Electrical machines for aircraft power and propulsion systems

A vertical take-off and landing, VTOL, aircraft 1 comprising an electrical propulsion unit 100f, 100r EPU is provided. The EPU includes a propeller or fan 110, an electric motor (120, fig 4) including a stator having insulated coils (214 fig 5A) for carrying current and a rotor (220, 5A) arranged to interact with the stator to produce a torque for driving rotation of the propeller or fan. In use, the insulated coils of the stator are supplied with a flow of coolant to remove heat therefrom. The coolant may be air. The annular frequency of rotation of the rotor of the electric motor is equal to an angular frequency of rotation of the propeller or fan. The stator coils may be directly exposed to the flow of air so as to increase a rate of heat transfer from the stator coils to the air. The electric motor may be a transverse flux electric motor. The cooling may be a liquid. The diameter of the active parts of the lectic motor may be 0.5 meters. The active parts mass of the motor may be less than or equal to 30kg.