Amt Oral Test Guide: Powerplant Theory And Maintenance

Front 1

How are conventtional reciprocating engines classified?

Back 1

They are classified according to cylinder arrangement with respect to the crankshaft (in-line, v-type, radial, and opposed), or according to method of cool (liquid cooled, or air cooled)

Front 2

What are the different types of piston rings?

Back 2

Compression rings, oil control rings, and scraper rings

Front 3

What is the purpose of the oil control rings?

Back 3

They are used to control the thickness of the oil film on the cylinder walls

Front 4

What may be the result of installing piston rings incorrectly?

Back 4

Excessive oil consumption

Front 5

What type of piston rods are commonly found in radial engines?

Back 5

A master and articulating rod assembly

Front 6

What type of bearings are in general use in reciprocating engines?

Back 6

Plain, roller, and ball bearings. Plain bearings are generally used for crankshaft, camshafts, and connecting rods. Roller bearings are used primarly as crankshat main bearings. And ball bearings are used for supercharger impreller shaft bearings and crankshaft thrust bearings on large radial engines

Front 7

What is the indication of valve blowby?

Back 7

Valve blowby is indicated by a hissing or whistle when pulling the propeller through by hand. A cylinder compression check should be completed to identify the fualty cylinder

Front 8

What is the purpose of using more than one spring for valve closing?

Back 8

Walve springs will resonate (or surge) at certain engine speeds. If only one spring is used, the valve will float as the spring surges. To eliminate this problem, two springs (one inside the other) are installed on each valve. Each spring will resonate at a different engine speed, eliminating valve float.

Front 9

What is the purpose of valve overlap?

Back 9

Walve overlap permits better volumetric efficiency and lowers the cylinder operating temperatures

Front 10

Describe the inspection you would give the valve springs during engine overhaul.

Back 10

They should be cleaned thoroughly, then visually inspected, for evidence of overheating, cracks, broken ends, and compression strength

Front 11

What is the purpose of using valves with sodium filled stems?

Back 11

Some intake and exhaust valve stems are hollow and partially filled with metallic sodium. Sodium is used because it is an excellent heat conductor. The sodium melts at a relatively low temperature, and as the valve moves and down the sodium is circulated, carrying the heat from the valve head to the stem. Then the heat is dissipated to the cylinder head.

Front 12

What causes engine sudden stoppage?

Back 12

Striking an object or engine seizure due to internal damage

Front 13

What type of inspection must be made after sudden stoppage of an engine?

Back 13

Most manufacturers require a complete engine tear down and inspection

Front 14

What is the purpose of the crankshaft dynamic dampers used in aircraft engines?

Back 14

Dampers are used to overcome forces which cause deflection of the crankshaft and torsional vibration. These forces are generated by the power impulses of the pistons. Crankshaft vibrations are reduced by placing floating dampers (weights) in the counterweight assembly, particularly in a single throw type crankshaft.

Front 15

How would you make a "runout" check on a crankshaft that is still installed in the engine?

Back 15

Remove the proppeller from the crankshaft and attach a dial indicator gauge to the front of the crankcase. Adjust the position of the gauge needle so that is is touching the shaft. Rotate the crankshaft and check for misallignment. Refer to the table of limits to checkthe allowance. Flanged crankshafts must also be checked from the front face of the flange

Front 16

What is detonation?

Back 16

All normal combustion of the air-fuel mixture burns at a uniform rate across the combustion chamber. The temperature and pressure within the cylinder rises at a normal rate as the mixture burns. All fuels have critical limits of temperature and compression, beyond this limit they will ignite spontaneously and burn with explosive violence. This instantaneous explosive burning of the last portion of the charge is called detonation.

Front 17

What is engine sudden speed reduction?

Back 17

This occurs when the propeller strikes an object but continues to run. When this occurs, a thorough external inspection should be carried out, including an oil analysis. The propeller should be inspected aling with a run-out check

Front 18

What can be learned about the condition of an engine by studying the results of a compression check?

Back 18

From the cylinder compression check you can determineif the valves, piston rings, and pistons are adequately sealing the combustion chamber

Front 19

How can a cold cylinder be located on a double row radial engine?

Back 19

A cold cylinder check can be made with a cold cylinder indicator, sometime called a "Magic Wand", to locate any cylinder that has a temperature lower than the normal operating temperature of the other cylinders. On most horizontal engines, you can simply place your hand on the rocker box to check for a cold cylinder

Front 20

What instrument can be used to check bore for out of roundness?

Back 20

A cylinder bore can be checked with a dial indicator, telescoping gauge and outside micrometer, or inside micrometer

Front 21

What would cold cylinder indicate?

Back 21

That there has been no combustion inside the cylinder, normally due to no ignition or a clogged fuel nozzle

Front 22

Where is a crack most likely to occur on a piston?

Back 22

A crack is most likely to occur where the piston pin connects. The metal is thinnest at this location.

Front 23

What are the major components of a typical gas turbine engine?

Back 23

A typical gas turbine engine consists of an air inlet, compression section, combustion section, turbine section, exhaust section, and accessory section.

Front 24

What are two principle types of compressors used in turbojet aircraft?

Back 24

The two most common compressors in use today are the centrifugal flow and axial flow types

Front 25

What are the four combustion chamber systems?

Back 25

They are the can, can-annular, annular, and reverse flow annular types

Front 26

What is the purpose of the interconnector tubes between can type combustion chambers?

Back 26

To spread the flame to the combustion chambers that are not equipped with igniter plugs during engine starting

Front 27

What prevents burning of the liner walls in can type combustion chambers?

Back 27

Louvers are provided along the axial length of the liners to direct a cooling layer of air along the inside wall of the liner

Front 28

What types of damage may be found when inspecting compressor blades?

Back 28

Dents, scartches, gouges, galling, burns, burrs, pitting, and cracks

Front 29

What is the location and function of the diffuser section in a turbine engine?

Back 29

The diffuser is the divergent section of the engine located between the compressor section and burner cans, Its function is to change the high velocity compressor discharge air to static pressure

Front 30

Where are stress rupture cracks most likely to occur on turbine blades?

Back 30

They usually appear as small hairline cracks on or across the leading or trailing edge of the blade. The cracks appear at right angles to the edge length

Front 31

How are compressor blades attached to a disk-type rotor?

Back 31

The compressor blades are fitted into the disks by either bulb-type, fir-tree, or dove tail type roots. The blades are then licked by means of screws, peening, locking wires, pins, or keys

Front 32

What is the purpose of the nozzle diaphragm, or turbine nozzle?

Back 32

The turbine nozzle prepares the combustion mass airflow to drive the turbine rotor. First they change a portion of the heat and pressure energy to velocity energy. The fixed vanes are shaped and set as such an angle that they form a number of small nozzles that discharge the gasses at extremely high speeds. The second purpose of the turbine nozzles is to deflect the gases so they strike the turbine at the most efficient angle for maximum turbine rotation.

Front 33

What is the major difference between turboprop and turbojet engines?

Back 33

A turboprop engine usually has more turbine stages than the turbojet engine. In addition to operating the compressor and accessories, the turboprop turbine must also drive a propeller

Front 34

What is a turbofan engine?

Back 34

A turbofan engine is in principle, the same as turboprop, except that the propeller is replaced by a duct-enclosed axial flow fan

Front 35

What is the effect of air density on the thrust of a turbine engine?

Back 35

Air density determines the mass of air that is used by a jet engine. The factors affect density are the temperature and pressure of the air. If density increases, thrust increases, and vice versa. An increase in air temperature entering an engine will cause a decrease in density and thrust. An increase in air pressure entering the engine will cause an increase in density and thrust. With a given throttle setting, engine thrust will vary if the temperature or pressure of the air entering the engine changes.

Front 36

What are the two most common types of thrust reverse?

Back 36

They are mechanical blockage type and aerodynamic blockage type

Front 37

What is a split compressor system is a turbine engine?

Back 37

The split compressor system requires two concrentric shafts joining the turbine stages to their respective compressors

Front 38

What is one method of relieving thermal stress on a turbine disk?

Back 38

One method is to direct cooling bleed air back onto the face of the disk

Front 39

What may be the indications if a turbojet engine is out of trim?

Back 39

The engine has high exhaust gas temperature (EGT at a target pressure ratio (EPR) for takeoff)

Front 40

What is free turbine?

Back 40

A turbine wheel that, rather driving the compressor rotor, drives a propeller or helicopter transmission

Front 41

What is the main purpose of the thrust reversers?

Back 41

For slowing the aircraft down to effective braking speeds.

Front 42

What steps must be taken in order to prepare an aircraft for a 100 inspection?

Back 42

Remove or open all necessary inspection plates, access doors, fairing and cowling. Then thoroughly clean then aircraft and the engine.

Front 43

What may be used as a guide for a 100 hour inspection on aircraft engines?

Back 43

FAR Part 43, Appendix D

Front 44

What additional inspection must be performed if the cylinder compression is weak?

Back 44

You must make an internal cylinder inspection for improper internal tolerances

Front 45

Where are the aircraft engine operating limitations found?

Back 45

In the Aircraft Specifications or Type Certificate Data Sheet

Front 46

Where can a mechanic look to identify an aircraft engine?

Back 46

On the engine identification plate that is affixed to the engine in an accessible location

Front 47

What publication is needed to inspect an engine for conformity with specifications?

Back 47

The Engine Specifications or Type Certificate Data Sheet

Front 48

What type of FAA approval is required when a change to an engine design is not enough to require a new Type Certificate?

Back 48

A Supplemental Type Certificate is required

Front 49

What type of FAA approval is required when a change is made to the engine principle of operation?

Back 49

A new Type Certified must be obtained.