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ASA POWERPLANT ORALS
| Question | Answer |
|---|---|
| What is the main advantage of a horizontally opposed engine over a radial engine for powering modern aircraft? | The horizontally opposed engine has a much smaller frontal area and is easier to streamline than a radial engine. |
| How many throws are there in the crankshaft of a six-cylinder horizontally opposed engine? | Six |
| What kind of connecting rod arrangement is used in a radial engine? | A master rod connects the single throw of the crankshaft with a piston. All of the other pistons are connected to the master rod with link rods. |
| Of what material are most piston rings made? | Gray cast iron. |
| What is the reason for using hydraulic valve lifters in an aircraft engine? | Hydraulic valve lifters keep all of the clearance out of the valve operating mechanism. This decreases the wear of the valve train components. |
| At what speed does the camshaft turn, relative to the crankshaft speed in a horizontally opposed engine? | The camshaft turns at one half of the crankshaft speed. |
| What kind of main bearings are used in a horizontally opposed engine? | Steel-backed, lead-alloy bearing inserts. |
| On what stroke is the piston of a reciprocating engine when the intake valve begins to open? | On the exhaust stroke. |
| On what stroke is the piston of a reciprocating engine when the exhaust valve begins to open? | On the power stroke. |
| Why are both the hot and cold valve clearances given for most radial engines? | The hot clearance is given for valve timing purposes. The timing is adjusted with the valves in cylinder number one, set with the hot clearance. When the timing is set, all of the valves are adjusted to their cold clearance. |
| What is meant by a cam-ground piston? | A piston that isn’t perfectly round. Its dimension parallel to the wrist pin is slightly less than its dimension perpendicular to the wrist pin. When the piston reaches op temp, the piston pin boss expands enough that the piston becomes perfectly round. |
| Where is the piston in a reciprocating engine when the ignition spark occurs? | About 30 degrees of crankshaft rotation before the piston reaches top center on the compression stroke. |
| What is meant by a full-floating wrist pin? | A wrist pin that is not clamped in either the piston or the connecting rod. Full-floating wrist pins are kept from scoring the cylinder walls by soft metal plugs in their ends. |
| Why do most aircraft reciprocating engines use more than one spring on each valve? | By using more than one spring and having the wire diameter and pitch of the springs different, valve float is minimized. The springs have different resonant frequencies, so at least one spring will always be exerting a force on the valve. |
| Would excessive valve clearance cause the valves to open early or late? | Excessive clearance will cause the valve to open late and close early. |
| What is the purpose of valve overlap in a reciprocating engine? | Valve overlap allows the inertia of the exhaust gases leaving the cylinder to help the fresh induction charge start flowing into the cylinder. |
| What type of piston rings are installed on the pistons of an aircraft reciprocating engine? | •Compression Rings (air seal) •Oil Control Rings (oil thickness) •Oil Wiper/Scraper Rings (oil retention) |
| Why are some exhaust valves partially filled with metallic sodium? | The metallic sodium melts at engine operating temperature & sloshes back & forth inside the hollow valve. It picks up heat from the valve head & transfers it into the valve stem, so it can be transferred to the cylinder head through the valve guide. |
| What causes detonation in an aircraft engine? | Excessive heat and pressure in the engine cylinder causes the air-fuel mixture to reach its critical pressure and temperature. Under these conditions, the mixture explodes rather than burns. This explosion is called detonation. |
| Why is a compression check important for determining the condition of an aircraft reciprocating engine? | A compression check can determine the condition of the seal between the piston rings and the cylinder walls, and the seal between the intake and exhaust valves and their seats. |
| What is meant by the compression ratio of a reciprocating engine? | The ratio of the volume of the cylinder with the piston at the bottom of its stroke to the volume with the piston at the top of its stroke. |
| What are the two basic sections of a turbine engine? | The hot section & the cold section. |
| What are the two basic types of compressors that are used in aircraft turbine engines? | Axial-Flow Centrifugal |
| 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. |
| What are three types of combustors used on aircraft turbine engines? | •Can-Type •Annular Type •Can-Annular-Type |
| How many igniters are there normally in an aircraft turbine engine? | Two |
| 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. |
| 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 section of the engine. This free turbine drives the propeller in a turboprop engine or the transmission & rotor of a helicopter. |
| 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. |
| 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. |
| 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 (by-pass flow). |
| 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. |
| 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 (as it cools) around the turbine wheel and seize the rotor. |
| 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. |
| 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. |
| 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. |
| How is the compressor of a turbine engine cleaned? | An emulsion-type cleaner is sprayed thru the engine while it is being motored by the starter or operated at a low RPM, followed by a clean water rinse. Or by injecting a mild abrasive (ground apricot pits or walnut shells) into the engine at low RPM. |
| Where is water injected into a turbine engine for cooling purposes? | Into the compressor inlet and into the engine diffuser case. |
| At what point in a turbine engine is the temperature the highest? | At the inlet to the high-pressure turbine. |
| 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. |
| What are two types of thrust reversers that are used on turbojet engines? | •mechanical blockage-type •aerodynamic blockage-type. |
| What is meant by trimming a turbojet engine? | Adjusting the fuel control to get the correct idling and maximum-thrust RPM. |
| Where are most APUs located in modern jet transport aircraft? | In the tail cone of the fuselage. |
| What is the function of an APU (Auxiliary Power Unit)? | An APU provides electric power and compressed air when the main engines are not operating. |
| What are two sources of compressed air from an APU? | From bleed air from the APU turbine compressor, or from a load compressor driven by a free turbine in the engine. |
| Where in maintenance information based on the ATA-100 system would you find instructions for inspecting and servicing the engine of an airborne APU? | In Section 49 20 |
| How is most of the troubleshooting done for a modern APU? | By the fault codes generated by the FADEC (Full Authority Digital Engine Controller). |
| What determines whether or not a 100-hour inspection is required for an aircraft? | 100-hour inspections are required only on aircraft that carry persons for hire or are used to give flight instruction for hire. |
| Where can you find a list of items that should be inspected on a 100-hour and an annual inspection of an aircraft engine? | In Appendix D of 14 CFR Part 43 |
| In what publication can a mechanic find the operating limitations for an aircraft engine? | In the Type Certificate Data Sheets (TCDS) for the engine. |
| Who is authorized to perform the powerplant inspection that is required for an annual inspection? | An A&P mechanic who holds an Inspection Authorization (IA). |
| What are two types of compression checks that can be performed on an aircraft reciprocating engine? | A differential compression check and a direct compression check. |
| What items are checked in a hot section inspection of a turbine engine? | The combustion section is checked for cracks or distortion. The turbine wheel, the turbine case, and the exhaust section are checked for cracks, indications of overheating, and any indication of warpage, ero-sion, or burning. |
| What is the most common type of damage that is found in the hot section of a turbine engine? | Cracks that are caused by the high concentration of heat in the hot section. |
| Is the use of a checklist required when performing an annual or 100-hour inspection on an aircraft engine? | Yes |
| What inspection must be performed on an aircraft reciprocating engine if it has been operated on turbine fuel? | The inside of the cylinders must be inspected with a borescope. The oil must be changed and the filters examined, and the engine given a careful run-up and operational check. |
| In what units is the tachometer for a reciprocating engine calibrated? | In hundreds of RPM. |
| In what units is the tachometer for a turbine engine calibrated? | In percent of the engine's rated takeoff RPM. |
| Where does the manifold pressure gage used on an aircraft reciprocating engine pick up the pressure it measures? | From the intake manifold of the engine. |
| What are two types of pickups used for measuring the cylinder head temperature of a reciprocating engine? | The thermocouple can be embedded in a gasket that is installed under the spark plug of the hottest running cylinder, or it can be in a bayonet that is held against the cylinder head by a spring. |
| Why do most engine oil pressure gages have a restrictor in the line between the engine and the instrument? | The restrictor damps out pressure pulsations in the oil to keep the needle from oscillating. |
| What is used to measure the fuel flow of a horizontally opposed, fuel-injected reciprocating engine? | A pressure gage that measures the pressure drop across injector nozzles. |
| What is indicated if the needle of a ratiometer-type oil temperature indicator pegs to the high side of the dial as soon as the aircraft master switch is turned on? | There is an open in the bulb circuit that causes the instrument to see an infinite resistance. The higher the resistance in the bulb circuit, the higher the temperature indication. |
| What type of indicating system is used to measure the exhaust gas temperature of a turbine engine? | A set of thermocouples arranged in an averaging circuit. These thermocouples are installed in the tail pipe of the engine. |
| What should a thermocouple-type cylinder head temperature indicator read when the engine is not operating? | The temperature of the outside air. |
| How does a torquemeter actually measure the torque produced by an engine? | A torquemeter is actually an oil pressure gage. The pressure it measures is produced in a torque sensor and is proportional to the amount of strain in the torsional shaft that drives the reduction gears of the turboprop engine. |
| What two pressures are measured to get the engine pressure ratio of a turbojet engine? | The turbine discharge total pressure and the compressor inlet total pressure. |
| Of what two materials are the thermocouples made that are used in a turbine engine exhaust gas temperature system? | Chromel & Alumel. |
| What kind of mechanism is normally used to measure oil pressure in a reciprocating engine? | A bourdon tube mechanism. |
| What is measured by the tachometers used on a two-spool gas turbine engine? | The N1 tachometer shows the RPM of the low pressure compressor, and the N2 tachometer shows the RPM of the high-pressure compressor. |
| Does the tachometer of a geared reciprocating engine indicate the speed of the crank shaft or of the propeller shaft? | The speed (RPM) of the crankshaft. |
| Can a thermal switch-type fire detection system indicate a general overheat condition? | No, this is a spot-type fire detection system, and it cannot indicate an overheat condition. |
| Can a thermocouple-type fire detection system indicate a general overheat condition? | No, this is a rate-of-temperature-rise-type of system, and it cannot indicate a general overheat condition. |
| How is a thermocouple-type fire detection system checked for operation? | Current thru the heater in the thermal test unit heats the thermocouple, which produces enough current to close the sensitive relay. Current through the contacts of the sensitive relay closes the slave relay & turns on the fire warning light. |
| Does a break in a continuous-loop fire detection system keep the system from detecting a fire? | No, the unit will show a fault when it is tested, but it will still warn of a fire. |
| Does the pressure-type continuous-element fire detector system detect a general overheat condition, as well as a fire? | Yes, a high temperature on a small portion of the sensor or a lower temperature over the entire sensor will cause it to release enough gas to close the diaphragm switch and warn of a fire. |
| What are the two most commonly used fire extinguishing agents used for engine fires? | Halogenated hydrocarbon, such as Halon 1301, and carbon dioxide. |
| What extinguishing agent is used in the high-rate-discharge (HRD) fire extinguishing systems installed in most turbojet engine installations? | Halon 1301 |
| What happens when the pilot pulls the fire-pull T-handle in the flight deck of a jet transport airplane? | The bottle discharge switch is uncovered & armed, the generator field relay is tripped, fuel is shut off to the engine, hydraulic fluid is shut off to the pump, the engine bleed air is shut off, & the hydraulic pump low-pressure lights are deactivated. |
| How can a mechanic determine the state of charge of the HRD bottles of fire extinguishing agent? | A pressure gage on the bottle shows the pressure of the contents of the bottle. |
| What method is used to discharge an HRD bottle in a turbine engine installation? | An electrically ignited powder charge blows a knife through the seal on the bottle and discharges the contents. |
| Which type of fire detection system operates on the rate of temperature rise? | The thermocouple system. |
| What is indicated if the yellow blow-out plug of the fire extinguisher system on the side of an engine nacelle is blown out? | The built-in fire extinguishing system has been discharged by normal operation. |
| What is indicated if the red blow-out plug of the fire extinguisher system on the side of an engine nacelle is blown out? | The built-in fire extinguishing system has been discharged by a high temperature condition. |
| How is a pressure-type continuous-element fire detector system checked for operation? | Low-voltage alternating current is sent through the sheath of the detector element. This heats the element, and it releases enough gas to close the diaphragm switch. |
| Why is stranded wire used rather than solid wire in most powerplant electrical systems? | Solid wire is likely to break when it is subjected to vibration. |
| What two things must be considered in selection of wire size when making an electrical installation in an aircraft? | The current-carrying capability of the wire and the amount of voltage drop that is caused by current flowing through the wire. |
| Why are the wires in certain electrical installations twisted together? | By twisting the wires together, the magnetic fields caused by current flowing in the wires are minimized. |
| What is used to protect a wire bundle from chafing where it passes through a hole in a bulkhead or frame? | A grommet around the edges of the hole. |
| How are electrical wires protected where they pass through an area of high temperature? | Wires passing through these areas are insulated with high temperature insulation, and the wires are enclosed in some type of protective conduit. |
| What is the minimum separation that is allowed between a wire bundle and a fluid line that carries combustible fluid or oxygen? | A minimum of six inches. |
| What is the significance of the color of the solderless connectors that are used on electrical wires? | The color of the insulation indicates the size of wire the connector will fit. Red terminals fit 22- through 18-gage wire, blue terminals fit 16- and 14-gage wire, and yellow terminals fit 12- and 10-gage wire. |
| What is the maximum number of wire terminals that may be stacked on a single stud in a terminal strip? | Four. |
| What is the purpose of the shielding that is used to encase some electrical wires? | Shielding intercepts radiated electromagnet energy and carries it to ground so it will not interfere with any nearby sensitive electronic equipment. |
| Why must a switch be derated if it is used in a circuit controlling a DC electric motor? | The initial current flowing into a DC electric motor is much higher than the current the motor uses after the armature begins to rotate. Because of this high inrush current, the controlling switches must be derated. |
| What is used as the rectifier to produce direct current in a DC generator? | Brushes and a commutator. |
| How does a vibrator-type voltage regulator control the output voltage of a DC generator? | The magnetic field in the regulator relay is proportional to the output volts. When the volts exceeds the regulated value, the relay vibrates putting a resistor in & out of the field circuit to control the volts produced. |
| What is meant by paralleling the generators of a twin-engine aircraft? | Adjusting the voltage of the generators so they will share the electrical load equally. |
| What is meant by flashing the field of a DC generator? | Restoring the residual magnetism to the frame of a generator by passing battery current through the field coils in the same direction it flows when the generator is producing current. |
| What kind of rectifier is used in a DC alternator of the type that is used on most of the modern light airplanes? | A full-wave, three-phase rectifier made up of six silicon diodes. |
| What is used to maintain a constant frequency of the alternating current that is produced by an AC alternator driven by an aircraft turbine engine? | A hydraulic constant-speed drive unit between the engine and the alternator. |
| What three things must be synchronized before a three-phase AC generator can be connected to a bus that is being served by another generator? | The voltage, frequency, and phase rotation of the generators. |
| What must be done to reverse the direction of rotation of the armature of a DC electric motor? | The current flow must be reversed through the armature or the field windings, but not through both of them. |
| Does a series-wound DC motor have a high or a low starting torque? | A high starting torque. |
| Which aircraft electrical circuit does not normally contain a fuse or circuit breaker? | The starter motor circuit. |
| When removing a battery from an aircraft, which connection should be removed first? | The ground connection must be disconnected first and connected last. |
| What is meant by the effective voltage of sine wave alternating current? | The value of the alternating current that is needed to produce the same amount of heat as this value of direct current. |
| What is a starter-generator that is used with many of the smaller gas turbine engines? | A single-engine-mounted component that serves as a starter for starting the turbine engine. When the engine is running, the circuitry can be shifted so it acts as a compound-wound generator. |
| When should aircraft wiring be installed in a conduit? | When the wiring passes through an area in the aircraft where open wiring could likely be damaged, such as through a wheel well. |
| What is meant by the viscosity of engine lubricating oil? | The resistance of the oil to flow. |
| What is meant by a wet sump lubrication system? | A lubrication system in which the oil is carried inside the engine itself. |
| What is meant by a dry sump lubrication system? | A lubrication system in which the oil is carried in a tank that is not a part of the engine. |
| How is oil temperature controlled in an aircraft reciprocating engine? | Hot oil is directed through the core of the oil cooler, but cold oil is directed around the outside of the core so it will not be further cooled. |
| Is the oil temperature shown on the aircraft instrument panel the temperature of the oil entering the engine or of the oil leaving the engine? | It is the temperature of the oil entering the engine. |
| What is the purpose of oil dilution in a reciprocating engine? | When very cold weather is anticipated, gasoline can be mixed with the lubricating oil before the engine is shut down. This reduces the viscosity of the oil and makes starting easier. When the engine is running, the gasoline evaporates out of the oil. |
| What is the function of the hopper in the oil tanks used with some reciprocating engines? | Hoppers are a part of the oil dilution system. Only the oil in the hopper is diluted. This speeds up dilution and requires less gasoline. |
| What happens to the gasoline that is used to dilute the oil in the crankcase of an aircraft reciprocating engine? | When the engine is running and the oil is warm, the gasoline evaporates out of it. |
| What is the purpose of the sludge plugs in the crankshaft of a reciprocating engine? | They trap sludge that is in the oil and hold it until the engine is disassembled at overhaul. |
| Which pump is the larger in a dry sump lubricating system, the pressure pump or the scavenger pump? | The scavenger pump has the greater volume. |
| Why do full-flow oil filters have a spring-operated bypass valve in them? | In case the filter should plug up so it cannot pass any oil, the bypass valve will open and allow unfiltered oil to flow through the system. |
| What is the function of a fue/oil heat exchanger in the lubrication system of a turbojet engine? | This allows heat from the oil to warm the fuel so ice will not form on the fuel filters. |
| What kind of oil is used in most turbojet engines? | Synthetic Oil |
| Where are the last chance oil filters located in a turbojet engine? | They are located inside the engine just ahead of the nozzles that spray oil onto the bearings. |
| Where is the oil tank in a dry sump reciprocating engine vented? | To the engine crankcase. |
| What information must be displayed around the oil filler opening for a turbojet engine? | The word "OIL" and the permissible oil designations, or references to the AFM for permissible oil designa-tions. |
| What is the function of the oil control rings on the piston of an aircraft reciprocating engine? | They maintain the proper quantity of oil between the piston and the cylinder wall. |
| What is meant by a spectrometric oil analysis? | Oil samples are taken regularly & sent to a lab. It is burned & analyzed for elements present in the sample. Traces of metals in the oil indicate wear of engine parts. There must be many samples at regularly to see changes in the results. |
| What indication would a pilot have if his oil supply was low? | The oil temperature would be high and the oil pressure would be low. |
| What is meant by a hot-tank lubrication system? | A lubrication system in which the oil cooler is located in the pressure subsystem. |
| What is meant by a cold-tank lubrication system? | A lubrication system in which the oil cooler is located in the scavenge subsystem. The oil that is returned to the tank has been cooled. |
| What is the main advantage of a magneto ignition system over a battery ignition system for an aircraft reciprocating engine? | A magneto has its own source of electrical energy, and it is not dependent upon the battery. |
| What is the function of the capacitor in a magneto? | The capacitor minimizes arcing at the breaker points, and it speeds up the collapse of the primary current as the breaker points open. |
| What is a compensated magneto cam, and on what kind of engine is one used? | It is a special cam used in magnetos in high-performance radial engines. The cam has 1 lobe for each cylinder, & the lobes are ground so that the breaker points open when the pistons in the different cylinders are the same linear distance from TDC. |
| What is the significance of the numbers on the distributor of an aircraft magneto? | These numbers are the sparking order of the mag-neto, not the firing order of the engine. |
| What happens in a magneto ignition system when the ignition switch is placed in the OFF position? | The primary circuit is connected to ground. |
| What is the reason for having a low-tension ignition system on some aircraft? | Low-tension magnetos are used on aircraft that fly at high altitudes where there is a problem with flashover in the high-tension magneto distributor. |
| What is the basic difference between a low-tension magneto and a high-tension magneto? | Low-tension has only 1 coil with a carbon-brush distributor. Lo-volt is sent to hi-tension transformers on each cylinder head. A hi-tension magneto produces hi-volt in the magneto coil. It is sent to the correct spark plug by the built-in distributor. |
| What is meant by an all weather spark plug? | A shielded spark plug that has a recess in the shielding in which a resilient grommet on the ignition lead forms a watertight seal. |
| What is meant by the reach of a spark plug? | The length of the threads on the spark plug that screw into the cylinder head. |
| What is the difference between a hot spark plug and a cold spark plug? | A hot spark plug has a long path for the heat to travel between the nose core insulator and the spark plug shell. In a cold spark plug, the heat has a shorter distance to travel, and the spark plug operates cooler than a hot spark plug. |
| What is checked when a magneto is internally timed? | Internally timing a magneto consists of adjusting the breaker points so they will open at the instant the rotating magnet is in its E-gap position, and the distributor rotor is in the position to direct the high voltage to cylinder number one. |
| What is the purpose of a vernier coupling used on some aircraft magneto drives? | Magnetos that are base mounted must have a vernier coupling between the magneto drive and the engine. This vernier coupling allows the magneto-to-engine timing to be varied in increments of less than one degree. |
| What is the advantage of fine-wire spark plugs over massive electrode spark plugs? | Fine-wire spark plugs have a firing end that is more open than that of a massive electrode spark plug. The open firing end allows the gases that contain lead to be purged from the spark plug so they will not form solid lead contaminates. |
| Why is it important that the spark plugs be kept in numbered holes in a tray when they are removed from an engine? | Spark plugs tell about the internal condition of the cylinders from which they were taken. By knowing the cylinder each plug came from, the mechanic can take the proper action when a spark plug indicates such conditions as detonation or overheating. |
| What is the purpose of staggered timing between the two magnetos on an aircraft engine? | Engines with uneven exhaust gas scavenging use staggered ignition timing. The plug near the exhaust valve, where the air-fuel mix is diluted, fires first. By staggered timing, the flame front from the 2 plugs will meet in the piston center. |
| In what position should the ignition switch be placed when using a timing light on the magnetos? | In the BOTH position. |
| Why is it important that a torque wrench always be used when installing spark plugs in an aircraft engine? | If the spark plugs are not put in tight enough, there is the possibility of a poor seal, and if they are put in too tight, there is danger of cracking the insulation. |
| Why are pressurized magnetos used on most reciprocating-engine-powered aircraft that fly at high altitudes? | Pressurized air is a better insulator than less dense air. By pressurizing the distributors, the high voltage is kept from arcing across to the wrong electrode and causing vibration and loss of engine power. |
| What type of ignition system is used on most turbine engines? | High-intensity, intermittent-duty, capacitor discharge ignition systems. |
| What is meant by the E-gap in magneto timing? | The E-gap angle is the position of the rotating magnet when the primary current flowing in the magneto coil is the greatest. The breaker points open when the rotating magnet is in its E-gap position. |
| What is the function of an impulse coupling? | It is a spring-driven coupling between the magneto & the engine. At engine start, it holds the rotating magnet until the piston passes over TDC & starts down. It then releases the magnet & the spring spins it fast so that it produces a hot, late spark. |
| What kind of gage should be used to measure the electrode gap in aircraft spark plugs? | A round wire gage. |
| How many igniters are used in most turbine engines? | Two. |
| What are two types of ignition systems used in turbine engines? | High-voltage systems and low-voltage systems. |
| With which type of ignition system is a glow plug igniter used? | A low-voltage system. |
| How is the strength of the magnet in a magneto checked? | The magneto is put on a test stand and rotated at a specified speed. The breaker points are held open and the primary current is measured. The strength of the magnet determines the amount of primary cur-rent. |
| In what position is the magnet in a magneto when the greatest change in flux density in the coil core takes place? | It is a few degrees beyond its neutral position. When it is in this position, the breaker points open and the primary current is interrupted. The flux change in the coil core is the greatest. |
| In what position is the magnet in a magneto when the breaker points begin to open? | In its E-gap position, just a few degrees beyond its neutral position. |
| What malfunction in the ignition system would cause an aircraft reciprocating engine to continue to run after the ignition switch is placed in the Off position? | The ignition switch is not grounding the magneto primary circuit. |
| What turns on the autoignition system in a turbo-prop engine? | A torque pressure switch energizes the system when the engine stops producing torque. |
| Where does the fuel metering system of a turbine engine discharge its fuel? | The fuel is discharged through spray nozzles into the combustion chambers. |
| What is adjusted when the fuel control unit of a turbine engine is trimmed? | The idle speed and the maximum-thrust speed. |
| What are two locations water may be injected into a turbine engine? | At the compressor inlet and at the inlet to the diffuser section. |
| What is meant by a duplex nozzle in a turbine engine fuel metering system? | A duplex nozzle is one that has 2 discharge passages. A divider sends fuel for low-pressure operation thru 1 discharge. When fuel demand increases, it is sprayed out through the second passage. The spray keeps the flame centered for all op conditions. |
| What is the function of a float carburetor? | Its function is to measure airflow thru the induction system & dispense the appropriate amount of gasoline into the airflow for all engine operating perimeters & conditions. It must also provide vaporized fuel by the time ignition occurs in the cylinders. |
| Does the air-fuel mixture provided by a float carburetor become richer or leaner as the aircraft goes up in altitude? | If the mixture is not adjusted, it will become richer as the aircraft gains in altitude. |
| Does the air-fuel mixture provided by a float carburetor become richer or leaner when carburetor heat is applied? | The mixture becomes richer when carburetor heat is applied. |
| What would happen to the air-fuel mixture ratio in a float carburetor if the main air bleed were to become plugged? | The mixture would become excessively rich. |
| How does the automatic mixture control in a pressure carburetor keep the air-fuel mixture constant as the aircraft changes altitude? | It automatically, and progressively, bleeds the air between the two sides of the air diaphragm and decreases the air metering force. This leans the mixture as the aircraft goes up in altitude. |
| What are two purposes of the manifold valve (or flow divider) in the fuel injection system of a horizontally opposed aircraft engine? | It provides a constant discharge fuel pressure for idling, and it provides a positive shutoff for the fuel when the engine is shut down. |
| How does the mixture control change the air-fuel mixture ratio on the Teledyne-Continental fuel injection system? | When the mixture control is in its FULL RICH position, all fuel goes to the manifold valve. When it is in the IDLE CUTOFF position, all fuel is returned to the pump inlet. Intermediate positions vary the amount of fuel that goes to the engine. |
| Why must the diaphragms of a pressure carburetor be soaked before the carburetor is ready for flight? | Soaking the diaphragms of a pressure carburetor restores them to the condition of flexibility that they had when the carburetor was calibrated. |
| What are two basic types of fuel controls for aircraft turbine engines? | •Hydropneumatic •Electro-Hydromechanical |
| How does the exhaust gas temperature of a reciprocating engine tell anything about the air-fuel mixture being burned by the engine? | A stoichiometric mixture (in which all of the constituents of the air-fuel mixture are burned) produces the highest EGT. The mixture is adjusted to get the highest EGT, and then it is enriched to place it on the rich side of stoichio-metric. |
| What two things are adjusted when adjusting the idling of a reciprocating engine? | The throttle stop, to get the proper idling RPM, and the idle mixture control, to get the smoothest operation. |
| What is controlled by the adjustment of the orifice in the fuel pump of a Teledyne-Continental fuel injection system? | The high unmetered fuel pressure. |
| What is the significance of the letters that are stamped on the flats of a fuel injection nozzle? | These letters designate the relative size of the orifice in the injector nozzle. The lower the letter in the alphabet, the smaller the amount of fuel the nozzle will flow. |
| What is the function of the derichment valve in a pressure carburetor used on an aircraft engine with an antidetonation injection system? | The derichment valve automatically closes to lean the air-fuel mixture when ADI fluid is flowing. As soon as the ADI fluid stops flowing, the derichment valve opens and the mixture returns to its rich condition. |
| What is the function of the economizer system in an aircraft engine carburetor? | The economizer allows the engine to operate with an economically lean mix for all conditions other than full power. With throttle at full power, the economizer automatically enriches the mix to remove some heat that is developed during this operation. |
| In what position is the mixture control placed for starting an engine that is equipped with a pressure carburetor? | In the IDLE CUTOFF position. The engine is started with fuel from the primer system. |
| In what position is the carburetor heat control placed when starting an aircraft engine? | In the COLD position. |
| Why is an aircraft reciprocating engine killed by placing the mixture control in the Cutoff position, rather than by using the magneto switch? | By shutting off the fuel to the cylinders, the combustion chambers are left full of air with no fuel. This makes the engine less likely to fire if the propeller is pulled through with the ignition switch accidentally on. |
| Where is the fuel from a continuous-flow fuel injection system discharged? | It is discharged through injector nozzles screwed into the cylinder heads near the intake valves. |
| In which direction relative to the wind should a turbine-powered aircraft be positioned when the fuel control is being trimmed? | If the wind velocity is less than 10 miles per hour, it can be faced in any direction. If the wind velocity is between 10 and 25 MPH, it should be trimmed facing into the wind. The engine should not be trimmed when the wind velocity is more than 25 MPH. |
| What engine parameters are sensed by the fuel control unit of a turbine engine? | •Engine RPM •Inlet air pressure •Compressor discharge pressure •Burner can pressure •Inlet air temperature. |
| When does the acceleration system operate on an aircraft carburetor? | When the throttle is suddenly opened. |
| What is the purpose of the bypass valve in an engine-driven fuel pump? | The bypass valve allows fuel to flow around the engine-driven pump for starting and for emergency operation if the engine-driven pump should fail. |
| On which side of the firewall is the engine fuel shutoff valve located? | The shutoff valve must be on the side of the firewall away from the engine. |
| What are three purposes for the boost pumps in an aircraft fuel system? | To provide fuel pressure for starting the engine, to pressurize the fuel lines to prevent vapor lock, and to transter fuel from one tank to another. |
| What kind of boost pump is used in most aircraft fuel systems? | Electrically operated centrifugal pumps. |
| Where does an engine-driven fuel pump direct the excess fuel from its pressure relief valve? | Back to the inlet side of the pump. |
| What causes a vapor lock in an aircraft fuel system? | The fuel becomes hot enough that it boils. Vapors are released from the liquid fuel, and these vapors block the fuel lines so the liquid fuel cannot flow to the engine. |
| What is done in most aircraft fuel systems to prevent vapor lock? | Boost pumps in the fuel tank pressurize the fuel in the lines and force the fuel into the fuel metering system. |
| What is meant by a compensated relief valve in an engine-driven fuel pump? | A pressure relief valve that is acted upon by a diaphragm & a spring. Atmospheric pressure acting on the diaphragm varies the pump discharge pressure so that it will remain a given amount higher than the pressure of the air entering the carburetor. |
| What is the purpose of the pressurizing and dump valve in the fuel system for a turbine engine? | For normal ops, the pressurizing & dump valve are flow dividers directing the fuel into the main or pilot manifold to be discharged from the proper orifice in the duplex nozzle. At shut down, the dump function dumps all of the fuel from the manifold. |
| What should be done to an aircraft reciprocating engine if it has been operated on turbine engine fuel? | All of the fuel should be drained & the system filled with avgas. The engine should be given a compression check, & all of the cylinders borescoped. The oil should be drained & the filters examined. The engine should be given a complete run-up check. |
| What are the two basic types of turbine engine fuel? | Jet A and A-1, which are a special type of kerosine-base fuel. This is similar to military JP-5. Jet B is a gasoline-base fuel similar to military JP-4. |
| Why do some turbine engine fuel systems incorporate a fuel heater? | The fuel heater keeps the fuel warm enough that any water that precipitates out of the fuel will not freeze on the filters. |
| What are two reasons Prist is used in turbine engine fuel? | As an antifreeze that lowers the freezing point of any water that precipitates out of the fuel. It is also a biocidal agent that kills the microbial growth that forms scum in fuel tanks & holds water against the aluminum alloy that causes corrosion. |
| Why do some aircraft fuel filters have a built-in relief valve? | This relief valve will open and allow unfiltered fuel to flow to the fuel control device if the filter should become plugged with ice or other contaminants. |
| Where is the heat taken from that is used to heat the induction air in a reciprocating engine? | From a muff that is installed around some part of the exhaust system. |
| Where does the alternate air come from that is used with a pressure carburetor or a fuel injection system? | From inside the engine cowling. |
| Where does carburetor ice normally form in a carburetor? | In the throat of the carburetor, on and around the throttle valve. |
| Does the application of carburetor heat cause the air-fuel mixture to become richer or to become leaner? | Heated air causes the air-fuel mixture to become richer. |
| What is used to drive most of the external superchargers used on modern reciprocating engines? | Exhaust gases. |
| What controls the speed of a turbocharger com-pressor? | The amount of exhaust gas that is forced to flow through the turbine. This is controlled by the position of the waste gate. |
| What is the danger of operating an aircraft reciprocating engine with too high a carburetor air temperature? | Too high a carburetor air inlet temperature can cause the air-fuel mixture to reach its critical temperature and detonate. |
| What is usually installed in a large reciprocating engine between the turbosupercharger and the carburetor? | An intercooler. This is an air-to-air heat exchanger. |
| In what position should the carburetor heat control be placed when starting a reciprocating engine? | In the COLD position. |
| How does an engine air inlet vortex destroyer help prevent foreign object damage to the engine? | A high-velocity stream of compressor bleed air is blown out in front of the engine to break up the vortices that form in front of the engine when it is operating at high power on the ground. |
| What is meant by pressure cooling of an aircraft engine? | Air cooling in which air is forced to flow through baffles and cylinder fins by a pressure differential across the engine. |
| What is the purpose of an augmentor tube in the cooling system of an aircraft reciprocating engine? | The augmentor tube uses the velocity of the exhaust gases to produce a low pressure on one side of the engine that helps pull cooling air through it. |
| Where is the highest temperature located in a turbine engine? | At the inlet to the high-pressure turbine. |
| How are the turbine inlet guide vanes and the first-stage turbine blades in some turbine engines cooled? | High-pressure compressor bleed air flows through the hollow guide vanes and hollow turbine blades. |
| Which side of an air-cooled engine cylinder has the greatest amount of cooling fins? | The side of the cylinder in which the exhaust valve is located. |
| What should be done to repair a bent cooling fin in a cast aluminum cylinder head? | It is normally best to leave a bent cast fin alone if it does not restrict the flow of air. Cast fins are brittle and could break off. |
| What is used in a helicopter to increase the amount of cooling air that flows over the engine cylinders? | A belt-driven fan. |
| What should be the position of the cowl flaps on a reciprocating engine when it is run on the ground? | They should be wide open when operating the engine on the ground. |
| What is the function of the majority of the air that passes through a turbine engine? | Most of the air is used for cooling. |
| How does metallic sodium in an exhaust valve aid in transferring heat? | The sodium melts when the engine is running, and it sloshes up and down as the valve operates. The sodium picks up heat from the valve head and carries it into the stem so it can be transferred to the cylinder head and dissipated into the air. |
| How is the structure around a turbine engine protected from excessive heat from the engine? | An insulating blanket protects the structure from excessive heat. |
| What is the function of blast tubes that are installed in a pressure cooling system of a reciprocating engine? | These blast tubes direct cooling air to the magnetos and the generator. |
| Of what material is the insulation blanket made that is used to protect the aircraft structure from the heat produced by a turbine engine? | Fiberglass sandwiched between sheets of metal foil. |
| What is meant by a convergent inlet duct for a turbine engine? | A convergent duct is one whose cross-sectional area becomes smaller in the direction the air flows. |
| What is meant by a divergent inlet duct for a turbine engine? | A divergent duct is one whose cross-sectional area becomes greater in the direction the air flows. |
| What kind of inlet duct is often used on turbine-pow-ered helicopters? | A bell-mouthed inlet duct. |
| Why do some turbine engines use variable inlet guide vanes? | These variable inlet guide vanes are automatically adjusted to direct the air into the engine in such a way that it keeps the RPM vs. velocity proper for the most efficient operation. |
| How do some turbine engines prevent ice formation on the inlet guide vanes? | Hot compressor bleed air flows through hollow inlet guide vanes. |
| Of what material are most reciprocating engine exhaust components made? | Corrosion-resistant steel. |
| How is the speed of a turbocharger controlled? | How is the speed of a turbocharger controlled? By controlling the amount of exhaust gas that flows through the turbine. This is controlled by the position of the waste gate that is in the exhaust pipe. |
| What type of actuator is used to control the position of the turbocharger waste gate? | A hydraulic actuator that uses engine oil pressure to move the piston. |
| How does a power recovery turbine increase the power of a reciprocating engine? | Exhaust-driven velocity turbines are coupled through a hydraulic drive to the engine crankshaft. Energy that would normally be lost is used to drive the tur-bines, and the turbines assist in turning the crank-shaft. |
| How tight should the clamps be tightened that hold sections of a reciprocating engine exhaust system together? | They should not be so tight that they will be damaged when heat expands the exhaust system components. |
| What would be the effect on engine performance of an internal failure of a muffler? | This will increase the exhaust back pressure and cause a loss of engine power. |
| What effect on turbine engine operation is caused by a change in the area of the exhaust nozzle? | Altering the area of the exhaust nozzle affects the compression ratio, the RPM, the mass airflow through the engine, and the EGT. |
| What are two types of thrust reversers that are used with turbojet engines? | •Mechanical blockage (clamshell) •Aerodynamic blockage (cascade). |
| How does a noise suppressor reduce the amount of noise produced by a turbojet engine? | It breaks up the low-frequency vibrations in the exhaust stream and converts them into higher fre-quencies. These high frequencies are dissipated by the air more easily than low frequencies. |
| What is the purpose of the ball joints and bellows in the exhaust system of a reciprocating engine? | The ball joints and bellows allow the exhaust system components to change their dimensions without causing any leaks. |
| Why do some supersonic aircraft use a convergent-divergent exhaust duct? | A convergent-divergent exhaust duct controls the gas expansion as it leaves the engine so the gases will produce thrust at supersonic velocities. |
| Why is it important that a lead pencil never be used to mark on an aircraft exhaust system? | The graphite in a lead pencil will infuse into the metal when it gets hot. It makes the metal brittle and likely to crack. |
| What type of damage is normally found in the hot section of a turbine engine? | Cracks caused by heat. |
| What type of device is used on propeller blades to remove ice that has formed on them? | Electrically heated deicer boots. |
| What is used to prevent ice forming on a propeller blade? | A mixture of ethylene glycol and isopropyl alcohol slung out along the blades. |
| Should an adjustable-pitch propeller be in high pitch or in low pitch for takeoff? | In low pitch. |
| What is done to cause a Hydromatic propeller to feather? | High-pressure engine oil is directed into the propeller through the governor. |
| What is done to cause a McCauley propeller to feather? | Oil is allowed to drain out of the propeller. |
| Does centrifugal twisting moment on a propeller blade tend to move the blades toward high pitch or toward low pitch? | Toward low pitch. |
| Do the flyweights on a propeller tend to move the blades toward high pitch or toward low pitch? | Toward high pitch. |
| What is the difference between a controllable propeller and a constant-speed propeller? | Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control the pitch, and a constant-speed propeller uses a governor to control the valve. |
| When making a magneto check on an engine equipped with a constant-speed propeller, should the propeller control be in the LOW PITCH or the HIGH PITCH position? | It should be in the LOW PITCH position. |
| What can be done to prevent the front cone from bottoming when installing a propeller on a splined shaft? | Install a spacer behind the rear cone to move the propeller forward on the shaft. |
| What is the purpose of the small holes that are drilled in the end of a wooden propeller? | These holes vent the inside of the propeller blade and allow moisture that collects in the wood to be released. |
| What is the function of the snap ring inside the hub of a propeller that is mounted on a tapered or splined shaft? | The snap ring allows the propeller to be pulled off of the shaft when the retaining nut is backed off. |
| What is adjusted inside the governor for a constant-speed propeller to change the speed at which the propeller is operating? | The compression of the speeder spring. |
| What is the function of the accumulator that is used with some McCauley feathering propellers? | The accumulator stores oil under pressure when the engine is operating normally. This oil is used to help the propeller blades move toward low pitch when the propeller is being unfeathered. |
| What is meant by the beta range of operation of a turboprop propeller? | This is the mode of ground operation, and it includes starting, taxiing, and ground reverse operation. |
| What is meant by the alpha range of operation of a turboprop propeller? | This is the in-flight mode of operation from takeoff to landing. |
| Is the flat surface of a propeller blade the face of the blade or the back of the blade? | It is the face of the blade. |
| What keeps a McCauley feathering propeller from feathering when the engine is shutdown on the ground? | A spring-loaded latch prevents the blades moving to the feather position at eng. shut down on the ground. In air, aerodynamic force spins the prop. Centrifugal force holds the blades unlatched allowing prop to the feather when oil press. leaves the prop. |
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