AET AET Aircraft Power Systems 1 — Questions and Answers
Question 1: In a typical general aviation aircraft, what is the primary function of the aircraft's alternator?
- To start the engine
- To charge the battery and power the electrical bus during engine operation (Correct answer)
- To provide emergency lighting only
- To power the landing gear actuators
Correct answer: To charge the battery and power the electrical bus during engine operation
The alternator charges the battery and supplies electrical power to the aircraft's bus systems whenever the engine is running above a threshold RPM.
Question 2: What is the nominal voltage of a standard 14-volt aircraft electrical system when measured at the bus with the alternator online?
- 12 volts
- 13.8–14.5 volts (Correct answer)
- 28 volts
- 24 volts
Correct answer: 13.8–14.5 volts
A 14V system typically operates at 13.8–14.5 volts at the bus when the alternator is charging, slightly above the 12V battery nominal voltage to maintain a charging state.
Question 3: Which component in an aircraft's DC power system prevents the battery from discharging through the alternator when the alternator output is lower than battery voltage?
- Voltage regulator
- Circuit breaker
- Isolation diode or split-bus relay (Correct answer)
- Current limiter
Correct answer: Isolation diode or split-bus relay
An isolation diode or split-bus relay prevents reverse current flow from the battery through the alternator when alternator output drops below battery voltage.
Question 4: What is the typical voltage output of an aircraft's 28V DC bus system when fully regulated?
- 24 volts
- 27.5–28.5 volts (Correct answer)
- 32 volts
- 26 volts
Correct answer: 27.5–28.5 volts
A regulated 28V system operates between approximately 27.5 and 28.5 volts to properly charge 24V batteries while powering the aircraft's electrical loads.
Question 5: In a constant-speed drive (CSD) generator system found on transport-category aircraft, what does the CSD unit do?
- Regulates AC voltage output
- Maintains constant generator shaft speed regardless of engine RPM (Correct answer)
- Converts DC to AC power
- Monitors generator temperature
Correct answer: Maintains constant generator shaft speed regardless of engine RPM
The CSD maintains a constant output shaft speed to the generator regardless of engine RPM changes, allowing the AC generator to produce a stable 400 Hz frequency.
Question 6: What is the standard AC power frequency used by most transport-category aircraft electrical systems?
- 50 Hz
- 60 Hz
- 400 Hz (Correct answer)
- 800 Hz
Correct answer: 400 Hz
Aircraft AC electrical systems operate at 400 Hz, which allows lighter and smaller transformers and motors compared to the 50/60 Hz used in ground power systems.
AET AET Aircraft Power Systems 1
In a typical general aviation aircraft, what is the primary function of the aircraft's alternator?