Mikeasimmons.files.wordpress.com 2012 11 Aircraft-general-knowledge1

 AIRCRAFT GENERAL KNOWLEDGE I

 AIRCRAFT TECHNICAL

LECTURE ONE: AERODYNAMICS AND ENGINES 1.

The Atmosphere

2.

Aerodynamics – Drag

3.

Aerodynamics Aerodynamics - Lift

4.

Aerodynamics - Weight

5.

Aerodynamics – Thrust (Propellers)

6.

Stalling

7.

Aircraft Stability Stability

8.

Engines

9.

Fires

 AIRCRAFT TECHNICAL

THE ATMOSPHERE: BASICS! The ATMOSPHERE ATMOSPHERE is a parcel of o f gases held to the earth by gravity Due to the fact that the earth ROTA ROTATES, the atmosphere atmo sphere is flung flu ng outwards at the equator meaning that it extends further toward space at the EQUATOR EQUATOR than at the POLES This is magnified by the fact that the air is hotter at the equator and rises

 AIRCRAFT TECHNICAL

THE ATMOSPHERE: COMPOSITION

1% OTHER GASES (including water vapour)

21% OXYGEN Knowledge of the atmosphere is important to pilots and aircraft designers because it is the medium we fly in and the air we breathe!

It is what the aircraft engine uses for combustion and what keeps us airborne

78% NITROGEN  AIRCRAFT TECHNICAL

INTERNATIONAL STANDARD ATMOSPHERE (ISA) ISA is a measuring stick against which we can compare the actual atmosphere to 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 the instruments perform in relation to their published performance criteria

 AIRCRAFT TECHNICAL

INTERNATIONAL STANDARD ATMOSPHERE (ISA)

Pressure change with altitude = -1mb per 30 feet

Sea Level Pressure = 1013mb

Temperature change with altitude = -1.98˚ C per 1000 feet

Sea Level Temperature = +15˚ C

Sea Level Density = 1225 gm / m 3

 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 24° colder than at the surface 15°C – 24°C = -9°C

It is actually -7 °C and so the deviation is ISA +2°C

 AIRCRAFT TECHNICAL

FOUR FORCES

LIFT generated by airflow over the wings and acting perpendicular to wing

DRAG Resistance to an object through the air

THRUST provided by propeller

More detail....

MASS Mass of aircraft acting straight down through centre of earth

 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  AIRCRAFT TECHNICAL

FOUR FORCES: LIFT If the same diagram is split in half the same effect will happen

Now let’s change that diagram a little...

So if we now imagine a wing – we have just created lift!

 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!

 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!

 AIRCRAFT TECHNICAL

FOUR FORCES: LIFT

Laminar flow boundary layer (very thin layer)

Lift force acts through centre of pressure

Transition point (where laminar flow becomes turbulent)

Turbulent boundary layer (slightly thicker)

Relative  Airflow Higher pressure beneath the wing

What are the bits of the wing called?...

 AIRCRAFT TECHNICAL

FOUR FORCES: LIFT

Leading Edge

Chord line

Maximum thickness

Trailing Edge

 AIRCRAFT TECHNICAL

FOUR FORCES: LIFT

 Aerofoils are designed so that the pressure distribution leads to a lifting force

We shall revisit this diagram more when we discuss stalling

 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

 AIRCRAFT TECHNICAL

FOUR FORCES: LIFT We couldn’t avoid formulas forever...  Air Density

(decreases with increased altitude)

Wing Surface Area

May be changed by some flaps (more later)

Lift = Cl ½ p V 2 S

Coefficient of Lift Includes many things but one important one is angle of attack of the wing

Speed Combination of wind speed and forward speed  AIRCRAFT TECHNICAL

FOUR FORCES: LIFT The lift force is perpendicular to the relative airflow and depends upon: Wing Shape  Angle of Attack

 Air Density Velocity Wing Surface Area

 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 °)  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

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG Drag is the resistance to movement and acts opposite to the direction of flight

TOTAL DRAG

PARASITE DRAG

Skin friction drag Interference drag

INDUCED DRAG

Form drag  AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: PARASITE DRAG Parasite Drag is caused by the aircraft being in the airflow

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

It is made up of 3 elements:  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

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: PARASITE DRAG FORM DRAG

Just like a swimmer – the way in which the airflow separates from the surface will cause drag The more eddies that are caused, the more drag is produced

Streamlining of the aircraft will reduce form drag

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: PARASITE DRAG INTERFERENCE DRAG

Drag due to junctions of surfaces giving off eddies which disrupts airflow over surfaces behind

Junctions are streamlined to reduce

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: INDUCED DRAG

Induced drag is caused by the generation of lift  As speed increases, induced drag decreases

This is because the wing works harder at slower speeds to produce lift

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: INDUCED DRAG Lift is created by the pressure differential between the upper and lower surfaces of the 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

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: INDUCED DRAG

The downward pressure on the wing causes drag as does the vortices which are created behind the wing

The flow along the wing and up over the wing tips is called spanwise flow

 AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: INDUCED DRAG Reduced by high aspect ratio wings (the spanwise flow has run out of energy by the time 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  AIRCRAFT TECHNICAL

FOUR FORCES: DRAG: TOTAL DRAG

PARASITE DRAG

TOTAL DRAG

INDUCED DRAG

Minimum Drag Speed (V )

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

Does induced drag increase or decrease as the aircraft speeds up?

Decreases

 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  AIRCRAFT TECHNICAL

FOUR FORCES: THRUST: PROPELLERS: BASICS Plane of rotation

Blade back

Blade face

Direction of flight

Blade angle

Chord line

 AIRCRAFT TECHNICAL

FOUR FORCES: THRUST: PROPELLERS: ROTATIONAL VELOCITY ROTATIONAL VELOCITY  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

 AIRCRAFT TECHNICAL

PROPELLERS: FORWARD VELOCITY & HELICAL MOTION With each rotation the propeller also moves forwards

The motion is “helical” –  like a screw Newton’s third law of motion states: For every action there is an equal and opposite reaction

Ie. The propeller accelerates air rearwards, so the propeller (and the attached aircraft) move forwards

Otherwise known as Noddy does propellers!  AIRCRAFT TECHNICAL

FOUR FORCES: THRUST: PROPELLERS: FORCES UPON The easiest way to see propellers is to treat them like a wing

PROPELLER TORQUE FORCE

THRUST

Wing produces lift at 90 ° to chord line – propeller produces thrust

Propellers are efficient only at one speed  – this is why variable speed propellers are used on aircraft with a larger speed range Relative airflow

 AIRCRAFT TECHNICAL

STALLING Stalling of the wing occurs above the “critical angle” of attack

This can occur at high or low speeds – it has nothing to do with speed (although stalling speeds may be used for references purposes)

Critical Angle of Attack

 AIRCRAFT TECHNICAL

STALLING : AIRFLOW During “Normal” flight angles, the airflow separates towards the rear of the wing

 At the critical angle the separation point is much further forwards – the aerofoil is now 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

 AIRCRAFT TECHNICAL

STALLING : CENTRE OF PRESSURE  At “Normal” flight angles the centre of pressure (where the lift is said to act through) 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 pressure moves rapidly rearwards causing a pitch down in most aircraft

 AIRCRAFT TECHNICAL

STALLING : RECOGNITION  APPROACHING A STALL

May get all or some of the following signs: Sloppy controls Less airflow over the surfaces makes them harder to move and they are moving less air molecules so have less effect

Yaw becoming more obvious Slipstream effect still occurring but less rudder authority to correct either through slower speed or because of turbulent airflow

Low / decreasing Airspeed and associated reducing airspeed Light Buffet as turbulent air reaches tailplane

Stall warner

 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 16 ° for a light aircraft)  AIRCRAFT TECHNICAL

STALLING : RECOVERY

 Aircraft exceeds critical angle and stalls

 Aircraft nearing critical angle

Control column centrally forward until stall symptoms stop

Stall symptoms stop – use ailerons to level wings

Recovered!  AIRCRAFT TECHNICAL

STALLING : FACTORS AFFECTING WEIGHT

 A 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

 AIRCRAFT TECHNICAL

STALLING : FACTORS AFFECTING LOAD FACTOR Load factor is a type of weight  – it affects the “G” of the aircraft and its effective weight

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 60 ° has 2g and the aircraft’s effective weight is doubled  AIRCRAFT TECHNICAL

STALLING : CHANGE OF STALLING SPEED If an aircraft usually stalls at 90 kts and is in a 60 ° banked turn, how do we work out what the new stall speed will be? New Stall speed = Old stall speed x load factor Turn has a load factor of 2 The square root of the load factor is 1.4

90 kts x 1.4 = 127 kts

 AIRCRAFT TECHNICAL

STALLING : FACTORS AFFECTING 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

 AIRCRAFT TECHNICAL

STALLING : FACTORS AFFECTING FLAPS Flaps are designed to increase the C LMAX (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

 AIRCRAFT TECHNICAL

STALLING : FACTORS AFFECTING 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

 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 can’t spin and so this is why so much emphasis is placed on stall recognition in the PPL syllabus!

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

When is the co-efficient of lift at its maximum?

Just before the stalling angle of attack (CL MAX)

 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 that is too stable may be impossible to control because it needs such large control inputs

 An aircraft with too little stability is very difficult to handle and may be uncontrollable

 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 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 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 TECHNICAL

AIRCRAFT STABILITY: LONGITUDINAL STABILITY

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 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 left the 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 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 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 induces a yaw to the right

 AIRCRAFT TECHNICAL

AIRCRAFT STABILITY: DIRECTIONAL STABILITY

Increased directional stability can be gained by: Greater fin area Greater keel surface behind centre of gravity Forward Centre of Gravity (bigger moment arm gives a bigger effect)

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

Directional Stability is achieved through what bit of the aircraft?

Fin (Vertical Stabiliser)

 AIRCRAFT TECHNICAL

AIRFRAMES: STRUCTURE

The airframe is made up of various components, we will examine each in turn:

 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 the aluminium skin

 AIRCRAFT TECHNICAL

AIRFRAMES: WINGS WINGS Used to generate lift required for flight and usually 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

 AIRCRAFT TECHNICAL

AIRFRAMES: EMPENNAGE EMPENNAGE / TAIL PLANE Many different designs used (as below, allflying 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 aircraft’s lifting ability  AIRCRAFT TECHNICAL

AIRFRAMES: FLIGHT CONTROLS RUDDER Used for movement about the directional (normal) axis

ELEVATORS Used for movement about the lateral axis

FLAPS Used to delay the stall and allow the aircraft to fly slower with a lower attitude

 AILERONS Used for movement about the longitudinal axis

 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-balance tabs make sure that stick loads increase as deflection increases – stops pilot damaging them!

 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!)

 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

 AIRCRAFT TECHNICAL

AIRFRAMES: LANDING GEAR Made up of three wheels – main wheels x 2 nosewheel or tailwheel

Wheels may be attached by shockabsorbed sections or fixed “spring leaf” sections

Landing gear is either fixed or retractable

 AIRCRAFT TECHNICAL

AIRFRAMES: NOSEWHEEL & GROUND STEERING

STEERING RODS Use of rudder pedal moves steering rods left and right

OLEO Mixture of air and fluid to provide shock absorption

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

 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

 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 aren’t touching the valve and tube will be being stressed and could fail  AIRCRAFT TECHNICAL

AIRFRAMES: BRAKING SYSTEMS

RUDDER PEDALS

The brakes on the rudder pedals push an actuator

BRAKE FLUID RESERVOIR

BRAKE LINE

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

BRAKE DISC

BRAKE PADS

 AIRCRAFT TECHNICAL

AIRFRAMES: SAFETY PRECAUTIONS

CONTROL LOCKS Can be internal or external Prevent control surface being damaged by high winds

PITOT COVERS Prevent pitot tubes becoming blocked by ice / insects etc  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  AIRCRAFT TECHNICAL

AIRFRAMES: SAFETY PRECAUTIONS

ENSURE all control locks, covers, tie downs and chocks are removed before attempting to taxy or fly!

 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

 AIRCRAFT TECHNICAL

ENGINES: BASIC CONSTRUCTION Most light aircraft have a four cylinder piston engine

SPARK PLUG To ignite mixture (most aircraft have 2)

INLET & OUTLET VALVES Control incoming fuel/air mixture and exiting exhaust

FINS Increase surface area to aid cooling

PISTON RINGS  Allow lubricating oil onto cylinder walls

CYLINDER Houses the moving parts

PISTON

CONNECTING ROD Turns linear motion into rotary motion

CRANKSHAFT Transfers power to propeller and controls valve timing

 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!

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) INTAKE STROKE

Piston moves down the cylinder to “bottom dead centre” –  its lowest position Inlet valve opens Pressure inside the cylinder decreases Fuel / Air Mixture is sucked into the cylinder

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) 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

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) POWER STROKE Spark plug discharges and the spark ignites the mixture

Piston is forced down the cylinder to “bottom dead centre” Pressure inside the cylinder decreases

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) EXHAUST STROKE Piston moves back up cylinder to top t op dead centre

Exhaust valve opens

Burnt gases are moved out through the exhaust system

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE)

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 time – this leads to smoother running

 AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) The compression ratio of an engine determines which fuel is used and how efficient it is

Total volume = space s pace left when piston pis ton at bottom dead centre

Clearance volume = space left when piston at top dead centre Swept volume = volume swept by the piston in one stroke  AIRCRAFT TECHNICAL

ENGINES: OTTO CYCLE (4 STROKE CYCLE) VALVE TIMING

Valve timing aids the engine’s efficiency

The modified Otto Cycle has a high degree of valve overlap – when both valves are open at the same time

 AIRCRAFT TECHNICAL

ENGINES: PRE-IGNITION & DETONATION 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  AIRCRAFT TECHNICAL

Both cause engine damage!

PRACTICE QUESTION!

How many times does each valve open during one cycle of the “Otto” cycle

Twice

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

What is the formula for the compression ratio of an engine?

Total volume divided by clearance volume

 AIRCRAFT TECHNICAL

ENGINES: COOLING Most aircraft engines are air-cooled – it is simpler, cheaper, and easier to maintain

Cowlings and baffles are designed to direct flow of air around to engine to cool it from the outside

Some components have “fins” which increase the surface area and assist with cooling  AIRCRAFT TECHNICAL

ENGINES: COOLING

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

 AIRCRAFT TECHNICAL

ENGINES: LUBRICATION 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)

 AIRCRAFT TECHNICAL

ENGINES: LUBRICATION 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 doesn’t coat the surfaces

Lubrication systems will have an oil filter to trap any particles being carried out of the engine – in this way the oil “cleans” the engine  Always check amount and type of oil is sufficient and correct before flight!

 AIRCRAFT TECHNICAL

ENGINES: LUBRICATION Most light aircraft have “wet sump” oil systems There is a sump where oil returns to by gravity

In a “dry sump” system scavenge 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

 AIRCRAFT TECHNICAL

ENGINES: LUBRICATION 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:  AIRCRAFT TECHNICAL

ENGINES: LUBRICATION: MALFUNCTIONS LOW OIL PRESSURE a.) insufficient oil b.) oil leak c.) failure of oil pump d.) engine problem (failed bearings) e.) oil pressure relief valve stuck open HIGH OIL PRESSURE

a.) oil pressure relief valve inoperative b.) excess oil in system

FLUCTUATING GAUGE

a.) gauge is broken! b.) other issue

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

Remember oil problem can lead to no oil which will lead to no engine! Land as soon as possible  AIRCRAFT TECHNICAL

PRACTICE QUESTION!

How are excessive engine oil pressures prevented?

 An oil pressure relief valve

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: CONSTRUCTION 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

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: CONSTRUCTION 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 not – engine must be shut down immediately to avoid damage to the starter motor and to the engine

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: MAGNETOS & IMPULSE COUPLING

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 coupling retracts

The impulse coupling can be powered by the battery or by handswinging the propeller

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: MAGNETOS & IMPULSE COUPLING Only one magneto is needed for engine start – it provides the electricity for the spark - this magneto has an impulse coupling It retards the spark to the engine so that it works at low rpm settings The impulse coupling rotates the magnet and generates a high voltage The high voltage is achieved by the magnet being stopped and then released suddenly

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: HOW TO USE 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 a spark

 AIRCRAFT TECHNICAL

IGNITION SYSTEMS: HOW TO USE DEAD CUT CHECK Should be done before taxy and just prior to shut down of the engine

x

x

x

x

x

When “left” is selected, the right magneto is earthed so that only sparks from the left magneto are generated  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  AIRCRAFT TECHNICAL

IGNITION SYSTEMS: HOW TO USE 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 providing even sparks and that engine is capable of sustaining with only one working  AIRCRAFT TECHNICAL

IGNITION SYSTEMS: MALFUNCTIONS 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. Ensure no-one touches propeller.

Rough running engine during power check Spark plugs are fouled up. Instructor will show you how to clear or inform engineering

Spark plug fouling is generally caused by an over-rich mixture

 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

 AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: BASICS The carburettor is where the fuel and air is mixed prior to entering the cylinders Butterfly valve controls amount of air to the engine (controlled by throttle in cockpit)

Fuel/air mixture to engine

Float chamber  has  has a store of fuel  – works like a toilet cistern!

Fuel inlet inlet from  from fuel tanks

Venturi creates low Venturi creates pressure area

 Air inlet to carburettor

Mixture Needle controls Needle controls amount of fuel that will be added (controlled by mixture knob in cockpit)  AIRCRAFT TECHNICAL

Mixture should be between 1:8 (rich) or 1:20

CARBURETTORS: CARBURETTORS: IDLING I DLING JET Idle jet

Idle metering unit

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 Idle air bleed  AIRCRAFT TECHNICAL

CARBURETTORS: ACCELERATOR PUMP Linkage attached to throttle

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

Spring adds more fuel in by separate route

 AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: MIXTURE CONTROL CONTROL Engines are designed to run at standard sea level (1013.2 mb/hp and +15 °C

 At altitude there is “less” air and so the aircraft will have too much fuel in comparison to air

The mixture knob / lever can be used 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

 AIRCRAFT TECHNICAL

CARBURETTORS: MIXTURE CONTROL 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

 AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: ICE CARBURETTOR ICE can form in temperatures up to +30˚C

 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 even ENGINE STOPPAGE

 AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: ICE 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 ALWAYS likely when the temperature is below +30˚C and the aircraft is within 200nm of any sea surface

This must be probably on about 99% of days in the UK!  AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: ICE

 AIRCRAFT TECHNICAL

CARBURETTORS: CARBURETTORS: ICE  ALWA  ALWAYS YS use CARB HEAT 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 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!  AIRCRAFT TECHNICAL

CARBURETTORS: ICE 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 more regularly!

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

In what flight condition is carburettor ice most common – climb, descent or cruise?

Descent (with low power setting)

 AIRCRAFT TECHNICAL

FUEL INJECTION Not all aircraft have carburettors – they use fuel injection instead

 DISADVANTAGES Hot starts are more difficult, small fuel lines are easier to block, surplus fuel may be vented overboard

 ADVANTAGES No fuel ice, no carburettor ice, better control of fuel/air ratio, easier maintenance, instant acceleration, increase efficiency of engine

X  AIRCRAFT TECHNICAL

FUEL: CLASSIFICATION OF AERO FUEL

 Aviation Gasoline (AVGAS) 100LL is used in the UK (100 is the octane level, LL is low lead)

Colour of AVGAS 100LL is blue

 AIRCRAFT TECHNICAL

FUEL: CLASSIFICATION OF AERO FUEL

 Aviation Jetfuel (JET A1)

Colour of fuel is straw

 Always confirm the fuel that your aircraft uses!

 AIRCRAFT TECHNICAL

FUEL: CLASSIFICATION OF AERO FUEL 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

 AIRCRAFT TECHNICAL

FUEL: INSPECTION Before flight all drain points on the aircraft should be inspected for fuel contamination Check colour is correct (don’t 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)  AIRCRAFT TECHNICAL

FUEL: SYSTEM Fuel quantity indicators

Fuel vent Fuel caps (one vented)

Contaminant screen Fuel tank

Fuel tank selector Primer control Fuel strainer Engine primer Carburettor

To engine

 AIRCRAFT TECHNICAL

FUEL: SYSTEM 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

 AIRCRAFT TECHNICAL

FUEL: SYSTEM 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  AIRCRAFT TECHNICAL

FUEL: SYSTEM 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.

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

 As the aircraft climbs the air density increases/decreases and so the fuel/air mixture becomes weaker/richer

 Air density – decreases

Fuel/air mixture – becomes richer

 AIRCRAFT TECHNICAL

FIRES  All fires associated with aircraft can be dangerous – always know how to extinguish each type of fire that could occur

Most extinguishers work on eliminating one side of the “fire triangle”

 AIRCRAFT TECHNICAL

FIRES: EXTINGUISHERS WATER extinguishers used for:

Wood

Paper

Cloth

 AIRCRAFT TECHNICAL

FIRES: EXTINGUISHERS FOAM extinguishers used for:

Wood

Paper

Cloth

Flammable Liquids  AIRCRAFT TECHNICAL

FIRES: EXTINGUISHERS CARBON DIOXIDE extinguishers used for:

Flammable Liquids

Electrical Fire

 AIRCRAFT TECHNICAL

FIRES: EXTINGUISHERS DRY POWDER extinguishers used for:

Flammable Liquids

Flammable Gases

Electrical Fires

Wheel Fires  AIRCRAFT TECHNICAL

FIRES: EXTINGUISHERS BCF HALON extinguishers used for:

BCF Halon is now illegal in the UK except in an aviation setting With all extinguishers – ALWAYS ventilate well after usage to ensure you don’t run out of oxygen!!

 Anything!

 AIRCRAFT TECHNICAL

PRACTICE QUESTION!

Which is the safest extinguisher to use on a wheel fire

Dry powder

 AIRCRAFT TECHNICAL

Lecture complete  Any Questions?

 AIRCRAFT TECHNICAL

LECTURE TWO: SYSTEMS, INSTRUMENTATION & AIRWORTHINESS 1.

Electrical System

2.

Vacuum System

3.

Pitot Static System

4.

Altimeter

5.

Vertical Speed Indicator

6.

Airspeed Indicator

7.

Gyroscopes - basics

8.

Attitude Indicator

9.

Directional Indicator

10.

Turn Co-ordinator

11.

Magnetic Compass

12.

Airworthiness Requirements

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM 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 battery when the engine is not running We will run through each element in turn...

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM BATTERY Provides electrical power when engine is not running or in case of electrical failure

Most aircraft use a lead-acid vented battery Usually a 12 or 24 volt battery which will also give a “amp -hours” on how long it will provide power Battery power used in start procedure is recharged during flight by the alternator

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM If more than one battery is used they can be connected in different ways to change the amp-hours:

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM MASTER SWITCH Selects whether battery power, alternator or both are required  AMMETER

Shows the state of charge of the battery LOW VOLTAGE LIGHT Illuminates when the battery is discharging  ALTERNATOR CIRCUIT BREAKER

Can be used to take alternator off-line if required  AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM  ALTERNATOR The alternator is powered by an enginedriven belt

The alternator produces alternating current which is rectified to direct current by the use of diodes

 Alternator also recharges the battery

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM BUS BAR

Distribution board which allows current supply to various elements of the system

Usually avionics will have a separate bus bar

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM CIRCUIT BREAKERS / FUSES

Protect the electrical equipment in the case of overload or other malfunction

Fuses should only ever be replaced once before seeking engineering assistance to investigate

Circuit breakers should only ever be reset once before seeking engineering assistance to investigate  AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM RELAYS Used so that one electrical circuit can produce a change in another electrical circuit – used in starters in aircraft Safety – means that high currents don’t need to be in the cockpit!

The magneto system is a form of relay

 AIRCRAFT TECHNICAL

INSTRUMENTS: ELECTRICAL SYSTEM: MALFUNCTIONS  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 engine – the 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  AIRCRAFT TECHNICAL

VACUUM SYSTEM: BASICS 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

 AIRCRAFT TECHNICAL

VACUUM SYSTEM: MALFUNCTIONS

BLOCKED AIR FILTER FILTER

X

Reduced airflow will cause gyros to run down

Suction gauge will will indicate low suction

 AIRCRAFT TECHNICAL

VACUUM SYSTEM: MALFUNCTIONS

X

VACUUM PUMP FAILURE

Zero reading on the suction gauge Gyros will wind down within a few minutes

 AIRCRAFT TECHNICAL

VACUUM SYSTEM: MALFUNCTIONS

X

EXCESSIVE HIGH SUCTION Vacuum relief valve should s hould prevent this

Failure of this valve means gyros will spin too fast and suffer damage Land as soon as possible

 AIRCRAFT TECHNICAL

INSTRUMENTS: PITOT STATIC SYSTEM The Pitot Static system provides data for 3 instruments:

 Altimeter

Vertical Speed Indicator (VSI)

Airspeed Indicator (ASI)

 AIRCRAFT TECHNICAL

INSTRUMENTS: PITOT STATIC SYSTEM 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 reading and reduce errors

 AIRCRAFT TECHNICAL

INSTRUMENTS: PITOT STATIC SYSTEM Gives Static Pressure

Gives total pressure (only used in the ASI)  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER The force exerted by the molecules in the air on a unit of surface area is ATMOSPHERIC PRESSURE

The nearer the earth’s 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)  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER Displays vertical displacement from the pressure datum set Uses Static Pressure only Basically a barometer with a scale in feet

 AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER Indicates 10,000s of feet

Hatching shows aircraft is below 10,000 feet

Short pointer shows 1000s of feet

 Altimeter subscale (here shows US format of inches, we have mb/hp in UK/Europe)

Long pointer shows 100s of feet  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER  As aircraft climbs, atmospheric 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

 AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: ISA

Pressure change with altitude = -1mb per 30 feet

 All altimeters are calibrated to the International Standard Atmosphere (ISA)

More details in the Meterorology lectures!

Sea Level Pressure = 1013mb  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: ERRORS 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  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: ERRORS STATIC BLOCKED, AIRCRAFT CLIMBS Pressure inside case should decrease but it will not – all inputs will stay the same STATIC BLOCKED, AIRCRAFT DESCENDS Pressure inside case should increase but it will not – all inputs will stay the same

If the static vent is blocked, the altimeter will continue to read the altitude indicated when the blockage occurred

 AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: PRACTICAL USES

 Altimeters would be easy if the pressure changes in the atmosphere happened like this  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: PRACTICAL USES

This situation is more likely and so it is VITAL that the altimeter is set correctly to the required setting  AIRCRAFT TECHNICAL

INSTRUMENTS: ALTIMETER: PRACTICAL USES  All aircraft actually at same level but altimeters reading differently

1013 hp

QFE Gives height above the airfield QNH Gives altitude above mean sea level (amsl)

Standard Gives flight level above 1013.2hp pressure level

 AIRCRAFT TECHNICAL

INSTRUMENTS: VERTICAL SPEED INDICATOR

Displays a rate of change indication in 100s or1000s of feet per minute

Uses Static Pressure only

Uses the principle of lag for its operation

 AIRCRAFT TECHNICAL

INSTRUMENTS: VERTICAL SPEED INDICATOR

Pointer shows 100s of feet of rate of change

Maximum that can be shown  AIRCRAFT TECHNICAL

INSTRUMENTS: VERTICAL SPEED INDICATOR Effectively 2 static inputs – one is direct and one is delayed (or leaked)

 AIRCRAFT CLIMBS New lower pressure is fed immediately into capsule Lower pressure into case is fed in with a slight delay

Difference in time forces capsule to contract which shows on the dial as a rate of climb and vice versa  AIRCRAFT TECHNICAL

INSTRUMENTS: VERTICAL SPEED INDICATOR: ERRORS 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

 AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR

Displays Indicated Airspeed (IAS)

Uses input from Pitot tube (total pressure) Uses input from Static Vent (static pressure)

Pitot – Static = Dynamic Pressure

 AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR

VSO Stall speed in landing configuration

VNE

VS1

Never exceed speed

Stall speed in clean configuration

GREEN ARC Normal operating speed range

YELLOW ARC

Cautionary speed range WHITE ARC

VNO

VFE

Maximum structural cruising speed

Maximum flap extension

Flap operation speed range  AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR 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  AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR  All airspeed indicators are calibrated to the International Standard  Atmosphere (ISA) Temperature change with altitude = -1.98˚ C per 1000 feet

More details in the Meterorology lectures!

Sea Level Temperature = +15˚ C

Sea Level Density = 1225 gm / m 3

 AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR: ERRORS Indicated Airspeed (IAS) INSTRUMENT ERROR

POSITION ERROR

Calibrated / Rectified  Airspeed (CAS / RAS) DENSITY ERROR Found in the POH

True Airspeed (TAS)

Used for navigation calculations

 AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR: IAS / TAS  As the aircraft climbs (density decreases) IAS under-reads in relation to TAS

This can be worked out using the CRP 1/5 or on some airspeed indicators

 AIRCRAFT TECHNICAL

INSTRUMENTS: AIRSPEED INDICATOR: ERRORS

BLOCKED PITOT TUBE

No input of pitot pressure so ASI will read zero (or reduce to zero)

BLOCKED STATIC PORT

Climb pressure trapped in case will be higher than it should be  – difference in pressures is less than it should be  –  ASI under-reads Descent

The opposite!

 AIRCRAFT TECHNICAL

INSTRUMENTS: CHECKS It is VERY important to check the pitot static system instruments prior to flight:  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 zero  As soon as possible after getting airborne, check showing rate of climb  AIRCRAFT TECHNICAL

INSTRUMENTS: CHECKS  AIRSPEED INDICATOR Glass should be clear & unbroken Should 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 ground  – may burn out the element)  AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS

Displays magnetic heading information

 Also known as a “direct reading compass”

“Lubber” line reads the magnetic heading of the aircraft

Directions are always expressed as a 3-digit grouping to avoid confusion (030°, 300°, 330° etc”

“north”, “south”, “east” and “west” also used but now not terms such as “north north west”  AIRCRAFT TECHNICAL etc

INSTRUMENTS: MAGNETIC COMPASS The earth has a magnetic field and acts like a weak magnet

The poles of a magnet are either “north seeking” or “south seeking” – more usually known as north and south poles

 A bar magnet which is allowed to float free will automatically align itself with the earth’s magnetic field

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS

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

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS 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”  AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS Every compass is “swung” so that amount of deviation indicated can be noted. Must be done when: New compass fitted New radio / electrical equipment fitted

 After aircraft has changed location north/south by over 1000 miles  After a heavy landing

 After flight through a magnetic storm  After any lightning strike Whenever the pilot believes it is necessary to ensure accuracy

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS MAGNETIC DIP

The compass aligns to the earth’s magnetic 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 above 60° north or south To counter this, compasses are pivoted slightly off-centre but this causes other errors:

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS Pivot line

S N

Vertical component of dip

In northern hemisphere, centre of gravity is arranged so that it is placed south of the pivot point

Weight This reduces errors due to dip but causes errors during turns or during accelerations / decelerations

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS  ACCELERATION ERRORS  Acceleration on easterly & westerly headings

Compass gets “left behind” due to inertia and the offset pivot causes the compass to swing away from the correct direction. In the northern hemisphere this is a swing to the north (the nearer pole)

Steady speed

Aircraft accelerates  AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS DECELERATION ERRORS Deceleration on easterly & westerly headings Pivot slows with aircraft but magnetic tries to continue at same speed due to inertia In the northern hemisphere this is a swing to the south (the nearer pole)

Steady speed

Aircraft accelerates  AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS  ACCELERATION & DECELERATION ERRORS Changes of speed on northerly / southerly directions

 Aircraft is accelerating in line with the compass so no swing occurs

This means no compass errors due to acceleration or deceleration

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS Easy way to remember compass acceleration & deceleration errors

“Accelerate North, Decelerate South”

“ANDS”

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS TURNING ERRORS 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

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS TURNING ERRORS – through northerly headings 4. For example, if a heading of north (360 °) is required, pilot must roll out when 030 ° is indicated and wait – the compass will indicate 360° after a short interval

N

3. Pilot must undershoot when using the compass because it has to “catch up” with the actual heading

2. Centre of gravity gets left behind due to inertia

1. Turning left through north  – acceleration is to the east

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS TURNING ERRORS – through southerly headings 1. Turning right through south  – acceleration is to the west

2. Centre of gravity gets left behind due to inertia N 3. Pilot must overshoot when using the compass because it has to “slow back” to the actual heading 4. For example, if a heading of south (180 °) is required, pilot must roll out when 210 ° is indicated and wait – the compass will indicate 180° after a short interval  AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: ERRORS Easy way to remember compass turning errors

“Undershoot North, Overshoot South”

“UNOS”

 AIRCRAFT TECHNICAL

INSTRUMENTS: MAGNETIC COMPASS: CHECKS Before taxy check:

no leaks and no bubbles Glass clear and unobstructed During taxy check:

Right turn – compass shows increase in heading Left turn – compass 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  AIRCRAFT TECHNICAL

ENGINE INSTRUMENTS: GYROSCOPES BASICS  A gyroscope is a rotating wheel 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”

 AIRCRAFT TECHNICAL

ENGINE INSTRUMENTS: GYROSCOPES BASICS Gyroscopes have two basic properties: RIGIDITY

The gyro’s 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 is displaced by 90° in the direction of rotation  AIRCRAFT TECHNICAL

ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR

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)

 AIRCRAFT TECHNICAL

ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR

Heading currently indicated

Setting knob (releases gyro so that compass card can be rotated)  AIRCRAFT TECHNICAL

INSTRUMENTS: DIRECTIONAL INDICATOR

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

 AIRCRAFT TECHNICAL

INSTRUMENTS: DIRECTIONAL INDICATOR: ERRORS INSTRUMENT ERROR 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

 AIRCRAFT TECHNICAL

ENGINE INSTRUMENTS: DIRECTIONAL INDICATOR: ERRORS  Apparent Drift

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 each other 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  AIRCRAFT TECHNICAL

INSTRUMENTS: DIRECTIONAL INDICATOR: CHECKS Before taxy check:

Glass is clear and unbroken  Align 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

 AIRCRAFT TECHNICAL

INSTRUMENTS: ATTITUDE INDICATOR Displays aircraft pitch and roll attitude

Does NOT necessarily indicate a climb or a descent

Does NOT necessarily indicate a turn

 AIRCRAFT TECHNICAL

INSTRUMENTS: ATTITUDE INDICATOR

Roll indicator “Rabbits ears”

Roll markers

Pitch markers Horizon

 Adjustor for aircraft datum

 AIRCRAFT TECHNICAL

INSTRUMENTS: ATTITUDE INDICATOR

The AI is an “earth” gyro which maintains its position relative to earth vertical

Some AIs can be “caged” during aerobatics to prevent damage as the instrument tries to keep up!

 AIRCRAFT TECHNICAL

INSTRUMENTS: ATTITUDE INDICATOR: ERRORS INSTRUMENT ERROR

Known errors caused by manufacture of the instrument

 ACCELERATION / DECELERATION ERRORS

The pendulous nature of the gyro will cause an indication of pitch during a rapid change of speed TOPPLE

 All gyros can “topple” if their limits of movement are exceeded. Some time will be needed to allow the gyro to then realign itself

 AIRCRAFT TECHNICAL

INSTRUMENTS: ATTITUDE INDICATOR: ERRORS Before taxy check:

Glass is clear and unbroken Mini aircraft is aligned to the horizon lines

During taxy check: When aircraft turns, the AI shows no movement (it shouldn’t show yaw)

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR Turn co-ordinator is a “rate” gyro

Two elements – one to show balance indication, one to show yaw The mini aeroplane does not necessarily show wings banked or level in reality

Usually powered by electric system to provide redundancy against AI failure

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR

Mini aircraft shows yaw information

Power failure indication flag

Rate one turn marker Balance ball

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR The gyro rotates up and away from the pilot’s perspective and is slanted by a 30° angle This allows instrument to show both yaw and rate of roll

If the aircraft yaws, the gyro stretches a spring which causes precession until the forces match

The instrument then indicates a “rate 1” turn (3° / second)

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR

CO-ORDINATED RATE 1 TURN

“needle” shows rate 1 indication Balance ball in the centre

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR

SKIDDING TURN

 Aircraft in right turn, but trying to “skid” right (into the turn) Needs more left rudder applied

SLIPPING TURN

 Aircraft in right turn, but trying to “slip” left (out of turn) Needs more right rudder applied

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR: ERRORS

INSTRUMENT ERROR Due to imperfections in manufacture

TOPPLE If limits are exceeded – gyro will realign itself with time

 AIRCRAFT TECHNICAL

INSTRUMENTS: TURN CO-ORDINATOR: CHECKS Before taxy check:

Glass is clear and unbroken Mini Aircraft wings level No bubbles in balance indicator Red “failure” flag disappears on master switch “on” During taxy check:  Aircraft turns right – ball skids left, right wing down  Aircraft turns left – ball skids right, left wing down

 AIRCRAFT TECHNICAL

AIRWORTHINESS: CERTIFICATE OF REGISTRATION  All aircraft must have a Certificate of Registration

Valid for the life of the aircraft

New certificate issued if aircraft has a change of registration

 AIRCRAFT TECHNICAL

AIRWORTHINESS: CERTIFICATE OF AIRWORTHINESS C of A is now non-expiring

Considered invalid if aircraft is modified, repaired or maintained in a manner other than that approved The original must be carried in the aircraft at all times

 AIRCRAFT TECHNICAL

AIRWORTHINESS: FLIGHT MANUAL / PILOT OPERATING HANDBOOK Published by aircraft manufacturer and will follow the aircraft

Limitations within this manual must be adhered to by the pilot

Older aircraft may have supplements issued by the CAA to “write down” certain performance aspects of the aircraft

 AIRCRAFT TECHNICAL

AIRWORTHINESS: PLACARDS Placards may also be placed in the aircraft

Placards are usually stricter than the information in the flight manual and MUST be adhered to

 AIRCRAFT TECHNICAL

AIRWORTHINESS: PILOT MAINTENANCE You may not always need an engineer!

 A licenced pilot can carry out certain maintenance under the ANO privileges including: Replacement tyres shock absorber changes replacement of split pins fabric / upholstery repairs replacement of seat belts replacement of bulbs replacement of spark plugs replacement of batteries replacement of comms equipment

... But only on private category aircraft!

 AIRCRAFT TECHNICAL

Syllabus complete  Any Questions?

 AIRCRAFT TECHNICAL