Device for folding/unfolding a tail boom of a rotorcraft, an associated rotorcraft, and a corresponding folding/unfolding method

A folding/unfolding device for folding/unfolding a tail boom, the device being arranged in association with a rear power transmission shaft of a tail rotor of the rotorcraft, the folding/unfolding device comprising pivot means enabling a movable portion of the tail boom to move in pivoting relative to a stationary portion of the tail boom, the relative pivoting movement being performed between two distinct extreme positions, namely an unfolded, working position enabling the rear power transmission shaft to transmit driving torque to the tail rotor, and a folded, rest position enabling the overall length of the rotorcraft to be reduced. According to the invention, the folding/unfolding device includes motor-driven decoupling/coupling means for mechanically decoupling/coupling together two portions of a single rear power transmission shaft before/after the relative pivoting movement of the movable portion of the tail boom relative to the stationary portion.