or pitching to accelerate.
So if we have an engine failure V2+20 up to Venr we're clean now (or in the middle of reconfiguring to clean). Keep the constant pitch and gently allow the speed to reduce back to V2+20. Its important not to pitch up because again the drag will increase (from the elevator) so just let the speed bleed back naturally. You are still well above the pitch for V2+20 clean so you'll still be trading speed for extra height and therefore definitely above the required gradient. The speed will bleed back to V2+20 and you pitch to maintain that. At 1500 feet (the platform we've all agreed on for a level acceleration) you can lower the pitch to accelerate to Venr and when you get there, climb away. There are conditions on this which you already do calculations for (I'm sure). Far out obstacles may require you to stay at your final segment climb gradient so you may have to do that but you're still in a much better position than the guys who left the flap selected as you don't have to pitch level and accelerate to get rid of the flap.
Engine failure after Venr up to cruise climb speed. Gently slow down to Venr because that gives you (roughly) the best climb clean OEI.
This is what isn't explained during perf lessons. It is, however, what the manufacturer thinks you're going to do. It leaves you in all cases after V2+20 with an aircraft thats climbing better and easier to fly than leaving the flap down past the flap retraction speed. It means you do the same thing whether all engines keep running or one fails ie:-
Take off, Retract the flap at V2+20, if you need a level acceleration platform to achieve flap retraction and a Venr climb use 1500 feet (subject to normal perf constraints)
its the same plan for every take off whether an engine fails or not.
Spandex (cool name) asked what maneuvering limitations we have at V2+20 clean. I can retract the flaps at 1.25Vs which is V2+4 when light and V2+7 when max weight and that will give the same maneuvering protection as flap 20 and V2 so there's already improved maneuvering margin but I'll look up the limits in the manual tomorrow.
Last edited by tommoutrie; 1st Dec 2012 at 22:42.