Abstract: A method for determining the speed of at least one rotating fan, such as a propeller, through sensing pressure waves generated by the blades of the fan. An apparatus operable to execute the method is also disclosed. The apparatus includes a fan having a hub portion and a plurality of blades extending radially outward from the hub portion. The apparatus also includes an engine operable to rotate the fan about an axis of rotation. The apparatus also includes a sensor spaced from the fan along the axis of rotation. The sensor is positioned to sense at least one physical condition that is external of the engine and is changed by rotation of the plurality of blades. The sensor is operable to emit a signal corresponding to at least one physical condition. The apparatus also includes a processor operably engaged with the engine and the sensor. The processor is operable to receive the signal from the sensor and change the operation of the engine in response to the signal to change a speed of the fan.

Abstract: A method for determining the speed of at least one rotating fan, such as a propeller, through sensing pressure waves generated by the blades of the fan. An apparatus operable to execute the method is also disclosed. The apparatus includes a fan having a hub portion and a plurality of blades extending radially outward from the hub portion. The apparatus also includes an engine operable to rotate the fan about an axis of rotation. The apparatus also includes a sensor spaced from the fan along the axis of rotation. The sensor is positioned to sense at least one physical condition that is external of the engine and is changed by rotation of the plurality of blades. The sensor is operable to emit a signal corresponding to at least one physical condition. The apparatus also includes a processor operably engaged with the engine and the sensor. The processor is operable to receive the signal from the sensor and change the operation of the engine in response to the signal to change a speed of the fan.