A&P Turbine Engine Theory Questions and Answers — Questions and Answers
Question 1: In a gas turbine engine, what is the primary function of the diffuser section located between the compressor and the combustor?
- To increase the velocity and decrease the static pressure of the air.
- To decrease the velocity and increase the static pressure of the air. (Correct answer)
- To mix fuel with the compressed air for ignition.
- To extract bleed air for cabin pressurization and anti-ice systems.
Correct answer: To decrease the velocity and increase the static pressure of the air.
The diffuser is a divergent duct that slows down the high-velocity air from the compressor. According to Bernoulli's principle, this decrease in velocity results in an increase in static pressure, creating the ideal low-velocity, high-pressure conditions required for stable and efficient combustion in the combustion chamber.
Question 2: Which of the following statements most accurately describes the primary source of thrust in a high-bypass turbofan engine?
- The majority of thrust is produced by the large fan section accelerating a mass of ducted air that bypasses the engine core. (Correct answer)
- Thrust is generated almost exclusively by the high-velocity exhaust gases exiting the core engine.
- Thrust is equally divided between the fan section and the core exhaust gases.
- All thrust is generated by the expansion of hot gases in the turbine section driving the fan.
Correct answer: The majority of thrust is produced by the large fan section accelerating a mass of ducted air that bypasses the engine core.
In a high-bypass turbofan engine, a large fan at the front moves a significant mass of air. Most of this air (often over 80%) is ducted around the core engine (bypass air) and accelerated rearward, producing the majority of the engine's total thrust. The remaining air goes through the core, which primarily serves to power the fan.
Question 3: A pilot reports hearing a loud bang from the engine, followed by a rapid rise in Exhaust Gas Temperature (EGT) and a loss of thrust. These symptoms are most indicative of which condition?
- Flameout
- Hot start
- Compressor stall or surge (Correct answer)
- Hung start
Correct answer: Compressor stall or surge
A compressor stall or surge is a breakdown of airflow through the compressor. This disruption can cause a momentary or complete reversal of airflow, resulting in a loud bang. The disruption starves the combustor of air, leading to an overly rich fuel-air mixture that burns in the turbine section, causing a rapid EGT spike and a significant loss of thrust.
Question 4: What is the primary purpose of the "fir-tree" root design commonly used to attach turbine blades to the turbine disk?
- To simplify the manufacturing and machining of the turbine disk.
- To act as a heat sink, drawing heat away from the blade airfoil.
- To create a lightweight connection that reduces rotational mass.
- To securely attach the blade while accommodating thermal expansion and high centrifugal loads. (Correct answer)
Correct answer: To securely attach the blade while accommodating thermal expansion and high centrifugal loads.
The fir-tree root has multiple serrations that evenly distribute the immense centrifugal forces generated by the rotating blade. This design provides a secure attachment while also allowing for slight movement as the blade and disk expand at different rates due to extreme temperatures, preventing excessive stress buildup.
Question 5: The continuous thermodynamic cycle of intake, compression, constant-pressure combustion, and exhaust that describes the operation of a gas turbine engine is known as the:
- Otto cycle
- Brayton cycle (Correct answer)
- Diesel cycle
- Rankine cycle
Correct answer: Brayton cycle
The Brayton cycle is the ideal thermodynamic cycle for a gas turbine engine. It consists of four processes: isentropic compression (compressor), constant-pressure heat addition (combustor), isentropic expansion (turbine), and constant-pressure heat rejection (exhaust).
Question 6: A technician is troubleshooting an aircraft's inoperative wing anti-icing and cabin pressurization systems. Which turbine engine system is the most likely common source for both of these issues?
- The engine fuel control unit.
- The accessory gearbox.
- The compressor bleed air system. (Correct answer)
- The engine lubrication system.
Correct answer: The compressor bleed air system.
The compressor bleed air system extracts hot, high-pressure air from the engine's compressor section. This air is then ducted to various aircraft systems, including wing and engine anti-icing, cabin pressurization, and air conditioning. A fault in the bleed air supply would affect all systems that rely on it.
A&P Turbine Engine Theory Questions and Answers
In a gas turbine engine, what is the primary function of the diffuser section located between the compressor and the combustor?