AC Generation and DistributionAircraft & Engines — DGCA CPL practice questions

All 5 questions — AC Generation and Distribution

Aircraft & Engines · DGCA CPL. The correct option is marked on each.

1. Q1. The standard AC frequency in aircraft electrical systems is:

   • A.50 Hz
   • B.60 Hz
   • C.400 Hz✓
   • D.1000 Hz

   Why: Aircraft use 400 Hz three-phase AC — higher frequency permits smaller, lighter machines.

2. Q2. A Constant Speed Drive Unit (CSDU) is used to:

   • A.Drive the alternator at constant speed despite varying engine RPM✓
   • B.Regulate DC voltage
   • C.Start the engine
   • D.Synchronise the propellers

   Why: The hydromechanical CSDU converts variable engine speed to constant output speed, holding the 400 Hz frequency. Combined with the generator it forms an IDG.

3. Q3. A Transformer Rectifier Unit (TRU) converts:

   • A.DC to AC
   • B.115V AC to 28V DC✓
   • C.28V DC to 115V AC
   • D.400 Hz to 50 Hz

   Why: The TRU steps the 115V AC down and rectifies it to 28V DC. The opposite job — battery DC to essential AC — is done by an inverter.

4. Q4. Before AC generators can be paralleled onto a common bus, they must match in:

   • A.Temperature and pressure
   • B.Voltage, frequency and phase sequence✓
   • C.RPM only
   • D.Field current

   Why: Voltage, frequency and phase rotation must be synchronised; the system then shares real (kW) and reactive (kVAR) load equally.

5. Q5. Static wicks on trailing edges serve to:

   • A.Improve aileron response
   • B.Discharge airframe static electricity safely into the atmosphere✓
   • C.Detect icing
   • D.Reduce drag

   Why: They bleed off static build-up, preventing interference with communications; bonding straps keep all metal parts at equal potential.