A&P - Powerplant Oral (Jeppesen)

What is the purpose of dynamic dampers on crankshafts?

To 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?

Piston ring gaps should be spread apart and not lined up. 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?

After an overhaul, the total engine time stays the same, and time since overhaul starts over.

If the manufacturer rebuilds the engine, it gets zero time and is treated like a new engine with no previous history.

What inspections should be performed after a propeller strike without sudden stoppage?

inspect the engine mounts, crankcase, nose, oil and filters for metal, and 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 install a tail stand if needed.

When inspecting a piston, where are cracks most likely to be found?

Cracks are found in high-stress areas, such as the base of the piston bosses, where the bore meets 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, inside micrometer, or telescopic gauge with micrometer, taking readings 90° apart.

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?

It checks metal particles in the oil to see engine wear and find problems early

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 and is calibrated in inches of mercury (inHg)

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?

Sudden oil pressure drop while oil temperature is normal and oil level is 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 has a large fan that bypass some air around the engine core to help produce thrust.

Advantage: It gives more thrust while using less fuel than a turbojet.

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?

two compressor rotor shafts connected to the turbine section, one inside the other, also called twin spool compressor.

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

What is the purpose of the interconnecting tubes attached between can-type combustion chambers?

To allow flame to spread during engine start.

What functions do axial flow turbine nozzles perform?

They direct the 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 disk or by cutting grooves in the disk.

What are carbon seals used for in turbine engines?

used as oil seals for the rotor shaft bearings

What is shaft horsepower?

is the torque developed by a turboprop or turboshaft engine.

What is the purpose of an APU?

Provides electrical and pneumatic power (bleed air) on the ground when engines are not running, and may also supply emergency electrical power in flight.

Name the main components of a typical APU.

A small turbine for power and bleed air, and 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?

APU operates at constant speed, and fuel control adjusts fuel flow to maintain that speed

What is used to prevent a heavily loaded A.P.U. from exceeding its maximum EGT?

A load control valve

How is an APU shut down and why is this procedure used?

The APU is shut down after unloading and is kept running for about three minutes to cool down and prevent thermal shock damage.

What powers the variable inlet guide vanes used on some A.P.U. to regulate compressor intake airflow?

Fuel pressure.

What is fan blade shingling?

It’s overlapping midspan shrouds of 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 dirt and contaminants to improve engine performance. Common methods are fluid wash and grit wash.

How can you tell if a turbofan or turbojet engine is out of trim?

There will be a high EGT at 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.
decreases turbine engine performance

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 it indicate the thrust developed by the engine.

On a turbine engine, what does exhaust gas temperature (EGT) indicate and how is it obtained?

EGT shows the average temperature of exhaust gases and is measured 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 produce full power or may not run at all. This may also indicate a dirty air filter.

How does induction icing affect engine performance?

It causes a reduction in power and unstable engine 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?

carburetor heat (preheater)
Raise the temperature of induction air with a preheater.

What causes fuel evaporation ice?

caused by fuel cooling the air as it evaporates, which can form ice.

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 produce full power and may not reach critical altitude.

What function does a turbocharger waste gate perform?

It controls how much exhaust gas goes to the turbocharger, which controls boost pressure.

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?

Most common ways are mechanical linkage or an oil-pressure actuator

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 speeds up incoming air so debris cannot follow the curved path to the engine and is separated 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?

The exhaust system removes hot and harmful 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?

is loss of horsepower due to exhaust 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.