Propellers Flashcards
The manifold pressure gauge on an inoperative engine would be expected to read
[a] 1013.2 hPa
[b] zero
[c] the ambient atmospheric pressure
[d] 30 Hg”
C
The manifold pressure gauge is simply a barometer which reads the pressure in the
inlet manifold between the throttle butterfly and the inlet valve. When the engine is
inoperative, the ambient atmospheric pressure floods into the inlet manifold since it is
open to the outside atmosphere.
If a propeller governor senses overspeed it will move the propeller blades towards
[a] fine pitch and increased propeller torque
[b] coarse pitch and increased propeller torque
[c] fine pitch and decreased propeller torque
[d] coarse pitch and decreased propeller torque
B
It is useful to think of the propeller as a brake on the engine [which it is in fact]. If the
governor senses overspeed, it sends a command to the propeller hub to ‘put the brakes
on’. The propeller moves towards coarse pitch, which increases the aerodynamic drag
[called propeller torque]. This makes the propeller more difficult to turn.
If a failure in the propeller hub of a CSU caused the blades to lock into one pitch setting the RPM would
[a] slowly increase to the red line
[b] gradually decrease
[c] change whenever engine power changed
[d] fluctuate
C
If the blades were unable to change their pitch the commands of the governor would be
ignored. The propeller would behave exactly like a fixed pitch propeller. It would
change its RPM whenever engine power or TAS changed.
When power is increased on an engine fitted with a CSU it is good practice to
[a] increase RPM before manifold pressure
[b] increase manifold pressure before RPM
[c] increase both manifold pressure and RPM together
[d] increase manifold pressure only with constant RPM
A
The idea is to try to avoid a combination of high manifold pressure and low RPM
beyond the recommendations of the manufacturer. The high manifold pressure means
the gas is pushed strongly towards the cylinder, while the low RPM means that the
inlet valve is open for a longer time. This results in overboosting.
Overboosting of an aircraft engine is most likely to occur
[a] when high manifold pressure and low RPM is used
[b] when the engine RPM is allowed to become too high
[c] when low manifold pressure and high RPM is used
[d] when low manifold pressure and low RPM is used
A
The idea is to try to avoid a combination of high manifold pressure and low RPM beyond the recommendations of the manufacturer. The high manifold pressure means the gas is pushed strongly towards the cylinder, while the low RPM means that the inlet valve is open for a longer time.
A turbocharger allows even higher manifold pressures to be achieved, increasing the likelihood of overboosting. The engine manufacturer publishes the combinations of manifold pressure and RPM that are permitted. The pilot should be sure to comply with these recommendations.
If an aeroplane fitted with a constant speed propeller suffered carburettor icing during cruising flight
[a] as the ice built up in the carburettor the RPM would drop
[b] the RPM would remain the same but the manifold pressure would drop
[c] both the RPM and the manifold pressure would drop
[d] both the RPM and the manifold pressure would remain the same
B
This is an important one! As the ice builds up in the carburettor the effect is exactly the
same as closing the throttle. But if the pilot made no adjustment to the pitch control
lever, the governor would move the propeller blades into a finer pitch to keep the RPM
constant. The pilot would not notice any change in RPM, but the manifold pressure
would drop as less air is being admitted past the throttle butterfly.
When carburettor heat is applied in an engine fitted with a CSU the presence of carburettor ice would be confirmed
by
[a] a drop in manifold pressure with no further change at constant RPM
[b] a drop in manifold pressure and RPM with no further change
[c] a drop in manifold pressure followed by a slight rise at constant RPM
[d] a drop in RPM with no further change at constant manifold pressure
C
Hot air is less dense than cold air. Hot air is directed to the carburettor when carburettor
heat is applied. Because ice takes a little time to melt, the first indication is a drop
in manifold pressure as both hot air and ice is present. As the ice melts, the manifold
pressure rises a little. The carburettor heat is returned to cold, when all of the ice has
melted and the manifold pressure increases to the normal figure.
If an engine fitted with a CSU is at cruise power and the throttle is closed slightly, the propeller will
[a] seek a finer pitch with a drop in RPM
[b] seek a finer pitch with and increase in RPM
[c] seek a coarser pitch at constant RPM
[d] seek a finer pitch at constant RPM
D
The governor will prevent a change in RPM by seeking a finer pitch.
Failure of the speeder spring in the governor of a CSU will cause the blades to move
[a] fully coarse with a drop in RPM
[b] fully fine with a rise in RPM
[c] fully coarse with a rise in RPM
[d] fully fine with a drop in RPM
A
The governor will be ‘fooled’ into believing that the engine is overspeeding.
If the sensor lead on a manifold pressure gauge becomes disconnected while cruising at an altitude of 5000 feet, the instrument would be expected to read approximately
[a] zero
[b] 30 Hg”
[c] 1013 hPa
[d] 25 Hg”
D
It will simply read the ambient atmospheric pressure.
If the pitch control lever on a normally aspirated engine fitted with a CSU is moved to decrease RPM with no
adjustment made to the position of the throttle, the manifold pressure will
[a] remain unaltered
[b] increase
[c] decrease
[d] increase then decrease
B
The flow rate through the valves will reduce causing a ‘pile up’ of gas at the inlet.
Manufacturers publish a list of various MAP and RPM values to achieve a given power setting. The most
efficient engine performance can be expected when the pilot selects -
[a] the combination which gives the lowest MAP and highest RPM for increased volumetric
efficiency.
[b] the combination which gives the lowest RPM and highest MAP for increased volumetric
efficiency.
[c] the combination which gives the lowest MAP and highest RPM for increased compression ratio.
[d] the combination which gives the lowest RPM and highest MAP for increased compression ratio.
B
This is because low RPM allows the valves to remain open longer during the induction and
exhaust stroke thereby impoving the flow of gas into and out of the cylinders. To put it
more technically, the volumetric efficiency is improved when low RMP is used with high
MAP.
Application of carburettor heat when 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
A
The manifold pressure will drop initially as the ice takes time to melt, so for a short
while the engine suffers from hot air and ice. The manifold pressure will rise again as
the ice melts. All the while the governor will maintain constant RPM.
Note: Because the RPM remains constant, ice formation can be harder to detect
in an engine fitted with a CSU because there is very little change in engine tone.
For any given value of RPM, an increase in TAS will cause:
[a] an increase of angle of attack
[b] a decrease in angle of attack
[c] an increase of blade angle
[d] a decrease in blade angle
B
For any given value of RPM, an increase in TAS will cause a decrease in angle of attack while a decrease in TAS will produce an increase in angle of attack. The blade angle remains constant.
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For any given value of RPM, a decrease in TAS will produce:
[a] an increase of angle of attack
[b] an increase of blade angle
[c] a decrease in angle of attack
[d] a decrease in blade angle
A
For any given value of RPM, an increase in TAS will cause a decrease in angle of attack while a decrease in TAS will produce an increase in angle of attack. The blade angle remains constant.
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