Method of driving in rotation at least one main rotor of a rotorcraft fitted with a power plant comprising a plurality of engines, the method implementing an in-flight simulation mode that simulates failure of one of the engines of the rotorcraft in order to train a pilot of the rotorcraft for such a failure, in which simulation mode: - at least two engines jointly deliver a power in order to drive the main rotor at a setpoint speed of rotation, said power being shared evenly between the engines which are kept as a whole in synchronous engagement on a power transmission train interposed between the power plant and the main rotor, - each of said at least two engines being operated in dependence on a first setpoint (OEI/2) predefined according to the value of a second setpoint selected by a trainer from a plurality of second setpoints, each defining for a given period a power that the engines are authorised to deliver when not in simulation mode in the event of a real failure of an engine, the value of the first setpoint (OEI/2) corresponding to the value of the second setpoint defining it shared evenly between the engines which are kept as a whole in synchronous engagement on said power transmission train in order to drive the main rotor in rotation in simulation mode, - a current speed of rotation of the main rotor detected as lower than a predetermined threshold speed of rotation, spontaneously giving rise to the performance of an operation of supplying power delivered by the engines within the limit imposed by a third setpoint, characterised in that said operation of supplying power is performed by actively maintaining the simulation mode and by generating a regulation command giving rise to a controlled gradual increase of the power delivered by the engines by authorising the limit imposed by the first setpoint (OEI/2) to be exceeded, said gradual power increase being interrupted at a current power delivered by the engines driving the main rotor at a speed of rotation greater than or equal to the predetermined threshold speed of rotation as a consequence of a collective pitch manoeuvre of the blades of the main rotor carried out by the pilot continuing training in simulation mode. - at least two engines jointly deliver a power in order to drive the main rotor at a setpoint speed of rotation, said power being shared evenly between the engines which are kept as a whole in synchronous engagement on a power transmission train interposed between the power plant and the main rotor, - each of said at least two engines being operated in dependence on a first setpoint (OEI/2) predefined according to the value of a second setpoint selected by a trainer from a plurality of second setpoints, each defining for a given period a power that the engines are authorised to deliver when not in simulation mode in the event of a real failure of an engine, the value of the first setpoint (OEI/2) corresponding to the value of the second setpoint defining it shared evenly between the engines which are kept as a whole in synchronous engagement on said power transmission train in order to drive the main rotor in rotation in simulation mode, - a current speed of rotation of the main rotor detected as lower than a predetermined threshold speed of rotation, spontaneously giving rise to the performance of an operation of supplying power delivered by the engines within the limit imposed by a third setpoint,