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J F Power Plants Oral

Terms in this set (276)

What is the purpose of dynamic dampers on crankshafts?
They reduce engine vibration.
What type of bearings are generally found in reciprocating engines?
Plain, ball and roller bearings.
Are the connecting rods used in each cylinder of a radial engine the same?
No. Radial engines use master and articulating rod assemblies
Name the different types of piston rings?
Oil control, compression and oil scraper.
Where should piston rings be installed relative to each other and why?
Compression rings should be staggered so they don't align. This prevents excessive blow-by.
What could result from incorrectly installed piston rings?
Excessive oil consumption.
What purpose do oil control rings serve?
They regulate the thickness of the oil film on the cylinder walls.
What is used to help prevent valve surge or floating in an aircraft engine?
Two or more springs are used on each valve.
On engines equipped with hydraulic valve lifters, what should the running valve clearance be?
Zero.
What is the purpose of valve overlap?
It allows better volumetric efficiency and lowers cylinder operating temperatures.
What indications are given in the event of a leaking or open primer while the engine is engaged?
The engine will not idle properly.
A cold cylinder is found when troubleshooting in a running engine. What does this indicate?
No combustion in that cylinder.
When pulling a propeller through, a hissing sound is heard, indicating blow-by. What procedure should be performed next?
A compression check should be done to identify the faulty cylinder.
What is the purpose of performing a compression test?
To determine if the valves, pistons and rings are sealing properly.
When an engine is overhauled, how is its total time affected? When an engine is rebuilt, how is its operating time history affected?
The total time on the engine must be continued and the time since major overhaul is entered into the engine log. If the manufacturer rebuilds the engine, it is granted a zero-time status and is considered to have no previous operating history.
What inspections should be performed after a propeller strike without sudden stoppage?
1. Inspect engine mounts, the crankcase, and the nose section for damage. 2. Inspect the oil and oil filter/screens for metal particles. 3. Inspect the crankshaft or drive-shaft for cracks and misalignment.
Name some of the precautions that should be performed prior to engine removal.
Disconnect the battery, turn off the fuel valves, chock the wheels, and if necessary, install a tail stand.
When inspecting a piston, where are cracks most likely to be found?
In those areas that are highly stressed; usually the base of the piston bosses, inside at the junction of the bore and walls, and the ring lands.
What does it mean if an engine part is within serviceable limits?
It means that the part is within the manufacturers limits and can be used in an engine (does not require replacement).
What tools or instruments are used to inspect a cylinder barrel for out of roundness?
A dial indicator or an inside micrometer is usually used to measure the top of the cylinder and at the skirt. A telescopic gauge and micrometer can also be used. Two readings should be taken 90 degrees to each other.
How can a loose stud in an engine crankcase be repaired?
Remove the loose stud and inspect the hole for size and thread condition. It may be necessary to use an oversize stud or heli-coil insert.
What publication is used to check an engine for normal operation?
Manufacturer's maintenance manual.
A weak cylinder is found during a compression check. What must be inspected?
Worn piston rings and cylinder walls; leaking valves caused by improper timing, valve clearance and particles keeping the valves from seating; warped or burnt valves.
What purpose does oil analysis serve?
Metal particles in the oil show normal and abnormal wear of the engine. This helps in evaluating the engine's internal condition.
What inspection should be performed on an engine that has been in storage?
Perform an inspection to determine if there is any corrosion damage.
Where would a carburetor air temperature bulb be located?
In the ram air intake duct.
What is the fuel pressure range on float type carburetors?
3 to 5 PSI
Where is the fuel flow indicating system generally connected within a carbureted reciprocating engine?
The transmitter and the indicator
What unit of measure is generally used to measure fuel flow?
Pounds or gallons per hour
Why is fuel flow monitored?
To determine fuel consumption and engine performance
What does the manifold gauge indicate and how is it calibrated?
It measures the absolute pressure in the engine manifold and is calibrated in inches of mercury
What directly controls manifold pressure?
Throttle opening and engine r.p.m
During engine operation, where should the propeller control be set when checking the manifold pressure?
Low pitch, high r.p.m.
Is the aircraft electrical system required to power a cylinder head temperature gauge?
No. A thermocouple is used as the electrical source.
What are the possible indications of an oil pressure transmitter or indicator malfunction?
A severe or sudden drop in oil pressure while the oil temperature remains normal and the oil supply remains full.
What does a tachometer indicate on a reciprocating engine?
Engine r.p.m.
Where should the thermocouple be installed on a reciprocating engine using a single probe cylinder head temperature system?
On the hottest cylinder.
Explain the difference and advantage of turbofan over turbojet engines.
A turbofan engine uses a fan to bypass some air around the engine core and to provide thrust. The advantage is that this provides additional thrust without increasing fuel flow.
Name the major components in a gas turbine engine.
Air inlet, compressor section, combustion section, turbine section, exhaust section gearbox and accessory section.
What determines the amount of airflow through a turbine engine?
The forward speed of the aircraft, compressor speed and air density.
Name the two types of compressors commonly used in turbine engines.
Axial and centrifugal flow compressors.
Name the two different methods for attaching turbine engine rotor blades to the rotor disks.
Dove-tail root, Bulb-type root, Fir tree-type root
What is a split compressor system?
Also called dual or twin spool compressors, these are connected to the turbine section with two rotor shafts, one inside the other.
What are the different types of combustion chambers used in turbine engines?
Can, annular, can-annular, and reverse flow annular.
What prevents the combustion chambers from burning?
Cooling air along the inside of the liner.
What is the purpose of the interconnecting tubes attached between can-type combustion chambers?
For flame propagation during start.
What function do axial flow turbine nozzles perform?
They direct the mass airflow to drive the turbine rotor at a specific angle.
How is thermal stress relieved on a turbine disc?
By directing bleed air onto the face of the disk, or by grooves being cut in the disk.
What are carbon seals used for in turbine engines?
They are used as oil seals for the rotor shaft bearings.
What is shaft horse power?
It is an indication of the torque developed by a turboprop or turbo-shaft engine.
What is the purpose of an APU
They provide ground electrical and pneumatic power for aircraft systems when the engines are not running. Pneumatic power can be used for engine starting, ground heating or air condition, and anti icing. Many APU's may also be used as an emergency source of inflight electrical power.
Name the main components of a typical APU
A small power turbine for power and bleed air, and an electrical generator.
When is the greatest demand placed on an APU?
When supplying bleed air.
How is an APU generally started?
With its own electrical starter and battery power.
Where does the APU get its fuel supply?
From one of the aircraft's main fuel tanks.
At what speed does a gas turbine APU operate and how is this speed maintained?
At or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed.
What is used to prevent a heavily loaded APU from exceeding its maximum EGT?
A load control valve modulates the pneumatic load to maintain EGT's within limits
How is an APU shut down and why is this procedure used?
After the APU is unloaded by closing the bleed air valve, it is run for a specified amount of time to allow the EGT to cool and stabilize. This cool down period is typically three minutes. If a heavily loaded APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock.
What powers the variable inlet guide vanes used on some APU's to regulate compressor intake air flow?
Fuel pressure.
What is fan blade shingling?
It is the overlapping of the mid-span shrouds of the fan blade.
When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coast down?
Any rubbing sound or other usual noises from the engine.
Why are compressor washes performed and what methods are commonly used?
To remove any contaminants from the compressor section and improve engine performance. The fluid wash and abrasive grit wash are commonly used.
How can you tell if a turbofan or turbojet engine is out of trim?
There will be a high exhaust gas temperature at the target engine pressure ratio for takeoff power.
Name the different types of compressor blade damage that may be found during inspection.
Dents, cracks, galling, pitting, scratches, burrs, burns, gouges.
What kind of markers can be used to mark the parts in hot and cold sections during repair?
Layout dye, felt tip marker, chalk.
How does relative humidity affect turbine engines?
Negligible effect.
What criteria determines replacement of life limited turbine engine components?
Cycles, hours and/or calendar time.
If turbine blades are removed from a turbine disc, why should they be re-installed in the same location?
To maintain the balance of the turbine wheel.
How are the gas turbine engine tachometers calibrated?
They are calibrated in percent r.p.m.
On a turbine engine, what is the engine pressure ratio and what does it indicate?
It is the ratio between the total inlet pressure and total turbine exhaust pressure and is used to indicate the thrust developed by the engine.
On a turbine engine, what does exhaust gas temperature (EGT) indicate and how is it obtained?
EGT is the average temperature of the turbine discharge gasses and is obtained by thermocouples placed near the turbine exit.
Can the EGT system on a turbine engine be checked without running the engine?
Yes, by checking the resistance of the thermocouples and circuits.
Name the three components on the induction system of a reciprocating engine.
The air scoop, carburetor or fuel control and the intake manifold.
What could happen if the induction system becomes obstructed?
The engine may not be able to produce its rated power or it may not run at all. This may also be an indication of a dirty air inlet filter.
How does induction icing affect engine performance?
It causes a reduction in power and possible erratic operation.
How is induction icing categorized?
As impact ice, fuel evaporation ice and throttle ice.
What is the common method used to prevent induction system ice in a reciprocating engine?
Raise the temperature of induction air with a preheater.
What causes fuel evaporation ice?
Fuel evaporation ice is formed because of the decrease in air temp resulting from evaporation of the fuel after it is introduced into the air stream.
Is carburetor throttle ice more likely to occur at a higher or lower power setting? Why?
At a lower power setting because the throttle is partly closed, offering a larger surface area for ice accumulation.
What may be the indication of leaking intake pipes?
The engine runs rough at low r.p.m.
What happens to engine power when the carburetor heat is applied?
There is a noticeable drop in power.
What could happen if carburetor heat is applied at high engine power settings?
Detonation.
What are two types of supercharged induction systems?
Internally driven and externally driven.
How and at what point does an internally driven supercharger boost air pressure?
An (engine-driven) impeller compresses the fuel/air mixture after it leaves the carburetor.
What is used to power a turbocharger?
Engine exhaust gas directed onto the turbocharger turbine.
What could result if the waste gate on a turbocharger system does not close fully?
The engine may not be able to produce its rated power at certain altitudes, and the aircraft may not be capable of reaching critical altitude.
What function does a turbocharger waste gate perform?
It controls the amount of exhaust gas either into or around the turbocharger, thus controlling the boost pressure of the turbocharger.
What could cause a turbocharged engine to surge?
There could be a waste gate or controller malfunction.
What are the most common ways to control a waste gate?
Either mechanically with linkages to the throttle or a separate control, or by an actuator that is driven by oil pressure.
In a pressurized reciprocating aircraft, what component in the turbocharger system is used to limit the amount of turbocharger airflow used for cabin pressurization?
The sonic venturi
What is the function of a divergent-shaped jet engine inlet during subsonic flight?
It causes the air velocity to decrease with a subsequent increase in air pressure.
Where are bellmouth inlet ducts typically found?
On helicopter engines
How do venturi -type particle separators, found on many turbine powered helicopters, function?
A venturi is used to accelerate the flow of incoming air and debris through a curved intake. The debris gains too much inertia to allow it to follow the curved intake towards the engine, and is channeled away from the compressor.
What are the most common methods used for anti-icing of turbine engine inlet ducts?
Engine bleed air and electric heating elements.
What is the purpose of the exhaust system?
To remove high temperature Exhaust gases from the engine.
Name two types of reciprocating engine exhaust systems.
The short stack and the collector system.
What drawback in using collector-type exhaust systems is more than offset when used on turbocharged engines?
The loss of horsepower due to exhaust system back pressure.
What could result if the internal baffles or diffusers in an exhaust system fail?
The flow of the exhaust gasses could be restricted, resulting in a loss of engine power.
What type of exhaust system is used on a turbocharged engines?
The collector system
What kind of material is normally used to make the muffler shrouds found in the exhaust system?
Stainless steel
How do you inspect the internal baffles and diffusers of an exhaust system?
By disassembling the exhaust system as necessary and visually inspecting the components.
Why is an exhaust system failure considered a severe hazard?
It can result in carbon monoxide poisoning, loss of engine power, or fire.
What could happen if lead, zinc, or galvanized marks are made on an exhaust system?
They cause a change in molecular structure, which could result in cracks when heated.
What happens if the heat exchanger leaks exhaust gasses into the induction system?
There is a loss of engine power.
what is an indication of an exhaust gas leak?
A flat gray or sooty black deposit in the area of the leak.
Where are the most common places to find cracks in an exhaust system?
At welded or clamped areas and at the flanges.
What is a common cause of turbocharger waste gate sticking?
Coke deposits or carbon buildup.
Why are the turbocharged exhaust system leaks very damaging at high altitudes?
Pressure differential will cause the leak to escape with intensity.
What are exhaust system coke deposits?
Excessive carbon buildup.
What is the result of changing the exhaust nozzle area of a turbine engine?
The engine's performance and exhaust gas temperature change.
Name the components of a typical turbine exhaust nozzle.
The tail cone, exhaust ducts and support struts.
What is the purpose of thrust reversers?
They help decellerate an aircraft after landing.
How does a noise suppressor found on older turbojet engines work?
It converts low frequency sound, which is audible over great distance, into high frequency sound, thus reducing the sound footprint.
What are the two most commonly used types of thrust reversers?
The clam-shell (or mechanically blocked) and the Cascade (or aerodynamically blocked.)
How much thrust do the thrust reversers produce compared to the engine's full forward thrust?
Substantially less.
What are the hazards of operating some thrust reversers at low ground speeds?
Ingestion of foreign objects stirred up by the exhaust gasses and re-ingestion of hot exhaust gasses.
What are some of the sources used to heat the fuel in a turbine engine fuel system?
Bleed air and engine lubricating oil.
What are the most common types of fuel metering systems used on small reciprocating engines?
float-type carburetors, pressure-injection carburetors and direct fuel injection systems.
What function does the mixture control perform?
Controls the fuel/air mixture.
What generally causes spark plug fouling?
Operating the engine with an excessively rich mixture at idle.
What is the purpose of an accelerating system?
It provides an immediate but brief increase in fuel flow in the venturi to enrich the mixture.
What is the carburetor economizer system?
It is a power enrichment system that provides a richer mixture at high power setting, where the excess fuel aids in engine cooling. This system functions at throttle settings above cruise power setting
When the mixture is placed in the idle-cutoff position, a slight rise in r.p.m. is noted prior to the engine decelerating. What does this indicate?
The idle mixture is set correctly.
Why should engine r.p.m. be accelerated periodically when making carburetor adjustment?
To clear the engine.
What maintains the fuel pressure in a pressure-injection carburetor?
An engine-driven fuel pump.
What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cutoff position?
The engine stops.
How does an automatic mixture control AMC function?
A sealed brass bellows connected to the fuel metering system, expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly.
What are some of the advantages of fuel injection systems over carburetor systems?
Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy, reduced overheating of individual cylinders.
What purpose do turbine engine fuel control units serve?
They automatically meter fuel to the engine.
What are the two basic types of turbine engine fuel control units?
Hydro-mechanical and electronic.
What are the engine variables detected by the fuel control unit?
Power lever position, engine rpm, compressor inlet temperature, compressor inlet pressure, compressor discharge pressure, burner pressure.
What are the two major components of a supervisory electronics engine control?
The electronic control unit (computer) and the hydro-mechanical fuel control.
What are some of the advantages of a full-authority digital engine control FADEC over a hydro-mechanical fuel control?
Better fuel economy, improved starts, requires no engine trimming, provides engine limit protection, fully modulates the active clearance control, allows more repeatable engine transients.
What do turbine engine fuel spray nozzles do?
they inject fuel into the combustion area.
What are the different engine indications used for trimming a turbine engine?
Either EPR or rpm is used depending on the particular engine.
What maintenance adjustments are normally allowed on an installed hyromechanical fuel control?:
Specific gravity for fuel, idle r.p.m. and maximum r.p.m. (or maximum EPR).
What type of pump can vary the amount of fuel discharged regardless of speed?
A variable displacement pump.
What is used to keep water, sediment and foreign matter out of the carburetor?
The main fuel strainer.
what is the purpose of a pressure relief valve in a constant displacement pump?
It returns excess fuel that is not required by the engine to the inlet side of the pump.
What type of engine-driven fuel pump is widely used other than gear or piston pumps?
A rotary vane type
What function do fuel boost pumps perform?
They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.
What is a commonly used type of fuel boost pump?
The centrifugal type.
What causes vapor lock and why is it of concern?
Vapor lock is caused by insufficient fuel pressure, high fuel temps and excessive fuel turbulence, which may completely block any fuel flow resulting in engine failure.
What function does the engine driven pump on a turbine engine perform?
It provides a continuous supply of fuel at the proper pressure while the engine is running.
Name the two categories of turbine engine pumps.
Constant and variable displacement.
What category is a gear-type pump classified in?
Constant displacement.
When performing an external inspection of an engine driven fuel pump, what should you look for?
Leaks and security of mounting.
What is the purpose of a shear section of the driveshaft in a duel element constant displacement pump?
If one element seizes, a portion of the driveshaft seizes, allowing the other element to continue to operate.
Where in a turbine engine fuel system is the ice formation likely to occur and how is it prevented?
The fuel filter is most susceptible to ice formation, so a fuel heater is used that consists of a heat exchanger using either engine oil or bleed air to warm the fuel.
What is the purpose of a bypass valve in an engine fuel system micron filter?
It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked.
What is the purpose of a duplex fuel nozzle?
A duplex fuel nozzle discharges two different spray patterns. The spray pattern wider during start up and acceleration and narrows when engine speed increases above idle.
What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?
-The pressurizing portion provides primary and secondary fuel flow to the dual-lines duplex fuel nozzles. The dump portion allows fuel to drain from the manifolds after engine shutdown.
What purpose do fuel selector valves serve?
They allow tank and engine selection and provide a means for shutting off fuel flow.
How can the remaining service life of starter-generator brushes be determined?
By visually inspecting the amount of wear of the brushes.
What components of the starter-generator require periodic inspection?
The commutator and brushes.
Between field and armature windings in starter-generators, which ordinarily receive current for operation in the start mode?
Generally, both field and armature receive current for operation in the start mode.
What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?
A ground power unit (GPU), an on-board auxiliary power unit (APU), compressed bleed air from an already running engine.
When should ignition ideally occur?
A specific number of degrees before the piston reaches top dead center on the compression stroke.
Why are dual magnetos used in the engine ignition system?
To improve combustion efficiency, and provide redundancy for safety.
Why is magneto timing so important?
For an engine to run properly, the spark plug in a cylinder has to fire at a specific time. To produce the required energy for the spark at the required time, the magneto must be in the E-gap position, the breaker points must start to open, and the distributor must be electrically aligned with the particular cylinder.
What function does a magneto perform?
It produces a high voltage that forces a spark to arc across a spark plug gap.
Name the components of a high tension magneto system.
Rotor, core, and pole shoes.
name the three main circuits of a high tension magneto system.
Magnetic, primary and secondary.
What is an E-gap angle?
It is an angle above the neutral position, where maximum magnetic field stress exists.
What reduces arcing in the points and also aids the collapsing of the magnetic field in a magneto?
A capacitor.
How does a magneto produce the high voltage required to fire a spark plug?
In the rotation cycle, when the magnetic rotor is in the E-gap position, the primary points open, and inducing a high voltage in the secondary coil.
What is the P-lead and how does it function?
The P-lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off, the P-leads on both magnetos are grounded. When the ignition switch is turned to the "LEFT" position, the right magneto is grounded, so that only the left magneto operates, and vise versa.
What is a magneto timing light used for, and what does it indicate?
It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.
Why are turbine engine igniters generally not susceptible to carbon fouling?
Because the high energy sparks they produce clean off any deposits on the firing end.
What is the function of a duty cycle in relation to a turbine engine ignition system?
Allows the operation of the ignition system for a given amount of time, and is then followed by a minimum specified cooling down period.
What are the three main components of a turbine engine ignition system?
Ignition exciters, high tension leads, igniters.
When the engine is operating, what does an ammeter / loadmeter indicate when connected to: 1. Battery positive lead? 2. Generator output lead?
When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging. When connected to the generator output lead, it indicates the current produced by the generator, or electrical system load.
What is done to ensure that each generator shares the load in a multiple generator system?
The generators are paralleled.
Where would you find generator rating and performance data?
On the data plate attached to the generator.
how is the voltage of a DC generator controlled?
By varying the field current strength.
What is the most common type of alternator used in most aircraft AC systems?
The three phase alternator.
How does a voltage regulator control the voltage of an alternator?
By regulating the voltage output of the DC exciter.
What does the speed of rotation and number of poles of an alternator determine?
The frequency of the alternator output.
What are some of the methods used to maintain 400 Hertz alternator output frequency on large turbojet or turbofan engines?
Constant speed drives, integrated drive generators, and variable-speed constant frequency (VSCF) power systems.
Name the major parts of a DC motor.
The armature, field, brushes and frame assembly.
Name the components of a direct cranking electric starter system.
An electric motor, reduction gears, and an automatic engaging and disengaging mechanism.
name three types of DC motors.
Series, shunt and compound.
What type of DC motor is commonly used for a reciprocating engine starter and why?
A series wound motor is commonly used because it has a high staring torque under heavy load conditions.
What are the operating modes of a turbine engine starter generator?
It operates first as a starter, then as a generator once the engine is running.
What is a possible indication when a starter drags?
A dirty or worn starter commutator.
Where would wire with high temperature insulation material be used?
When they run close to high temperature areas such as exhaust stacks or heating ducts.
What is the size standard for electrical wire used in US manufactured aircraft?
The American Wire Gauge.
How are wire sizes represented?
By a numbered gauge size. The smaller wires are represented by larger numbers. The smallest size wire normally used in aircraft is 22-gauge.
What is the maximum slack allowed between the supports of a single wire or bundle installation?
Not more than 1/2 inch.
Why are wires bonded on power plant installations?
To provide a current return path , and to prevent static discharge.
A reciprocating engine is found to have excessive oil consumption without evidence of any oil leaks. What is the likely cause?
The piston rings are worn or broken.
What are the functions of lubricating oil in reciprocating engines?
To reduce friction between moving parts and remove heat.
Name two important characteristics of aircraft engine oil.
The oil must be thin to circulate freely and heavy engough to provide the proper oil film at engine operating temperatures.
What could happen to an oil that is too low in viscosity at normal engine operating temperatures?
it may not maintain the oil reasonable film, resulting in premature wear.
What are some of the factors that must be considered by an engine manufacturer in determining the proper grade of oil for a particular engine?
The operating load and temperature as well as the rotational speed.
Why do aircraft reciprocating engines use a relatively high viscosity oil?
Because they usually have large operating clearances, and operate at high temperatures and pressures.
Name some oil contaminants.
Metal particles, dirt, carbon, moisture and acids.
What is a possible indication of low oil pressure together with high oil temperature?
A low or inadequate oil supply.
In ashless dispersant (AD) oils, what function does the dispersant perform?
It keeps the oil passages and the inside of the engine clean.
Why do oil reservoirs have expansion space?
To provide for oil foaming, thermal expansion, and air in the return oil.
What could cause oil foaming?
Diluted oil, contaminated oil, and the oil level being too high.
What controls oil pressure in a gear-type oil pressure pump?
An oil pressure relief valve.
What function does an oil cooler bypass valve perform?
It directs the oil either through the cooler or around it in order to maintain proper operating oil temperatures.
What could be a possible indication if the oil cooler passage becomes obstructed?
A high oil temperature.
Where is the oil temperature bulb usually located?
At the engine oil inlet.
What does the presence of metal particles in an engine oil filter indicate?
Depending on the type and size of the metal particles, this usually indicates abnormal wear and possible engine internal failure.
What should be done if metal particles are found in an engine oil filter?
Follow engine manufacturer's maintenance instruction.
Where is the most critical point of lubrication in a gas turbine engine?
At the turbine bearing.
What type of oil is used in a turbine engine oil system?
Synthetic oil.
Where are oil screens or filters most likely located in a turbine engine oil system?
At the oil pressure system (main filter), scavenge system, and at or just before the oil jet (last chance).
Name two types of turbine engine oil coolers.
Air cooled and fuel cooled.
What effect does excessive heat have on reciprocating engines?
it shortens the life of the engine parts, changes the behavior of combustion, and impairs lubrication.
What is the purpose of cooling fins?
They provide a larger cooling surface area for removing heat from cylinder heads of air-cooled reciprocating engines. Airflow around the cooling fins transfers the heat from the cylinder heads to the air.
What are the reasons for using engine cowlings, baffles and cowl air seals?
The cowling performs two main functions: it streamlines the engine area to reduce drag, and is used together with the baffles and cowl air seals to direct airflow over the cylinders for cooling.
What is the purpose of cowl flaps and how are they operated?
They are used to control the amount of airflow through the cowling. They are either mechanically, electrically or hydraulically operated.
How does an augmenter cooling system work?
An outer tube placed over the exiting exhaust gas creates a venturi effect that draws more airflow over the engine, thus providing additional cooling.
Where should cowl flaps be positioned for ground operations?
Fully open.
What type of power is used to operate cowl flaps?
Manual, hydraulic, or electrical.
What should be done when cooling fin damage is discovered?
Depending on the scope of damage, some cooling fins may be repaired subject to the manufacturer's overhaul and repair limitations. if an excessive amount of the cooling fin is broken off, the cylinder should be replaced.
Why is cowl flap adjustment important?
The movement must be within tolerances to keep cylinder head temperatures within allowable limits.
How are turbine engines cooled?
They are cooled by air passing through the engine. About 75% of the air passing through the engine is used for cooling which leaves only about 25% for combustion. This air is used to cool the combustion chamber and turbine.
In a turbine engine, where does bleed air come from that is used to cool bearings and other parts?
The engine compressor.
What is the relationship between turbine engine upper temperature limits and power produced?
The higher the combustion temperatures that an engine can withstand without damage, the more power it is capable of producing.
What is the approximate percentage of air passing through a turbine engine that is used for cooling rather than combustion?
Approximately 75%
What can be done to effectively allow higher gas temperatures in the turbine section of some engines?
Compressor bleed air ducted through hollow sections in the turbine inlet guide vanes and first stage rotor blades can lower temperatures enough to prevent heat damage.
What types of fire detector systems are used for engine fire detection?
Overheat, rate of rise, and flame detectors.
How does a thermal switch fire protection system operate?
When heated and pass a temperature limit temperature, the switch closes causing the warning devices in the cockpit to activate.
How many thermal switches are needed in a thermal switch fire protection system?
At least one.
What kind of fire detection system allows more complete coverage than a spot-type system?
A continuous loop system.
What happens if an engine equipped with a thermocouple fire warning system overheats slowly?
Nothing, because this system require a fast temperature rise to operate.
What electrical power is required for a thermocouple fire protection system to operate?
Both the thermocouple-produced power and the aircraft electrical system are required for this type of fire protection system to operate.
What is the likely cause of a false fire warning?
The engine fire sensing loop is bent or kinked excessively.
What are fire extinguishing systems designed to do?
They are designed to dilute the oxygen levels around the engine to a point that does not allow combustion, or to reduce temperatures below the ignition point.
Describe how a Kidde continuous loop fire protection system functions.
A Kidde system has a sensing element consisting of a sealed Inconel tube containing two conductors that are embedded in a thermistor material. One wire is electrically grounded to the outer tube at each end and acts as an internal ground, and the other is a positive lead. When a fire or overheat occurs, the resistance of the thermistor material drops, allowing current to flow between the two wires to activate an alarm.
Describe how a Fenwal continuous loop fire protection system functions.
A Fenwal system uses a sensing element consisting of a small diameter flexible Inconel tube containing a single wire electrode surrounded by ceramic beads. These ceramic beads prevent the electrode and tube from touching each other. Current is applied to the elctrode while the outer tube is grounded to the aircraft structure. When a fire or overheat occurs, the core resistance of the cramic beads drops, allowing current to flow between the center elctrode and ground, energizing the alarm system
What elements must be present for a fire occur?
An ignition source such as heat or a spark, fuel and oxygen.
What group of fire extinguishing agents are no longer manufactured because of environmental concerns?
Halons (or Freon or chlorofluorocarbons) were no longer manufactured after 1995. However existing stocks of CFC may still be used and are subject to strict handling and disposal regulations.
How are fire extinguishing agents distributed?
Through perforated tubing and discharge nozzles.
What is the purpose of the discharge cartridge and how is it activated?
The discharge cartridge, or squib, which is electrically ignited, fires a projectile into the frangible disk, thereby releasing fire extinguishing agent.
How is a fire extinguisher system with a high rate of discharge classified?
As an HRD fire extinguisher system.
What do the red and yellow discs in a fire extinguishing system indicate?
A yellow disc indicates a normal discharge. A red disc indicates a thermal discharge.
How is the fire extinguishing agent in an HRD system distributed, and how long does it take to discharge?
The agent is distributed through series of high pressure tubes and takes one to two seconds to discharge.
What is the purpose of a pressure gauge in a fire extinguishing system?
Indicates pressure within the container. To check if the pressure is within limits, a pressure-temperature chart is used.
What is the function of a propeller?
The propeller blades create thrust to pull or push an airplane through the air.
What is the difference between a fixed pitch propeller and controllable pitch propeller?
A fixed pitch propeller is one that has a built-in blade angle that cannot be changed by the pilot. These propellers can have the blade angle changed by the manufacturer or an approved repair station to optimize performance. A controllable pitch propeller is one that can be changed by the pilot and is usually controlled by a governor that maintains a constant speed. Some controllable propellers also provide reverse pitch and feathering.
how are some wooden propeller blades protected from wear and damage?
By metal tipping fastened to the leading edge and tip.
what happens to the blade angle of a constant speed propeller during a constant power dive?
The blade angle increases to prevent an over-speed.
What are the functions of a constant speed propeller governor?
it boosts engine oil pressure before it enters the propeller hub, it senses rotational speed of the propeller, and then adjusts the oil flow to the propeller hub to change pitch and , therefore, speed of the propeller.
what is the purpose of propeller counterweights?
Centrifugal force acting on the counterweights causes the blade angle to increase.
What is meant when a propeller governor is in an "on-speed"condition?
The governor is not accelerating or decelerating and the speeder spring and flyweight forces are in balance.
How is a constant speed feathering propeller feathered?
By releasing oil pressure in the governor, the counterweights and feathering spring move the propeller into feather. This happens automatically if the governor oil pressure drops to zero or can be manually controlled by the pilot by moving the propeller control ito the feathering detent.
What is an unfeathering accumulator?
It is an oil accumulator used to provide oil pressure to unfeather a propeller.
What is "alpha range" and "beta range" and where are they found?
The alpha and beta ranges pertain to the operating modes of turboprop reversible-pitch propellers. in the alpha range, the propeller is operating in the standard, constant speed mode, which is usually in flight. In the beta range, the propeller is operating in the zero or minimum thrust range and negative thrust or reverse thrust mode, which is usually on the ground.
What systems are commonly used for propeller ice control?
Fluid (alcohol) and electrical heat applied to the propeller blade root.
What propeller repairs can be performed by a certified mechanic with a power plant rating?
Only minor repairs and alterations can be performed by a certified mechanic with a power plant rating.
How are wooden propellers generally cleaned?
With a brush or cloth and warm water with mild soap.
Where would you find the correct method and technique for cleaning an aluminum propeller and hub?
The propeller manufacturer's maintenance instructions.
What type of nondestructive testing should be accomplished to a propeller after blending?
The procedures recommended by the manufacturer.
What are the two criteria used by many manufacturers to determine the amount of bend damage that can be repaired by cold bending of aluminum propellers?
The extent of the bend and its blade station location.
How can repair file marks be removed from an aluminum propeller?
With very fine sandpaper.
When performing a static balance on a two bladed propeller, what positions must the propeller be placed in when measurements are taken?
Vertical and Horizontal positions.
What is a propeller protractor used for?
It is used to measure propeller blade angle.
What blade conditions can cause engine vibration?
Vibration can be caused by a propeller being out of track and/or balance, as well as incorrect blade angle setting.
What is blade tracking?
Blade tracking is the position of the propeller blade tips relative to each other.
What controls both manifold pressure and r.p.m. on an engine equipped with a fixed pitch propeller?
The throttle.
What publications can be used as a guide for 100-hour inspections on aircraft engines?
Manufacturers maintenance manuals and FAR part 43, Appendix D.
How do you identify the engine serial number?
It is on the engine data plate.
prior to returning a reciprocating engine to service after a 100-hour inspection, what operational checks must be performed?
Check the power output (static and idle r.p.m.), check magnetos, fuel and oil pressure check, cylinder and oil temperature check.
Where are life-limited parts of an engine listed?
Engine maintenance manuals, Type Certificate Data Sheets, and the Airworthiness Limitations section of the instructions for continued airworthiness.
Where can engine operating limits be found?
Engine manual, engine specification, type certificate data sheet, and aircraft manufacturer's maintenance manual.
Why are hot section inspections performed on turbine engines?
To determine the integrity and wear of the hot section components.
What inspections must be performed following a turbine engine overspeed?
Consult the engine manufacturer's maintenance manual .
What inspections must be performed on a turbine engine if the exhaust gas temperature exceeds limitations?
A hot section inspection.
What FAA approvals are required when installing an engine that is not on the aircraft type certificate?
An STC (supplemental type certificate) or an FAA field approval.
Under what conditions is compliance with an engine service bulletin mandatory?
When an airworthiness directive references the service bulletin or when compliance is part of the approved operating specifications for a commercial or air carrier operator. When engine or component overhaul procedures require compliance at time of overhaul.
What are the possible causes for a turbojet or turbofan engine having high exhaust gas temperatures, low r.p.m., and high fuel flow at all engine pressure ratios?
Turbine damage or loss of turbine efficiency due to wear.
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