Complex sentence: Helicopters have no need for a tail rotor when equipped with contra-rotating rotors, as the two rotors cancel out each others' angular momentum; this aids maneuverability and allows the design to be more compact.
Split into simpler sentences: Helicopters have no need for a tail rotor when equipped with contra-rotating rotors, as the two rotors cancel out each others' angular momentum. This aids maneuverability and allows the design to be more compact.