hello mr k
I can do a first principles net take off flight path calculation, thats not the issue here. My problem is that all engines operating, most biz jet pilots go rattling through the speed that they can retract the flaps and continue on up to whatever speed they get to by the time they get to 1000' or 1500' or whatever their particular company chooses to to use as a totally arbitrary flap retraction height.
Flap retraction heights don't exist - they are a figment of crappy understanding. There are level acceleration platforms which you can use to get from V2 to whatever speed you need to raise the flaps to the next position but all engines running you don't need them. So you can raise the flaps whenever you like as long as you have achieved the necessary speed.
Its incredible to me that very very few of us do whats in the aircraft manual. A mixture of tribal knowlege and lack of understanding has taught an enormous number of people to do something that doesnt make sense and can't be justified.