A&P Turbine Engine Theory 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?

Accepted Answer

To decrease the velocity and increase the static pressure of the air.

Answer

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?

Accepted Answer

The majority of thrust is produced by the large fan section accelerating a mass of ducted air that bypasses the engine core.

Answer

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?

Accepted Answer

Compressor stall or surge

Answer

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?

Accepted Answer

To securely attach the blade while accommodating thermal expansion and high centrifugal loads.

Answer

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:

Accepted Answer

Brayton cycle

Answer

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).

A&P - Certified Airframe and Powerplant Mechanics Practice Test

A&P - Certified Airframe and Powerplant Mechanics Practice Test

A&P Turbine Engine Theory Questions and Answers