Is the APU starter motor DC or AC?

Is the APU starter motor DC or AC?

• A. DC
• B. AC
• C. Both
• D. Neither

Answer: (A)

Starting an APU requires delivering high torque at low speed in a compact, easily controllable package. A DC motor fits this role well because it provides strong starting torque and straightforward speed control when fed from the aircraft’s 28 V DC electrical system or a dedicated DC power source. The starter motor’s job is simply to spin the APU turbine up to speed; once running, the APU can generate the needed electrical power (AC and DC) for the aircraft. Some systems can start the APU pneumatically with an air turbine starter instead of an electric motor, but when an electric starter is used, it is typically a DC motor.

Starting an APU requires delivering high torque at low speed in a compact, easily controllable package. A DC motor fits this role well because it provides strong starting torque and straightforward speed control when fed from the aircraft’s 28 V DC electrical system or a dedicated DC power source. The starter motor’s job is simply to spin the APU turbine up to speed; once running, the APU can generate the needed electrical power (AC and DC) for the aircraft. Some systems can start the APU pneumatically with an air turbine starter instead of an electric motor, but when an electric starter is used, it is typically a DC motor.