Originally Posted by Tourist
If that is the case, why extra nose down for tailwind?
You only have tailwind until you hit 10kts GS, after that it is just a normal take-off as if you started at nil wind. The apparent wind vector very quickly moves forward.
If the extra down load on the nose wheel, produced by the tail, is proportional to the airspeed squared, then at around 40 kts in still air (or 30 kts with a 10 kt tail wind) the tail loads are 16 units versus 9 units. Therefore you'd need almost double the amount of down elevator for the same effect in the tailwind case.
Obviously the difference diminishes with increasing airspeed (64 units v 49 units at 80 kts in still air (i.e. 70 kts with 10 kt tail)).
It is the extra nose tyre adhesion which helps keep the aircraft straight with a crosswind and initially when an engine failure is recognised. If one method is approved for still air and all head winds, then it is prudent to modify the technique for tailwind take offs.