A&P - Powerplant Oral (Jeppesen)

What is the purpose of dynamic dampers on crankshafts?

They reduce engine vibration.

What types 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? Explain.

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 ring gaps be installed relative to each other, and why?

Compression ring gaps should be staggered so that they do not 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 running?

The engine will not idle properly.

A cold cylinder is found when troubleshooting a running engine. What does this indicate?

No combustion in that cylinder.

When pulling a propeller through, a hissing sound is heard, indicating valve blow-by. What procedure should be performed next?

A compression check should be performed 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 the total time affected? When an engine is rebuilt, how is its operating history affected?

The total time on the engine must be continued and the time since major overhaul is entered into the engine log. It 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 filters/screens for metal particles.
3.Inspect the crankshaft or driveshaft 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 the 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 manufacturer's 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# 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.

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?

The inside of the cylinder.

What purpose does an 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 inspections 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?

Between the engine fuel pump and the indicator.

Name the basic components of a fuel flow system.

The transmitter and the indicator.

What unit of measure is generally used to indicate 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 rpm.

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 main difference and advantage a 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 two different methods for attaching turbine engine rotor blades to the rotor disks.

Dovetail-type 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 functions 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 horsepower?

It is an indication of the torque developed by a turboprop or turboshaft 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 conditioning, and anti-icing. Many APUs may also be used as an emergency source of in flight 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 EGTs 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 APUs to regulate compressor intake airflow?

Fuel pressure.

What is fan blade shingling?

It is the overlapping of the midspan shrouds of the fan blade.

When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coastdown?

Any rubbing sound or other unusual 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 gas turbine engine tachometers calibrated?

They are calibrated in percent rpm.

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 temperature 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 boot 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 noxious gases.

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 turbocharged engines?

The collector system.