Complex sentence: The multiplane idea was taken a step further by a small number of quadruplanes but none were successful, and as biplane design advanced it became clear that the disadvantages of the triplane and quadruplane outweighed their advantages.
Split into simpler sentences: The multiplane idea was taken a step further by a small number of quadruplanes. None were successful, and as biplane design advanced, it became clear that the disadvantages of the triplane and quadruplane outweighed their advantages.