Could someone briefly explain the tailplane flaps. What were they, why were they needed and why not design the tailplane to move over a greater range?
Deployment of mainplane flaps and drooped ailerons alone would cause a significant n-d pitching moment. To counter this and avoid the need for significant retrimming of the varialble incidence tailplane by the pilot, simultaneous upward extension of a tailplane flap provides an equal and opposite n-u pitching moment. The pilot does not need to make significant control column movements during flap extension and only needs to retrim with IAS change as normal.