H-60 Tail Rotor Drive Shaft Thomas Coupling Transient Overload Capacity

The UH-60 helicopter has proven its true utility by being successfully adapted to a wide range of missions since it's original introduction into service. The aircraft is currently being operated at significantly increased gross weight over the original design. While the engines and main transmission have been grown to supply additional power to the main rotor, the tail rotor drive train remains essentially identical to what was originally qualified in 1976. Even at very high gross weights, the majority of flight maneuvers are not taxing to the tail rotor drive system. However, there are several maneuvers that can result in high transient tail drive train torque loads. The installation of special mission equipment and an increase in both frequency and duration of these maneuvers raises concern regarding the ultimate torque capability of the tail rotor drive train. This paper summarizes static testing performed on a section of the tail drive shaft and Thomas couplings to substantiate their capability to withstand high transient torque loading.