Lesson 1 Piston Engines

Question 1

What is the equation for calculating power in a piston engine?

Answer 1

Power = Torque x RPM

Question 2

Piston engines produce power by converting what two types of energy?

Answer 2

Chemical energy into Mechanical energy

Fuel and air are burned in a confined space (cylinder) to release energy in the form of heat which raises pressure and moves the piston to create a mechanical movement. Mechanical energy drives the propeller which accelerates air rear wards to produce thrust

CHEMICAL to HEAT to PRESSURE to MECHANICAL

Question 3

POWER = ____ x ____

Answer 3

TORQUE X RPM

Question 4

TORQUE = ____ x ____

Answer 4

FORCE x DISTANCE

Question 5

FORCE = ____ x ____

Answer 5

PRESSURE x AREA

Question 6

A piston engine draws in air and mixes it with fuel to create what?

Answer 6

Charge

The charge combusts and is ignited by a spark plug to generate heat.

Heat generates pressure

Pressure drives piston downwards

Question 7

How many full rotations are there if the crankshaft in a 4 stroke cycle?

Answer 7

Two full turns through 720deg

Question 8

One movement between TDC and BDC is called what?

Answer 8

Stroke

Question 9

Name the four cycles of a stroke:

Answer 9

INDUCTION
COMPRESSION
POWER
EXHAUST

I . C . P . E .

Question 10

Are torque and speed proportional or inversely proportional?

Answer 10

Inversely proportional

The rated output of a motor is a fixed value. As speed increases the torque decreases to maintain a constant power output. As speed decreases, torque increases proportionally to maintain the same output.

Question 11

The “working fluid” of all combustion engines is ____?

Answer 11

Air

Question 12

A piston engine has what type of movement?

Answer 12

Reciprocal.

The crankshaft converts linear motion into rotary motion. The up and down motion of the piston is called reciprocal movement hence RECIPROCATING ENGINE

Question 13

Does ignition take place before, at or after TDC?

Answer 13

Just before to take advantage of INEFFECTIVE CRANK ANGLE

Question 14

The part of the piston movement around TDC and BDC where there is very little movement compared to rotation of crankshaft is called what?

Answer 14

Ineffective crank angle

Question 15

Name the Piston Cycle:

Inlet valve still open as compression stroke begins and beyond BDC.
As piston comes out of BDC inlet valve starts to close and combustion can happen

Answer 15

INLET VALVE LAG

Keeping the valve open beyond BDC ensures that the mixture continues to flow into the cylinder even though the piston is barely moving.

Question 16

Name the Piston Cycle:

As exhaust stroke comes to an end, but before TDC, the inlet valve opens.

Answer 16

INLET VALVE LEAD

Opening the valve before TDC is valve lead. This allows fresh mixture into the cylinder before the start of the induction stroke.

Question 17

Name the Piston Cycle:

Both valves closed at start of power stroke
Most work done before BDC in power stroke
Exhaust valve opens before end of power stroke

Answer 17

EXHAUST VALVE LEAD

Question 18

Name the Piston Cycle:

Exhaust valve remains open until slightly after TDC
Remaining exhaust gas exits under its own momentum

Answer 18

EXHAUST VALVE LAG

Longer period available to clear cylinder of waste gas helped by residual pressure

Question 19

Where does valve overlap happen?

Answer 19

Around TDC between EXHAUST and INDUCTION stroke

Question 20

The period when both inlet and exhaust valves are open at the end of the exhaust stroke and start of the induction stroke is known as what?

Answer 20

VALVE OVERLAP

Overlap of exhaust gases exiting the cylinder helps to draw in fresh mixture.

Question 21

When is ignition timed to occur during the stroke to maximise ignition occurring at peak pressure?

Answer 21

Just before TDC.

This increases peak pressure and maximises power generated on the power stroke

Question 22

What speed does the camshaft rotate in relation to the crankshaft?

Answer 22

Half, 50%

Question 23

The distance from the centre of the crankshaft to the centre of the crank pin is called what?

Answer 23

The THROW

Question 24

How many Throws in a Stroke

Answer 24

Two

Question 25

The starter operating light must go out within how long to indicate that the starter motor has disengaged with the flywheel?

Answer 25

30 seconds

Question 26

What does impulse coupling give you?

Answer 26

HIGH ENERGY RETARDED SPARK

Question 27

What two checks need to be carried out on the magnetos?

Answer 27

DEAD CHECK
DROP CHECK

If either reveals an issue the aircraft must be shut down and the fault logged in the AML

Question 28

How do you carry out a DROP CHECK?

Answer 28

At 1000-1200RPM switch magnetos off in turn. Monitor for a drop in RPM and change in engine sound.

If ok increase RPM to 75% of max (2000-2200RPM) and perform again.

Monitor RPM gauge, should drop 100-175RPM indicating normal RPM

If greater than 400RPM there may be a faulty spark plug, in which case shut down and report to AML.

Question 29

How do you carry out a DEAD CHECK?

Answer 29

Carry out after DROP CHECK and when engine is at 75%RPM.

Briefly switch off ignition
RPM should significantly decay as magnetos are turned off
Switch ignition back on before engine stops completely

Question 30

What does correct tapper clearance ensure?

Answer 30

That the valves close completely at all operating temperatures