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POWER PLANT
J TURBINE ENGINES, OPERATION, INSTRUMENTS, MAINTENANCE, AND OVERHAUL
| Question | Answer |
|---|---|
| 1. Explain the main difference and advantage of turbofan over turbojet engines. | A turbofan engine uses a fan to bypass some air around the engine core and to provide thrust. The advantage is that this provides additional thrust without increasing fuel flow. |
| Name the major components in a gas turbine engine. | - Air inlet, compressor section, combustion section, turbine section, exhaust section, gearbox and accessory section. |
| What determines the amount of airflow through a turbine engine? | The forward speed of the aircraft, compressor speed, and air density. |
| Name the two types of compressors commonly used in turbine engines. | Axial and centrifugal flow compressors. |
| Name two different methods for attaching turbine engine rotor blades to the rotor disks. | Dovetail-type root -or- Bulb-type root -or- Fir tree-type root |
| What is a split compressor system? | Also called dual or twin spool compressors, these are connected to the turbine section with two rotor shafts, one inside the other. |
| What are the different types of combustion chambers used in turbine engines? | - Can, annular, can-annular, and reverse flow annular. |
| What prevents the combustion chambers from burning? | Cooling air along the inside of the liner. |
| What is the purpose of the interconnecting tubes attached between can-type combustion chambers? | For flame propagation during start. |
| What functions do axial flow turbine nozzles perform? | They direct the mass airflow to drive the turbine rotor at a specific angle. |
| How is thermal stress relieved on a turbine disc? | By directing bleed air onto the face of the disk, or by grooves being cut in the disk. |
| What are carbon seals used for in turbine engines? | They are used as oil seals for the rotor shaft bearings. |
| What is shaft horsepower? | It is an indication of the torque developed by a turboprop or turboshaft engine. |
| Name the main components of a typical APU. | - A small power turbine for power and bleed air, and an electrical generator. |
| When is the greatest demand placed on an APU? | When supplying bleed air. |
| How is an APU generally started? | - With its own electrical starter and battery power. |
| Where does the APU get its fuel supply? | From one of the aircraft's main fuel tanks |
| At what speed does a gas turbine APU operate and how is this speed maintained? | At or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed. |
| What is used to prevent a heavily loaded APU from exceeding its maximum EGT? | A load control valve modulates the pneumatic load to maintain EGTs within limits. ( |
| How is an APU shut down and why is this procedure used? | After the APU is unloaded by closing the bleed air valve, it is run for a specified amount of time to allow the EGT to cool and stabilize. This cool down period is typically three minutes. If a heavily loaded APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock. |
| What powers the variable inlet guide vanes used on some APUs to regulate compressor intake airflow? | Fuel pressure. |
| What is fan blade shingling? | It is the overlapping of the midspan shrouds of the fan blade. |
| When a turbofan or turbojet engine is shut down, what should a mechanic listen for during Coast down? | Any rubbing sound or other unusual noises from the engine. |
| Why are compressor washes performed and what methods are commonly used? | To remove any contaminants from the compressor section and improve engine performance. The fluid wash and abrasive grit wash are commonly used. |
| How can you tell if a turbofan or turbojet engine is out of trim? | There will be a high exhaust gas temperature at the target engine pressure ratio for takeoff |
| Name the different types of compressor blade damage that may be found during inspection. | Dents, cracks, galling, pitting, scratches, burrs, burns, gouges. |
| What kind of markers can be used to mark the parts in hot and cold sections during repair? | Layout dye, felt tip marker, chalk. |
| How does relative humidity affect turbine engines | Negligible effect |
| What criteria determines replacement of life limited turbine engine components? | Cycles, hours and/or calendar time. |
| If turbine blades are removed from a turbine disc, why should they be re-installed in the same location? | To maintain the balance of the turbine wheel |
| How are gas turbine engine tachometers calibrated? | They are calibrated in percent r.p.m. |
| On a turbine engine, what is the engine pressure ratio and what does it indicate? | - It is the ratio between the total inlet pressure and total turbine exhaust pressure and is used to indicate the thrust developed by the engine. |
| On a turbine engine, what does exhaust gas temperature (EGT) indicate and how is it obtained? | EGT is the average temperature of the turbine discharge gasses and is obtained by thermocouples placed near the turbine exit |
| Can the EGT system on a turbine engine be checked without running the engine? | Yes, by checking the resistance of the thermocouples and circuits. |
Created by:
S_A_J
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