Fuel + Fuel Systems Flashcards
As mixture is progressively leaned from full rich condition, the engine will experience
[a] best power, then rough running, then peak exhaust gas temperature
[b] best economy, then best power, then rough running
[c] best power, then best economy, then rough running
[d] peak exhaust gas temperature, then best power, then best economy
C
The extra fuel supplied at the fully rich mixture setting assists in cooling the engine,
but it also reduces the combustion temperature. As mixture is leaned from fully rich
with a constant throttle setting, power output increases to produce best power.
Further leaning causes a drop in power, but also a drop in fuel consumption. Economy,
ie miles per gallon, increases until best economy is achieved. Finally, after the peak
combustion temperature is reached, the mixture becomes too lean to burn, producing
lean misfire.
If mixture is correctly set to peak EGT, moving the mixture control to fully rich with throttle setting unchanged,
will cause power output to
[a] decreases continuously
[b] increase then decrease
[c] increase continuously
[d] decrease then increase
B
Best power always occurs between peak exhaust gas temperature and fully rich. Power
output will increase until best power is achieved, then it will decrease as the mixture
control continues to move toward fully rich.
If mixture is correctly set for best power, an increase in altitude with no adjustment in mixture or throttle position
will produce
[a] a richer mixture and less power
[b] a leaner mixture and less power
[c] no change in mixture strength
[d] a richer mixture and more power
A
Efficient combustion requires the correct ratio between fuel and air. Increased altitude
reduces the mass of air induced because the outside air density is lower. If the amount
of fuel metered is not reduced, the mixture will become richer and power will reduce.
Operating an engine with high power and the mixture very lean can cause
[a] plug fouling and overheating
[b] backfiring and overheating
[c] backfiring and low temperatures
[d] a decrease in indicated air speed and low temperatures
B
Lean mixtures take longer to burn. The slow burning charge is pushed back up into the
cylinder head during the exhaust stroke, increasing engine temperature. As the inlet
valve opens for induction, the still-burning charge ignites the fresh mixture in the inlet
manifold causing backfiring.
On application of carburettor heat when ice is present, the manifold pressure will
[a] drop initially, then slowly increase
[b] rise initially, then slowly decrease
[c] drop continuously
[d] drop initially and remain at the lower value
A
Ice takes some time to melt. Initially, the engine will suffer from hot air and ice. The
manifold pressure will drop and then begin to rise again as the ice melts. The manifold
pressure will return to normal when the carburettor heat is returned to the cold position
after the ice has melted.
For take off under very high altitude conditions
[a] the mixture must be left fully rich
[b] the mixture must be leaned to peak EGT
[c] the mixture should be leaned to best economy
[d] fully rich may be too rich and the mixture should be leaned to smooth running
D
A high strip and a hot day combined with fully rich mixture at take-off power, can
produce a mixture which is far too rich. Some leaning may be required to restore
smooth running. This should only be considered in extreme cases and then only after
checking the manufacturers recommendations.
If throttle and mixture levers remain unchanged during a long climb from sea-level, the power available will
decrease because
[a] the decreased air density produces a leaner mixture
[b] volumetric efficiency reduces and mixture becomes too rich
[c] a richer mixture produces rising cylinder head temperatures
[d] decreased air density provides too little cooling of the engine
B
The reducing ambient air density reduces the mass of air induced during the induction
stroke, ie the volumetric efficiency is reduced. If no adjustment is made with the
mixture control, the resulting mixture will be too rich.
Take off power is
[a] the same as maximum continuous power
[b] higher than maximum continuous power but may be used providing the mixture is fully rich
[c] used for short periods such as at take off with a time limit of about three minutes
[d] used only during an emergency take off
C
Take off power represents more than 100% power. Because of the increased engine
temperatures and decreased cooling airflow at take off, a time limit is normally
imposed.
The purpose of a booster pump is
[a] to provide extra power at take off
[b] to transfer fuel from one tank to another
[c] to prevent the mixture from becoming too lean at high altitude
[d] to guard against fuel vapour accumulation [ vapour locking]
D
Booster pumps assist the fuel to flow through the lines without breaking up into
bubbles of vapour. This is especially likely when demand is high and the fuel is warm.
One disadvantage of a carburettor as compared to a fuel injection system is
[a] uneven mixture distribution to the cylinders
[b] it is prone to fuel vaporisation
[c] it requires a high pressure prime pump for starting
[d] its relatively high cost
A
Low atmospheric pressure also encourages vapour formation.
The carburettor mixes fuel and air some distance away from the cylinders. Initially,
much of the fuel is still in the form of liquid droplets. If some of these droplets stick to
the walls of the pipes, the mixture strength can change on route to the cylinders.
Because the induction pipes running to the cylinders from the carburettor are not all
the same length, mixture strength can vary from cylinder to cylinder [not a serious
problem in smaller engines].
If an engine is flooded and difficult to start, an appropriate technique would be
[a] crank continuously and swear like mad
[b] mixture fully rich, throttle closed and crank
[c] mixture to idle cut off, throttle wide open, crank and re-set after start
[d] crank initially with magnetos off, then turn magnetos on
C
If mixture is too rich to burn, the situation can be remedied by cutting off the fuel
supply and providing maximum airflow. Again the manufacturer’s recommendations
should be considered and use of the starter motor should be limited to short periods to
prevent overheating.
Application of carburettor heat when no ice is present on an engine fitted with a CSU will be accompanied by
[a] an initial drop, then an increase in manifold pressure at constant RPM
[b] a drop in manifold pressure and RPM
[c] a drop in manifold pressure with constant RPM
[d] an initial drop, then an increase in manifold pressure and RPM
C
The initial drop is caused by the introduction of hot air into the induction system. If no
ice is present, the drop will be observed while ever the carburettor heat is applied.
There will be no subsequent change in manifold pressure due to melting ice. The
propeller governor will maintain constant RPM throughout.
The colour of pure gasoline is
[a] green
[b] red
[c] blue
[d] clear
D
Pure gasoline is actually a colourless liquid.
The colour of 100/130 AVGAS is
[a] green
[b] red
[c] blue
[d] clear
A
The colour is a dye introduced to assist in visual identification.
The colour of 100 octane low lead aviation fuel is
[a] green
[b] red
[c] blue
[d] clear
C
The colour is a dye introduced to assist in visual identification.
One difference between an exhaust gas temperature gauge and a cylinder head temperature gauge is that
[a] the exhaust gas temperature gauge responds more slowly to combustion temperature change
[b] the cylinder head temperature gauge responds more slowly to combustion temperature change
[c] the exhaust gas temperature gauge is always colour coded
[d] the cylinder head temperature gauge is a better indicator of mixture condition
B
The cylinder head temperature gauge is connected to the cylinder body, usually at one
of the spark plugs. A large metal object such as a cylinder, cannot suddenly change its
temperature, so changes in combustion temperature take time to be reflected as
changes in cylinder head temperature. The exhaust gas temperature gauge [EGT], on
the other hand, senses temperature via a thin metal probe in an exhaust pipe. It is able
to change its temperature almost immediately the temperature of the exhaust gas
changes. This gives the pilot a much more direct indication of mixture condition.
The theoretical maximum range [nil wind], for a piston engine aeroplane is obtained by operating at the IAS that produces the best lift/drag ratio and flying:
[a] as low as possible
[b] as high as possible
[c] at full throttle height
[d] with fully rich mixture.
C
Full throttle height is the height at which the use of full throttle produces the required
power. Since most light aircraft enjoy the best lift/drag ratio at a speed of about 65 or
70 knots [best gliding speed], full throttle height would be the height at which the use
of full throttle produced that IAS. This is purely a theoretical consideration as the fuel
used to climb to such a height would probably be more than you would save by being
there!
The fuel flow gauge on many general aviation aeroplanes actually measure fuel pressure with a transducer and
indicate an equivalent fuel flow. One consequence of this is
[a] the gauge is absolutely reliable as an indicator of fuel flow since fuel flow and fuel pressure must
always be proportional to each other
[b] the gauge does not measure fuel flow directly and may give incorrect readings if the filters or
discharge nozzles become blocked.
[c] the gauge is absolutely reliable at normal power setting but may be incorrect at high power
[d] the gauge is likely to over read at high power settings
B
Many small engines use a fuel flow gauge which actually measure fuel pressure and
displays it on a gauge calibrated in flow. Such a system assumes that the fuel flow is
proportional to fuel pressure. This is a pretty safe bet provided the size of the orifice in
the injector nozzle or fuel lines remains the same. Any partial blockage due to dirt will
cause pressure to rise while flow actually falls. The pilot will usually notice a fluctuation
in fuel pressure.
When using the carburettor heat control on an engine not fitted with a CAT gauge you should -
[a] use only enough heat to melt the ice.
[b] use partial heat throughout the flight to prevent ice from forming.
[c] use full heat only if the engine is at low power or at idle.
[d] use full heat when gliding or when symptoms are noticed and then return to the ‘off’ position.
D
The correct technique without a CAT gauge is to wait until the symptoms appear and
then apply full carburettor heat to melt the ice. Return the control to ‘off’ and repeat if
symptoms reappear. It is good practice to apply full heat whenever the aircraft is
gliding as a preventitive measure.
The flight manual specifies that the fuel required for the aircraft is 100LL. During a daily inspection you notice
that the fuel obtained in the fuel drain is red. Engine operation with this fuel would be:
[a] normal since 100LL should be that colour.
[b] likely to result in reduced engine performance and detonation.
[c] likely to result in oil fouling of the spark plugs.
[d] likely to result in overboosting and engine damage.
B
A red colour indicates that the fuel is Mogas. This is normal motor car fuel and is not
permitted for use in aircraft engines unless it is specifically indicated in the aircraft’s
flight manual. If Mogas is used in an engine that normally requires 100LL, reduced
performance and detonation is likely.
Fluctuating fuel pressure indications when all other instrument indications are normal is a likely indication of;
[a] fuel vaporization
[b] detonation
[c] carburettor ice
[d] overboosting
A
As the vapour pockets pass through the system the fuel pressure falls to zero. It then
returns to normal when fuel passes through. This causes fluctuating pressure readings.
The colour of 100 octane low lead aviation fuel is
[a] green
[b] red
[c] blue
[d] clear
C
The colour is a dye introduced to assist in visual identification.
Throttle ice is the name given to ice that forms as a result of:
[a] adiabatic cooling due to the sudden pressure drop across the throttle butterfly
[b] supercooled water droplets striking the external components of the induction
system
[c] the cooling effect of evaporating fuel
[d] flying when the outside air temperature is below freezing.
A
Adiabatic cooling occurs when a gas suffers a sudden pressure drop. The pressure
behind the throttle is much lower than the pressure before it - especially when the
throttle is closed as in a glide descent.
Vaporising of fuel in the fuel lines (vapour locking), can be caused by
[a] high engine temperatures and high power
[b] excessively lean mixtures
[c] using the boost pump at low engine power
[d] using rich mixtures at high altitudes
A
The hotter the fuel and the faster it is pulled through the fuel lines, the more likely it is
break down into vapour.
