Which of the devices listed is commonly used to compensate for the expansion and minor misalignments occurring between the main turbine rotor and the reduction gear?

Correct Answer: Option D — Gear-type flexible coupling

Gear-type flexible couplings accommodate axial thermal expansion and minor angular or parallel misalignments between high-speed propulsion turbine rotors and reduction gear trains, protecting high-tolerance rotating components from excessive mechanical binding and fatigue.