Complex sentence: The fin was triangular, carrying a flat topped rudder which extended down to the bottom of the fuselage in a cut out between the elevators; the latter were aerodynamically balanced but the rudder was not.
Split into simpler sentences: The fin was triangular, carrying a flat topped rudder which extended down to the bottom of the fuselage in a cut out between the elevators. The elevators were aerodynamically balanced but the rudder was not.