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AIRCRAFT TECHNICAL
AIRCRAFT GENERAL KNOWLEDGE I
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AIRCRAFT TECHNICAL
LECTURE ONE: AERODYNAMICS AND ENGINES
1. The Atmosphere
2. AerodynamicsDrag
5. Aerodynamics Thrust (Propellers)
6. Stalling
4. Aerodynamics - Weight
3. Aerodynamics - Lift
7. Aircraft Stability
8. Engines
9. Fires
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AIRCRAFT TECHNICAL
THE ATMOSPHERE: BASICS!
The ATMOSPHERE is a parcel of gases
held to the earth by gravity
Due to the fact that the earth
ROTATES, the atmosphere is flung
outwards at the equator meaning that it
extends further toward space at theEQUATOR than at the POLES
This is magnified by the fact that the air
is hotter at the equator and rises
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AIRCRAFT TECHNICAL
THE ATMOSPHERE: COMPOSITION
1% OTHER GASES(including water vapour)
21% OXYGEN
78% NITROGEN
Knowledge of the atmosphere is
important to pilots and aircraft designers
because it is the medium we fly in andthe air we breathe!
It is what the aircraft engine
uses for combustion and what
keeps us airborne
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AIRCRAFT TECHNICAL
INTERNATIONAL STANDARD ATMOSPHERE (ISA)
ISA is a measuring stick against which
we can compare the actual atmosphereto a convenient constant atmosphere
Some instruments, such as the Airspeed
Indicator are calibrated to ISA conditions
Aircraft take-off, landing and climb
performance may be based on ISA conditions
If the temperature at a certain altitude is
colder or hotter than it should be under
ISA, this will affect how the aircraft or theinstruments perform in relation to their
published performance criteria
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AIRCRAFT TECHNICAL
INTERNATIONAL STANDARD ATMOSPHERE (ISA)
Pressure change with altitude =-1mb per 30 feet
Temperature change with altitude
= -1.98 C per 1000 feet
Sea Level Pressure
= 1013mb
Sea Level Temperature =
+15 C
Sea Level Density =
1225 gm / m3
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
If the air temperature at 12000 feet is -7 C what is the deviation from ISA?
At 12000 feet the temperature should be 24colder than at the surface
15C24C = -9C
It is actually -7C and so the deviation is ISA +2C
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AIRCRAFT TECHNICAL
FOUR FORCES
MASS
Mass of aircraft acting
straight down through
centre of earth
DRAG
Resistance to an
object through the
air
THRUST
provided by
propeller
LIFT
generated by airflow
over the wings and
acting perpendicularto wing
More detail....
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
STATIC PRESSURE
Pressure exerted by the atmosphere
We feel this all the time
DYNAMIC PRESSURE
Caused by movement through the air
As the speed in increases so does the dynamic
pressure
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
If the same diagram is split in half
the same effect will happen
Now lets change that diagram a
little...
So if we now imagine a wingwe have just created lift!
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
Static Pressure + Dynamic Pressure = constant
If static pressure falls, dynamic pressure must increase to maintain the constant
If you get two pieces of paper and blow between
them they will get sucked together as the static
pressure reduces with increased dynamic
pressure
Otherwise known as the Bernoulli Principle!
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
So why are wings shaped like they are?
FLAT PLATE
Great in one direction but always some, if not a lot
of stagnant airflow which creates drag
BALL
Too much separated flow at the rear of the object
AEROFOIL
Not perfect but close!
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
Relative
Airflow
Laminar flow boundary layer(very thin layer)
Turbulent boundary
layer
(slightly thicker)
Transition point(where laminar flow
becomes turbulent)
Higher pressure
beneath the
wing
Lift force acts
through centre ofpressure
What are the bits of the wing called?...
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
Leading Edge
Trailing EdgeChord line
Maximum thickness
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
Aerofoils are designed so that thepressure distribution leads to a lifting
force
We shall revisit this diagrammore when we discuss stalling
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
Relative airflow is the airflow which hits
the leading edge of the wing
It is the opposite of flight path
The angle between the relative
airflow and the chord line of the
wing is the ANGLE OF ATTACK
As the angle of attack changes so will the
pressure distribution you saw in the
previous diagram
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
We couldnt avoid formulas forever...
Lift = Cl p V2S
Coefficient of Lift
Includes many things but
one important one is angle
of attack of the wing
Air Density
(decreases with
increased altitude)
Speed
Combination of wind
speed and forward
speed
Wing Surface Area
May be changed by
some flaps (more
later)
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
The lift force is perpendicular to the relative airflow and depends upon:
Wing Shape
Velocity
Air Density
Angle of Attack
Wing Surface Area
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AIRCRAFT TECHNICAL
FOUR FORCES: LIFT
As the angle of attack increases, so does
the CL (or amount of lift being produced
by the wing)
This rises to a maximum (CLMAX) just
before the aircraft reaches the critical
angle of attack
Beyond the critical angle of attack,
the wing will stall
Most cambered aerofoils will begin producing lift at a
negative angle of attack (about -4)
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
Air over the top surface of the wing is at a greater or lower pressure than the
surrounding air?
Lower pressure
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG
Drag is the resistance to movement and acts opposite to the
direction of flight
TOTAL DRAG
PARASITE DRAG INDUCED DRAG
Skin
friction
drag
Interference drag
Form
drag
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: PARASITE DRAG
Parasite Drag increases as speed increases
As speed increases more air molecules are
hitting the surface and so more air
molecules can be slowed down by drag
Parasite Drag is caused by the aircraft being
in the airflow
It is made up of 3 elements:
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: PARASITE DRAG
SKIN FRICTION DRAG
Friction caused by the surface
moving through the airflow
Surface roughness and thickness of
aerofoil have an impact
Skin friction is reduced by:
Clean surfaces
Less rivets on surface
Thin aerofoil sections
Flight at low angles of attack
Smaller surface areas
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: PARASITE DRAG
FORM DRAG
Just like a swimmerthe way in which the
airflow separates from the surface will
cause drag
Streamlining of the aircraft will
reduce form drag
The more eddies that are caused,
the more drag is produced
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: PARASITE DRAG
INTERFERENCE DRAG
Drag due to junctions of surfaces giving offeddies which disrupts airflow over surfaces
behind
Junctions are streamlined to reduce
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: INDUCED DRAG
As speed increases, induced drag
decreases
Induced drag is caused by the generation of lift
This is because the wing works
harder at slower speeds to produce
lift
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: INDUCED DRAG
Lift is created by the pressure differential
between the upper and lower surfaces ofthe wing
The higher pressure below the wing is
trying to get to the lower pressure above
the wing to equalise the pressure total
At the wing tips, the easiest way for this to
happen is for the airflow to be up and over
the wing tips
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: INDUCED DRAG
The downward pressure on the wing causesdrag as does the vortices which are created
behind the wing
The flow along the wing and up over thewing tips is called spanwise flow
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: INDUCED DRAG
Reduced by high aspect ratio wings (the
spanwise flow has run out of energy by thetime it gets to the wingtips)
Reduced by tapered wings (less for the
downward force to push upon)
Reduced by washout (wing twist) so
that most lift is created by the wing root
Reduced by tip tanks, winglets, wing
fences etc to stop the spanwise flow
leaving at the wingtip
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AIRCRAFT TECHNICAL
FOUR FORCES: DRAG: TOTAL DRAG
PARASITE DRAG
INDUCED DRAG
TOTAL
DRAG
Minimum Drag Speed
(VMD)
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
Does induced drag increase or decrease as the aircraft speeds up?
Decreases
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AIRCRAFT TECHNICAL
FOUR FORCES: WEIGHT
Weight acts through the centre of
gravity
Wing loading is a function of
weight and the wing area of the
aircraft
Wing Loading = Weight of aircraft
Wing Area
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AIRCRAFT TECHNICAL
FOUR FORCES: THRUST: PROPELLERS: BASICS
Direction of
flight
Plane of rotation
Chord line
Blade angle
Blade face
Blade back
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AIRCRAFT TECHNICAL
At one rpm setting, the outer sections of the
propeller travel through a much further distance
This would lead to the different sections of the
blade producing different amounts of lift
Like a wing, the blade is twisted so that a
constant angle of attack is maintained
ROTATIONAL VELOCITY
FOUR FORCES: THRUST: PROPELLERS: ROTATIONAL VELOCITY
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AIRCRAFT TECHNICAL
PROPELLERS: FORWARD VELOCITY & HELICAL MOTION
With each rotation the propeller also
moves forwards
The motion is helical like a screw
Newtons third law of motion states:
For every action there is an equal andopposite reaction
Ie. The propeller accelerates air rearwards, so the propeller (and the
attached aircraft) move forwards
Otherwise known as
Noddy does propellers!
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AIRCRAFT TECHNICAL
THRUST
PROPELLERTORQUE
FORCE
Relative
airflow
The easiest way to see
propellers is to treat them like a
wing
Wing produces lift at 90to
chord linepropeller
produces thrust
Propellers are efficient only at one speedthis is why variable speed propellers are
used on aircraft with a larger speed range
FOUR FORCES: THRUST: PROPELLERS: FORCES UPON
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AIRCRAFT TECHNICAL
STALLING
Stalling of the wing occurs above the
critical angle of attack
This can occur at high or low
speedsit has nothing to do
with speed (although stalling
speeds may be used forreferences purposes)
Critical Angle of Attack
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AIRCRAFT TECHNICAL
STALLING : AIRFLOW
During Normal flight angles, theairflow separates towards the rear of
the wing
At the critical angle the separation point
is much further forwardsthe aerofoil isnow struggling to produce lift in the
turbulent airflow over it
As the aircraft stalls there is little or
no laminar flow over the wing surface
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AIRCRAFT TECHNICAL
STALLING : CENTRE OF PRESSURE
At Normal flight angles the centre of
pressure (where the lift is said to actthrough) is about 1/3 chord
As the angle of attack is increased,
the centre of pressure moves
forwards (the lift is having to pick up
more of the wing)
At the stall the centre of pressuremoves rapidly rearwards causing a
pitch down in most aircraft
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AIRCRAFT TECHNICAL
STALLING : RECOGNITION
APPROACHING A STALL
Sloppy controlsLess airflow over the surfaces makes them harder
to move and they are moving less air molecules so
have less effect
Low / decreasing Airspeed and associated
reducing airspeed
Yaw becoming more obvious
Slipstream effect still occurring but less rudder
authority to correct either through slower speed or
because of turbulent airflow
Stall warner
Light Buffet as turbulent air reaches tailplane
May get all or some of the following signs:
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AIRCRAFT TECHNICAL
STALLING : RECOGNITION
THE STALL
At the stall the following usually happens:
Aircraft pitches nose down
Designed to do so as centre of pressure moves rearwards
angle of attack automatically reduces
Heavy Buffet
May be felt with large amount of turbulent airflow reaching
the tailplane
Stall warning
Will continue to sound until angle of attack is
reduced below the stalling angle (usually about 16for a light aircraft)
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AIRCRAFT TECHNICAL
STALLING : RECOVERY
Aircraft nearing
critical angle
Aircraft
exceeds critical
angle and stalls
Control column
centrally forward
until stall symptoms
stop
Stall symptoms
stopuse
ailerons to level
wings
Recovered!
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AIRCRAFT TECHNICAL
STALLING : FACTORS AFFECTING
WEIGHTA heavier aircraft will need to produce
more lift to stay airborne
The stall will still occur at the same
angle but the speed will change
In this example the left
aircraft is lighter and would
stall at 40 kts, the right
aircraft is heavier and would
stall at 50 kts
The angle is the same
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AIRCRAFT TECHNICAL
LOAD FACTOR
STALLING : FACTORS AFFECTING
Load factor is a type of weightit affects
the G of the aircraft and its effectiveweight
The more weight, the harder the wing
has to work to produce the lift
A higher angle of attack is needed
and this brings the aircraft closer to
the critical angle
For example, a 60has 2g and the
aircrafts effective weight is doubled
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AIRCRAFT TECHNICAL
STALLING : CHANGE OF STALLING SPEED
If an aircraft usually stalls at 90 kts and is in a 60banked turn, how do we
work out what the new stall speed will be?
Turn has a load factor of 2
The square root of the load factor is 1.4
90 kts x 1.4 = 127 kts
New Stall speed = Old stall speed x load factor
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AIRCRAFT TECHNICAL
POWER
STALLING : FACTORS AFFECTING
Thrust from the propeller accelerates the
airflow and adds kinetic energy to it
This delays the separation of the airflow
from the wing surfaces
This means that the stall is delayed in
terms of speed (still the same angle!)
Wing drop in the stall is more likely due to uneven
amounts of stalling on the wings
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AIRCRAFT TECHNICAL
FLAPS
STALLING : FACTORS AFFECTING
Flaps are designed to increase the CLMAX(Critical angle) of the wing
Can make the wing stall at a higher
angle of attack and at a lower speed
The effect depends upon the amount of flap
selected and the type of flap being used
STALLING FACTORS AFFECTING
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AIRCRAFT TECHNICAL
WASHOUT
STALLING : FACTORS AFFECTING
The twist of the wing ensures that
the outer section of the wing has a
lower angle of attack than the inner
portion
This helps the wing stall at the root first
This is preferable because it means
that ailerons are effective much longer
STALLING SPINNING
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AIRCRAFT TECHNICAL
STALLING : SPINNING
Spinning occurs when one wing stalls
more than the other and is uncorrected
autorotation follows
If the aircraft is not stalled it cant spin and so
this is why so much emphasis is placed on
stall recognition in the PPL syllabus!
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
When is the co-efficient of lift at its maximum?
Just before the stalling angle of attack (CLMAX)
AIRCRAFT STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY
Stability is the natural tendency of an aircraft to
return to its original state after it has been disturbed
An aircraft with too little stability is very
difficult to handle and may be uncontrollable
An aircraft that is too stable may be
impossible to control because it needs
such large control inputs
AIRCRAFT STABILITY BASICS
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: BASICS
POSITIVE STATIC STABILITY
After a disturbance returns to original position
NEUTRAL STATIC STABILITY
After a disturbance stays in new position
NEGATIVE STATIC STABILITY
After a disturbance does not return to original position
AIRCRAFT STABILITY BASICS
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: BASICS
Dynamic stability refers to how much time it takes
for an aircraft to recover to its original position
Again, to be on the positive side is better but
too much positivity is also bad!
We will look at the 3 types of aircraft stability...
AIRCRAFT STABILITY LONGITUDINAL STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: LONGITUDINAL STABILITY
Longitudinal Stability is about the
lateral axis (pitching)
Provided by the tailplane
If a gust makes the aircraft pitch up,
the tailplane is presented at a greater
angle of attack to the airflow
This creates a restoring force which
pitches the aircraft down
AIRCRAFT STABILITY: LONGITUDINAL STABILITY
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AIRCRAFT TECHNICAL
Increased longitudinal stability can be
gained by:
Forward Centre of Gravity (bigger moment
makes a bigger restoring force)
Longitudinal dihedral (difference between
wing angle and tailplane angle)
Longer aspect ratio
AIRCRAFT STABILITY: LONGITUDINAL STABILITY
AIRCRAFT STABILITY: LATERAL STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: LATERAL STABILITY
Lateral Stability is about the
longitudinal axis (rolling)
Provided by wing dihedral, sweep
back and high wing configuration
If a gust makes the aircraft roll leftthe dihedral of the wing makes the
downgoing wing have a greater
angle of attack
This increases the lift on the
downgoing wing and will induce a roll
back to the right
AIRCRAFT STABILITY: LATERAL STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: LATERAL STABILITY
Increased lateral stability can be gained by:
Increased wing dihedral (bigger restoring
force due to greater inbalance in angle of
attack)
Sweepback (lower wing creates more lift
due to the angle of presentation to airflow)
High Keel Surface
High Wing Configuration (pendulous
stability)
AIRCRAFT STABILITY: DIRECTIONAL STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: DIRECTIONAL STABILITY
Directional Stability is about the
directional / normal axis (yawing)
Provided by the vertical stabilser
If a gust yaws the aircraft to the left
the vertical stabiliser is presented at
an angle to the airflow which inducesa yaw to the right
AIRCRAFT STABILITY: DIRECTIONAL STABILITY
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AIRCRAFT TECHNICAL
AIRCRAFT STABILITY: DIRECTIONAL STABILITY
Increased directional stability can be gained
by:
Greater fin area
Greater keel surface behind centre ofgravity
Forward Centre of Gravity (bigger moment
arm gives a bigger effect)
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
Directional Stability is achieved through what bit of the aircraft?
Fin (Vertical Stabiliser)
AIRFRAMES STRUCTURE
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AIRCRAFT TECHNICAL
AIRFRAMES: STRUCTURE
The airframe is made up of various components, we will examine each in turn:
AIRFRAMES FUSELAGE
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AIRCRAFT TECHNICAL
AIRFRAMES: FUSELAGE
FUSELAGE
Forms main body of airframe to which all other
components are fixed
Most training aircraft have a semi-monocoque
construction (framework covered by a skin)
Stresses on airframe are shared
between the formers, bulkheads
and stringers and also with thealuminium skin
AIRFRAMES: WINGS
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AIRCRAFT TECHNICAL
AIRFRAMES: WINGS
WINGS
Used to generate lift required for flight andusually also carry fuel tanks
Internal structure made up of ribs
and stringers. A main spar runs
along the length of the wing
High wing aircraft also generally
have a strut to give the wing
more strength
AIRFRAMES: EMPENNAGE
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AIRCRAFT TECHNICAL
AIRFRAMES: EMPENNAGE
EMPENNAGE / TAIL PLANE
Many different designs used (as below, all-
flying tailplane, T-tail etc)
Internal structure as per the wings
Carries the rudder, elevators and trim tabs
Horizontal stabiliser also produces a component of
lift downwards to balance the aircrafts lifting ability
AIRFRAMES: FLIGHT CONTROLS
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AIRCRAFT TECHNICAL
AIRFRAMES: FLIGHT CONTROLS
RUDDER
Used for movement about the
directional (normal) axis
ELEVATORS
Used for movement about
the lateral axis
AILERONS
Used for movement
about the longitudinalaxis
FLAPS
Used to delay the stall
and allow the aircraft
to fly slower with a
lower attitude
AIRFRAMES: TRIM TABS
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AIRCRAFT TECHNICAL
AIRFRAMES: TRIM TABS
Used to relieve control pressures for the
pilot
All aircraft have trim tabs on the elevators
but some also have trim tabs on rudders
and ailerons
The trim tab moves in the opposite
direction to the control surface to
provide an opposing force which
maintains the main surface in place
Anti-balancetabs make sure that stick loads increase as
deflection increasesstops pilot damaging them!
AIRFRAMES: FLAPS
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AIRCRAFT TECHNICAL
AIRFRAMES: FLAPS
Flaps increase the camber of the wing and
help the aircraft produce more lift
The later stages of flap stick into the
airflow so much they cause extra drag
Fowler flaps are used so that larger
angles of flap can be used but so that the
airflow does not separate from the upper
surface
Flaps give a LOWER stalling angle of attack when related to
a clean aerofoil (seems backwards but trust me!)
AIRFRAMES: SLATS
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AIRCRAFT TECHNICAL
AIRFRAMES: SLATS
Slats are flaps at the leading edge of the wing
Used to re-energise the boundary layer and
to delay separation of the airflow on the wing
upper surface
Rare on training aircraft as flaps are
cheaper and easier to maintain
AIRFRAMES: LANDING GEAR
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AIRCRAFT TECHNICAL
AIRFRAMES: LANDING GEAR
Made up of three wheelsmain wheels x 2
nosewheel or tailwheel
Wheels may be attached by shock-
absorbed sections or fixed spring leaf
sections
Landing gear is either fixed or
retractable
AIRFRAMES: NOSEWHEEL & GROUND STEERING
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AIRCRAFT TECHNICAL
AIRFRAMES: NOSEWHEEL & GROUND STEERING
STEERING RODS
Use of rudder pedal
moves steering
rods left and right
SHIMMY DAMPER
Prevents sideways
oscillation of the
nosewheel
TORQUE LINK
Some suspension, keeps
wheel straight and keeps
wheel attached to aircraft!
FORK
Attaches nose
wheel assembly to
tyre
OLEO
Mixture of air
and fluid to
provide shock
absorption
AIRFRAMES: NOSEWHEEL & GROUND STEERING
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AIRCRAFT TECHNICAL
AIRFRAMES: NOSEWHEEL & GROUND STEERING
Nose wheels are not built to take the initial impact of landing!
When the aircraft becomes
airborne, the oleo extends to its
maximum and rudder pedal
movement no longer makes the
wheel move left and right
AIRFRAMES: TYRES
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AIRCRAFT TECHNICAL
AIRFRAMES: TYRES
Aircraft tyres made up of
many different layers
There is no legal
requirement for tyre tread
depth on aircraft tyres
If a tyre has no tread it will
take longer to stop and be
less secure in wet conditions
Creep marks show if a tyre has moved from its
initial fit position
If the creep marks arent touching the valve
and tube will be being stressed and could fail
AIRFRAMES: BRAKING SYSTEMS
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AIRCRAFT TECHNICAL
AIRFRAMES: BRAKING SYSTEMS
RUDDERPEDALS
BRAKE DISCBRAKE
PADS
BRAKE FLUID
RESERVOIR
BRAKE
LINE
The brakes on the rudder
pedals push an actuator
This then pushes
hydraulic fluid
(pink/orange colour)
Hydraulic fluid
squeezes the brake
pads against the brake
disc
Friction from the disc slows
the tyre
AIRFRAMES: SAFETY PRECAUTIONS
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AIRCRAFT TECHNICAL
AIRFRAMES: SAFETY PRECAUTIONS
CONTROL LOCKS
Can be internal or external
Prevent control surface being damaged by
high winds
PITOT COVERSPrevent pitot tubes becoming
blocked by ice / insects etc
AIRFRAMES: SAFETY PRECAUTIONS
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AIRCRAFT TECHNICAL
AIRFRAMES: SAFETY PRECAUTIONS
AIRCRAFT COVERS AND TIE
DOWNS
Prevent icing up, water ingress and the
aircraft not being there when you return
to it!
WHEEL CHOCKS
Used on slopes or when the pilot
does not trust the parking brake of
the aircraft
AIRFRAMES: SAFETY PRECAUTIONS
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AIRCRAFT TECHNICAL
AIRFRAMES: SAFETY PRECAUTIONS
ENSURE all control locks,
covers, tie downs and
chocks are removed before
attempting to taxy or fly!
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
What does an aircraft creep mark look like and what is it for?
Painted mark on tyre / wheel to show whether the tyre has moved in relation to
its original fitted position
ENGINES: BASIC CONSTRUCTION
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AIRCRAFT TECHNICAL
ENGINES: BASIC CONSTRUCTION
Most light aircraft have a four cylinder piston engine
CYLINDER
Houses the
moving parts
FINS
Increase surface
area to aid cooling
INLET & OUTLETVALVES
Control incoming
fuel/air mixture and
exiting exhaust
PISTON
PISTON RINGS
Allow lubricating
oil onto cylinder
walls
SPARK PLUG
To ignite mixture
(most aircraft have 2)
CONNECTING ROD
Turns linear motion
into rotary motion
CRANKSHAFT
Transfers power to
propeller and
controls valve timing
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
The 4-stroke cycle consists of 4 strokes
of the piston travelling in the cylinder. The
four strokes are:
Intake
Compression
Power
Exhaust
Or... Suck, Squeeze, Bang, Blow!
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
INTAKE STROKE
Fuel / Air Mixture is sucked into the cylinder
Piston moves down the cylinder to bottom
dead centre its lowest position
Pressure inside the cylinder decreases
Inlet valve opens
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
COMPRESSION STROKE
Piston moves up the cylinder to top dead
centre its highest position
Pressure inside the cylinder increases
Fuel / Air Mixture is compressed in the gap remaining
Temperature in the cylinder increases
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
POWER STROKE
Piston is forced down the cylinder to bottom
dead centre
Pressure inside the cylinder decreases
Spark plug discharges and the spark ignites
the mixture
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
EXHAUST STROKE
Piston moves back up cylinder to top dead
centre
Exhaust valve opens
Burnt gases are moved out through the
exhaust system
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
Every completed 4 strokes leads to 2
rotations of the crankshaft
If an engine has 4 cylinders, each
cylinder will be on a different stroke at
any one timethis leads to smoother
running
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
The compression ratio of an engine
determines which fuel is used and howefficient it is
Total volume = space left when piston at
bottom dead centre
Clearance volume = space left when piston at
top dead centre
Swept volume = volume swept by the
piston in one stroke
ENGINES: OTTO CYCLE (4 STROKE CYCLE)
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AIRCRAFT TECHNICAL
( )
VALVE TIMING
Valve timing aids the engines
efficiency
The modified Otto Cycle
has a high degree of
valve overlapwhen
both valves are open atthe same time
ENGINES: PRE-IGNITION & DETONATION
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AIRCRAFT TECHNICAL
PRE-IGNITION
Occurs when ignition of the mixture occurs before the spark
Caused by overheated spark plug tip, carbon deposits, hot spots on the cylinder wall
DETONATION
Occurs when ignition of the mixture occurs after the main spark and burn
Caused by spontaneous combustion of unburnt mixture
Both cause engine damage!
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
What is the formula for the compression ratio of an engine?
Total volume divided by clearance volume
ENGINES: COOLING
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AIRCRAFT TECHNICAL
Cowlings and baffles are designed to
direct flow of air around to engine to
cool it from the outside
Most aircraft engines are air-cooledit is simpler, cheaper, and easier to
maintain
Some components have fins which increase the
surface area and assist with cooling
ENGINES: COOLING
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AIRCRAFT TECHNICAL
Some aircraft have Cylinder Head Temperature(CHT) gauges to monitor engine heat build up
These aircraft often also have cowl flaps which
can direct extra air across the engine for cooling
ENGINES: LUBRICATION
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AIRCRAFT TECHNICAL
Engine components require oil-based lubrication for a number of reasons:
To prevent friction between moving surfaces
To cool hot sections of the engine more efficiently than air
To carry contaminants in the system away to a safe area to prevent
damage
To provide a seal to certain components (such as the piston and
the cylinder wall)
ENGINES: LUBRICATION
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AIRCRAFT TECHNICAL
Oil for engines must have a high flash point so that it does not
catch fire easily
Oil must be chemically stable
It must be viscous enough to flow easily at all operating
temperatures but not so liquid it doesnt coat the surfaces
Lubrication systems will have an oil filter to
trap any particles being carried out of the
enginein this way the oil cleans the
engine
Always check amount and type of oil is sufficient andcorrect before flight!
ENGINES: LUBRICATION
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AIRCRAFT TECHNICAL
Most light aircraft have wet
sump oil systems
There is a sump where oil
returns to by gravity
In a dry sump systemscavenge pumps are used
to collect oil
An oil cooler ensures that
the oil does not get too hot
Oil pressure relief valve will vent oil overboard in
the case where the pressure would damage the
engine
ENGINES: LUBRICATION
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AIRCRAFT TECHNICAL
OIL TEMPERATURE GAUGE
Measures temperature of oil after the oil
cooler and before it enters hot section of
engine
OIL PRESSURE GAUGE
Measures pressure of oil after oil pump and
before it enters hot section of engine
These gauges can show up malfunctions in the
lubrication system:
ENGINES: LUBRICATION: MALFUNCTIONS
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AIRCRAFT TECHNICAL
LOW OIL PRESSURE
a.) insufficient oil
b.) oil leakc.) failure of oil pump
d.) engine problem (failed bearings)
e.) oil pressure relief valve stuck open
HIGH OIL PRESSUREa.) oil pressure relief valve inoperative
b.) excess oil in system
HIGH OIL TEMPERATURE
a.) oil quantity is insufficient
b.) prolonged operation at high power
settings
c.) oil filter is blocked and oil is bypassing
the cooler
FLUCTUATING GAUGE
a.) gauge is broken!
b.) other issue
Remember oil problem can lead
to no oil which will lead to no
engine! Land as soon as possible
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
How are excessive engine oil pressures prevented?
An oil pressure relief valve
IGNITION SYSTEMS: CONSTRUCTION
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AIRCRAFT TECHNICAL
Various components of the aircraft
ignition system
When the key is turned, a small current
energises a solenoid (electromagnet)
which closes the circuit between the
battery and the starter motor
IGNITION SYSTEMS: CONSTRUCTION
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AIRCRAFT TECHNICAL
The solenoid allows a much higher
current to do the work required
A starter warning light indicates
when the starter motor is engaged
Once the key is released, the
starter warning light should go out
If it does notengine must be shut down immediatelyto avoid damage to thestarter motor and to the engine
IGNITION SYSTEMS: MAGNETOS & IMPULSE COUPLING
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AIRCRAFT TECHNICAL
The RAPID collapse of the magnetic
field provides the first sparks needed
to start the engine
After start the sparks are provided by
the engine and the impulse couplingretracts
The impulse coupling can be
powered by the battery or by hand-swinging the propeller
IGNITION SYSTEMS: MAGNETOS & IMPULSE COUPLING
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AIRCRAFT TECHNICAL
Only one magneto is needed for engine
startit provides the electricity for the
spark - this magneto has an impulsecoupling
The impulse coupling rotates the
magnet and generates a high voltage
It retards the spark to the engine so
that it works at low rpm settings
The high voltage is achieved by the
magnet being stopped and thenreleased suddenly
IGNITION SYSTEMS: HOW TO USE
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AIRCRAFT TECHNICAL
The key at start position engages the impulse coupling to
provide the initial sparks required
When the key is released it springs back to the both
position so that both magnetos are in use
The right magneto powers one spark plug in
each cylinder
And the left does the other spark plug in
each cylinder!
If one magneto fails, all cylinders still get aspark
IGNITION SYSTEMS: HOW TO USE
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AIRCRAFT TECHNICAL
DEAD CUT CHECK
Should be done before taxy and just prior
to shut down of the engine
When left is selected, the right
magneto is earthed so that only
sparks from the left magneto are
generated
x
x
xx
x
A drop in rpm should be noticed but the
engine should continue to run
Repeat for right selection
Make sure both is selected for taxy
IGNITION SYSTEMS: HOW TO USE
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AIRCRAFT TECHNICAL
POWER CHECK
Should be done prior to take off
Same check as before but note rpm
drop and check it is within limits for your
aircraft
For a C152 maximum drop of 125rpm
but no more than 50 rpm drop
between the two
Ensures that magnetos are providingeven sparks and that engine is capable
of sustaining with only one working
IGNITION SYSTEMS: MALFUNCTIONS
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AIRCRAFT TECHNICAL
Engine cuts out during dead cut check
One magneto is not working. Shut down
and inform engineering.
No rpm drop on dead cut check
One magneto is not earthing. Shut
down and inform engineering. Ensureno-one touches propeller.
Rough running engine during power check
Spark plugs are fouled up. Instructor willshow you how to clear or inform
engineering
Spark plug fouling is generally caused by an over-rich
mixture
PRACTICE QUESTION!
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
When a magneto is switched off is the primary circuit switch open or closed
and is it earthed or not earthed?
Circuit is open and switch is earthed
CARBURETTORS: BASICS
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AIRCRAFT TECHNICAL
The carburettor is where the fuel and air is mixed prior to entering the cylinders
Mixture Needlecontrols amount of
fuel that will be added (controlled
by mixture knob in cockpit)
Butterfly valve
controls amount of
air to the engine
(controlled by
throttle in cockpit)
Fuel/air
mixture toengine Float chamberhas a store of fuel
works like a toilet cistern!
Fuel inletfrom fuel
tanks
Air inlet to
carburettor
Venturicreates low
pressure area
Mixture should be between 1:8 (rich) or 1:20
(lean) to ensure smooth running of engine
CARBURETTORS: IDLING JET
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AIRCRAFT TECHNICAL
Idle air
bleed
Idle jet
Idle
meteringunit
When throttle butterfly is almost closed
the pressure differential between venturi
and float chamber is very small
Can cause a idle cut off when all fuel flow
stops to the engine
Idle jet experiences enough pressure
differential and feeds small amount of
fuel in downstream of butterfly
CARBURETTORS: ACCELERATOR PUMP
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AIRCRAFT TECHNICAL
If throttle is opened rapidly the
amount of air increases initially at a
greater rate than the fuel
This would cause the engine to lag
and maybe a weak cut
Accelerator pump is activated when
throttle gets to full power and spurts
extra fuel into the carburettor
Linkage
attached to
throttle
Spring adds
more fuel in by
separate route
CARBURETTORS: MIXTURE CONTROL
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AIRCRAFT TECHNICAL
Engines are designed to run at standard sea level (1013.2 mb/hp and +15C
At altitude there is less air and so
the aircraft will have too much fuel in
comparison to air
The mixture knob / lever can beused to select the best mixture
During climb, mixture should be rich to aid engine cooling
In cruise, lean the mixture to obtain the best fuel/air ratio and
best fuel economy
CARBURETTORS: MIXTURE CONTROL
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AIRCRAFT TECHNICAL
It is safer to shut down an engine using the
mixture control at idle cut off
In this way there is no fuel in the lines and if a
magneto has failed and is still live, the engine
will not start if someone turns the propeller
Fuel is cut off between float chamber and
venturi
CARBURETTORS: ICE
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AIRCRAFT TECHNICAL
CARBURETTOR ICE can form
in temperatures up to +30C
As air passes through the
VENTURI, it is forced to speed
up and this causes the
temperature to decrease
If the air is moist then ICE will
form and may block airflow into
the engine
This causes ENGINE
ROUGH RUNNING and evenENGINE STOPPAGE
CARBURETTORS: ICE
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AIRCRAFT TECHNICAL
This is more likely at LOW
POWER SETTINGS where
the gap between the
THROTTLE BUTTERFLY
and the outer wall of the
carburettor is smaller
Carburettor icing is ALWAYSlikely when the temperature
is below +30C and the
aircraft is within 200nm of
any sea surface
This must be probably on
about 99% of days in the UK!
CARBURETTORS: ICE
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AIRCRAFT TECHNICAL
CARBURETTORS: ICE
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AIRCRAFT TECHNICAL
ALWAYS use CARB HEAT
selected to ON / HOT when
using throttle settings below the
GREEN ARC on the RPM gauge
Check for CARB ICE every 10-15
minutes by selecting CARB
HEAT to ON / HOT for at least 30
seconds
The RPM should drop due to the
hotter air entering the engine and
the engine should run smoothly
If the RPM does not fall, or RISES when carb
heat is on, or the engine runs rough then you
have carburettor ice!
CARBURETTORS: ICE
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AIRCRAFT TECHNICAL
What do you do if you have
carburettor icing?
Natural instinct when engine runs
rough is to put the carb heat back
into the off / cold position
DO NOT DO THIS!
LEAVE the carb heat selector in
the ON / HOT position until the
engine has been cleared of ice
Then do checks moreregularly!
PRACTICE QUESTION!
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AIRCRAFT TECHNICAL
PRACTICE QUESTION!
In what flight condition is carburettor ice most commonclimb, descent or
cruise?
Descent (with low power setting)
FUEL INJECTION
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AIRCRAFT TECHNICAL
Not all aircraft have carburettorsthey use fuel
injection instead
ADVANTAGES
No fuel ice, no carburettor ice, better
control of fuel/air ratio, easier
maintenance, instant acceleration,
increase efficiency of engine
DISADVANTAGES
Hot starts are more difficult, small
fuel lines are easier to block,
surplus fuel may be vented
overboard X
FUEL: CLASSIFICATION OF AERO FUEL
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AIRCRAFT TECHNICAL
Aviation Gasoline (AVGAS)
100LL is used in the UK
(100 is the octane level, LL is low lead)
Colour of AVGAS 100LL is blue
FUEL: CLASSIFICATION OF AERO FUEL
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AIRCRAFT TECHNICAL
Aviation Jetfuel (JET A1)
Colour of fuel is straw
Always confirm the fuel that your aircraft uses!
FUEL: CLASSIFICATION OF AERO FUEL
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AIRCRAFT TECHNICAL
Motor Gasoline (MOGAS)
Subject to rigorous conditions of use
CAA Safety Sense Leaflet 4A and
Airworthiness Notice 98 refer
Can only be used in certain aircraft
FUEL: INSPECTION
B f fli ht ll d i i t th i ft h ld b
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AIRCRAFT TECHNICAL
Before flight all drain points on the aircraft should be
inspected for fuel contamination
Check colour is correct
(dont check avgas is blue by holding up tester to a
blue sky!
Check no bits in the strainer
(metal, dirt, paint etc)
Check no water is in the strainer
(it will sink to the bottom because it is heavier)
Check smell
(however be aware that only a small amount of fuel
will cause water to smell)
FUEL: SYSTEMFuel quantity indicators
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AIRCRAFT TECHNICAL
Fuel tank
q y
Fuel caps(one vented)
Fuel vent
Contaminantscreen
Fuel tank selector
Fuel strainer
Carburettor
Engine
primer
Primer control
To engine
FUEL: SYSTEM
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AIRCRAFT TECHNICAL
FUEL TANKS
Usually in wings
Can be separate or cross-fed with each other
Screens fitted to prevent contaminants entering
the fuel lines
Drain points below allow fuel samples to be taken
FUEL: SYSTEM
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AIRCRAFT TECHNICAL
FUEL GAUGES
Most light aircraft have electrical gauges
Never rely upon the gauges!
Legally only have to be accurate when empty
FUEL VENTING
One filler cap is vented to allow air into tank
Fuel tank is vented to allow fuel to escape
Required to keep constant pressure inside
fuel tank
FUEL: SYSTEM
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AIRCRAFT TECHNICAL
TANK SELECTOR
To select individual tanks (in Cessna 152/172 the
fuel is crossfed from both tanks at the same time)
FUEL STRAINER
Allows fuel sample to be taken from lowest
point in system
PRIMER
Allows neat fuel to be fed direct into
cylinders for starting (use during flight
would cause a rich cut)
In low winged aircraft a fuel pump will be required for
starting to begin flow of fuel. High wings rely on gravity.
PRACTICE QUESTION!
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AIRCRAFT TECHNICAL
As the aircraft climbs the air density increases/decreases and so the fuel/air
mixture becomes weaker/richer
Air densitydecreases
Fuel/air mixturebecomes richer
FIRES
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AIRCRAFT TECHNICAL
All fires associated with aircraft can be dangerousalways know how to extinguish each type of fire that
could occur
Most extinguishers work on eliminating one side
of the fire triangle
FIRES: EXTINGUISHERS
WATER ti i h d f
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AIRCRAFT TECHNICAL
Wood
Paper
Cloth
WATERextinguishers used for:
FIRES: EXTINGUISHERS
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AIRCRAFT TECHNICAL
Wood
Paper
Cloth
Flammable Liquids
FOAMextinguishers used for:
FIRES: EXTINGUISHERSCARBON DIOXIDE extinguishers used for:
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AIRCRAFT TECHNICAL
Flammable Liquids
Electrical Fire
FIRES: EXTINGUISHERSDRY POWDERextinguishers used for:
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Wheel Fires
Flammable Liquids
Flammable Gases
Electrical Fires
FIRES: EXTINGUISHERS
BCF HALONextinguishers used for:
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AIRCRAFT TECHNICAL
BCF Halon is now illegal in the UK exceptin an aviation setting
With all extinguishersALWAYS ventilate well after
usage to ensure you dont run out of oxygen!!
g
Anything!
PRACTICE QUESTION!
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AIRCRAFT TECHNICAL
Which is the safest extinguisher to use on a wheel fire
Dry powder
Lecture complete
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AIRCRAFT TECHNICAL
Lecture complete
Any Questions?
LECTURE TWO: SYSTEMS, INSTRUMENTATION & AIRWORTHINESS
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3. Pitot Static System
5. Vertical Speed Indicator
4. Altimeter
6. Airspeed Indicator
7. Gyroscopes - basics
8. Attitude Indicator
9. Directional Indicator
10. Turn Co-ordinator
11. Magnetic Compass
12. Airworthiness Requirements
2. Vacuum System
1. Electrical System
INSTRUMENTS: ELECTRICAL SYSTEM
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Most light aircraft run on a
Direct Current (DC) electrical
system
Current is provided from an
alternator when the engine is
running and from a batterywhen the engine is not
running
We will run through each
element in turn...
INSTRUMENTS: ELECTRICAL SYSTEM
BATTERY
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BATTERY
Provides electrical power when
engine is not running or in case ofelectrical failure
Most aircraft use a lead-acid
vented battery
Usually a 12 or 24 volt batterywhich will also give a amp-hours
on how long it will provide power
Battery power used in start
procedure is recharged duringflight by the alternator
INSTRUMENTS: ELECTRICAL SYSTEM
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AIRCRAFT TECHNICAL
If more than one battery is used
they can be connected in different
ways to change the amp-hours:
INSTRUMENTS: ELECTRICAL SYSTEM
MASTER SWITCH
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AIRCRAFT TECHNICAL
Selects whether battery power,
alternator or both are required
AMMETER
Shows the state of charge of
the battery
ALTERNATOR CIRCUIT BREAKER
Can be used to take alternator off-line
if required
LOW VOLTAGE LIGHT
Illuminates when the battery is
discharging
INSTRUMENTS: ELECTRICAL SYSTEM
ALTERNATOR
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AIRCRAFT TECHNICAL
ALTERNATOR
The alternator is powered by an engine-driven belt
The alternator produces alternating
current which is rectified to direct
current by the use of diodes
Alternator also recharges the
battery
INSTRUMENTS: ELECTRICAL SYSTEM
BUS BAR
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AIRCRAFT TECHNICAL
BUS BAR
Distribution board which allows
current supply to various
elements of the system
Usually avionics will have aseparate bus bar
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INSTRUMENTS: ELECTRICAL SYSTEM
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AIRCRAFT TECHNICAL
RELAYS
Used so that one electrical circuit canproduce a change in another electrical
circuitused in starters in aircraft
Safetymeans that high currents dont
need to be in the cockpit!
The magneto system is a form of
relay
INSTRUMENTS: ELECTRICAL SYSTEM: MALFUNCTIONS
Alternator Malfunction
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AIRCRAFT TECHNICAL
Alternator Malfunction
Switch off alternator side of master switch and load shed to ensure battery
lasts the maximum amount of time (30 minutes in C152)
Starter Warning Light stays on after start
Immediately shut down enginethe battery is trying to run the alternator and
this will cause damage
Low voltage light illuminates
Load shed to reduce load on system sometimes, however, during taxying on
a hot day is not a problem.
More details in the individual POH for your aircraft
VACUUM SYSTEM: BASICS
Used to spin gyroscopes in the
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AIRCRAFT TECHNICAL
Used to spin gyroscopes in the
Attitude Indicator (AI) and
Directional Indicator (DI)
Suction pump driven by the
engine
Filtered air sucked through filter,via suction gauge and then
through instruments
Vacuum relief valve operates in
event of over-vacuum situation
VACUUM SYSTEM: MALFUNCTIONS
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AIRCRAFT TECHNICAL
BLOCKED AIR FILTER
Reduced airflow will cause gyros to run down
Suction gauge will indicate low suctionX
VACUUM SYSTEM: MALFUNCTIONS
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AIRCRAFT TECHNICAL
X
VACUUM PUMP FAILURE
Zero reading on the suction gauge
Gyros will wind down within a few minutes
VACUUM SYSTEM: MALFUNCTIONS
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AIRCRAFT TECHNICAL
XEXCESSIVE HIGH SUCTION
Vacuum relief valve should prevent this
Failure of this valve means gyros will spin
too fast and suffer damage
Land as soon as possible
INSTRUMENTS: PITOT STATIC SYSTEM
The Pitot Static system provides data for 3 instruments:
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The Pitot Static system provides data for 3 instruments:
Altimeter Vertical Speed Indicator Airspeed Indicator
(VSI) (ASI)
INSTRUMENTS: PITOT STATIC SYSTEM
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AIRCRAFT TECHNICAL
There are 2 elements to the Pitot-Static System
PITOT TUBE
Usually beneath a wing. In free-stream
airflow. Often heated to avoid the entrance
being blocked by ice
STATIC VENT
Usually on side of fuselage. Out of airflow.
Some aircraft have 2 to average out readingand reduce errors
INSTRUMENTS: PITOT STATIC SYSTEM
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Gives Static
Pressure
Gives total pressure
(only used in the ASI)
The force exerted by the molecules in the air
it f f i ATMOSPHERIC
INSTRUMENTS: ALTIMETER
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AIRCRAFT TECHNICAL
on a unit of surface area is ATMOSPHERIC
PRESSURE
The nearer the earths surface, the more air
molecules are pressing down from above
Atmospheric pressure, therefore, INCREASES
with a DECREASE in altitude
An aircraft at 3000 feet is experiencing less
atmospheric pressure than one at 1000 feet.
The rule of thumb: For every 30 feet gained in
altitude the pressure drops by 1mb (h/p)
INSTRUMENTS: ALTIMETER
Displays vertical displacement from the pressure datum set
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AIRCRAFT TECHNICAL
Displays vertical displacement from the pressure datum set
Uses Static Pressure only
Basically a barometer with a scale in feet
INSTRUMENTS: ALTIMETERIndicates 10,000s of feet
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AIRCRAFT TECHNICAL
Long pointer shows 100s of feet
Short pointer
shows 1000s of
feet
Hatching shows
aircraft is below10,000 feet
Altimeter
subscale (here
shows US
format of
inches, we
have mb/hp inUK/Europe)
INSTRUMENTS: ALTIMETER
As aircraft climbs, atmospheric
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AIRCRAFT TECHNICAL
, p
pressure drops and capsule
expands
This is because the pressure
inside the case is less than the
pressure inside the capsule and
so allows the expansion to occur
As aircraft descends, atmospheric
pressure increases and capsule
compresses
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INSTRUMENTS: ALTIMETER: ERRORS
INSTRUMENT ERROR
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AIRCRAFT TECHNICAL
INSTRUMENT ERROR
Known errors caused by manufacture of the instrument
INSTRUMENT LAG
Rapid pressure changes will be displayed with a slight lag while
capsule expands / contracts
POSITION ERROR
Caused by poor siting of the static port (reduced in aircraft with two
static ports)
BLOCKAGES OF THE STATIC PORT
Caused by ice / insects / sticky tape over the static port
INSTRUMENTS: ALTIMETER: ERRORS
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AIRCRAFT TECHNICAL
STATIC BLOCKED, AIRCRAFT CLIMBS
Pressure inside case should
decrease but it will notall inputs willstay the same
STATIC BLOCKED, AIRCRAFT DESCENDS
Pressure inside case should increase
but it will notall inputs will stay the
same
If the static vent is blocked, the altimeter will
continue to read the altitude indicated when the
blockage occurred
INSTRUMENTS: ALTIMETER: PRACTICAL USES
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AIRCRAFT TECHNICAL
Altimeters would be easy if the pressure changes in
the atmosphere happened like this
INSTRUMENTS: ALTIMETER: PRACTICAL USES
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AIRCRAFT TECHNICAL
This situation is more likely and so it is VITAL that the
altimeter is set correctly to the required setting
INSTRUMENTS: ALTIMETER: PRACTICAL USES
All aircraft
t ll t
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QFE
Gives height
above the airfield
QNH
Gives altitude
above mean sea
level (amsl)
1013 hp
Standard
Gives flight level
above 1013.2hp
pressure level
actually at same
level but
altimetersreading
differently
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INSTRUMENTS: VERTICAL SPEED INDICATOR
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AIRCRAFT TECHNICAL
Pointer shows100s of feet of
rate of change
Maximum that can
be shown
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INSTRUMENTS: VERTICAL SPEED INDICATOR: ERRORS
INSTRUMENT ERROR
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AIRCRAFT TECHNICAL
INSTRUMENT ERROR
Known errors caused by manufacture of the instrument
POSITION ERROR
Caused by poor siting of the static port (reduced in aircraft with two
static ports)
BLOCKAGES
If static vent or line becomes blocked, the instrument will sense no
pressure differential and so will always indicate zero
INSTRUMENTS: AIRSPEED INDICATOR
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AIRCRAFT TECHNICAL
Displays Indicated Airspeed (IAS)
Uses input from Pitot tube (total pressure)
Uses input from Static Vent (static pressure)
PitotStatic = Dynamic Pressure
INSTRUMENTS: AIRSPEED INDICATOR VSO
Stall speed in landing
configuration
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AIRCRAFT TECHNICAL
GREEN ARC
Normaloperating
speed range
WHITE ARC
Flap operation speed range
YELLOW ARC
Cautionary speed
range
VNE
Never exceed
speed
VNO
Maximum structural
cruising speed
VS1Stall speed in clean
configuration
VFE
Maximum flap
extension
speed
INSTRUMENTS: AIRSPEED INDICATOR
Static pressure is fed into the case of
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AIRCRAFT TECHNICAL
Static pressure is fed into the case of
the instrument
Pitot pressure is fed into the
expandable diaphragm
Because the diaphragm has to
push against the air inside the
case, the 2 static pressures cancel
each other out
A series of linkages then transfer this
information onto the face of the
instrument
INSTRUMENTS: AIRSPEED INDICATOR
All airspeed indicators are calibrated
t th I t ti l St d d
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AIRCRAFT TECHNICAL
to the International Standard
Atmosphere (ISA)
More details in the Meterorology
lectures!
Sea Level Density =
1225 gm / m3
Sea Level Temperature =
+15 C
Temperature change with altitude
= -1.98 C per 1000 feet
INSTRUMENTS: AIRSPEED INDICATOR: ERRORS
Indicated Airspeed
(IAS)
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AIRCRAFT TECHNICAL
INSTRUMENT ERROR
(IAS)
POSITION ERROR
Calibrated / Rectified
Airspeed
(CAS / RAS)
DENSITY ERROR
True Airspeed
(TAS)
Found in the
POH
Used for
navigation
calculations
INSTRUMENTS: AIRSPEED INDICATOR: IAS / TAS
As the aircraft climbs (density
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AIRCRAFT TECHNICAL
( y
decreases) IAS under-reads in
relation to TAS
This can be worked out using the CRP
1/5 or on some airspeed indicators
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INSTRUMENTS: CHECKS
It is VERY important to check the pitot static system instruments prior to flight:
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AIRCRAFT TECHNICAL
ALTIMETER
Glass should be clear & unbroken
Zero the altimeter
Add on 10 mb / hp
Altimeter should increase by 280 feet
Subtract 10mb/hp from original setting
Altimeter should decrease by 280 feet
VERTICAL SPEED INDICATOR
Glass should be clear & unbroken
Should be indicating zeroAs soon as possible after getting
airborne, check showing rate of climb
INSTRUMENTS: CHECKS
AIRSPEED INDICATOR
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AIRCRAFT TECHNICAL
AIRSPEED INDICATOR
Glass should be clear & unbrokenShould be reading zero
During take-off roll, ensure that indication
is being seen
Also ensure on the walk-round that you have checked:
1. Static port is clear and unobstructed
2. Pitot tube is clear and unobstructed
3. Pitot heat works (do not leave heat on for too long on groundmay burn
out the element)
INSTRUMENTS: MAGNETIC COMPASS
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AIRCRAFT TECHNICAL
Displays magnetic heading information
Also known as a direct reading compass
Lubber line reads the magnetic
heading of the aircraft
Directions are alwaysexpressed as a 3-digit
grouping to avoid
confusion (030, 300,
330etc
north, south, eastand west also used
but now not terms such
as north north west
etc
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INSTRUMENTS: MAGNETIC COMPASS
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AIRCRAFT TECHNICAL
The compass shows MAGNETIC north
Maps and charts are aligned to TRUE north
The difference between the two is known as
VARIATION
Lines of equal variation are known as
ISOGONALS
INSTRUMENTS: MAGNETIC COMPASS
The aircraft is made of metal and has lots of radio
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AIRCRAFT TECHNICAL
The aircraft is made of metal and has lots of radio
equipment and so the compass is not very
accurate!
The inaccuracies are know and are displayed in
the aircraft on a DEVIATION card
Compass Heading +/- Deviation = Magnetic Heading +/- Variation = True Heading
or CDMVT
or cadburys dairy milk is very tasty
or true virgins make dull companions
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INSTRUMENTS: MAGNETIC COMPASS: ERRORS
MAGNETIC DIP
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AIRCRAFT TECHNICAL
The compass aligns to the earthsmagnetic field
At latitudes near the poles, the
magnetic field dips in so that it
enters the ground nearly vertical
The compass will try to follow this!
The compass will indicate poorly and
is generally useless in latitudes above60north or south
To counter this, compasses are pivoted slightly off-centre
but this causes other errors:
INSTRUMENTS: MAGNETIC COMPASS: ERRORS
Pivot line
I th h i h t f it
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Vertical component
of dip
Weight
In northern hemisphere, centre of gravity
is arranged so that it is placed south ofthe pivot pointN
S
This reduces errors due to dip but
causes errors during turns or during
accelerations / decelerations
INSTRUMENTS: MAGNETIC COMPASS: ERRORS
ACCELERATION ERRORS
Acceleration on easterly & westerly headings
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AIRCRAFT TECHNICAL
Acceleration on easterly & westerly headings
Compass gets left behind due to inertia and the offset pivot causes the compassto swing away from the correct direction.
In the northern hemisphere this is a swing to the north (the nearer pole)
Steady speed Aircraft accelerates
INSTRUMENTS: MAGNETIC COMPASS: ERRORS
DECELERATION ERRORS
Deceleration on easterly & westerly headings
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AIRCRAFT TECHNICAL
Deceleration on easterly & westerly headings
Pivot slows with aircraft but magnetic tries to continue at same speed due toinertia
In the northern hemisphere this is a swing to the south (the nearer pole)
Steady speed Aircraft accelerates
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INSTRUMENTS: MAGNETIC COMPASS: ERRORS
Easy way to remember compass acceleration & deceleration errors
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AIRCRAFT TECHNICAL
Accelerate North, Decelerate South
ANDS
INSTRUMENTS: MAGNETIC COMPASS: ERRORS
TURNING ERRORS
During a turn the aircraft experiences centripetal force acting towards the centre
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AIRCRAFT TECHNICAL
During a turn the aircraft experiences centripetal force acting towards the centre
of the turn
This force is essentially an acceleration
The force acts on the compass pivot and accelerates it towards the centre of
the turn
The compass is left behind due to inertia
INSTRUMENTS: MAGNETIC COMPASS: ERRORS
TURNING ERRORSthrough northerly headings
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AIRCRAFT TECHNICAL
N
1. Turning left through north
acceleration is to the east
2. Centre of gravity gets left behind due
to inertia
3. Pilot must undershoot when using the
compass because it has to catch up withthe actual heading
4. For example, if a heading of north (360)
is required, pilot must roll out when 030isindicated and waitthe compass will
indicate 360after a short interval
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INSTRUMENTS: MAGNETIC COMPASS: ERRORS
Easy way to remember compass turning errors
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AIRCRAFT TECHNICAL
Undershoot North, Overshoot South
UNOS
INSTRUMENTS: MAGNETIC COMPASS: CHECKS
Before taxy check:
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AIRCRAFT TECHNICAL
y
no leaks and no bubbles
Glass clear and unobstructed
During taxy check:
Right turncompass shows increase in heading
Left turncompass shows decrease in heading
On runway check:
Compass is reading correctly in relation to runway heading
In flight check:
When aligning DI to compass, the aircraft must not be
turning or accelerating or decelerating
ENGINE INSTRUMENTS: GYROSCOPES BASICS
A gyroscope is a rotating wheel
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AIRCRAFT TECHNICAL
gy p g
mounted so that it can turn freely in one
or more directions
It is capable of maintaining a fixed
position in space
The aircraft will move around the
gyroscope while the gyroscope
remains effectively stationary
ENGINE INSTRUMENTS: GYROSCOPES BASICS
Gyroscopes have two basic properties:
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AIRCRAFT TECHNICAL
Gyroscopes have two basic properties:
RIGIDITY
The gyros ability to maintain its fixed position in space
Dependent upon mass of the rotor and the speed at
which it is rotating
PRECESSION
When a force is applied to the gyroscope the effect isdisplaced by 90in the direction of rotation
ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR
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AIRCRAFT TECHNICAL
Displays heading information(ONLY if aligned to the magnetic compass!)
Used in place of compass because
more steady to read and not subject to
errors of the compass
Known as Direction Indicator (DI),
Directional Gyro (DG) or Heading
Indicator (HI)
ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR
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AIRCRAFT TECHNICAL
Heading
currently
indicated
Setting knob (releases gyro so that compass card
can be rotated)
INSTRUMENTS: DIRECTIONAL INDICATOR
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AIRCRAFT TECHNICAL
The DI is an space gyro it maintains a
fixed position in space
The aircraft turns around the gyro and
the gyro stays in the same place
Most DIs in light aircraft are spun by
the suction / vacuum system
INSTRUMENTS: DIRECTIONAL INDICATOR: ERRORS
INSTRUMENT ERROR
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AIRCRAFT TECHNICAL
Known errors caused by manufacture of the instrument
MECHANICAL DRIFT
Friction in the workings of the instrument which will
cause it to drift off the set heading
APPARENT DRIFT
Explanation coming up!
TRANSPORT WANDER
DI is adjusted to oppose apparent drift at a particular
latitude, large distances from this latitude will cause
inaccuracies until adjusted
ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR: ERRORS
Apparent Drift
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AIRCRAFT TECHNICAL
The gyro remains effectively aligned to the north star
This is initially the same as for magnetic north on earth
As the earth turns, the two points diverge from eachother
This is even seen if the aircraft is on the ground and
stationary
The DI will need to be manually realigned about
every 15 minutes
INSTRUMENTS: DIRECTIONAL INDICATOR: CHECKS
Before taxy check:
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AIRCRAFT TECHNICAL
Glass is clear and unbrokenAlign DI to compass (with engine running)
Check suction is in the green
During taxy check:
Aircraft turning right, DI increasing
Aircraft turning left, DI decreasing
During flight check:
Aircraft in straight, level & unaccelerated flight
Re-align DI with compass
INSTRUMENTS: ATTITUDE INDICATOR
Displays aircraft pitch and roll attitude
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AIRCRAFT TECHNICAL
Does NOT necessarily indicate a
climb or a descent
Does NOT necessarily indicate a
turn
INSTRUMENTS: ATTITUDE INDICATOR
Roll indicator
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AIRCRAFT TECHNICAL
Roll markers
Pitch markersHorizon
Rabbits ears
Adjustor for aircraft
datum
INSTRUMENTS: ATTITUDE INDICATOR
The AI is an earth gyro which
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