BOOK 04: PISTON ENGINES

The temperature of the gases within the cylinder of a four stroke engine during the power stroke will:

a) Be constant.

b) Decrease.

c) Increase.

d) Follow Charles's Law.

b

The number of revolutions of the crankshaft required to complete a full cycle in a four stroke engine is:

a) 6

b) 4

c) 2

d) 8

c

The inlet valve opens before T.D.C. in the exhaust stroke to:

a) Increase the pressure in the cylinder on completion of the induction stroke.

b) Reduce engine vibration.

c) Allow the incoming mixture to mix with a certain proportion of the exhaust gases.

d) Induce a greater amount of mixture into the cylinder.

d

The correct working cycle of a four stroke engine is:

a) Exhaust, power, induction, compression.

b) Compression, power, exhaust, induction.

c) Induction, power, compression, exhaust.

d) Power, exhaust, compression, induction.

b

Valve overlap is incorporated in the valve timing of a piston engine to:

a) Improve volumetric efficiency.

b) Reduce wear on the big end bearings.

c) Increase the engine's compression ratio.

d) Prevent a weak cut when the engine is accelerated rapidly.

a

With an increase in the rotational speed of a four stroke engine, the valve overlap:

a) Increases.

b) Decreases.

c) Remains constant.

d) Increases up to ground idle and thereafter decreases.

c

In a normally aspirated engine, exhaust back pressure:

a) Decreases as an aircraft climbs and thereby reduces the rate of decline of the engine power output.

b) Increases as an aircraft climbs and thereby reduces the engine power output.

c) Is affected by the power lever position.

d) Decreases as an aircraft descends and thereby improves the engine power output.

a

When the spark ignites the mixture:

a) The explosion pushes the piston down.

b) The mixture changes from rich to weak forward of the flame front.

c) Complete combustion occurs within 8 to 10 microseconds.

d) Temperature and pressure increase within the cylinder.

d

If the volume of a quantity of gas is halved during compression:

a) Its pressure is approximately doubled.

b) Its temperature remains constant.

c) Its mass is approximately doubled.

d) Its pressure is approximately halved.

a

The term "Indicated Mean Effective Pressure" refers to:

a) The maximum working pressure in the engine cylinder.

b) The effective working pressure in the cylinder during the power stroke.

c) The pressure achieved during compression.

d) The minimum working pressure applied to the piston during the cycle.

b

The degrees of rotation to complete a full cycle 'on a nine cylinder engine will be:

a) 180

b) 360

c) 720

d) 80

c

The firing interval of a six cylinder horizontally opposed engine will be:

a) 180

b) 120

c) 60

d) 360

b

Which of the following statements would be correct for a double banked radial engine?

a) There will always be an odd number of cylinders.

b) Radial engines are generally liquid cooled.

c) The linear distance from TDC to BDC will accommodate two throws.

d) Radial engines cannot suffer from hydraulicing.

c

On a four cylinder engine with a total volume of9600cc, bore area of 100cm2 and a crank throw of 10cm, what would the Compression Ratio be?

a) 7:1

b) 8:1

c) 24:1

d) 6:1

d

With an increase in outside air temperature, specific fuel consumption will:

a) Increase.

b) Decrease.

c) Stay the same.

d) Stay the same for all temperatures up to and including 15°C and thereafter increase.

a

Combustion, in a four stroke engine, theoretically occurs at:

a) A constant pressure.

b) A constant temperature.

c) A constant volume.

d) A constant velocity.

c

In a convergent duct:

a) The pressure and velocity increase, the temperature decreases.

b) The pressure and temperature decrease, the velocity increases.

c) The temperature and velocity increase, the pressure decreases.

d) The pressure and velocity remain constant, the temperature decreases.

a

During the compression stroke:

a) The temperature of the gases remains constant.

b) The volume of the gases increases.

c) The mass of the mixture decreases.

d) The mass of the mixture remains constant.

d

From Top Dead Centre (TDC) to Bottom Dead Centre (BDC) on the practical power stroke:

a) The temperature of the gases rises for a short time then decreases.

b) The pressure of the gases remains constant.

c) The temperature of the gases decreases from TDC to BDC.

d) The density of the gas remains constant.

a

In a divergent duct:

a) The velocity and temperature increase, the pressure decreases.

b) The temperature and pressure increase, the velocity decreases.

c) The temperature and pressure decrease, the velocity increases.

d) The velocity and temperature decrease, the pressure increases.

b

During the induction stroke:

a) The mixture becomes weaker.

b) The volume of the gases becomes smaller.

c) The temperature of the gases reduces.

d) The pressure of the gases increases.

c

Ideally, maximum pressure is attained within the cylinder:

a) When combustion is complete.

b) At the end of the compression stroke.

c) During the period of valve overlap.

d) When combustion temperature is at a minimum.

a

The power output of an internal combustion engine:

a) Is proportional to the volume of mixture induced into the cylinder.

b) Increases with increased humidity.

c) Falls as the charge temperature falls.

d) Is proportional to the weight of the mixture induced into the cylinder.

d

During the period of valve overlap:

a) The action of the exhaust gases flowing past the exhaust valve increases the pressure within the cylinder.

b) The temperature of the exhaust gases increases the mass of incoming mixture.

c) The action of the exhaust gases flowing out past the exhaust valve tends to reduce the pressure in the cylinder.

d) The crankshaft is moving past Bottom Dead Centre.

c

The power output of an internal combustion engine can be increased by:

a) Increasing the area of the cylinder.

b) Increasing the length of the stroke.

c) Increasing the engine R.P .M.

d) All of the above.

d

"Valve Overlap" is:

a) The number of degrees of camshaft rotation during which the inlet and exhaust valves are open at the same time.

b) The number of degrees of crankshaft movement during which the inlet and exhaust valves are open at the same time.

c) The distance the piston travels while the inlet valve remains open after B.D.C.

d) The number of degrees of crankshaft rotation during which the inlet and exhaust valves are open at the same time around B.D.C.

b

The purpose of a valve spring is to: .a) Close the valve.

b) Cause a snap opening of the valve.

c) Allow the valve timing to vary with changing R.P .M.

d) Maintain the valve clearance within tolerance.

a

Excessive blue smoke from the exhaust of a~ engine that has been warmed up to normal operating temperature may indicate that:

a) The mixture is too rich.

b) The oil pressure relief valve has stuck in the open position.

c) The piston rings are worn or stuck in their grooves.

d) The oil pressure is too low.

c

The camshaft of a horizontally opposed four stroke engine rotates at:

a) Twice engine speed.

b) Engine speed.

c) Twice magneto speed.

d) Half engine speed.

d

A reduction gear is fitted:

a) Between the camshaft and the propeller.

b) Between the pushrods and the valves.

c) Between the crankshaft and propeller.

d) Between the connecting rod and the crankshaft.

c

Prolonged use of low R.P .M. could cause contamination of the:

a) Oil filter.

b) Spark plug.

c) Carburetor.

d) Oil pump.

b

If the Starter Engaged Light remains on after engine start, you should:

a) Shut the engine down immediately.

b) Ignore it if it remains on for longer than 30 seconds.

c) Shut the engine down if the light remains on for more than 30 seconds.

d) Shut the engine down if the light remains on for more than 60 seconds.

a

The crankshaft of an 'in line' four cylinder aircraft engine:

a) Rotates at half the speed of the camshaft.

b) Will have the crank throws spaced 90 degrees apart.

c) Allows a firing order of 1-3-4-2.

d) Will not flex or twist.

c

Two valve springs are fitted to each valve:

a) To minimise camshaft wear.

b) To allow a greater cam rise.

c) To prevent valve rotation.

d) To reduce valve bounce.

d

Excessive valve clearance:

a) Will prevent the valve closing completely.

b) Is eliminated when the engine reaches working temperature.

c) Will cause the valve to open early and close late.

d) Will cause the valve to open late and close early.

d

Valve lead occurs when:

a) The inlet valve opens before bottom dead centre.

b) The exhaust valve opens before the inlet valve.

c) The exhaust valve opens before top dead centre.

d) The inlet valve opens before top dead centre and the exhaust valve opens before bottom dead centre.

d

Insufficient tappet clearance at the inlet valve would cause:

a) The valve to open early and close late.

b) The valve to open late and close early.

c) The mixture in that cylinder to be weak.

d) Misfiring.

a

The length of the stroke is:

a) Equal to the length of the cylinder.

b) Determined by the size of the piston.

c) Equivalent to twice the crank throw.

d) Inversely proportional to the engine power output.

c

Tappet clearance is measured between the:

a) Push rod and the valve tip.

b) Valve tip and the rocker pad.

c) Valve spring and the rocker pad.

d) Valve tip and the rocker cover.

b

The number of revolutions required to complete the induction and compression stroke in a six cylinder four stroke engine is:

a) 1

b) 2

c) 6

d) 4

a

The purpose of a crankcase breather is to:

a) Maintain the oil tank pressure at atmospheric.

b) Prevent distortion of the crankcase.

c) Allow the oil to breathe.

d) Prevent pressure building up inside the crankcase.

d

Tappet clearance is provided in a piston engine to:

a) Adjust the valve timing.

b) Allow for expansion of the valve gear as the engine warms up.

c) Allow for manufacturing tolerances.

d) Prevent valve bounce.

b

Piston rings are manufactured from cast iron:

a) Because it has a negative coefficient of expansion.

b) To take advantage of its extreme malleability.

c) Because of its self lubricating qualities.

d) To take advantage of its brittleness.

c

The exhaust valves:

a) Are opened directly by the action of push rods which are in tum operated by cams on the crankshaft.

b) Are less affected by the heat of combustion than the inlet valves.

c) Are opened by the valve springs and closed by the rocker gear.

d) Sometimes have their stems partly filled with sodium to assist cooling.

d

Hydraulic valve tappets are used on some engines to:

a) Eliminate valve bounce.

b) Eliminate constant valve adjustment and checks.

c) Give a more positive closing action.

d) Give a more positive opening action.

b

The swept volume of a cylinder is:

a) The area of the piston crown x the stroke.

b) The area of the cylinder cross section x the cylinder length.

c) Half of the clearance volume.

d) The total volume + the piston volume.

a

The thermal efficiency of a piston engine can be increased by:

a) Increasing the R.P .M.

b) Increasing the combustion chamber volume.

c) Advancing the ignition point into the direction of rotation.

d) Increasing the compression ratio.

d

A normally aspirated engine is one which:

a) Has four cylinders.

b) Is not supercharged.

c) Is never air cooled.

d) Is all of the above.

b

The Compression Ratio of an engine may be defined as the:

a) Swept volume + clearance volume -+- swept volume.

b) Swept volume + clearance volume -+- clearance volume.

c) Total volume - clearance volume -+- clearance volume.

d) Swept volume -+- (swept volume + clearance volume).

b

An engine has a total volume of 2,100 cm3 and a swept volume of 1,800 cm3 • Its compression ratio is:

a) 7:6

b) 6:1

c) 7:1

d) 6:7

c

Volumetric efficiency may be defined as:

a) The ratio of the volume of the mixture drawn into the cylinder during normal engine working, to the volume of the mixture which would be required to fill the cylinder under normal temperatures and pressures.

b) The ratio of the volume of air and the volume of fuel drawn into the cylinder.

c) The ratio of the volume of one of the cylinders to the volume of all of the cylinders in the engine.

d) The efficiency with which the air and fuel mix together in the cylinder.

a

The ratio of the power produced by an engine to the power available in the fuel is known as the:

a) Specific fuel consumption.

b) Indicated horse power.

c) Volumetric efficiency.

d) Thermal efficiency.

d

Specific Fuel Consumption (S.F.C.)

a) Is the inability of the internal combustion engine to use any fuel other than that specified by the manufacturer.

b) Becomes greater as the efficiency of the engine improves.

c) Is the weight of fuel used by an engine per unit horse power per unit time.

d) Increases in proportion to the thermal efficiency.

c

Brake Horsepower is:

a) Theoretical power in the cylinder.

b) Useful power at the propeller.

c) Power lost in the engine.

d) Power required to slow the aircraft down.

b

A method of improving "Volumetric Efficiency" is:

a) Valve overlap.

b) The use of carburettor heat.

c) Weakening the mixture.

d) To make the mixture richer.

a

From the following list select the correct combination of statements.

The primary task of the lubrication is to:

1. Reduce friction

2. Cool the engine

3. Clean the engine

4. Reduce component wear

5. Act as a hydraulic medium

a) 1 and 3

b) 2 and 5

c) 1 and 4

d) 1 and 5

c

In a piston engine dry sump oil system, the oil temperature and pressure are sensed:

a) When the oil is leaving the sump.

b) For the temperature when the oil is leaving the tank, and for the pressure when the oil is leaving the pressure pump.

c) For the oil temperature when the oil is entering the tank and for the pressure when it is entering the pressure pump.

d) At the same point.

b

Oil returning to the oil tank is filtered by:

a) The oil pressure filter.

b) The oil tank filter.

c) A micron size multi-bore filters assembly.

d) The scavenge filter.

d

Engine oil pressure is:

a) Low at idle R.P.M. and high at high R.P.M.

b) Controlled by the oil cooler.

c) Substantially decreased when the oil pressure relief valve opens.

d) Relatively unaffected by engine speed.

d

The purpose of the crankcase breather is to:

a) Maintain the pressure in the oil tank at atmospheric pressure.

b) Ease the task of the oil scraper ring.

c) Prevent pressure building up inside the crankcase.

d) Prevent distortion of the crankcase.

c

The most probably cause of small fluctuations in the oil pressure would be:

a) Lack of oil.

b) The pressure relief valve sticking.

c) Air in the oil tank.

d) The scavenge pump working at a greater capacity than the pressure pump.

b

The extra space in the oil tank is to cater for:

a) Frothing and aeration of the oil as it passes through the engine.

b) Fire protection.

c) The accommodation of extra oil contents on long duration flights.

d) Anti-surge action.

a

The scavenge pump system in a lubrication system has:

a) A by-pass in case of blockage.

b) A smaller capacity than the pressure pump.

c) A bifurcated tertiary drive system.

d) A larger capacity than the pressure pump.

d

In a "wet sump" oil system, the oil is contained in the:

a) Engine and tank.

b) Tank and oil cooler.

c) Sump and tank.

d) Engine and sump.

d

The oil contents of a piston engine (wet sump) are checked:

a) When the engine is running at idle power.

b) As soon as possible after the engine is stopped because the oil will drain away from the sump.

c) After approximately 15 minutes once the engine has stopped.

d) When the oil has reached a specific temperature.

c

The most efficient method for cooling a piston engine is to use ______ . However, the most common method of cooling is to use ________ because of the __________ involved.

a) air cooling; liquid cooling; reduced costs

b) liquid cooling; air cooling; reduced costs

c) fuel cooled; air cooling; reduced costs

d) liquid cooling; fuel cooling; reduced costs

b

At take off Cowl flaps should be selected:

a) Fully closed to decrease drag.

b) Open

c) Partially closed

d) Fully closed to increase drag.

b

A typical piston engine has a maximum thermal efficiency of:

a) 70%

b) 80%

c) 90%

d) 30%

d

In a four cylinder in line engine air cooled, (No 1, 2, 3, 4 from the front) the coolest cylinder while running will be:

a) 1

b) 2

c) 3

d) 4

a

The device utilised to measure temperature on a piston engine is:

a) Thermometer.

b) Barometer.

c) Thermocouple.

d) Thermostat.

c

The temperature measuring device fitted in a four cylinder in line engine, (No 1,2,3,4 from the front), would normally be fitted to which cylinder:

a) 1

b) 2

c) 3

d) 4

d

The spark appears at the plug electrodes when:

a) The contact breaker closes.

b) The contact breaker opens.

c) The contact breaker stays open.

d) The magneto switch is made.

b

The ignition switch is fitted in:

a) The primary coil circuit.

b) The secondary coil circuit.

c) The engine starter motor circuit.

d) The battery circuit.

a

When the ignition switch is placed in the 'ON' position it:

a) Isolates the breaker points.

b) Makes the engine starter motor circuit.

c) 'Earths' or 'grounds' the secondary winding.

d) Breaks the primary to earth circuit.

d

The purpose of a condenser as fitted in a magneto is:

a) To assist in the rapid collapse of the primary current and prevent arcing at the contact breaker points.

b) To prevent the rapid collapse of the primary circuit and arcing at the points.

c) To reduce the high tension voltage of the secondary circuit.

d) To earth the primary circuit.

a

The engine is checked for dead cut at:

a) A power check.

b) Slow running.

c) Cruising RPM.

d) Full throttle.

b

The distributor directs:

a) Voltage from the primary winding to the spark plug.

b) Voltage from the secondary winding to the primary winding.

c) Voltage from the magneto secondary winding to the spark plug.

d) Voltage from the secondary winding to the contact breaker.

c

To obtain a spark across the gap between two electrodes:

a) The circuit must have high EMF.

b) The circuit must have high ohms.

c) The circuit must have high current flow.

d) The circuit must have an impulse union.

a

The purpose of an ignition switch is:

a) To control the primary circuit of the magneto.

b) To prevent condensation.

c) To connect the secondary coil to the distributor.

d) To connect the battery to the magneto.

a

In a complex engine as RPM increases the ignition timing may be:

a) Advanced.

b) Retarded.

c) Not altered.

d) Only retarded.

a

An impulse starter is a device to assist in starting an engine which uses:

a) A leaf spring.

b) A coil spring to increase temporarily the speed of rotation of the magneto.

c) A special starting battery which provides a sudden impulse of electricity to the plugs.

d) An explosive inserted in a special tube.

b

If the specific gravity of a fuel is known to be 0.7, 100 gallons of it will weigh:

a) 700lb

b) 70lb

c) 7000lb

d) 7,1001b

a

A fuel grade which is used in typical aircraft engines is:

a) D.T.D.5851100

b) D.E.R.D.2479

c) AVGAS 100

d) D.E.R.D.2484

c

The "anti-knock" value of a fuel is its:

a) Degree of resistance to pre-ignition.

b) Resistance to adiabatic combustion.

c) Ability to oppose burning.

d) Resistance to detonation.

d

The differences between AVGAS 100 and AVGAS 100LL are:

Colour Anti-Knock value

a) Same Same

b) Same Different

c) Different Same

d) Different Different

c

The Octane rating of a fuel is determined by comparison with mixtures of:

a) Methane and orthodentine.

b) Heptane and iso octane.

c) Methane and iso octane.

d) Heptane and orthodentine.

b

In the internal combustion engine, detonation occurs due to:

a) The use of too high an R.P.M. with too little manifold pressure.

b) The use of the wrong grade of oil.

c) The cylinder temperatures and pressures being too low.

d) Excessive combustion temperatures and pressures.

d

The calorific value of a fuel is the:

a) Kinetic energy contained within it.

b) Heat energy in the fuel.

c) Heat energy required to raise the temperature of the fuel to its boiling point.

d) Heat energy required to raise the temperature of the fuel to its boiling point from absolute zero.

b

The octane rating of a particular grade of fuel is given as 100/130, this indicates that:

a) It will act as both 100 octane and 130 octane fuel at take off power settings.

b) With a rich mixture it will act as 100 octanes, and with a weak mixture it will act as 130 octanes.

c) Its "anti-knock" qualities are identical to iso-octane.

d) With a weak mixture it will act as 100 octane, and with a rich mixture it will act as a 130 octane fuel.

d

Tetra ethyl lead is added to some aviation fuel to:

a) Decrease its octane rating.

b) Decrease the risk of detonation.

c) Increase its calorific value.

d) Increase its specific gravity.

b

If the vent pipe of an aircraft's fuel tank becomes blocked, it will cause:

a) The pressure in the tank to fall when fuel is used.

b) The pressure in the tank to rise when fuel is used.

c) The evaporation rate of the fuel to decrease as fuel is used from the tank.

d) The fuel pressure at the carburettor to rise.

a

Detonation is liable to occur in the cylinders:

a) With an over rich mixture at idle power.

b) With a weak mixture and high cylinder head temperature.

c) With a rich mixture at high power settings.

d) At very low engine speed.

b

Pre-ignition refers to the condition when:

a) A rich mixture is ignited by the spark plug.

b) The spark plug ignites the mixture too early.

c) The mixture is ignited by abnormal conditions within the cylinder before the normal ignition point.

d) The mixture bums in the inlet manifold.

c

An exhaust gas temperature gauge is powered by:

a) 12v DC

b) 115v AC

c) 28v DC

d) A thermocouple which generates its own voltage

d

"Flame Rate" is the term used to describe the speed at which:

a) The mixture bums within the cylinder.

b) The combustion pressure rises within the cylinder.

c) Peroxide forms within the cylinder.

d) Fulminates form with the cylinder.

a

The colour of 100 / 130 grade low lead fuel is:

a) Green.

b) Blue.

c) Red.

d) Straw yellow.

b

Weakening the mixture below the best fuel/air ratio will cause the engine power to:

a) Decrease.

b) Increase initially, but decrease below take off power.

c) Increase.

d) Be unaffected by altitude increase.

a

For maximum endurance the mixture control should be set to:

a) Weak.

b) The chemically correct state.

c) Between rich and weak.

d) Rich.

a

An air/fuel ratio of 9: 1 would be considered:

a) Chemically correct.

b) Extravagant.

c) Rich.

d) Weak.

c

Because of the reduction in the density of the atmosphere associated with an increase in altitude:

a) The mixture control must be moved towards the weak position.

b) The throttle must close progressively to maintain the best air/fuel ratio.

c) The mixture must be progressively richened to compensate for the power loss.

d) The octane rating of the fuel must be increased.

a