Filtering device with integrated bypass for an air inlet

A filtering device for an engine or a for power unit with a radial air intake (2), comprising a ring-shaped filter (3) for covering the radial air intake, characterised in that the ring-shaped filter comprises a first fixed part (3a) and a second mobile part (3b) which is movable with respect of the first fixed part through actuator means (6), from a filtering position in which the whole radial air intake is covered by the ring-shaped filter, to a bypass position in which the second mobile part uncovers at least partly the radial air intake.