Term
| Explain the main difference and advantage of turbofan over turbojet engines. |
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Definition
| 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. |
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Term
| Name the major components in a gas turbine engine. |
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Definition
| Air inlet, compressor section, combustion section, turbine section, exhaust section, gearbox and accessory section. |
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Term
| What determines the amount or airflow through a turbine engine? |
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Definition
| The forward speed of the aircraft, compressor speed, and air density |
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Term
| Name the two types of compressors commonly used in turbine engines |
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Definition
| Axial and centrifugal flow compressors |
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Term
| Name two different methods for attaching turbine engine rotor blades to the rotor disk |
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Definition
| Dovetail-type root, bulb-type root, or fir tree-type root |
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Term
| What is a split compressor system? |
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Definition
| Also called dual or twin spool compressors, these are connected to the turbine section with two rotor shafts, one inside the other |
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Term
| what are the different types of combustion chambers used in turbine engines? |
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Definition
| Can, annular, can-annular, and reverse flow annular |
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Term
| What prevents the combustion chamber from burning? |
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Definition
| Cooling air along the inside of the liner |
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Term
| What is the purpose of the interconnecting tubes attached between can-type combustion chambers? |
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Definition
| For flame propagation during start |
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Term
| What functions do axial flow turbine nozzles perform? |
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Definition
| They direct the mass airflow to drive the turbine rotor at a specific angle. |
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Term
| How is thermal stress relieved on a turbine disc? |
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Definition
| By directing the bleed air onto the face of the disk, or by grooves being cut into the disk |
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Term
| what are carbon seals used for in turbine engines? |
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Definition
| They are used as oil seals for the rotor shaft bearings |
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Term
| What is shaft horsepower? |
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Definition
| It is an indication of the torque developed by a turboprop or turboshaft engine |
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Term
| Name the main components of a typical APU. |
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Definition
| A small power turbine for power and bleed air, and an electrical generator |
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Term
| When is the greatest demand placed on the APU? |
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Definition
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Term
| How is the APU generally started? |
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Definition
| With its own electrical starter and battery power |
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Term
| Where does the APU get it's fuel supply? |
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Definition
| From one of the aircraft's main fuel tanks |
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Term
| At what speed does the gas turbine APU operate and how is this speed maintained? |
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Definition
| At or near its rated speed regardless of the electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed. |
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Term
| What is used to prevent a heavily loaded APU from exceeding its maximum EGT? |
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Definition
| A load control valve modulates the pneumatic load to maintain EGT's within limits |
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Term
| How is an APU shut down and why is this procedure used? |
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Definition
| 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 heavy loaded APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock. |
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Term
| What powers the variable inlet guide vanes used on some APUs to regulate compressor intake airflow? |
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Definition
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Term
| What is fan blade shingling? |
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Definition
| It is the overlapping of the midspan shrouds of the fan blade. |
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Term
| When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coastdown? |
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Definition
| Any rubbing sound or other unusual noises coming from the engine |
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