Complex sentence: The M39 design had inboard flaps and outboard ailerons on the rear wing and the front wing had a auxiliary aerofoil/flap/elavator device, which could vary the wing area without changing lift coefficient.
Split into simpler sentences: The M39 design had inboard flaps and outboard ailerons on the rear wing. The front wing had a auxiliary aerofoil/flap/elavator device; it could vary the wing area without changing lift coefficient.