turbines

Ball and roller bearings that are in good condition but are shown to have magnetism in them may have the magnetism removed with a suitable degausser. If the bearings are allowed to remain in their magnetized state they will be damaged by the foreign ferrous particles they attract.

131. If, during inspection at engine overhaul, ball or roller bearings are found to have magnetism but otherwise have no defects, they A— cannot be used again. B— are in an acceptable service condition. C— must be degaussed before use.

shrouded turbine blades are used to reduce blade vibration and improve the airflow characteristics through the turbine.

155. Reduced blade vibration and improved airflow char- acteristics in gas turbines are brought about by A— fir-tree blade attachment. B— impulse type blades. C— shrouded turbine rotor blades.

When subsonic air flows through a convergent nozzle, its velocity increases and its pressure decreases. This action is in accordance with Bernoulli's principle, which gives us the relationship between kinetic energy and potential energy in a column of moving fluid. The kinetic energy relates to the velocity of the fluid and the potential energy relates to the pressure of the fluid.

179. The velocity of subsonic air as it flows through a convergent nozzle A— increases. B— decreases. C— remains constant.

The highest gas pressure in an axial-flow turbojet engine occurs at the outlet of the compressor. The compressor outlet is the same as the burner inlet.

8108. At what point in an axial-flow turbojet engine will the highest gas pressures occur? A— At the turbine entrance. B— Within the burner section. C— At the compressor outlet.

One of the functions of the nozzle diaphragm in a turbine engine is to deflect the gases to a specific angle in the direction of the turbine wheel rotation.

8109. One function of the nozzle diaphragm in a turbine engine is to? A— Decrease the velocity of exhaust gases. B— Center the fuel spray in the combustion chamber. C— Direct the flow of gases to strike the turbine blades at the desired angle.

"Profile" in a rotor blade of a turbine-engine compressor is a reduction in the thickness of the blade tip. Profiles prevent serious damage to the blade or the housing if the blade should contact the compressor housing.

8110. What is the profile of a turbine engine compressor blade? A— The leading edge of the blade. B— A reduced blade tip thickness. C— The curvature of the blade root.

he fan is a portion of the low-pressure compressor of a dual axial-flow compressor. The rotor blades in the fan section are long enough that the air they move passes around the outside of the gas generator portion of the engine. The fan rotational speed is the same as that of the low-pressure compressor.

8111. The fan rotational speed of a dual axial compressor forward fan engine is the same as the A— low-pressure compressor. B— forward turbine wheel. C— high-pressure compressor.

pressures in a turbine engine are identified according to their type and to the location at which they are measured. P t7 is the total pressure (the pressure a body of moving fluid has when its movement is stopped) measured at station 7, the turbine discharge.

8112. The abbreviation P t7 used in turbine engine terminology means A— the total inlet pressure. B— pressure and temperature at station No. 7. C— the total pressure at station No. 7.

Blending is a method of hand recontouring damaged compressor blades and vanes using small files, emery cloth and honing stones. Blending is done parallel to the length of the blade to minimize stress concentrations and to restore a smooth a shape to the surface.

8113. The blending of blades and vanes in a turbine engine A— is usually accomplished only at engine overhaul. B— should be performed parallel to the length of the blade using smooth contours to minimize stress points. C— may sometimes be accomplished with the engine installed, ordinarily using power tools.

In a turbojet engine, compressed air from the compressor is directed into the combustion section. Fuel is sprayed from nozzles in the combustion section where it mixes with the air and burns.

8114. What turbine engine section provides for proper mixing of the fuel and air? A— Combustion section. B— Compressor section. C— Diffuser section.

the energy exchange cycle used in a turbojet engine is the Brayton cycle which is a constant-pressure cycle. The pressure of the air remains relatively constant as the energy from the burning fuel is added to it. Since the pressure remains constant as the volume of the gas increases, its velocity increases.

8115. In a gas turbine engine, combustion occurs at a constant A— volume. B— pressure. C— density.

the relationship between thrust and RPM is such that the amount of thrust increases rapidly as the engine speed increases. A small change in speed at low RPM will not produce nearly as much increase in thrust as the same amount of change at high RPM.

8116. Which statement is true regarding jet engines? A— At the lower engine speeds, thrust increases rapidly with small increases in RPM. B— At the higher engine speeds, thrust increases rapidly with small increases in RPM. C— The thrust delivered per pound of air consumed is less at high altitude than at low altitude.

The high-pressure rotor of a two-spool (split-spool) compressor is governed for speed, but the low-pressure rotor is free to operate at its own best speed. As the air density decreases at altitude, the compressor load decreases and the low-pressure rotor increases its speed.

8117. Some high-volume turboprop and turbojet engines are equipped with two-spool or split compressors. When these engines are operated at high altitudes, the A— low-pressure rotor will increase in speed as the compressor load decreases in the lower density air. B— throttle must be retarded to prevent overspeeding of the high-pressure rotor due to the lower density air. C— low-pressure rotor will decrease in speed as the compressor load decreases in the lower density air.

One of the functions of the nozzle diaphragm in a turbojet engine is to increase the velocity of the heated gases f lowing through it. In speeding up this gas, a portion of the heat and pressure energy is turned into velocity energy, which is converted to mechanical energy by the turbine rotor blades.

8118. Turbine nozzle diaphragms located on the upstream side of each turbine wheel, are used in the gas turbine engine to A— decrease the velocity of the heated gases flowing past this point. B— direct the flow of gases parallel to the vertical line of the turbine blades. C— increase the velocity of the heated gases flowing past this point.

The highest gas pressure in a turbojet engine occurs at the outlet of the compressor. The compressor outlet is the same as the entrance of the burner section.

8119. Where is the highest gas pressure in a turbojet engine? A— At the outlet of the tailpipe section. B— At the entrance of the turbine section. C— In the entrance of the burner section.

the exhaust cone on a turbojet engine forms a divergent duct, which increases the pressure of the exiting gases and decreases their velocity.

8120. An exhaust cone placed aft of the turbine in a jet engine will cause the pressure in the first part of the exhaust duct to A— increase and the velocity to decrease. B— increase and the velocity to increase. C— decrease and the velocity to increase.

The stator vanes at the discharge of an axial-flow compressor are called the straightening vanes. They are used to straighten the airflow to eliminate turbulence.

8121. What is the function of the stator vane assembly at the discharge end of a typical axial-flow compressor? A— To straighten airflow to eliminate turbulence. B— To direct the flow of gases into the combustion chambers. C— To increase air swirling motion into the combustion chambers.

One of the major functions of the turbine section in a turbojet or turbofan engine is to drive the compressor.

8122. The turbine section of a jet engine A— increases air velocity to generate thrust forces. B—utilizes heat energy to expand and accelerate the incoming gas flow. C—drives the compressor section.

a hot start is indicated if the engine starts but the exhaust gas temperature exceeds specified limits.

8123. When starting a turbine engine, A— a hot start is indicated if the exhaust gas temperature exceeds specified limits. B— an excessively lean mixture is likely to cause a hot start. C— release the starter switch as soon as indication of light-off occurs.

The first-stage turbine in a twin-spool turbojet engine drives the high-pressure compressor. This is the second stage of compression and is called the N 2 compressor.

8124. In the dual axial-flow or twin spool compressor system, the first stage turbine drives the A— N 1 and N 2 compressors. B— N 2 compressor. C— N 1 compressor.

Materials used to mark the components in the hot section of a turbine engine must be carefully chosen so that they do not contaminate the structure of the metal when it is exposed to high temperatures. Materials such as lead pencils and wax or grease pencils which contain carbon, will cause granular embrittlement and lead to cracking, must not be used. Layout dye, commercial felt tip markers, and chalk are normally allowed.

8125. During inspection, turbine engine components exposed to high temperatures may only be marked with such materials as allowed by the manufacturer. These materials generally include 1. layout dye. 2. commercial felt tip marker. 3. wax or grease pencil. 4. chalk. 5. graphite lead pencil. A— 1, 2, and 4. B— 1, 3, and 4. C— 2, 4, and 5.

A hung start in a turbine engine is a start in which the engine lights off, but is unable to accelerate to a speed high enough to keep running without help from the starter.

8126. When starting a turbine engine, a hung start is indicated if the engine A— exhaust gas temperature exceeds specified limits. B— fails to reach idle RPM. C— RPM exceeds specified operating speed.

the turbine section of a gas turbine engine consists of two basic elements, the stator and the rotor.

8127. What are the two basic elements of the turbine section in a turbine engine? A— Impeller and diffuser. B— Hot and cold. C— Stator and rotor.

The primary function of an exhaust cone assembly used on a turbine engine is to collect the exhaust gases after they pass through the turbine and convert them into a solid, high-velocity exhaust jet.

8128. The function of the exhaust cone assembly of a turbine engine is to A— collect the exhaust gases and act as a noise suppressor. B— swirl and collect the exhaust gases into a single exhaust jet. C— straighten and collect the exhaust gases into a solid exhaust jet.

A centrifugal compressor used in a gas turbine engine has two basic functional elements, the impeller and the diffuser. The impeller adds energy to the air flowing through the engine and speeds it up. The diffuser slows the air down and increases its pressure.

8129. What are the two functional elements in a centrifugal compressor? A— Turbine and compressor. B— Bucket and expander. C— Impeller and diffuser.

After a fuel control has been replaced on a turbine engine, the engine must be re-trimmed. Trimming a gas turbine engine consists of adjusting the fuel control to give the engine the correct idle and maximum RPM.

8130. What must be done after the fuel control unit has been replaced on an aircraft gas turbine engine? A— Perform a full power engine run to check fuel flow. B— Recalibrate the fuel nozzles. C— Retrim the engine.

centrifugal compressor with vanes on both sides of the impeller is called a double-entry centrifugal compressor.

8132. A turbine engine compressor which contains vanes on both sides of the impeller is a A— double entry centrifugal compressor. B— double entry axial-flow compressor. C— single entry axial-flow compressor.

when starting a gas turbine engine, the first indication of a successful start is a sudden rise in the exhaust-gas temperature.

8133. What is the first engine instrument indication of a successful start of a turbine engine? A— A rise in the engine fuel flow. B— A rise in oil pressure. C— A rise in the exhaust gas temperature.

Turbine-discharge total pressure is identified in maintenance manuals by the abbreviation P t7 . P t2 is compressorinlet total pressure, and T t7 is turbine-discharge total temperature .

8134. Some engine manufacturers of twin spool gas turbine engines identify turbine discharge pressure in their maintenance manuals as A— P t7 . B— P t2 . C— T t7 .

the engine manufacturer establishes the recommended TBO of a turbine engine, and these times are approved by the FAA.

8135. Who establishes the recommended operating time between overhauls (TBO) of a turbine engine used in general aviation? A— The engine manufacturer. B— The operator (utilizing manufacturer data and trend analysis) working in conjunction with the FAA. C— The FAA.

statement (1) is not true. The cold section of a turbine engine does not include the turbine sections. Statement (2) is not true because the diffuser is part of the cold section of the engine.s

8136. The basic gas turbine engine is divided into two main sections: the cold section and the hot section. (1) The cold section includes the engine inlet, compressor, and turbine sections. (2) The hot section includes the combustor, diffuser, and exhaust sections. Regarding the above statements, A— only No. 1 is true. B— only No. 2 is true. C— neither No. 1 nor No. 2 is true

neither statement is true. Welding and straightening of rotating airfoils in a gas turbine engine require special equipment. Quite often, neither procedure is authorized by the engine manufacturer.

8137. (1) Welding and straightening of turbine engine rotating airfoils does not require special equipment. (2) Welding and straightening of turbine engine rotating airfoils is commonly recommended by the manufacturer. Regarding the above statements, A— only No. 1 is true. B— only No. 2 is true. C— neither No. 1 nor No. 2 is true.

Materials used to mark the components in the hot section of a turbine engine must be carefully chosen so that they do not contaminate the structure of the metal when it is exposed to high temperatures. Materials such as lead pencils and wax or grease pencils which contain carbon will cause granular embrittlement and lead to cracking must not be used.

8138. Turbine engine components exposed to high temperatures generally may NOT be marked with 1. layout dye. 2. commercial felt tip marker. 3. wax or grease pencil. 4. chalk. 5. graphite lead pencil. A— 1, 2, and 3. B— 3 and 5. C— 4 and 5.

the Instructions for Continued Airworthiness, prepared by the engine manufacturer and approved by the FAA, contain the mandatory replacement times for critical components of the engines to which the instructions apply.

8139. Who establishes mandatory replacement times for critical components of turbine engines? A— The FAA. B— The operator working in conjunction with the FAA. C— The engine manufacturer.

the bearing housing of a turbine engine usually contains seals to prevent loss of oil into the gas path. Oil seal are usually of the labyrinth or carbon rubbing type.

8140. Main bearing oil seals used with turbine engines are usually what type(s)? A— Labyrinth and/or carbon rubbing. B— Teflon and synthetic rubber. C— Labyrinth and/or silicone rubber.

the use of two axial-flow compressors turning at different speeds allows higher compression ratios to be obtained without the danger of compressor stall.

8141. How does a dual axial-flow compressor improve the efficiency of a turbojet engine? A— More turbine wheels can be used . B— Higher compression ratios can be obtained. C— The velocity of the air entering the combustion chamber is increased.

three basic types of turbine blades used in gas turbine engines are impulse, reaction and impulse-reaction.

8142. Three types of turbine blades are A— reaction, converging, and diverging. B— impulse, reaction, and impulse-reaction. C— impulse, vector, and impulse-vector.

The basic difference in the thrust produced by a turbojet or turbofan engine and that produced by a turboprop engine is in the mass of air moved and amount of acceleration imparted to it. An engine-driven propeller imparts a relatively small amount of acceleration to a large mass of air, and a turbojet or turbofan engine imparts a greater amount of acceleration to a smaller mass of air. Almost all of the useful heat energy in a turboprop engine is used to drive the compressor and the propeller, and very little is used to provide exhaust thrust.

8143. Which statements are true regarding aircraft engine propulsion? 1. An engine driven propeller imparts a relatively small amount of acceleration to a large mass of air. 2. Turbojet and turbofan engines impart a relatively large amount of acceleration to a smaller mass of air. 3. In modern turboprop engines, nearly 50 percent of the exhaust gas energy is extracted by turbines to drive the propeller and compressor with the rest providing exhaust thrust. A— 1, 2, 3. B— 1, 2. C— 1, 3.

An axial-flow compressor has an advantage over a centrifugal-flow compressor in that it has a higher peak efficiency.

8144. An advantage of the axial-flow compressor is its A— low starting power requirements. B— low weight. C— high peak efficiency.

the stator blades in an axial-flow compressor convert the high-velocity energy of the air into pressure energy. They also direct the airflow from each of the rotor stages to obtain the maximum possible blade efficiency.

8145. What is one purpose of the stator blades in the compressor section of a turbine engine? A— Stabilize the pressure of the airflow. B— Control the direction of the airflow. C— Increase the velocity of the airflow.

The diffuser section in a centrifugal-flow turbojet engine reduces the velocity of the air as it leaves the compressor and increases its pressure.

8146. What is the purpose of the diffuser section in a turbine engine? A— To increase pressure and reduce velocity. B— To convert pressure to velocity. C— To reduce pressure and increase velocity.

Stress rupture cracks usually appear as tiny hairline cracks on or across the leading or trailing edge of the turbine blades at right angles to the edge length of the blade.

8147. Where do stress rupture cracks usually appear on turbine blades? A— Across the blade root, parallel to the fir tree. B— Along the leading edge, parallel to the edge. C— Across the leading or trailing edge at a right angle to the edge length.

The can-type combustion chamber of a turbojet engine consists of an outer case, or housing, and inside it is a perforated stainless steel combustion chamber or liner. The case and liner are removed as a unit for routine maintenance.

8148. In which type of turbine engine combustion chamber is the case and liner removed and installed as one unit during routine maintenance? A— Can. B— Can annular. C— Annular.

The diffuser is an annular chamber fitted with a number of vanes that form a series of divergent passages between the centrifugal compressor and the burner section. As the diffuser vanes direct the flow of air into the burn- ers, they increase the pressure of the air and decrease its velocity.

8149. The diffuser section of a jet engine is located between A— the burner section and the turbine section. B— station No. 7 and station No. 8. C— the compressor section and the burner section.

Stress rupture cracks or deformation of the leading edge of the first-stage turbine blades are usually caused by an overtemperature condition. Overtemperature operation must be suspected when finding this type of damage.

8150. When the leading edge of a first-stage turbine blade is found to have stress rupture cracks, which of the follow- ing should be suspected? A— Faulty cooling shield. B— Overtemperature condition. C— Overspeed condition.

Turbine blades are generally more susceptible to operat- ing damage than compressor blades because they are continually exposed to such extremely high temperatures.

8151. Turbine blades are generally more susceptible to operating damage than compressor blades because of A— higher centrifugal loading. B— exposure to high temperatures. C— high pressure and high velocity gas flow.

the turbine-inlet temperature (TIT) is the ultimate limiting factor in the operation of a turbojet engine. The temperature in a turbine engine is the highest at the inlet of the turbine.

8152. Which of the following is the ultimate limiting factor of turbine engine operation? A— Compressor inlet air temperature. B— Turbine inlet temperature. C— Burner-can pressure.

dust and other fine airborne particulates can damage a turbine engine by eroding components in the compressor and turbine stages. Turbine engines operated in a dusty environment nor- mally have efficient dust and particle separators in their induction sections.

8153. The recurrent ingestion of dust or other fine air- borne particulates into a turbine engine can result in A— foreign object damage to the compressor section. B— the need for less frequent abrasive grit cleaning of the engine. C— erosion damage to the compressor and turbine sections.

Turbine-inlet temperature is the highest temperature inside a turbine engine. Therefore, it is the most critical variable of engine operation. It is impractical to measure turbine-inlet temperature in most engines. So, the temperature-measuring thermo- couples are usually installed at the turbine discharge. The turbine-outlet temperature gives a relative indication of the temperature at the turbine inlet. Therefore, if the turbine-outlet temperatures are kept within range, it can be assumed that the turbine-inlet temperatures are also within range.

8154. Which of the following engine variables is the most critical during turbine engine operation? A— Compressor inlet air temperature. b— Compressor RPM. C— Turbine inlet temperature

the two-spool (split-spool) axial-flow compressor offers the greatest starting flexibility and improved high-altitude per- formance of any of the gas turbine engine configurations.

8156. Which turbine engine compressor offers the great- est advantages for both starting flexibility and improved high-altitude performance? A— Dual-stage, centrifugal-flow. B— Split-spool, axial-flow. C— Single-spool, axial-flow.

Turbine blades are individually weighed and coded for installation in the disks in such a way that they best distribute the weight evenly around the disk. If a blade is removed from a disk for inspection, it must be reinstalled in the same slot from which it was removed.

8157. Jet engine turbine blades removed for detailed inspection must be reinstalled in A— a specified slot 180° away. B— a specified slot 90° away in the direction of rotation. C— the same slot.

A centrifugal compressor is simple and rugged and it can be made at a relatively low cost. The pressure rise, which is produced by expansion of the gas in the diffuser manifold and by the conversion of kinetic energy of motion into static pressure, is high for each stage.

8158. An advantage of the centrifugal-flow compressor is its high A— pressure rise per stage. B— ram efficiency. C— peak efficiency.

The highest heat-to-metal contact inside a jet engine occurs at the entrance to the first stage of the turbine. This is at the turbine-inlet guide vanes.

8159. The highest heat-to-metal contact in a jet engine is the A— burner cans. B— turbine inlet guide vanes. C— turbine blades.

An axial-flow compressor is made up of rotors (the rotating part of the compressor) and stators (the stationary part of the compressor).

8160. Which two elements make up the axial-flow compressor assembly? A— Rotor and stator. B— Compressor and manifold. C— Stator and diffuser.

The two types of centrifugal compressors used in turbojet engines are single-entry and double-entry. A single-entry compressor has scrolls on only one side, while a double-entry compressor has scrolls on both sides. A double-entry compressor is much like two single-entry compressors back to back.

8161. The two types of centrifugal compressor impellers are A— single entry and double entry. B— rotor and stator. C— impeller and diffuser.

The stationary blades between each set of rotating blades in an axial-flow turbine-engine compressor are called stators. The function of the stators is to receive the air from each stage of the compressor and deliver it to the next stage at the proper velocity, direction, and pressure.

8162. Between each row of rotating blades in a turbine engine compressor, there is a row of stationary blades which act to diffuse the air. These stationary blades are called A— buckets. B— rotors. C— stators.

standard sea-level atmospheric pressure is 29.92 inches of mercury ("Hg), 760 millimeters of mercury (mm Hg), 1013.2 millibars (mb), or 14.69 pounds per square inch (psi).

8163. Standard sea level pressure is A— 29.00" Hg. B— 29.29" Hg. C— 29.92" Hg.

the standard sea-level temperature for computing the power of a gas turbine engine is 15° Celsius, or 59° Fahrenheit.

8164. Using standard atmospheric conditions, the standard sea level temperature is A— 59°F. B— 59°C. C— 29°C.

A turbine that has been subjected to excessive temperatures is likely to have blades that show indications of stress-rupture failure. Stress-rupture cracks appear as minute hairline cracks on or across the leading edge of the blade at right angles to the edge.

8165. When aircraft turbine blades are subjected to excessive heat stress, what type of failures would you expect? A— Bending and torsion. B— Torsion and tension. C— Stress rupture.

The stator vanes located at the discharge end of an axialf low compressor are used to straighten the airflow and eliminate turbulence of the air as it enters the combustors.

8166. In an axial-flow compressor, one purpose of the stator vanes at the discharge end of the compressor is to A— straighten the airflow and eliminate turbulence. B— increase the velocity and prevent swirling and eddying. C— decrease the velocity, prevent swirling, and decrease pressure.

Foreign deposits on the compressor rotor and stator vanes reduce aerodynamic efficiency of the blades, degrade the engine performance, and increase fuel costs. Compressor f ield cleaning removes salt or dirt deposits from the blades and vanes, restores efficiency, and prevents corrosion of the surfaces along the gas path.

8167. Compressor field cleaning on turbine engines is performed primarily in order to A— prevent engine oil contamination and subsequent engine bearing wear or damage. B— facilitate flight line inspection of engine inlet and compressor areas for defects or FOD. C— prevent engine performance degradation, increased fuel costs, and damage or corrosion to gas path surfaces.

A hot-section inspection of a gas turbine engine consists of a visual and dimensional inspection of components in the hot section, which includes the combustion section, turbine inlet guide vanes, turbine wheels, and all of the other components that operate in the high-temperature gas path. Hot-section inspections are regularly conducted on a time or cycle basis, and when there has been a deterioration of certain of the engine parameters, such as EGT, EPR, or fuel flow.

8168. Hot section inspections for many modern turbine engines are required A— only at engine overhaul. B—only when an overtemperature or overspeed has occurred. C—on a time or cycle basis.

Some turbine blades have shrouds on their outer ends that contact the shroud on the adjacent blade. These shrouds form a band around the outer perimeter of the wheel that improves the efficiency of the wheel and reduces the vibration of the blades.

8169. A purpose of the shrouds on the turbine blades of an axial-flow engine is to A— reduce vibration. B— increase tip speed. C— reduce air entrance.

The first-stage turbine in a twin-spool turbojet engine drives the high-pressure compressor, the N 2 compressor.

8170. In a dual axial-flow compressor, the first stage turbine drives A— N 2 compressor. B— N 1 compressor. C— low pressure compressor.

If a turbine engine catches fire in the process of starting, turn the fuel off and continue rotating the engine with the starter to force enough air through the engine to blow the f ire out.

8171. What should be done initially if a turbine engine catches fire when starting? A— Turn off the fuel and continue engine rotation with the starter. B— Continue engine start rotation and discharge a fire extinguisher into the intake. C— Continue starting attempt in order to blow out the fire.

The proper sequence for starting a turbojet engine is to engage the starter to start the compressor turning, then turn on the ignition and finally, turn on the fuel.

8172. What is the proper starting sequence for a turbojet engine? A— Ignition, starter, fuel. B— Starter, ignition, fuel. C— Starter, fuel, ignition.

If the fuel furnished to a turbine engine is decreased to the point that there is a weak fuel to air mixture with a normal flow of air through the engine, there is a danger of a lean die-out.

8173. A weak fuel to air mixture along with normal airflow through a turbine engine may result in A— a rich flameout. B— a lean die-out. C— high EGT.

Some axial-flow gas turbine engines use variable inlet guide vanes and bleed-air valves to stabilize the airflow through the compressor during low-thrust operations. If the compressor RPM is high, relative to the amount of air flowing through the engine, the angle of attack of the compressor blades will become excessive and a compressor surge or stall can develop. To prevent a compressor stall, the inlet guide vanes are turned to the correct angle, and the bleed-air valves are automatically opened by actuators controlled by the fuel control. The bleed-air valves reduce the back pressure and allow more air to flow through the compressor to reduce the angle of attack of the compressor blades.

8174. What is used in turbine engines to aid in stabilization of compressor airflow during low thrust engine operation? A— Stator vanes and rotor vanes. B— Variable guide vanes and/or compressor bleed valves. C— Pressurization and dump valves.

The high-pressure rotor of a two-spool (split-spool) compressor is governed for speed, but the low-pressure rotor is free to operate at its own best speed. As the air density decreases at altitude, the compressor load decreases and the low-pressure rotor increases its speed.

8175. In a turbine engine with a dual-spool compressor, the low speed compressor A— always turns at the same speed as the high speed compressor. B— is connected directly to the high speed compressor. C— seeks its own best operating speed.

inlet guide vanes used with an axial-flow compressor change the angle of airflow to direct it into the first stage rotor blades at the proper angle. The inlet guide vanes do not change either the velocity or the pressure of the inlet air.

8176. What is the function of the inlet guide vane assembly on an axial-flow compressor? A— Directs the air into the first stage rotor blades at the proper angle. B— Converts velocity energy into pressure energy. C— Converts pressure energy into velocity energy.

Hot spots, which are localized areas of overheating in the tail cone of a gas turbine engine, are usually caused by a malfunctioning fuel nozzle or a faulty combustion chamber that prevent a uniform flow of cooling air.

8177. Hot spots on the tail cone of a turbine engine are possible indicators of a malfunctioning fuel nozzle or A— a faulty combustion chamber. B— a faulty igniter plug. C— an improperly positioned tail cone.

Stator vanes in an axial-flow compressor convert velocity energy that has been put into the air by the rotors into pressure energy. The stator vanes also direct the air into the following stage of rotor blades in the correct direction.

8178. The stator vanes in an axial-flow compressor A— convert velocity energy into pressure energy. B— convert pressure energy into velocity energy. C— direct air into the first stage rotor vanes at the proper angle.

When supersonic air flows through a divergent nozzle (a nozzle whose cross-sectional area increases in the direction of air flow), its velocity increases and its pressure decreases.

8180. The velocity of supersonic air as it flows through a divergent nozzle A— increases. B— decreases. C— is inversely proportional to the temperature.

When subsonic air flows through a convergent nozzle, its velocity increases and its pressure decreases. This action is in accordance with Bernoulli's principle, which gives us the relationship between kinetic energy and potential energy in a column of moving fluid. The kinetic energy relates to the velocity of the fluid and the potential energy relates to the pressure of the fluid.

8181. The pressure of subsonic air as it flows through a convergent nozzle A— increases. B— decreases. C— remains constant.

When supersonic air flows through a divergent nozzle (a nozzle whose cross-sectional area increases in the direction of air flow), its velocity increases and its pressure decreases.

8182. The pressure of supersonic air as it flows through a divergent nozzle A— increases. B— decreases C— is inversely proportional to the temperature.

anti-icing (preventing the formation of ice) is accomplished on the air inlets of a turbojet engine by ducting hot engine bleed-air through the areas on which the ice is likely to form.

8183. Anti-icing of jet engine air inlets is commonly accomplished by A— electrical heating elements inside the inlet guide vanes. B— engine bleed air ducted through the critical areas. C— electrical heating elements located within the engine air inlet cowling.

When starting a turbojet engine, the starter is left engaged until the engine reaches its self-accelerating speed. If the starter is disengaged too soon, the engine may fail to accelerate to its idle RPM, and a "hung start" results.

8184. Generally, when starting a turbine engine, the starter should be disengaged A— after the engine has reached self-accelerating speed. B— only after the engine has reached full idle RPM. C— when the ignition and fuel system are activated.

the primary advantage of an axial-flow compressor over a centrifugal compressor is that axial-flow compressors are capable of producing higher pressure ratios and they have relatively high efficiencies.

8185. What is the primary advantage of an axial-flow compressor over a centrifugal compressor? A— High frontal area. B— Less expensive. C— Greater pressure ratio.

some aircraft gas turbine engines have automatic bleed valves that prevent compressor stall or surge by venting overboard some of the air from the compressor. This prevents the air from "piling up" in the higher-pressure stages of the compressor and restricting the flow of air through the engine.

8186. The purpose of a bleed valve, located in the beginning stages of the compressor, in an aircraft gas turbine engine is to A— vent some of the air overboard to prevent a compressor stall. B— control excessively high RPM to prevent a compressor stall. C— vent high ram air pressure overboard to prevent a compressor stall.

A double-entry centrifugal compressor is a compressor that has vanes on both sides of the impeller. The intake air is ducted into the impeller at both its front and back sides. The accelerated air is taken from its rim.

8187. What is meant by a double entry centrifugal compressor? A— A compressor that has two intakes. B— A two-stage compressor independently connected to the main shaft. C— A compressor with vanes on both sides of the impeller.

The major function of the turbine assembly in a turbojet engine is that of supplying power to turn the compressor.

8188. What is the major function of the turbine assembly in a turbojet engine? A— Directs the gases in the proper direction to the tailpipe. B— Supplies the power to turn the compressor. C— Increases the temperature of the exhaust gases.

Stator vanes in an axial-flow compressor convert velocity energy that has been put into the air by the rotors into pressure energy. They slow the air, which increases its pressure. The stator vanes also direct the air into the following stage of rotor blades in the correct direction.

8189. Stator blades in the compressor section of an axialf low turbine engine A— increase the air velocity and prevent swirling. B— straighten the airflow and accelerate it. C— decrease the air velocity and prevent swirling.

The three main sections of a turbine engine are: the compressor, which increases the pressure of the air entering the engine; the combustors, in which energy from burning fuel is added to the compressed air; and the turbine, which drives the compressor.

8190. A gas turbine engine comprises which three main sections? A— Compressor, diffuser, and stator. B— Turbine, combustion, and stator. C— Turbine, compressor, and combustion.

The most common type of turbine blades used in modern aircraft jet engines is the impulse-reaction type. An impulse-reaction turbine blade has an impulse section at its root and a reaction section at its tip. The exit pressure of a impulse-reaction turbine blade is relatively constant across its length.

8191. What type of turbine blade is most commonly used in aircraft jet engines? A— Reaction. B— Impulse. C— Impulse-reaction.

The pressure ratio of an axial-flow compressor is a function of the number of stages of compression (the number of stages of compressor rotors and stators).

8192. What is the primary factor which controls the pressure ratio of an axial-flow compressor? A— Number of stages in compressor. B— Compressor inlet pressure. C— Compressor inlet temperature.

The nonrotating airfoils in an aircraft gas turbine engine axial-flow compressor are called stator vanes.

8193. The non-rotating axial-flow compressor airfoils in an aircraft gas turbine engine, are called A— pressurization vanes. B— stator vanes. C— bleed vanes.

Both statements are true. Each consecutive pair of rotor blades and stator vanes in an axial-flow compressor constitutes a pressure stage. The number of pressure stages in the compressor is determined by the amount of air and the total pressure rise required by the engine.

8194. (1) In a turbine engine axial-flow compressor, each consecutive pair of rotor and stator blades constitutes a pressure stage. (2) In a turbine engine axial-flow compressor, the number of rows of stages is determined by the amount of air and total pressure rise required. Regarding the above statements, A— only No. 1 is true. B— only No. 2 is true. C— both No. 1 and No. 2 are true.

Part of the air flowing through the combustion chamber of a jet engine mixes with the fuel for combustion. The majority of the air, however, passes between the outer casing and the liner and is used to cool the combustion gases.

8195. The air passing through the combustion chamber of a turbine engine is A— used to support combustion and to cool the engine. B— entirely combined with fuel and burned. C— speeded up and heated by the action of the turbines.

The turbine in a gas turbine engine extracts energy from the burning gases as they pass through it. The stators in front of the rotating turbine wheels increase the velocity of the gases and direct them so they will strike the rotors at the correct angle.

8196. The stators in the turbine section of a gas turbine engine A— increase the velocity of the gas flow. B— decrease the velocity of the gas flow. C— increase the pressure of the gas flow.

the stator vanes in an axial-flow compressor are placed to the rear of the rotor blades to receive the high-velocity air and act as diffusers. They change some of the kinetic energy of velocity into potential energy of pressure.

8197. The compressor stators in a gas turbine engine act as diffusers to A— decrease the velocity of the gas flow. B— increase the velocity of the gas flow. C— increase the velocity and decrease the pressure of the gas.

Field cleaning of a turbine engine is the removal of contaminants from the blades of the compressor by running wash water or an abrasive through the engine.

8198. The procedure for removing the accumulation of dirt deposits on compressor blades is called A— the soak method. B— field cleaning. C— the purging process.

The inspection of the interior of a turbine engine installed on an aircraft can be performed by the use of a borescope.

8199. Which of the following may be used to accomplish internal inspection of an assembled turbine engine? 1. Infrared photography. 2. Ultrasound. 3. A borescope. 4. Fluorescent penetrant and ultraviolet light. A— 1, 2, 3. B— 1, 3. C— 3.

Too high a lubricating-oil temperature, with no change in the power setting parameters, could indicate that the main bearing is overheating and this heat is being absorbed in the oil.

8200. What is the possible cause when a turbine engine indicates no change in power setting parameters, but oil temperature is high? A— High scavenge pump oil flow. B— Engine main bearing distress. C— Turbine damage and/or loss of turbine efficiency.

Newton's second law deals with the idea of momentum. When a force acts on an object the momentum of that object is changed. The relationship between force applied (F), the mass of the object (m), and the acceleration that the object experiences (a) is: F = ma.

8201-1. Newton's Law of Motion, generally termed the "Law of Momentum," states: A— Acceleration is produced when a force acts on a mass. The greater the mass, the greater the amount of force needed. B— For every action there is an equal and opposite reaction. C— Every body persists in its state of rest, or of motion in a straight line, unless acted upon by some outside force.

Newton's First Law of Motion tells us that every body at rest will try to remain at rest and every body in motion will try to remain in motion in a straight line, at the same speed, unless it is acted upon by an outside force.

8201. Newton's First Law of Motion, generally termed the Law of Inertia, states: A— To every action there is an equal and opposite reaction. B— Force is proportional to the product of mass and acceleration. C— Every body persists in its state of rest, or of motion in a straight line, unless acted upon by some outside force.

Cracking is one of the most widely found forms of damage in the hot section of a gas turbine engine. Vibration and the extremes of temperature cause the thin metal of which hot-section components are made, to crack.

8202. A turbine engine hot section is particularly susceptible to which kind of damage? A— Scoring. B— Cracking. C— Galling.

Dirt particles introduced into the turbine engine will cause a coating to form on the casings, inlet guide vanes and compressor blades. The extreme heat in the turbine section prevents the coating from forming on the turbine blades.

8203. Dirt particles in the air being introduced into the compressor of a turbine engine will form a coating on all but which of the following? A— Turbine blades. B— Casings. C— Inlet guide vanes.

Severe rubbing of the turbine-engine compressor blades will usually result in galling, which is a transfer of metal from one surface to another.

8204. Severe rubbing of turbine engine compressor blades will usually cause A— bowing. B— cracking. C— galling.

Most automatic fuel control units for turbojet engines sense inlet air temperature, compressor RPM, burner pressure (compressor discharge pressure) and the position of the power lever (throttle).

8205. Which of the following influences the operation of an automatic fuel control unit on a turbojet engine? A— Burner pressure. B— Mixture control position. C— Exhaust gas temperature.

When a turbine engine compressor is contaminated or damaged, the airflow is disturbed, and the EGT limit may be reached before takeoff EPR is attained. This condition may be corrected by field cleaning the compressor or retrimming the fuel control.

8206. If a turbine engine is unable to reach takeoff EPR before its EGT limit is reached, this is an indication that the A— fuel control must be replaced. B— EGT controller is out of adjustment. C— compressor may be contaminated or damaged.

the Brayton cycle of energy release used in a gas turbine engine is known as the constant-pressure cycle. Energy added to the air flowing through the engine by the burning fuel causes the volume of the air to increase, but the pressure remains relatively constant.

8207. The Brayton cycle is known as the constant A— pressure cycle. B— temperature cycle. C— mass cycle.

Creep, which is a permanent elongation of the turbine blades caused by heat loads and centrifugal loads, is likely to occur when the engine has been exposed to continued and/or excessive heat.

8208. Continued and/or excessive heat and centrifugal force on turbine engine rotor blades is likely to cause A— profile. B— creep. C— galling.

Two factors affecting the angle of attack of an axial-flow compressor blade are the velocity of the air through the engine and the RPM of the compressor. If the airflow entering the engine is restricted, reducing its velocity, the angle of attack of the compressor blade will increase to such a point that compressor stall can occur.

8209. If the RPM of an axial-flow compressor remains constant, the angle of attack of the rotor blades can be changed by A— changing the velocity of the airflow. B— changing the compressor diameter. C— increasing the pressure ratio.

The compression ratio of an axial-flow compressor is determined by the number of stages of compression.

8210. The compression ratio of an axial-flow compressor is a function of the A— number of compressor stages. B— rotor diameter. C— air inlet velocity.

Three factors that affect the density of the air taken into the inlet air system of a turbojet engine are the speed of the aircraft, the altitude at which the aircraft is flying and the ambient (surrounding) air temperature.

8211. Which of the following variables affect the inlet air density of a turbine engine? 1. Speed of the aircraft. 2. Compression ratio. 3. Turbine inlet temperature. 4. Altitude of the aircraft. 5. Ambient temperature. 6. Turbine and compressor efficiency. A— 1, 3, 6. B— 1, 4, 5. C— 4, 5, 6.

Three factors that affect the thermal efficiency of a turbine engine are the turbine-inlet temperature, the compression ratio of the compressor and the turbine and compressor efficiency.

8212. Which of the following factors affect the thermal efficiency of a turbine engine? 1. Turbine inlet temperature. 2. Compression ratio. 3. Ambient temperature. 4. Speed of the aircraft. 5. Turbine and compressor efficiency. 6. Altitude of the aircraft. A— 3, 4, 6. B— 1, 2, 5. C— 1, 2, 6.

Some turbine engines have more than one turbine wheel on a single shaft in order to extract more power from the exhaust gases than a single turbine wheel can absorb.

8213. Why do some turbine engines have more than one turbine wheel attached to a single shaft? A— To facilitate balancing of the turbine assembly. B— To help stabilize the pressure between the compressor and the turbine. C— To extract more power from the exhaust gases than a single wheel can absorb.

The exhaust section of a turbojet engine is designed in such a way that it gives a high velocity to the exhaust gases leaving the engine.

8214. The exhaust section of a turbine engine is design ed to A— impart a high exit velocity to the exhaust gases. B— increase temperature, therefore increasing velocity. C— decrease temperature, therefore decreasing pressure.

three basic types of combustion sections used in gas turbine engines are the multiple-can type, the annular type, and the can-annular type.

8215. Which of the following types of combustion sections are used in aircraft turbine engines? A— Annular, variable, and cascade vane. B— Can, multiple-can, and variable. C— Multiple-can, annular, and can-annular.

A rule of thumb for turbine engine operation: when an engine has been operated above approximately 85% RPM for periods longer than one minute; during the last five minutes before shutdown, the engine should be operated below 85% RPM (preferably at idle) for a period of five minutes. This prevents the possibility of the engine case contracting around the turbine wheels before they have cooled and contracted to their normal size. It is also important that all surfaces contacted with engine oil be cooled to their normal operating temperature, to prevent oil left on a hot surface from coking (turning into a hard carbon deposit).

8216. A cool-off period prior to shutdown of a turbine engine is accomplished in order to A— allow the turbine wheel to cool before the case contracts around it. B— prevent vapor lock in the fuel control and/or fuel lines. C— prevent seizure of the engine bearings.

Self-ionizing shunted-gap igniters are used in the lowtension ignition system of some aircraft turbofan engines. These igniters have a ceramic semiconductor material between the center electrode and the shell. The resistance of this semiconductor is low when it is relatively cool, but it increases as it heats up. When the storage capacitor discharges through the igniter, the current initially flows Self-ionizing shunted-gap igniters are used in the lowtension ignition system of some aircraft turbofan engines. These igniters have a ceramic semiconductor material between the center electrode and the shell. The resistance of this semiconductor is low when it is relatively cool, but it increases as it heats up. When the storage capacitor discharges through the igniter, the current initially flows

8217. What type igniter plug is used in the low tension ignition system of an aircraft turbofan engine? A—Low voltage, high amperage glow plug. B—Self-ionizing or shunted-gap type plug. C—Recessed surface gap plug.

A shrouded turbine is one in which each of the blades is made in the shape of the letter T. Each bar on the end of the blades touches the other to form a band, or shroud, around the turbine wheel. The shrouds increase the efficiency of the turbine and improve the vibration characteristics of the turbine blades.

8218. What is meant by a shrouded turbine? A— The turbine blades are shaped so that their ends form a band or shroud. B— The turbine wheel is enclosed by a protective shroud to contain the blades in case of failure. C— The turbine wheel has a shroud or duct which provides cooling air to the turbine blades.

Creep is the stretching (elongation) of a turbine blade caused by prolonged exposure to high temperatures and centrifugal force.

8219. What term is used to describe a permanent and cumulative deformation of the turbine blades of a turbojet engine? A— Stretch. B— Distortion. C— Creep.

The dump valve, which is a portion of the pressurizing and dump valve assembly, dumps the fuel from the fuel manifold when the engine is shut down. Dumping this fuel sharply cuts off combustion and prevents the fuel boiling as a result of residual engine heat.

8220. What is the purpose of the dump valve used on aircraft gas turbine engines? A— The fuel is quickly cut off to the nozzles and the manifolds are drained preventing fuel boiling off as a result of residual engine heat. B— The valve controls compressor stall by dumping compressor bleed air from the compressor discharge port under certain conditions. C— Maintains minimum fuel pressure to the engine fuel control unit inlet and dumps excessive fuel back to the inlet of the engine-driven fuel pump.

The gas pressure inside a turbine engine is the greatest at the compressor outlet.

8221. At what stage in a turbine engine are gas pressures the greatest? A— Compressor inlet. B— Turbine outlet. C— Compressor outlet.

the rear opening of a turbine-engine exhaust duct is called the exhaust nozzle (jet nozzle). The nozzle acts as an orifice, the size of which determines the density and velocity of the gases as they leave the engine.

8222. In what section of a turbojet engine is the jet nozzle located? A— Combustion. B— Turbine. C— Exhaust.

Both statements are true. Accumulation of contaminants in the compressor reduces aerodynamic efficiency of the blades and reduces engine performance. Two common methods for removing dirt deposits are a fluid wash and an abrasive grit blast.

8223. (1) Accumulation of contaminates in the compressor of a turbojet engine reduces aerodynamic efficiency of the blades. (2) Two common methods for removing dirt deposits from turbojet engine compressor blades are a fluid wash and an abrasive grit blast. Regarding the above statements, A— only No. 1 is true. B— only No. 2 is true. C— both No. 1 and No. 2 are true.

Hot spots are possible indicators of a serious condition, such as malfunctioning fuel nozzles or other fuel-system malfunctions.

8224. Hot spots in the combustion section of a turbojet engine are possible indicators of A— faulty igniter plugs. B— dirty compressor blades. C— malfunctioning fuel nozzles.

Fan blade shingling is a condition of the fan in a turbofan engine when the midspan shrouds on the fan blades overlap in much the same way shingles on a roof overlap. Fan blade shingling is caused by the rotating fan encountering opposition such as engine stall, bird strike, foreign object damage (FOD), or by engine overspeed.

8225. Which of the following can cause fan blade shingling in a turbofan engine? 1. Engine overspeed. 2. Engine overtemperature. 3. Large, rapid throttle movements. 4. FOD. A— 1, 2. B— 1, 2, 3, 4. C— 1, 4.

A compressor stalls when the angle of attack of the blades becomes excessive. Two factors affecting the angle of attack of an axial-flow compressor blade are the velocity of the air through the engine and the RPM of the compressor. If the airflow entering the engine is restricted, reducing its velocity, the angle of attack of the compressor blade will increase to such a point that compressor stall can occur.

8226. Compressor stall is caused by A— a low angle of attack airflow through the first stages of compression. B— a high angle of attack airflow through the first stages of compression. C— rapid engine deceleration.

Hot streaking is a hot-section condition in which the flame penetrates through the entire turbine system to the tail pipe. Hot streaking is caused by a partially clogged fuel nozzle which does not atomize the fuel into a cone-shaped pattern but rather, allows a small fuel stream to flow with sufficient force to cut through the cooling air blanket and impinge directly on the turbine surfaces.

8227. A condition known as "hot streaking" in turbine engines is caused by A— a partially clogged fuel nozzle. B— a misaligned combustion liner. C— excessive fuel flow.