Turbine Engines
15. What is meant by creep of the turbine blades?
A condition of permanent elongation of the turbine blades. Creep is caused by the high temperatures and the high centrifugal loading imposed on the blades.
13. What is meant by a hung start in a turbine engine?
A start in which ignition occurs but the engine does not accelerate to a self-sustaining speed.
14. What is meant by a hot start in a turbine engine?
A start in which ignition occurs but the internal temperatures go high enough that they can damage the engine.
7. What is meant by a free-turbine turboshaft engine?
A turboshaft engine that has a turbine wheel or stage of turbine wheels that is not used to drive the compressor of the gas generator section of the engine. This free turbine drives the propeller in a turboprop engine or the transmission and rotor of a helicopter.
8. Why do some axial-flow turbine engines have more than one set of turbines and compressors?
A two-spool turbine engine has a low-pressure and a high-pressure compressor each driven by its own turbine. The two independent systems operate at the speed at which they are most efficient.
21. What is meant by trimming a turbojet engine?
Adjusting the fuel control to get the correct idling and maximum-thrust RPM
10. What is meant by a turbofan engine?
An axial-flow turbine engine in which the first stage of compressor blades are lengthened so they can force air around the outside of the gas generator portion of the engine.
16. How is the compressor of a turbine engine cleaned?
An emulsion-type cleaner is sprayed through the engine while it is being motored by the starter or operated at a low speed. The wash is followed by a clean water rinse.
9. What kind of bearings are used to support the rotor shaft of an aircraft turbine engine?
Anti-friction bearings such as ball bearings or roller bearings.
18. At what point in a turbine engine is the temperature the highest?
At the inlet to the high-pressure turbine.
2. What are the two basic types of compressors that are used in aircraft turbine engines?
Axial-flow and centrifugal.
4. What are three types of combustors used on aircraft turbine engines?
Can-type annular-type and can-annular-type.
12. Why is it important that a turbojet engine be allowed to cool before it is shut down after it has been operated at a high power setting?
If the engine is shut down while it is hot there is a possibility that the shroud will contract around the turbine wheel and seize the rotor.
11. Where can you find the limits of repair allowed for the compressor blades of an aircraft turbine engine?
In the FAA-approved service manual issued by the manufacturer of the engine.
17. Where is water injected into a turbine engine for cooling purposes?
Into the compressor inlet and into the engine diffuser case.
1. What are the two basic sections of a turbine engine?
The hot section and the cold section.
20. What are two types of thrust reversers that are used on turbojet engines?
The mechanical blockage-type and the aerodynamic blockage-type.
3. What is the purpose of the stators in an axial-flow compressor?
The stators convert some velocity energy into pressure energy and change the direction of the air so it is proper for the next stage of rotors.
6. What is the main purpose of the turbine nozzle in an aircraft turbine engine?
The turbine nozzle directs the hot gases as they leave the combustors so they will turn the turbine wheel with maximum efficiency.
19. What is the function of the interconnect tubes between the cans of a turbine engine that uses can-type combustors?
These tubes allow the flame to travel from the cans that contain the igniters to all of the other cans when the engine is being started.
5. How many igniters are there normally in an aircraft turbine engine?
Two.
