mikeasimmons.files.wordpress.com 2012 11 aircraft-general-knowledge1

8/13/2019 Mikeasimmons.files.wordpress.com 2012 11 Aircraft-general-knowledge1

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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


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


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


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


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


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


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


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


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


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


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



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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: LATERAL STABILITY


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AIRCRAFT TECHNICAL


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



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AIRCRAFT TECHNICAL


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


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



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AIRCRAFT TECHNICAL


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


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



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AIRCRAFT TECHNICAL


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


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



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AIRCRAFT TECHNICAL


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



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AIRCRAFT TECHNICAL


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


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!



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AIRCRAFT TECHNICAL


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



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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



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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



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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



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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



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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



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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)



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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!



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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



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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



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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



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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



120/218

AIRCRAFT TECHNICAL

Aviation Jetfuel (JET A1)

Colour of fuel is straw

Always confirm the fuel that your aircraft uses!



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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:



130/218

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:


132/218

AIRCRAFT TECHNICAL

Wheel Fires

Flammable Liquids

Flammable Gases

Electrical Fires


BCF HALONextinguishers used for:


133/218

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!


134/218

AIRCRAFT TECHNICAL

Which is the safest extinguisher to use on a wheel fire

Dry powder

Lecture complete


135/218

AIRCRAFT TECHNICAL

Lecture complete

Any Questions?

LECTURE TWO: SYSTEMS, INSTRUMENTATION & AIRWORTHINESS


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AIRCRAFT TECHNICAL

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


137/218

AIRCRAFT TECHNICAL

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...


BATTERY


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AIRCRAFT TECHNICAL

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



139/218

AIRCRAFT TECHNICAL

If more than one battery is used

they can be connected in different

ways to change the amp-hours:


MASTER SWITCH


140/218

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


ALTERNATOR


141/218

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


BUS BAR


142/218

AIRCRAFT TECHNICAL

BUS BAR

Distribution board which allows

current supply to various

elements of the system

Usually avionics will have aseparate bus bar


143/218



144/218

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


145/218

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


146/218

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


147/218

AIRCRAFT TECHNICAL

BLOCKED AIR FILTER

Reduced airflow will cause gyros to run down

Suction gauge will indicate low suctionX



148/218

AIRCRAFT TECHNICAL

X

VACUUM PUMP FAILURE

Zero reading on the suction gauge

Gyros will wind down within a few minutes



149/218

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:


150/218

AIRCRAFT TECHNICAL

The Pitot Static system provides data for 3 instruments:

Altimeter Vertical Speed Indicator Airspeed Indicator

(VSI) (ASI)



151/218

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



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AIRCRAFT TECHNICAL

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


153/218

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)


Displays vertical displacement from the pressure datum set


154/218

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


155/218

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)


As aircraft climbs, atmospheric


156/218

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


157/218

INSTRUMENTS: ALTIMETER: ERRORS

INSTRUMENT ERROR


158/218

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


160/218

AIRCRAFT TECHNICAL

Altimeters would be easy if the pressure changes in

the atmosphere happened like this



161/218

AIRCRAFT TECHNICAL

This situation is more likely and so it is VITAL that the

altimeter is set correctly to the required setting


All aircraft

t ll t


162/218

AIRCRAFT TECHNICAL

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


163/218

INSTRUMENTS: VERTICAL SPEED INDICATOR


164/218

AIRCRAFT TECHNICAL

Pointer shows100s of feet of

rate of change

Maximum that can

be shown


165/218

INSTRUMENTS: VERTICAL SPEED INDICATOR: ERRORS

INSTRUMENT ERROR


166/218

AIRCRAFT TECHNICAL

INSTRUMENT ERROR


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


167/218

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


168/218

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


Static pressure is fed into the case of


169/218

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


All airspeed indicators are calibrated

t th I t ti l St d d


170/218

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


172/218

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


173/218

INSTRUMENTS: CHECKS

It is VERY important to check the pitot static system instruments prior to flight:


174/218

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


175/218

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


176/218

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


177/218



178/218

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


The aircraft is made of metal and has lots of radio


179/218

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


180/218

INSTRUMENTS: MAGNETIC COMPASS: ERRORS

MAGNETIC DIP


181/218

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:


Pivot line

I th h i h t f it


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AIRCRAFT TECHNICAL

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


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


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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Easy way to remember compass acceleration & deceleration errors


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AIRCRAFT TECHNICAL

Accelerate North, Decelerate South

ANDS


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


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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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


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


Roll indicator


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AIRCRAFT TECHNICAL

Roll markers

Pitch markersHorizon

Rabbits ears

Adjustor for aircraft

datum


The AI is an earth gyro which

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