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CHAPTER 4 : AIRPLANE SYSTEMS (C-152)
A. Aircraft and Engine Operations
1. What are the four main control surfaces and what are
their functions?
A. Elevators – The elevators control the movement of the
airplane about its lateral ais. The motion is called
pitch
B. Ailerons – The ailerons control the airplane’s
movement about its longitudinal axis. The mortion is
called roll
C. Rudder – The rudder controls movement of the airplane
about its vertical axis. This motion is called yaw
D. Trim Tabs – Trim tabs are small, adjustable hinged-
surfaces on the rudder, ailerons or elevator control.
They are labor-saving devices than enable the pilot to
release manual pressure on the primary control.
2. How are the various flight controls operated
The flight controls are manually actuated through use of
either a rond or cable system. A control wheel actuates
the ailerons and elevator, and rudder/brake pedals
actuate the rudder.
3. What are flaps and what is their function
The wing flaps are movable panels on the inboard trailing
edges of the wings. They are hinged so that they may be
extended downward into the flow of air beneath the wing
to increase both lift & drag.
Their purpose is to permit a slower airspeed and a
steeper angle of descend during a landing approach. In
some cases, they may also be used to shorten take-off
distance.
1
4. Describe the landing gear system on your airplane (C-
152)
The landing gear consists of a tricycle-type system
utilizing two main wheels and a steerable nosewheel.
Tubular spring steel main gear struts provide main gear
shock absorption, while nose gear shock absorption is
provided by a combination air/oil strut.
5. Describe the braking system of this aircraft
Hydraulically actuated disc-type brakes are utilized on
each main gear wheel. A hydraulic line connects each
brake to a master cylinder located on each pilot’s rudder
pedals. By applying pressure to the top of either the
pilot’s or copilot’s set of rudder pedals, the brakes may
be applied.
6. How is steering accomplished on the ground
Light airplanes are generally provided with nosewheel
steering capabilities through a simple system of
mechanical linkage connected to the rudder pedals. When a
rudder pedal is dpressed, a spring-loaded bungee (push-
pull rod) connected to the pivotal portion of a nosewheel
strut will turn the nosewheel.
7. What type of engine does your aircraft have
- Normally Aspirated (not turbo-charged)
- Direct driven
- Horizontally-opposed
- Four-cylincder,
- Air-cooled,
- Carbureted equipped engine.
The Engine is manufactured by Lycoming at 110 HP/2550 RPM
2
8. What series of operations or events must occur in each
cylinder of a typical four-stroke reciprocating engine in
order for it to produce full power
The cycle begins at Top Dead Centre (TDC), when the
piston is farthest away from the axis of the crankshaft.
A cycle refers to the full travel of the piston from Top
Dead Centre (TDC) to Bottom Dead Centre (BDC). (See Dead
centre.)
3
1. INTAKE stroke: on the intake or induction stroke of
the piston , the piston descends from the top of the
cylinder to the bottom of the cylinder, reducing the
pressure inside the cylinder. A mixture of fuel and air
is forced by atmospheric (or greater) pressure into the
cylinder through the intake port. The intake valve(s)
then close. The volume of air/fuel mixture that is drawn
into the cylinder, relative to the volume of the cylinder
is called, the volumetric efficiency of the engine.
2. COMPRESSION stroke: with both intake and exhaust
valves closed, the piston returns to the top of the
cylinder compressing the air, or fuel-air mixture into
the combustion chamber of the cylinder head.
3. POWER stroke: this is the start of the second
revolution of the engine. While the piston is close to
Top Dead Center, the compressed air–fuel mixture is
ignited by a spark plug, which ignites due to the heat
generated in the air during the compression stroke. The
resulting massive pressure from the combustion of the
compressed fuel-air mixture forces the piston back down
toward bottom dead centre.
4. EXHAUST stroke: during the exhaust stroke, the piston
once again returns to top dead center while the exhaust
valve is open. This action evacuates the burnt products
of combustion from the cylinder by expelling the spent
fuel-air mixture out through the exhaust valve(s).
9. What does the carburetor do?
Carburetion may be defined as the process of mixing fuel
and air in the correct proportions so as to form a
combustible mixture.
4
The fuel/air mixture is then drawn through the intake
manifold and into the combustion chambers, where it is
ignited. The “float-type carburetor” acquires its name
from a float, which rests on fuel within the float
chamber. A needle attached to the float opens and closes
an opening at the bottom of the carburetor bowl.
This meters the correct amount of fuel into the
carburetor, depending upon the position of the float,
which is controlled by the level of fuel in the float
chamber. When the level of the fuel forces the float to
rise, the needle valve closes the fuel opening and shuts
off the fuel flow to the carburetor. The needle valve
opens again when the engine requires additional fuel.
The flow of the fuel/air mixture to the combustion
chambers is regulated by the throttle valve, which is
controlled by the throttle in the cockpit.
Mixture control
Carburetors are normally calibrated at sea-level
pressure, where the correct fuel-to-air mixture ratio is
established with the mixture control set in the FULL RICH
position. However, as altitude increases, the density of
air entering the carburetor decreases, while the density
of the fuel remains the same. This creates a
progressively richer mixture, which can result in engine
roughness and an appreciable loss of power. The roughness
normally is due to spark plug fouling from excessive
carbon buildup on the plugs. Carbon buildup occurs
because the excessively rich mixture lowers the
temperature inside the cylinder, inhibiting complete
combustion of the fuel. This condition may occur during
the pre-take-off run-up at high-elevation airports and
during climbs or cruise flight at high altitudes. To
maintain the correct fuel/air mixture, you must lean the
mixture using the mixture control. Leaning the mixture
decreases fuel flow, which compensates for the decreased
air density at high altitude.
During a descent from high altitude, the opposite is
true. The mixture must be enriched, or it may become too
lean. An overly lean mixture causes detonation, which may
result in rough engine operation, overheating, and a loss
of power. The best way to maintain the proper mixture is
to monitor the engine temperature and enrichen the
mixture as needed.
That’s why we do a pre-descend/pre-climb checklist:
Mixture rich/ Engine gauges in the green/ Look out
5
10. How does the carburetor heat system works?
One disadvantage of the float-type
carburetor is its icing tendency.
Carburetor ice occurs due to the effect
of fuel vaporization and the decrease
in air pressure in the venturi, which
causes a sharp temperature drop in the
carburetor. If water vapor in the air
condenses when the carburetor
temperature is at or below freezing,
ice may form on internal surfaces of
the carburetor, including the throttle valve.
The reduced air pressure, as well as the vaporization of
fuel, contributes to the temperature decrease in the
carburetor. Ice generally forms in the vicinity of the
throttle valve and in the venturi throat. This restricts
the flow of the fuel/air mixture and reduces power. If
enough ice builds up, the engine may cease to operate.
Carburetor ice is most likely to
occur when temperatures are
below 21°C and the relative
humidity is above 80%. However,
due to the sudden cooling that
takes place in the carburetor,
icing can occur even with
temperatures as high as 38°C and
humidity as low as 50%.
The first indication of carburetor icing in an airplane
with a fixed-pitch propeller is a decrease in engine
r.p.m., which may be followed by engine roughness.
Although carburetor ice can occur during any phase of
flight, it is particularly dangerous when using reduced
power during a descent. Under certain conditions,
carburetor ice could build unnoticed until you try to add
power. To combat the effects of carburetor ice, engines
with float-type carburetors employ a carburetor heat
system.
Carburetor heat is an anti-icing system that preheats the
air before it reaches the carburetor. Carburetor heat is
intended to keep the fuel/air mixture above the freezing
temperature to prevent the formation of carburetor ice.
Carburetor heat can be used to melt ice that has already
formed in the carburetor provided that the accumulation
is not too great. The emphasis, however, is on using
carburetor heat as a preventative measure.
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When conditions are conducive to carburetor icing during
flight, periodic checks should be made to detect its
presence. If detected, full carburetor heat should be
applied immediately, and it should be left in the ON
position until you are certain that all the ice has been
removed. If ice is present, applying partial heat or
leaving heat on for an insufficient time might aggravate
the situation. In extreme cases of carburetor icing, even
after the ice has been removed, full carburetor heat
should be used to prevent further ice formation.
The use of carburetor heat causes a decrease in engine
power, sometimes up to 15 percent, because the heated air
is less dense than the outside air that had been entering
the engine. This enriches the mixture. When ice is
present in an airplane with a fixed-pitch propeller and
carburetor heat is being used, there is a decrease in
r.p.m., followed by a gradual increase in r.p.m. as the
ice melts. The engine also should run more smoothly after
the ice has been removed. If ice is not present, the
r.p.m. will decrease, then remain constant.
Since the use of carburetor heat tends to reduce the
output of the engine and also to increase the operating
temperature, carburetor heat should not be used when full
power is required (as during takeoff) or during normal
engine operation, except to check for the presence or to
remove carburetor ice.
11. What change occurs to the fuel/air mixture when
applying carburetor heat?
Normally, the introduction of heated air into the
carburetor will result in a richer mixture. Warm air is
less dense, resulting in less air for the same amount of
fuel.
12. What does the throttle do?
The throttle allows the pilot to manually control the
amount of fuel/air charge entering the cylinders. This in
turn regulates the engine speed and power.
13. What does the mixture control do?
It regulates the fuel-to-air ratio. All airplane engines
incorporate a device called a mixture control, by which
the fuel/air mixture ratio can be controlled by the pilot
during the flight. The purpose of a mixture control is to
prevent the mixture becoming too rich at high altitudes,
due to decreasing air density. It is also used to lean
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the mixture during cross-country flights to conserve fuel
and provide optimum power.
14. What type of ignition system does your airplane have?
Engine ignition is provided by 2 engine-driven magneto’s,
and two spark plugs per cylinder. The ignition system is
completely independent of the aircraft electrical system.
The magnetos are engine-driven self-contained units
supplying electrical current without using an external
source of current.
The magneto generates sufficiently high voltage to jump a
spark across the spark plug gap in each cylinder. The
system begins to fire when you engage the starter and the
crankshaft begins to turn. It continues to operate
whenever the crankshaft is rotating.
A dual ignition system with two individual magnetos,
separate sets of wires, and spark plugs is used to
increase reliability of the ignition system. Each magneto
operates independently to fire one of the two spark plugs
in each cylinder. The firing of two spark plugs improves
combustion of the fuel/air mixture and results in a
slightly higher power output. If one of the magnetos
fails, the other is unaffected. The engine will continue
to operate normally, although you can expect a slight
decrease in engine power. The same is true if one of the
two spark plugs in a cylinder fails.
The operation of the magneto is controlled in the cockpit
by the ignition switch.
15. What are the two advantages of a dual ignition
system?
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1. Increased safety: in case one system fails the engine
may be operated on the other until a landing can be made
safely.
2. More complete and even combustion of the mixture, and
consequently, improved engine performance; i.e. the
fuel/air mixture will be ignited on each side of the
combustion chamber and burn towards the center.
16. What type of fuel system does your aircraft have?
The fuel system is “gravity feed” system. Using gravity,
the fuel flows from two wing fuel tanks to a fuel shut-
off valve which, in the “on” position, allows fuel to
flow through a strainer and then to the carburetor. From
there, the fuel is mixed with air and then flows into the
cylinders through the intake manifold.
17. What purpose do fuel tank vents have?
As the fuel level in a aircraft fuel tank decreases, a
vacuum would be created within the tank which would
eventually result in a decreasing fuel flow and finally
engine stoppage. Fuel system venting provides a way of
replacing fuel with outside air, preventing formation of
a vacuum.
9
18. Does your aircraft use a fuel pump?
No, the fuel is transferred from the wing tanks to the
carburetor by the “gravity feed” system. The gravity
system does not require a fuel pump because the fuel in
always under positive pressure to the carburetor.
19. What type fuel does your aircraft require
100LL – color = blue
20. Can other types of fuel be used if the specified
grade is not available?
You may use fuel of a higher grade but only as a
temporary solution. In no case should you ever use a fuel
of a lower grade such as 80/87. If you must use a
different grade of fuel, use a grade as close as possible
to 100LL such as 1--/130 or 115/145, and use it only for
a short period.
21. What is the function of the manual primer, and how
does it operate?
The manual primer’s main function is to provide
assistance in starting the engine. The primer draws fuel
from the fuel strainer and injects it directly into the
cylinder intake ports. This usually
results in a quicker, more efficient
engine start.
22. Describe the electrical system in
your aircraft?
Electrical energy is provided by a
10
28-volt DC, direct-current system powered by
Engine-driven 60-amp alternator, and
24-volt battery
23. How are the circuits for the various electrical
accessories within the aircraft protected?
Most of the electrical circuits in an airplane are
protected from an overload condition by either circuit
breakers or fuses or both.
Circuit breakers perform the same function as fuses
except that when an overload occurs, a circuit breaker
can be reset.
24. the electrical system provides power for what
equipment in the aircraft?
A. Radio equipment
B. Turn coordinator
C. Fuel Gauges
D. Pitot Heat
E. Landing Light
F. Taxi Light
G. Strobe Lights
H. Interior lights
I. Instrument lights
J. Position Lights
K. Flaps
L. Oil Temperature
24. What does the ammeter indicate?
The ammeter indicates the flow of current, in ampere,
from the alternator to the battery and from the battery
to the electrical system.
11
With the engine running and master
switch on, the ammeter will indicate
the charging rate of the battery. If
the alternator has gone off-line and
is no longer functioning, or the
electrical load exceeds the output of
the alternator, the ammeter indicates
the discharge rate of the battery.
25. What function does the voltage regulator have?
The voltage regulator is a device which monitors system
voltage, detects changes, and makes the required
adjustments in the output of the alternator to maintain a
constant regulated system voltage. It must do this at low
RPM, such as taxi, as well at high RPM in flight. In a
28-volt system, it will maintain 28 volt +/- 0.5 volt.
26. How does the aircraft cabin heat work?
Fresh air, heated by an exhaust shroud, is directed to
the cabin through a series of ducts. The temperature is
controlled by mixing outside air (cabin air control) with
heated air (cabin heat control) in a manifold near the
cabin firewall. The air is then ducted to vents located
on the cabin floor.
27. What are the two types of oil available for use in
your airplane?
Mineral oil – also known as nondetergent oil. It contains
no additives. This type of oil is normally used after an
engine overhaul or when an aircraft engine is new, for
engine break-in purposes.
Ashless dispersant – Mineral oil with additives. It has
high antiwear properties along with multi-viscoisty
(ability to perform in a wide range of temperatures). It
also picks up contamination and carbon particles and
keeps them suspended so that buildups and sludge do not
form in the engine.
12
B. SYSTEMS AND EQUIPMENT MALFUNCTIONS
1. What causes “carburetor icing” and what are the first
indications of its presents?
The vaporization of fuel, combined with the expansion of
air as it passes through the carburetor, causes a sudden
cooling of the mixture. The temperature of the air
passing through the carburetor may drop as much as 15C
within a fraction of a second. Water vapor is squeezed
out by this cooling, and if the temperature in the
carburetor reaches 0C or below, the moisture will be
deposited as frost or ice inside the carburetor.
For airplane with a fixed pitch prop. the first
indication is a drop in RPM.
For airplanes with controlled-pitch (constant-speed)
propellers, the first indication is usually a drop in
Manifold Pressure.
2. What conditions are favorable for carburetor icing?
13
On dry days, or when the temperature is well below
freezing, the moisture in the air is not generally enough
to cause trouble. But if the temperature is between -6C
and + 22C with visible moisture or high humidity, the
pilot should be alert.
Also during low or closed throttle settings, an engine is
particularly susceptible to carburetor icing. That’s why
you turn the carburetor heat on when the RPM setting is
outside the green arc on the RPM gauge)
3. What is “detonation”
Detonation is caused when the fuel/air mixture is
subjected to a combination of excessively high
temperature and high pressure within the cylinder,
resulting in an instantaneous burning (explosion) of the
mixture).
This form of combustion causes a definite loss of power,
engine overheating and pre-ignition and, if allowed to
continue, physical damage to the engine.
4. What action should be taken if detonation is
suspected?
Corrective action for detonation may be accomplished by
adjusting any of the engine controls which will reduce
both temperature and pressure of the fuel charge:
A. Reduce power
B. Reduce the climb rate for better cooling
C. Enrich the fuel/air mixture
D. Open cowl flaps if available
5. What is “pre-ignition”?
Pre-ignition is defined as ignition of the fuel prior to
normal ignition, or ignition before the electrical arcing
occurs at the spark plugs.
Pre-ignition may be caused by excessively
hot exhaust valves, carbon particles or
spark plug electrodes heated to a glowing
state. In most cases these local “hot
spots” are caused by the high temperatures
encountering during detonation.
6. What actions should be taken if pre-ignition is
suspected?
14
Corrective action actions for pre-ignition include any
type of engine operation which would promote cooling:
A. Reduce power
B. Reduce climb rate
C. Enrich fuel/air mixture
D. Open cowl flaps if available.
7. During the run-up, while doing the magneto checks,
there is no drop in RPM on one of the mags. What
condition does this indicate?
The Mag is not grounding (a live mag.), or
The engine has been running on only one mag because the
other mag has totally failed.
8. Interpret the following ammeter indications:
A. Ammeter indicates a right deflection (positive)
i. After starting – Power from the battery used for
starting is being replenished by the alternator;
or, if a full-scale charge is indicated for more
than 1 min, the starter is still engaged and a
shutdown is indicated.
ii. During flight – A faulty voltage regulator is
causing the alternator to overcharge the battery.
Reset the system and if the condition continues,
terminate the flight as soon as possible.
B. Ammeter indicates a deflection to the left (negative)
i. After starting – It is normal during start. At
other times this indicates the alternator is not
15
functioning or an overload condition exists in the
system. The battery is not receiving a charge.
ii. During flight – The alternator is not functioning
or an overload exists in the system. The battery
is not receiving a charge. Possible causes: The
master switch was accidentally switched off, or
the alternator circuit breaker tripped.
9. What action should be taken if the ammeter indicates a
continues discharge while in flight?
The alternator has quit producing a charge, so the
alternator circuit breaker should be checked and reset if
necessary. If this does not correct the problem, the
following should be accomplished
A. The alternator should be turned off; pull the
circuit breaker (the field circuit will continue to
draw power from the battery.
B. All electrical equipment not essential to flight
should be turned off (the battery is now the only
source of electrical power)
C. The flight should be terminated and an landing made
a.s.a.p
10. What action should be taken if the ammeter indicates
a continuous charge while in flight (more than two needle
widths)?
If a continuous excessive rate of charge were allowed for
any extended period of time, the battery would overheat
and evaporate the electrolyte at an excessive rate. A
possible explosion of the battery could result.
Also, electronic components in the electrical system
would be adversely affected by higher than normal
voltage.
Protection is provided by an over-voltage sensor which
will shut the alternator down if an excessive voltage is
detected. If this should occur, the following should be
done:
A. The alternator should be turned off; pull the
circuit breaker (the field circuit will continue to
draw power from the battery)
B. All electrical equipment not essential to flight
should be turned off (the battery is now the only
source of power)
C. The flight should be terminated and a landing made
a.s.a.p
16
11. During a cross-country flight you notice that the oil
pressure is low, but the oil temperature is normal. What
is the problem and what action should be taken?
A low oil pressure in flight could be the result of any
one of the several problems:
1. Insufficient oil (most common problem)
2. If the oil temp continues to remain normal, a clogged
oil pressure relief valve or an oil pressure gauge
malfunction could be the culprit.
In any case, a landing at the nearest airport is
advisable to check for the cause of trouble.
12. What procedure should be followed concerning a
partial loss of power in flight?
If a partial loss of power occurs, the first priority is
to establish and maintain a suitable airspeed (best
glide). Then select an emergency landing area and remain
within gliding distance. As time allows, attempt to
determine the cause and correct it.
Complete the following checks:
1. Carburetor heat
2. Amount of fuel in each tanks (switch fuel tanks if
necessary/possible)
3. Position of Fuel Selector valve
4. Primer in & locked
5. Check magneto’s in all 3 positions: BOTH, L and R
13. What procedure should be followed if an engine fire
develops in flight?
In the event of an engine fire in flight, the following
procedures should be used:
1. Mixture “cut-off”
2. Fuel selector valve “off”
3. Master switch “off”
4. Cabin heat and vents “off”
5. Airspeed: 100 kts / increase the decent, to find an
airspeed that will provide an incombustible mixture.
6. Execute forced landing checklist
14. What procedure should be followed if an engine fire
develops on the ground during starting?
Continue to attempt an engine start as a start will cause
flames and excess fuel to be sucked back trough the
carburetor.
a. If the engine starts:
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Increase power to a higher RPM (1700) for 2 minutes
Shut-down the engine
b. If the engine does not start:
Throttle “full”
Mixture “cut-off”
Continue to try an engine start (crank the engine) in
an attempt to put out the fire by vacuum
c. If the fire continues:
Ignition “Off”
Master “Off”
Fuel selector “Off”
In all cases, evacuate the aircraft and obtain a fire
extinguisher and/or assistance
D. FLIGHT INSTRUCMENTS
PITOT/STATIC SYSTEM
1. What instruments operate off the pitot/static system?
Altimeter, Vertical Speed indicator, Airspeed Indicator
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2. How does an altimeter work?
Aneroid wafers expand and contract as atmospheric
pressure changes, and through a shaft and gear linkage,
rotate pointers on the dial of the instrument.
3. What are the limitations of a pressure altimeter?
Non-standard pressure and temperature; temperature
variations expand or contract the atmosphere and raise or
lower pressure levels that the altimeter senses.
On a warm day – The pressure level is higher than on a
standard day. The altimeter indicates lower than actual.
On a cold day – The pressure level is lower than on a
standard day. The altimeter indicates higher than actual
altitude.
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Remember: From hot to cold, look out below!
Higher than standard pressure – The pressure level is
higher than on a standard day. The altimeter indicates
lower than actual altitude
Lower than standard pressure – The pressure level is
lower than on a standard day. The altimeter indicates
higher than actual altitude.
Remember: From High to Low, look out below
4. Define and state how you would determine the following
altitudes:
Indicated Altitude: Read off the face of the altimeter
Pressure altitude: Indicated with 1013mb/29.92” set in
the Kollsman window
True Altitude: Height above sea level. (use E6B)
Density Altitude: Pressure altitude corrected for non-
standard temperature (use E6B)
20
Absolute altitude: Height above ground. (Subtract terrain
elevation from True altitude)
5. How does the airspeed indicator work?
It measures the difference between RAM air pressure from
the pitot tube head and atmospheric pressure from the
static source.
6. What is the limitation of the airspeed indicator?
21
The airspeed indicator is subject to proper flow of air
in the pitot/static system.
7. What are the errors of the airspeed indicator?
A. Position Error - Caused by static ports sensing
erroneous static pressure; slipsteam flow causes
disturbance at the static port preventing actual
atmospheric pressure measurements. It varies with
airspeed, altitude and configuration.
B. Density Error - Changes in altitude and temperature
are not compensated for by the instrument.
C. Compressibility - Caused by the packing of air into
the pitot tube at high airspeeds, resulting in higher
than normal indications. It is usually not a factor at
lower airspeeds.
8. What are the different types of airspeeds?
IAS: Indicated Airspeed - read off the instrument
CAS: Calibrated airspeed – IAS corrected for instrument
and position errors (POH)
EAS: Equivalent Airspeed – CAS corrected for adiabatic
compressible flow at altitude. (At standard sea level
pressure, calibrated airspeed and equivalent airspeed are
equal. Up to about 200 knots CAS and 10,000 feet the
difference is negligible, but at higher speeds and
altitudes CAS must be corrected for compressibility error
to determine EAS.)
TAS: True Airspeed – EAS corrected for non standard
temperature and pressure (E6B/POH)
GS: Ground Speed – TAS corrected for wind; speed across
ground (E6B)
9. Are the color bands on an airspeed indicator indicated
or calibrated airspeeds?
Airspeed indicators indicate calobrated airspeed (usually
in mph) if manufactured in 1975 or before, and indicated
airpeed (usually in knots) if manufactured in 1976 or
after.
22
10. What airspeed limitations apply to the color-coded
marking system of the airspeed indicator?
White arc—This arc is commonly referred to as the flap operating
range since its lower limit represents the full flap stall speed and
its upper limit provides the maximum flap speed. Approaches
and landings are usually flown at speeds within the white arc.
Lower limit of white arc (VS0)—The stalling speed or the minimum
steady flight speed in the landing configuration. In small
airplanes, this is the power-off stall speed at the maximum
landing weight in the landing configuration (gear and flaps
down).
Upper limit of the white arc (VFE)—The maxi-mum speed with the
flaps extended.
Green arc—This is the normal operating range of the airplane.
Most flying occurs within this range.
Lower limit of green arc (VS1)—The stalling speed or the minimum
steady flight speed obtained in a specified configuration. For
most airplanes, this is the power-off stall speed at the maximum
takeoff weight in the clean configuration (gear up, if retractable,
and flaps up).
Upper limit of green arc (VNO)—The maximum structural cruising
speed. Do not exceed this speed except in smooth air.
Yellow arc—Caution range. Fly within this range only in smooth
air, and then, only with caution.
Red line (VNE)—Never-exceed speed
23
Some important airspeed limitations are not marked on the face of the
airspeed indicator, but are found on placards and in the AFM or POH.
These airspeeds include:
Design maneuvering speed (VA)—This is the “rough air” speed
and the maximum speed for abrupt maneuvers. If during flight,
rough air or severe turbulence is encountered, reduce the
airspeed to maneuvering speed or less to minimize stress on the
airplane structure. It is important to consider weight when
referencing this speed. For example, VA may be 100 knots when
an airplane is heavily loaded, but only 90 knots when the load is
light.
Landing gear operating speed (VLO)—The maximum speed for
extending or retracting the landing gear if using an airplane
equipped with retractable landing gear.
Landing gear extended speed (VLE)—The maximum speed at
which an airplane can be safely flown with the landing gear
extended.
Best angle-of-climb speed (VX)—The airspeed at which an
airplane gains the greatest amount of altitude in a given
distance. It is used during a short-field takeoff to clear an
obstacle.
Best rate-of-climb speed (VY)—This airspeed provides the most
altitude gain in a given period of time.
11. How does the vertical speed indicator work?
Although the vertical speed indicator
operates solely from static pressure, it
is a differential pressure instrument.
The inside of the diaphragm is connected
directly to the static line of the
pitot-static system. The area outside
the diaphragm, which is inside the
instrument case, is also connected to
the static line, but through a
restricted orifice (calibrated leak).
Both the diaphragm and the case receive air from the
static line at existing atmospheric pressure. When the
airplane is on the ground or in level flight, the
pressures inside the diaphragm and the instrument case
remain the same and the pointer is at the zero
indication. When the airplane climbs or descends, the
pressure inside the diaphragm changes immediately, but
due to the calibrated leak, the case pressure remains
higher or lower for a short time, causing the diaphragm
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to contract or expand. This causes a pressure
differential that is indicated on the instrument needle
as a climb or descent. When the pressure differential
stabilizes at a definite ratio, the needle indicates the
rate of altitude change.
The vertical speed indicator is capable of displaying two
different types of information:
Trend information shows an immediate indica-tion of
an increase or decrease in the airplane’s rate of
climb or descent.
Rate information shows a stabilized rate of change
in altitude.
12. What are the limitations of the vertical speed
indicator?
It is not accurate until the aircraft is stabilized.
Sudden or abrupt changes in the aircraft attitude will
cause erroneous instrument readings as airflow
fluctuations over the static port. These changes are not
reflected immediately by the VSI due to the calibrated
leak (6 – 9 sec lag).
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D. VACUUM/GYROSCOPIC SYSTEM
1. What instruments contain gyroscopes?
a. Turn Coordinator
b. Directional Gyro/Heading Indicator
c. Attitude Indicator/Artificial Horizon
1A. What are the two fundamental properties of gyroscopic
action?
Rigidity in space and precession.
RIGIDITY IN SPACE
Rigidity in space refers to the principle that a gyro-
scope remains in a fixed position in the plane in which
it is spinning. By mounting this wheel, or gyroscope, on
a set of gimbal rings, the gyro is able to rotate freely
in any direction. Thus, if the gimbal rings are tilted,
twisted, or otherwise moved, the gyro remains in the
plane in which it was originally spinning
PRECESSION
Precession is the tilting or turning of a gyro in
response to a deflective force. The reaction to this
force does not occur at the point where it was applied;
rather, it occurs at a point that is 90° later in the
direction of rotation. This principle allows the gyro to
determine a rate of turn by sensing the amount of
pressure created by a change in direction. The rate at
which the gyro precesses is inversely proportional to the
speed of the rotor and proportional to the deflective
force.
Precession can also create some minor errors in some
instruments.
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2. What instruments operate off the vacuum system?
Heading Indicator and Attitude Indicator.
Turn Coordinator is electrically driven.
3. How does the vacuum system operate?
An engine-driven vacuum pump provides suction which pulls
air from the instrument case. Normal pressure entering
the case is directed against rotor vanes to turn the
rotor (gyro) at high speed, much like a water wheel or
turbine operates. Air is drawn into the instrument
through a filter from the cockpit and eventually vented
outside. Vacuum values vary but provide speeds from 8,000
to 18,000 RPM
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4. How does the Attitude Indicator work?
A gyro stabilizes the artificial horizon parallel to the
real horizon
5. What are the limitations of an Attitude Indicator?
The pitch and bank limits depend upon the make and model
of the instrument. Usually the limits are:
Banking plane: 100 – 110 Degrees
Pitch Limits: 60 – 70 Degrees
If either limit is exceeded, the instrument will tumble
and spill and will give incorrect indications until re-
set.
6. What are the errors of the Attitude Indicator?
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Errors in both pitch and bank occur during normal
coordinated turns. Turning errors - These errors are
caused by the movement of the pendulous vanes by
centrifugal force resulting in precession of the gyro
towards the inside of the turn. The greatest error occurs
in 180 degree of turn.
In a 180-degree turn to the right, on rollout the
attitude indicator will indicate a slight climb and turn
to the left.
Acceleration Errors - Acceleration and deceleration error
case the attitude indicator to indicate:
- A climb when the aircraft is accelerated
- A descent when the aircraft is decelerated.
7. How does the Directional Gyro/Heading Indicator work?
A Gyro stabilizes the Heading Indicator. The speed of the
gyro is usually 10,000 – 18,000 RPM
8. What are the limitations of a Directional Gyro/Heading
Indicator?
The bank and pitch limits of the Heading Indicator vary
with the particular design and make of the instrument.
55 Degree of Bank
55 Degree of Pitch
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When either of these attitude limits is exceeded, the
instrument “tumbles” or “spills” and no longer gives the
correct indication until reset.
9. What error is the directional gyro subject to?
Precession of the gyro
E. ELECTRICAL/GYROSCOPIC SYSTEM
1. What instrument operates on this system?
Turn Coordinator
2. How does the turn coordinator operate?
The turn part of the
instrument uses precession to
indicate direction and
approximate rate of turn. A
gyro reacts by trying to move
in reaction to the force
applied thus moving the needle
or miniature aircraft in
proportion to the rate of
turn.
The slip/skid indicator is a
liquid-filled tube with a ball
that reacts to centrifugal
force and gravity.
3. What information does the turn coordinator provide?
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The miniature aircraft of the
turn coordinator displays the
rate of turn and rate of roll.
The ball in the tube indicates a
slipping or skidding condition.
Slip – Ball on the inside of
turn; not enough rate of turn
for the amount of bank
Skid – Ball to the outside of
the turn; too much rate of turn
for the amount of bank
4. What limitations apply to the turn coordinator?
A spring is attached between the instrument case and the
gyro assembly in order to hold the gyro upright when no
precession force is applied. Tension on the spring may be
adjusted to calibrate the instrument for a given rate of
turn. The spring restricts the amount of gyro tilt. Stops
prevent the gyro assembly from tilting more than 45
degrees to either side of the upright position.
F. MAGNETIC COMPASS
1. How does the magnetic compass work?
Magnets mounted on the compass card align themselves
parallel to the earth’s lines of magnetic force.
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A simple bar magnet has two centers
of magnetism which are called
poles. Lines of magnetic force flow
out from each pole in all
directions, eventually bending
around and returning to the other
pole. The area through which these
lines of force flow is called the
field of the magnet. For the
purpose of this discussion, the
poles are designated “north” and
“south.” If two bar magnets are
placed near each other, the north
pole of one will attract the south
pole of the other. There is
evidence that there is a magnetic
field surrounding the Earth, and
this theory is applied in the design of the magnetic
compass. It acts very much as though there were a huge
bar magnet running along the axis of the Earth which ends
several hundred miles below the surface.
The geographic north and south poles form the axis for
the Earth’s rotation. These positions are also referred
to as true north and south. Another axis is formed by the
magnetic north and south poles. Lines of magnetic force
flow out from each pole in all directions, and eventually
return to the opposite pole. A compass aligns itself with
the magnetic axis formed by the north/south magnetic
field of the Earth.
The lines of force have a vertical component (or pull)
which is zero at the Equator, but builds to 100 percent
of the total force at the magnetic poles. If magnetic
needles, such as in the airplane’s magnetic compass, are
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held along these lines of force, the vertical component
causes one end of the needle to dip or deflect downward.
The amount of dip increases as the needles are moved
closer and closer to the poles. It is this deflection, or
dip, that causes some of the larger compass errors.
2. What limitations does the magnetic compass have?
The float assembly of the compass is balanced on a pivot,
which allows free rotation of the card, and allows it to
tilt at an angle up to 18 degree.
3. What are the various compass errors?
A. Variation Error -
The angular difference between magnetic north (the
reference for the magnetic compass) and true north is
variation.
Lines that connect points of equal variation are called
isogonic lines. The line connecting points where the
magnetic variation is zero is an agonic line. To convert
from true courses or headings to magnetic, subtract
easterly variation and add westerly variation. Reverse
the process to convert from magnetic to true.
To remember: East = Least (subtract), West = Best (Add)
B. Deviation Errors:
Besides the magnetic fields generated by the Earth, other
magnetic fields are produced by metal and elec-trical
accessories within the airplane. These magnetic fields
distort the Earth’s magnetic force, and cause the compass
to swing away from the correct heading. This error is
called deviation. Manufacturers install compensating
magnets within the compass housing to reduce the effects
of deviation. However, it is not possible to completely
eliminate deviation error; therefore, a compass
correction card is mounted near the compass. This card
corrects for deviation that occurs from one heading to
the next as the lines of force interact at different
angles.
(MH) 0° 30° 60° 90° 120° 150° 180° 210° 240°
270° 300° 330°
(CH) 359° 30° 60° 88° 120° 152° 183° 212° 240° 268° 300°
329° RADIO ON ✓ RADIO OFF
C. Oscillation Error – Erratic movement of the compass
card caused by turbulence or rough control technique.
D. Dip Errors -
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i. Acceleration error:
On East or West Headings, while accelerating, the
magnetic compass shows a turn to the North, and when
decelerating a turn to the South
Remember: ANDS
A ccelerate
N orth
D ecelerate
S outh
ii. Northerly turning error:
The compass leads in the south half of a turn, and lags
in the north half of a turn.
Remember: UNOS
U ndershoot
N orth
O vershoot
S outh
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