Abstract: A rotary electrical machine comprising a stator (10) and at least one rotor (12) having a plurality of permanent magnets (14). The rotor consists of a rotor disc, at the outer edge of which the permanent magnets are mounted. The rotor disc (12) is provided with airgap varying means (19) which are angled towards the stator (10) and mounted on the rotor hub (24) for rotation therewith. When the rotor is stationary, the airgap (30) between the magnets (14) and the stator (10) is at a minimum. In operation, as the speed of rotation of the rotor (12) increases, a centrifugal force is generated which acts to bend the airgap varying means (19) and, therefore, the rotor disc (12) back, away from the stator (10), thereby drawing the magnets (14) away from the stator and increasing the size of the airgap (30). The increase in size of the airgap results in a corresponding decrease in flux and therefore a decrease in the maximum output voltage for that rotor speed.

Abstract: A rotary electrical machine (1) has at least one stator (23). The stator is provided with at least one radial channel (107) for ducting cooling air. The channel (107) extends between a first position (113) at or substantially near the rim (109) of a winding region of the stator (23) and a second position (119) at or substantially near the center (51) of the winding region. The machine (1) has cooling means (91-97) for causing cooling air to enter the radial channel (107) via the second position (119) and exit via the first portion (113). The stator may have electrical windings arranged as coil sectors (183-197) disposed substantially equi-angularly in a generally circular pattern. At least some of the coil sectors are wound in a generally spiral fashion when viewed axially. A rotor (13), for the machine may have a plurality of equi-angularly spaced magnets (127), which are generally circular but with a cut-away portion, when viewed axially.