Engine

Question 1

What function does the carburettor perform?

Answer 1

Fuel arrives under low pressure. Mixes the fuel and air correctly and controls its delivery to the cylinders.

Question 2

Fuel injection system

Answer 2

Where the fuel is injected into the inlet port under higher pressure to be mixed with the air after it has arrived at the cylinders.

Question 3

Gravity fed systems

Answer 3

Where the fuel tanks are far enough above the engine to allow the fuel to flow into the engine system by gravity alone. (high wing aircraft with carburettor equipped engines)

Question 4

Pressure or pump fed systems

Answer 4

Where the fuel tanks are not high enough to allow gravity flow, or where the engine system requires the fuel to be delivered under higher pressure. (low winged aircraft or aircraft equipped with fuel injection systems)

Question 5

Detonation

Answer 5

If fuel becomes too hot before it is ignited by the spark plugs, there is a drastic change in the way it burns. Instead of burning at a uniform rate for a given time, it explodes releasing all of its energy in an instant. At lean mixture, high power setting resulting in hot engine.

Question 6

Symptoms of detonation

Answer 6

• Rising cylinder head or oil temperature indication
• Significant power loss
• Engine vibration
• A ‘pinging’ sound coming from the engine

Question 7

To prevent detonation

Answer 7

Anything that helps cool the engine will help prevent detonation. Steps:

1. ensure the mixture control is in the fully rich position
2. reduce engine power
3. if climbing, climb at a higher IAS to improve

Question 8

Alternator

Answer 8

The alternator can be thought of as a pump. The alternator generates electrical power and pushes it through the system. Unlike the battery, it cannot store electricity. It is driven by the engine and can supply power only when the engine is running.

Question 9

The magneto

Answer 9

A magneto produces an electric current by spinning a magnet within a coil. This current is then boosted to produce the high voltage required for a spark hot enough to ignite the mixture.

Question 10

Factors affecting the engine power output (6 factors)

Answer 10

The strength of the push that acts on the piston during the power stroke depends upon:

1. The amount of gas that is induced into the cylinders
2. The temperature reached during combustion
3. The position of the throttle control
4. The engine RPM
5. Mixture condition
6. Supercharging (turbocharging)

Question 11

The octane rating of a fuel is a measure of

Answer 11

its resistance to detonation

Question 12

The pressure exerted on the piston during the power stroke increases as the amount of gas induced

Answer 12

increases and combustion temperature increases.

Question 13

Functions of the oil system

Answer 13

1. It lubricates by providing an unbroken surface to support and separate adjacent metal surfaces.
2. It cools by absorbing heat from the engine components and dissipating it to the airstream as it passes through the oil cooler.
3. It cleans by carrying microscopic particles of carbon or metal in suspension and depositing them in the filter.

Question 14

Manifold pressure

Answer 14

The amount of gas that gets into the cylinders depends upon the pressure in the inlet manifold before the valve opens.

Question 15

Carburettor ice - conditions necessary

Answer 15

• most likely when temp is below about 20 degrees

- relative humidity is above 80%

Question 16

What is the bus bar and what does it power?

Answer 16

Bus bar is a common source of electrical energy to which all of the system’s appliances are connected to including fuel pump, light, radio, flaps, nav aid.

Question 17

What is an alternator failure indicated by?

Answer 17

Indicated by a discharge on the centre-zero ammeter and the illumination of the warning light.

Question 18

Why is impulse coupling necessary and how does it work?

Answer 18

When the engine is turning very slowly such as during cranking for start-up, the magneto is not spinning fast enough to produce a spark. Impulse coupling is provided to overcome this. Impulse coupling is a spring mechanism which delays the spark until it gets closer to the full compression of the cylinder. As the engine turns during start up, part of the shaft turns with it, while the part that drives the magnet remains stationary. As the part of the shaft continues to turn a strong spring is wound until, at the appropriate time, a trigger releases the spring and the part that drives the magnet flicks quickly to catch up.

Question 19

spark plug fouling

Answer 19

During long periods at taxi power and idling, the engine temperatures are low enough to allow some of the oil to remain unburnt in the cylinders. Unburnt oil pools in the lowest part of the cylinder. If this oil forms drops across the spark plug electrodes, it will conduct the high voltage current across the gap preventing the spark from occurring.

Question 20

What is the function of the battery?

Answer 20

A battery should do nothing except start the engine. Its only function after that is to stand by in case the alternator should fail. The battery stores electrical energy for use if the alternator should fail.

Question 21

What is the function of the alternator?

Answer 21

The alternator supplies all electrical demands of the system during flight and keep the battery fully charged.

Question 22

What is the purpose and function of the cylinders?

Answer 22

The cylinder is made up of two parts, the cylinder head which contains valves and ports by which the fuel-air mixture enters and exits, spark plugs which ignite it, and the cylinder barrel. The cylinders are responsible for powering the four-stroke cycle of induction, compression, power and exhaust.

Question 23

What is the purpose and function of the pistons?

Answer 23

The piston slides up and down inside the barrel in accordance with each of the strokes, to either let the mixture fill the cylinder, compress the mixture or release the mixture.

Question 24

What is the purpose and function of the piston rings?

Answer 24

Piston rings reduce friction and form a gas-tight seal preventing high pressure gas from leaking past.

Question 25

What is the purpose and function of the inlet/exhaust valves?

Answer 25

The inlet valve controls the flow of gas into the engine through the inlet port, the exhaust valve controls the flow of gas out of the engine through the exhaust port.

Question 26

What is the purpose and function of the crankshaft?

Answer 26

The crank shaft is attached to the connecting rod which is attached to a pin inside the piston allowing it to move. The connecting rod converts the up and down motion of the piston to the rotary motion of the crankshaft. The propellers is usually attached directly to the crankshaft so that it spins at the same rpm as the engine.

Question 27

What is the purpose of the camshaft?

Answer 27

Controls the valve. When the cam on the rotating camshaft passes under the push rod it lifts the push rod up forcing it to lift one end of the rocker arm. As the rocker arm pivots about its hinge it forces the valve to open against the vale spring.

Question 28

Function of the throttle?

Answer 28

controls the amount of fuel provided to the engine.

Question 29

What is the function of the propeller?

Answer 29

As the propeller rotates air accelerates over the front surface, causing a reduced static pressure ahead of the blade, this results in forward thrust, which pulls the aircraft along.

Question 30

What is the function of a circuit breaker?

Answer 30

A circuit breaker is a device placed between the bus bar and the appliance to prevent too much current flowing. When too much current flows the circuit breaker pops out.

Question 31

What is the function of a fuse?

Answer 31

A fuse is a device placed between the bus bar and the appliance to prevent too much current flowing. When too much current flows the fuse melts.

Question 32

What is the function of the oil cooler?

Answer 32

The oil cooler is a radiator, which as oil passes through it, carries the heat away by the outside air which is directed to the cooler via a duct.

Question 33

Purpose of a fuel tank vent?

Answer 33

It allows air to flow into the tank to replace the fuel as it is used, this provides a positive pressure in the tank by transferring the total pressure of what the outside air stream to the inside of the tank.

Question 34

What is the result of a blockage in the fuel tank vent (in a gravity fed fuel system)?

Answer 34

Decreased fuel flow, as the fuel can continue to flow to the engine only if air is allowed to flow into the tank to replace it. A blockage of the fuel tank vent can cause the fuel to stop flowing.