FAA Powerplant Written Practice Test

Which type of electric motor is typically used with a direct-cranking engine starter?

1. AC synchronous motor

2. DC brushless motor

3. DC series wound motor

4. Universal motor

The correct answer is: DC series wound motor

The correct answer is a DC series wound motor. This type of motor is commonly used in direct-cranking engine starters because it provides a high starting torque. The construction of a DC series wound motor includes windings that are connected in series with the armature winding, allowing the motor to draw a high current when starting. This high current generates a strong magnetic field, which results in the high torque necessary to turn an engine over. DC series wound motors also have the advantage of being able to speed up as the load decreases, making them well-suited for applications like starting engines where rapid initial torque is critical. Their ability to handle variations in voltage without significant loss of performance is also beneficial in a starter application, as it ensures reliable engine starting even under different conditions. Other types of motors are less suitable for this application. For instance, AC synchronous motors are generally used for applications requiring constant speed, which is not ideal for starting engines. DC brushless motors, while efficient, typically require more complex control systems and may not produce the high torque needed for engine starting. Universal motors, capable of running on both AC and DC, are more suited for applications where variable speed and load characteristics are encountered, rather than the high torque requirement of a direct-cranking