Use of the Flaps on Take Off

[pj997]

Hi

I always wonder why a small amount of flaps (15%?) is applied before the plane takes off, and not during the take off run..

I always understood that the flaps increase the amount of lift, but at the same time the amount of drag increases.

So surely the take off run would be shorter, with faster acceleration and less fuel used if the flaps were applied when the aircraft was say at 50% of the rotation speed?

Any thoughts

PJ