FAA Powerplant Written Practice Test

The type of electric motor typically used with a direct-cranking engine starter is the DC series wound motor. This motor design is ideal for starting applications because it provides high starting torque, which is necessary to turn over an engine from a standstill.

In a DC series wound motor, the field windings are connected in series with the armature winding. This configuration means that when the motor is first energized, the current flowing through the field windings is high, leading to a strong magnetic field. This strong field results in a significant torque output, which is essential for overcoming the initial inertia of an engine and starting it effectively.

Furthermore, DC series wound motors have a relatively simple construction and can handle varying load conditions, making them suitable for the brief, high-demand bursts of power required during engine starting. Their ability to provide a large amount of torque at low speeds aligns perfectly with the operational requirements of an engine starter system.

While other motors like AC synchronous motors and universal motors have their applications, they do not specialize in the high torque needed at startup. DC brushed motors are capable of providing torque, but they do not match the efficiency and effectiveness of series wound motors in this specific situation.