The Aeroplane Engine

Question 1

What are the two main types of engine?

Answer 1

Piston/reciprocating Gas turbine (jet)

Question 2

Name the 5 main types of piston engine cylinder configuration

Answer 2

Radial In-line upright In-line inverted Horizontally opposed Vee

Question 3

Picture the location and purposes of the following:

Inlet valve

Combustion chamber

Outlet valve

Spark plug

Cylinder

Piston

Connecting rod

Crankshaft

Answer 3

Question 4

What piston configuration is most common in light aircraft?

Answer 4

Horizontally opposed

Question 5

Name each stage of the four-stroke engine cycle

Answer 5

Intake

Compression

Power

Exhaust

Question 6

What is the compression ratio?

Answer 6

The total difference between the cylinder volume at BDC and the clearance volume when at TDC

Question 7

At what stage does the spark ignition take place?

Answer 7

Shortly before TDC

Question 8

How is valve timing controlled?

Answer 8

By a camshaft rotating at half speed, gear-driven by the crankshaft

Question 9

What is meant by valve lead and valve lag?

Answer 9

The premature and delayed opening and closing of valves during intake stroke in order to allow for maximum fuel amount prior to combustion

Question 10

What is ‘valve overlap’?

Answer 10

The brief period during which the inlet valve and the exhaust valve are open at the same time

Question 11

Describe generally, the ignition system in a single piston aircraft

Answer 11

Most usually have dual, independent ignition systems supplying each spark plug

Question 12

What supplied the high tension current for each spark plug?

Answer 12

Magnetos

Question 13

What drives the magnetos?

Answer 13

The magnetos are mechanically driven by the engine

Question 14

Describe the structure and operation of a magneto

Answer 14

• A magnet rotated near a conductor
• Coil of wire wound around the conductor
• Rotation of magnetic field causes a current through the coil
• Transformer (coil with many more turns) is wound around the primary coil
• Transformer creates higher voltage, which is fed to spark plugs
• Spark jumps across electrodes

Question 15

How is the charge in a magneto timed?

Answer 15

• Specifically placed breaker points in the primary coil are forced open and shut by a small cam
• The sudden collapse of the current in the primary coil creates a large current in the secondary coil

Question 16

What regulates the timing of the distribution of electricity to each spark plug?

Answer 16

The distributor

Question 17

How many times must a cylinder fire (per revolutions)?

Answer 17

Once in every two revolutions

Question 18

How is the timing of the distrubutor regulated?

Answer 18

It has a rotor which is geared to the crankshaft in such a way that it turns once for every two turns of the crankshaft

Question 19

What is an ignition harness and what is its purpose?

Answer 19

The name for ignition leads being bound together

Question 20

Leakage of current from the ignition harness will lead to…

Answer 20

Rough running

Question 21

What effect may altitude have upon ignition harnesses?

Answer 21

It may create rough running without current leakage

Question 22

How must the ignition harness be included in a pre-flight inspection?

Answer 22

It must be checked for chafing and heat-cracking

Question 23

How is the electric starter motor powered?

Answer 23

By the battery

Question 24

Describe the current between the battery and the starter motor

Answer 24

It is very high and requires heavy duty wiring

Question 25

What would be the impact of the ignition switch being directly connected to the starter circuit?

Answer 25

The required high voltage would result in very heavy cabling, heavy weight, significant loss of charge over a small distance and high energy currents in the cockpit environment

Question 26

How are the dangers of connecting the ignition to the starter circuit avoided?

Answer 26

The connection from the battery to the starter motor is remotely controlled by a solenoid-activated switch