CPL Aerodynamics and Aircraft Systems 3 — Questions and Answers
Question 1: What is the primary purpose of a hydraulic accumulator in an aircraft hydraulic system?
- To filter contaminants from the hydraulic fluid
- To store pressurized fluid for emergency use and dampen pressure fluctuations (Correct answer)
- To convert hydraulic pressure to electrical power
- To regulate fluid temperature during high-demand operations
Correct answer: To store pressurized fluid for emergency use and dampen pressure fluctuations
A hydraulic accumulator stores pressurized fluid under a nitrogen gas charge to provide emergency pressure, dampen pump pressure spikes, and supplement pump output during peak demand.
Question 2: In a typical aircraft fuel system, the crossfeed function allows:
- Fuel to be transferred from one tank to another by gravity
- Any engine to draw fuel from any tank regardless of normal feed configuration (Correct answer)
- Fuel to bypass the fuel filters during an emergency
- The APU to draw fuel directly from the wing tanks
Correct answer: Any engine to draw fuel from any tank regardless of normal feed configuration
Crossfeed permits an engine to be fed from a tank on the opposite side of the aircraft, enabling fuel balancing and engine operation in the event of a fuel pump failure.
Question 3: Aircraft bleed air, tapped from jet engine compressor stages, is primarily used for:
- Fuel pressurization and tank venting
- Cabin pressurization, air conditioning, and wing anti-icing (Correct answer)
- Hydraulic system cooling and brake cooling
- Avionics bay cooling and battery ventilation
Correct answer: Cabin pressurization, air conditioning, and wing anti-icing
Bleed air extracted from the compressor provides the main source of airflow for cabin pressurization, environmental control, and thermal anti-icing of wing leading edges and engine inlets.
Question 4: A constant-speed propeller governor maintains a selected RPM by automatically adjusting:
- Engine throttle position to match propeller pitch
- Propeller blade pitch to balance engine torque and aerodynamic load (Correct answer)
- Propeller diameter through a variable-hub mechanism
- Mixture ratio to keep combustion power constant
Correct answer: Propeller blade pitch to balance engine torque and aerodynamic load
The governor senses propeller RPM and adjusts blade pitch (increasing pitch in light load, decreasing in heavy load) to keep RPM constant as power demand changes.
Question 5: The pressurization differential limit (max differential pressure) on a transport aircraft is primarily set by:
- Passenger comfort limits and oxygen partial pressure requirements
- Structural limits of the fuselage pressure vessel (Correct answer)
- Engine bleed air capacity at cruise altitude
- APU output pressure limitations
Correct answer: Structural limits of the fuselage pressure vessel
The maximum cabin differential pressure is determined by the structural design limit of the fuselage, which must withstand repeated pressurization cycles throughout the aircraft's service life.
Question 6: In a typical transport category aircraft electrical system, the AC buses are normally powered by:
- Engine-driven DC generators connected through inverters
- Engine-driven AC generators (alternators) synchronized to the same frequency (Correct answer)
- The APU battery pack through a transformer-rectifier unit
- Ground power units connected via the external power receptacle
Correct answer: Engine-driven AC generators (alternators) synchronized to the same frequency
Large transport aircraft use engine-driven AC generators (integrated drive generators or variable-frequency generators) as the primary AC power source during normal flight.
Question 7: What is the function of a transformer-rectifier unit (TRU) in an aircraft electrical system?
- Converts DC battery power to AC for avionics
- Converts AC generator output to DC for DC bus loads (Correct answer)
- Regulates generator voltage by varying field current
- Provides galvanic isolation between AC and DC systems
Correct answer: Converts AC generator output to DC for DC bus loads
A TRU steps down and rectifies AC generator output to provide regulated DC power for DC buses, battery charging, and DC-powered equipment.
CPL Aerodynamics and Aircraft Systems 3
What is the primary purpose of a hydraulic accumulator in an aircraft hydraulic system?