Mr Vortex
Inboard ailerons are there because at high IAS, when you move the ordinary aileron, instead of rolling the a/c, it simply bends (flexes) the wing tip in the opposite direction. I think it's called 'aileron reversal'. The inboard ailerons are mounted on a very thick almost bendable inboard section of wing.
Most a/c have reduced roll rates and heavier aileron forces at high IAS.
Someone more knowledgable than me will soon explain exactly why.
