Abstract: An auxiliary propulsion system includes a case for connection to at least one input or output device, a first flange associable with a power input, a power drive shaft with a first end placed substantially in a position corresponding to the first flange and a second end opposite the first end, a second flange in one piece with the second power drive shaft placed in a position corresponding to the second end, an electric motor connected to the second flange, a clutch including a first disc assembly rotating as a unit with the first flange, a second disc assembly rotating as a unit with the power drive shaft, elements to engage the first disc assembly with the second disc assembly. The elements include a piston to compress the first and second disc assemblies and make them rotate as a unit, the piston being connected to at least one centrifugal weight.