Try these sample questions to review concepts for the Module 15 Gas Turbine Engine exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which thermodynamic cycle represents the ideal working cycle of a gas turbine engine?

A.Otto cycle

B.Brayton cycle

C.Diesel cycle

D.Carnot cycle

Explanation: The constant-pressure heat addition cycle used in gas turbine engines is the Brayton cycle (also known as the Joule cycle), consisting of ambient compression, constant-pressure combustion, expansion through the turbine, and constant-pressure exhaust.

2How is Gross Thrust ($F_g$) defined for a gas turbine engine operating under static conditions?

A.Total thrust produced by exhaust gas momentum plus nozzle pressure differential force, without subtracting inlet ram drag

B.Net thrust remaining after airframe parasite drag subtraction

C.Thrust produced exclusively by the fan rotor in a high-bypass turbofan

D.Difference between total exhaust momentum and incoming ram momentum

Explanation: Gross Thrust ($F_g$) is the total rearward force created by the engine exhaust gas stream ($F_g = \dot{m} V_j + (P_j - P_0) A_j$). It does not take into account the momentum of incoming air entering the intake (ram drag).

3What is the mathematical relationship between Net Thrust ($F_n$), Gross Thrust ($F_g$), and Ram Drag ($F_{ram}$)?

A.$F_n = F_g + F_{ram}$

B.$F_n = F_g - F_{ram}$

C.$F_n = F_g \times F_{ram}$

D.$F_n = F_{ram} - F_g$

Explanation: Net Thrust ($F_n$) is the net propulsive force available to accelerate or maintain aircraft flight speed. It equals Gross Thrust minus Ram Drag ($F_n = F_g - \dot{m} V_0$).

4In a high-bypass turbofan engine, how is bypass ratio defined?

A.Ratio of fuel flow to core air flow

B.Ratio of mass airflow passing through the bypass duct to mass airflow passing through the engine core

C.Ratio of compressor outlet pressure to turbine inlet pressure

D.Ratio of fan diameter to core tailpipe diameter

Explanation: Bypass ratio is defined as $\dot{m}_{bypass} / \dot{m}_{core}$. High-bypass turbofans divert 5:1 to 10:1 or more air around the core combustion engine to maximize propulsive efficiency.

5What is the primary function of a convergent subsonic engine inlet duct?

A.Increase air velocity and decrease static pressure before entering the compressor

B.Decrease air velocity and increase static pressure before entering the compressor

C.Maintain supersonic airflow velocity up to the first stage compressor rotor

D.Mix bypass air with primary combustion core air

Explanation: A subsonic intake duct acts as a divergent diffuser internally, causing air velocity to decrease and static pressure to increase, ensuring uniform subsonic flow enters the compressor rotor at optimum angle of attack.

6Why are bellmouth inlets used during engine ground testing in test cells?

A.To maximize ram recovery during high-speed ground runs

B.To provide smooth, aerodynamic, non-turbulent airflow with minimal boundary layer loss into the engine compressor

C.To filter out large foreign objects without reducing air velocity

D.To induce controlled swirl into the first-stage compressor blades

Explanation: Bellmouth inlets feature deeply curved bell-shaped rims that draw air smoothly from all surrounding directions with virtually zero inlet losses, ensuring exact engine aerodynamic performance measurement in ground test beds.

7What is the main advantage of a centrifugal compressor compared to an axial compressor?

A.Higher pressure ratio per single stage and robust construction

B.Smaller frontal area for a given mass airflow rate

C.Higher overall efficiency in multi-stage engine applications

D.Lower rotational speed requirements for supersonic aircraft

Explanation: Centrifugal compressors deliver high pressure rise per stage (typically 4:1 to 5:1 compared to 1.1:1 - 1.2:1 for axial stages), have simple rugged construction, and are resistant to foreign object damage.

8What are the two main component assemblies of a single stage in an axial flow compressor?

A.Rotor blades and Stator vanes

B.Impeller and Diffuser

C.Turbine disk and Nozzle guide vanes

D.Swirl vanes and Fuel spray nozzles

Explanation: An axial compressor stage consists of a rotating set of rotor blades followed by a stationary set of stator vanes. The rotor imparts kinetic energy to the air, and the stator converts kinetic energy into static pressure while redirecting airflow to the next stage.

9What is the primary function of stator vanes in an axial flow compressor stage?

A.To increase air velocity while decreasing static pressure

B.To convert kinetic energy into static pressure by acting as divergent passages and direct air at the correct angle to the next rotor stage

C.To extract mechanical energy from the gas stream to drive accessories

D.To atomize fuel before it enters the combustor liner

Explanation: Stator vanes create divergent passages between adjacent blades. This diffuses the high-velocity air exiting the upstream rotor, raising static pressure and turning the flow to the proper entry angle for the downstream rotor stage.

10Which blade root design is most commonly used to attach high-pressure turbine and compressor blades to rotor disks?

A.Dovetail root

B.Fir-tree root

C.Pin joint

D.Welded seam

Explanation: The fir-tree blade root design features multiple interlocking serrations that distribute heavy centrifugal forces across multiple contact shoulders while allowing thermal expansion and replacement during maintenance.

About the Module 15 Gas Turbine Engine Exam

UK CAA Part-66 Module 15 covers jet engine principles, compressor surge control, turbine construction, lubrication, fuel systems, and ground testing for Category B1 AME candidates. Exam includes 92 MCQs with a 75% pass mark.

Exam sponsor: UK Civil Aviation Authority (CAA). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Questions

92 questions

Time Limit

115 minutes

Passing Score

75%

Exam / Certification Fees

£75

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

UK Civil Aviation Authority (CAA): official exam information

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

50%

Core Knowledge & Regulations

Fundamental principles, laws, and operating requirements.

50%

Applied Systems & Calculations

Practical application, calculations, and maintenance procedures.

Preparing for the Module 15 Gas Turbine Engine Exam

What You Need to Know

Passing score: 75%
Exam length: 92 questions
Time limit: 115 minutes
Exam / certification fees: £75 Official sources

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Module 15 Gas Turbine Engine: Suggested Study Strategy

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Frequently Asked Questions

What is the pass mark for Module 15 Gas Turbine Engine?

The pass mark required by the UK CAA is 75%.