Aircraft General Flashcards
Fuselage description
Semi-monocoque
Light frame with a structural skin
Components of fuselage
Frames at cross sectional points
Longerons connect them
Wing components
Ribs (and stringers connected to them) form cross sectional shape
Spar is the beam that connects ribs together and all to the fuselage
Stress
The internal resistance of a material to deformation - an internal force which opposes deformation.
Strain
The degree of deformation experienced on a material when exposed to a force of load.
5 forms of stress
- Tension
- Compression
- Torsional
- Shear
- Bending
Combination of stresses in bending
- Compression on inside of bend
- Tension on outside of bend
- Shearing between the two
Which stresses are aircraft designed to cope with?
Tension and compression
Not bending
How is stress in airframe assessed?
FM/Operating Handbook will have G force limits. If these are exceeded must report to a ground engineer as the stress limits on airframe will have been exceeded.
Required equipment to secure parked aircraft
> = 3 tie downs (with pegs)
= 2 chocks
3 types of control
i) Mechanical
ii) Hydro-mechanical
iii) Fly-by-wire
Artificial force feedback
Required for hydro-mechanical and fly by wire controls to allow pilot the sense of how controls are behaving or responding to inputs
4 stroke engine cylinder diagram
4 stroke engine phases
i) Intake
ii) Compression
iii) Power
iv) Exhaust
Name for the 4 stroke engine process
Otto cycle
Which component controls inlet and exhaust valve timing?
Camshaft
How many rotations does camshaft do in a full OTTO cycle?
One - to allow a single inlet and outlet valve open/closing in each cycle.
Valve overlap
Exhaust valve remains open until just after inlet is opened so there is some overlap where they are both open
Compression ratio
Total cylinder volume / Clearance volume
Where total volume is volume with piston at “bottom dead centre” and clearance volume is with piston at “top dead centre”
Spark timing
Just before piston reaches top dead centre to allow flame front to move through the fuel/air mixture in time for the power phase.
Magneto functionality
Magnet rotates (driven by engine) in a conductor with two coils (primary - ignition and secondary - distributor), generating a current in them.
Breakers in the primary coil cause interruptions in its voltage, causing a spike in voltage of secondary coil, which is used to create the spark.
Magneto Distributor functionality
Distributor has a rotating finger which connects secondary magento coil to one of four connections (one for each cylinder) as it rotates.
Magneto p-wire
This is the earthing wire. If it is broken the magneto will not earth and rpm is unchanged when switched off during check.
Voltage generated by magnetos
20,000 V
Distributor rotations vs crankshaft rotations
Each cylinder needs a spark once for every two rotations of the crankshaft, therefore gearing from crankshaft to distributor is such that distributor rotates once for every two turns of the crankshaft.
Ignition harness
- issue
The leads from the distributors to the sparkplugs are bound together as an ignition harness.
Leakage from the ignition harness can cause rough running.
Starter motor wiring
Starter requires high current (thick wiring) which would be difficult to connect to ignition.
So the ignition instead powers a low current solenoid, which closes the main high power circuit for the starter motor (which also powers the starter light).
2 issues with magnetos at startup
i) Magnetos rotate at half crank shaft speed, so low rpm (e.g. 120) leads to very low (e.g. 60) magneto rpm, which doesn’t generate enough current.
ii) Spark advance (spark before top dead centre of cylinder) is timed based on normal crankshaft speed, but at low rpm can be too early and cause kickback.
Impulse coupling jobs (3)
i) Switch one magneto off at startup (only need left one)
ii) Store energy from rotating magnetos initially in a spring then release to generate a high voltage
iii) Retard ignition spark at low engine rpm so that it occurs just after top dead centre
Features of impulse coupling
Requires no power. Thus can be used to allow hand starting of prop.
Dead cut
Turning ignition to off temporarily before engine shut down to check for sudden loss of power.
If engine continues it suggests one of the magnetos may not be earthing properly with ignition off - can cause accidental hand starting of prop.
This can be bad for the engine.
Tachometer
Measures “time” on the basis of rpm, so gives an idea of useage of the engine.
Hobbs meter
Simple time elapsed instrument which advances in real time whenever master switch is closed.
2 stroke engine diagram
2 stroke engine inlet/outlet functionality
The piston closes off the inlet and outlet at the appropriate times in the cycle.
Why are 2 stroke engines noisy?
Muffling the engine noise restricts the flow of exhaust fumes. The need to allow easy escape of exhaust fumes causes the noise.
2 stroke ignition systems
i) Dual magneto system
ii) Capacitive Discharge Ignition (CDI) system, which is light and simple but requires battery power
Lubrication of 2 stroke systems
Used to mix oil to fuel at 25:1 however getting the ratio wrong would cause problems and the burning oil would lead to blue smoke and pollution.
Modern systems deliver oil to the cylinder walls directly from a sump.
Does 2 stroke system recover oil?
No, dry sump system is a “total loss” system and has to be refilled between flights
2 stroke induction system
A “sidedraught” device uses venturi effect with air flowing over an outlet from the fuel.
A slide and needle system regulates the amount of fuel pulled in by venturi effect from a float bowl.
The fuel spraying past the needle into the air flow creates the fuel/air mix.
2 stroke cooling
Used to be air cooled, but liquid cooling is more popular as heat transfer is more uniform.
It is however more complex and heavy.
2 stroke rpm
Optimal power rpm is about 5,000 to 7,000 rpm so gearing is required to deliver propellor rotation speeds (around 1:2 to 1:2.6 ratio).
Starting a 2 stroke engine
Usually started via hand or pull cord (can also have electric starter).
Diesel engine advantages
Wide cut (as opposed to petrol narrow cut) fuel is cheaper than AVGAS and engines are more economical.
Diesel engine ignition
Impact on engine design
Spontaneous ignition of compressed fuel so no spark plugs, magnetos, camshafts (etc.) needed.
High compression ratio of 12:1 required for this however which requires the engines to be very strong.
Diesel fuel delivery
Diesel doesn’t atomise well so fuel injection is required.
With no induction manifold air pressure is needed from some kind of fan (turbo or supercharger).
Turbo vs supercharger
Turbo is a turbine compressor driven by exhaust gases, but doesn’t work well at low rpm.
Supercharger works mechanically from the engine instead and is more efficient at low rpm.
Comparison of super-turbocharged diesel and petrol engines
The super-turbocharged engine will be big, but will be around 20% lighter and maintenance/operating costs around 30% less.
Correct fuel ratio
Rich & lean ratios
Correct: 1:12
Lean: 1:20
Rich: 1:8
Term for chemically correct fuel/air mixture
ccm or stoichiometric mixture
Diagram of throttle side of carburettor
Venturi draws fuel into carburettor, butterfly valve (throttle) restricts flow of fuel/air mix
Accelerator pump
Gives an extra spurt of fuel as throttle is opened to prevent a weak-cut due to sudden high air flow in carburettor making the mixture too lean.
Diffuser
Carburettor device that premixes fuel and air to prevent excessive fuel from main jet and helps fuel vaporisation at low speeds.
How is carb fuel tank refilled
Float and needle valve
Idling jet
Allows a small amount of fuel past butterfly valve when it is almost closed to allow engine to idle
Mixture in take off and climb, reasons
Fully rich mixture used in climb and take off, when power level is high.
Excess fuel will protect against detonation, pre-ignition and cylinder overheating.
Mixture in cruise
If cruise is at below 75% max power (usually 55-65%) leaning mixture is advisable to improve fuel economy.
Mixture at high density altitude
At higher altitude air pressure reduces and so the mixture needs to be leaned to maintain an appropriate mix. This might be the case in high altitude, high temperature take offs.
How to lean mixture
Gradually lean the mix and rpm should increase as chemically correct mixture is approached. When it starts to fall again, return to the peak and stay just on rich side of peak.
Detonation
Explosive combustion in cylinders, perhaps due to high heat. This causes cylinder damage.
Pre-ignition
Combustion before the spark plugs spark, perhaps due to heat spots.
Effect of overly rich mixture
Carbon from unburnt fuel can form on the piston heads and valves.
Cylinder heads will run cool.
Effect of overly lean mixture
High cylinder head temperatures can lead to detonation and potentially serious engine issues.
Idle cut off/out
When mixture is fully leaned a needle will cut out the fuel from from the float chamber to the venturi. Engine continues to run on fuel that is present, leaving no fuel/air mixture in the manifold.
Response to suspected detonation
Enrichen the mixture
Reduce pressure in cylinders by pulling throttle back
Increase airspeed to aid cooling
Impact ice
When it happens
When below freezing water droplets impact metal surfaces of carburettor inlet and form ice.
Can occur if outside temperature is near or below zero and cloud/rain/sleet is around, or if the aircraft is freezing and enters a warm humid area (e.g. descending from cloud).
Fuel ice
When it happens
If fuel air mix is 0 to -8 degrees C, water in the air will freeze around the venturi where fuel comes out of jet.
Can happen with ambient temperatures high (20 to 30) if relative humidity is over 50%.
Throttle ice
When it happens
As mixture passes the edges of the throttle and accelerates, temperature falls and ice can form.
Higher risk when throttle is close to closed, e.g. during descent.
Fuel injection
- Description
- Carb heat?
Alternative to carburettor. Venturi used to detect air flow which fuel control unit assesses to meter fuel flow. Each cylinder can have individual fuel flow.
No carb heater but there will be an alternative air intake in case of impact icing.
Fuel injection advantages
- No fuel ice
- Uniform delivery of fuel to each cylinder
- Improved mixture control
- Less maintenance
- Instance acceleration
- Increased efficiency
Fuel injection disadvantages
- Starting a hot engine can be hard due to vapor lock in fuel lines (electric boost pump can solve this)
- Fine fuel lines can block easily
- Surplus fuel will be returned to a tank, need to monitor which one.
Fuel tank vent purpose
Allows fuel to flow out
Primer
Allows fuel to bypass the carburettor to allow a rich start
Action if engine slows due to fuel tank issues
i) Close the throttle to prevent a surge when engine re-starts
ii) Set mixture to full rich
iii) Fuel pump on
iv) Check fuel tank selection/content
Bourdon tube gauge
Used to indicate fuel or oil pressure.
A bent tube is fixed at one end into which fuel flows. As pressure increases the tube straightens, which is used to move a needle in an indicator.
Fuel flow meter - purpose
To assess performance, generally as part of a fuel injected system.
Important note about fuel flow meters
A blocked fuel line can lead to an increase in pressure which might show up as a pressure increase (not a pressure drop as you might expect).
Alternative to fuel flow meter
Exhaust gas temperature gauge
Fuel marking colours
AVGAS - Red
AVTUR (aka JET A1) - Black
Typical light aircraft fuel designation
- meaning
110LL
- 110 is power level before detonation
- LL means low lead
Purpose of oil
i) Lubricates
ii) Cools
iii) Removes dirt through filtering
iv) Prevents escape of fuel/air from cylinder
Viscosity considerations
May need higher viscosity (thickness) in hotter environments
Oil sump systems
Wet sump - Common in light aircraft, used oil is stored in an oil sump in the engine from where it is used.
Dry sump - Common in aerobatic craft, a scavenge pump refills an oil tank from the engine sump.
Where is oil temp monitored?
After cooling, before entering the engine
Changes in oil that necessitate changing
- Dirt
- Oxidation
- Absorption of water
How are cylinders cooled?
Cooling fins use air cooling.
Effectiveness of cylinder fins
At high power but low airspeed not very effective.
Can get shock cooling at high speed and low engine power (e.g. descent).
Prevention of shock cooling
In long descent leave some power on and give a burst of power every 500ft.
Cowl flaps
Optional feature which allows air intake into engine to be controlled, thus giving control over cooling.
Reaction to overheating engine
i) Open cowl flaps
ii) Mixture rich
iii) Reduce power
iv) Increase airspeed
Detecting cylinder temperature
Cylinder head temperature (CHT) gauge can be used.
If not, use oil temperature.
Where does cylinder head temperature gauge read from?
The critical cylinder head, this is the cylinder that will be hottest due to engine design.
Effect of running engine at low rpm excessively
Spark plug fouling
How to clear vapour from fuel injection lines
Set mixture to idle-cut-off and and turn on fuel pumps. Fuel will push out the vapour but idle-cut-off prevents fuel from getting to the cylinders.
Starting hot/over-primed engine
Start engine with mixture at idle cut-off.
When mixture approaches the right mixture it will fire, then you can move mixture back to rich.
Normally aspirated engine - impact of altitude
Carburettor manifold pressure reduces at high altitude.
Supercharged engine - impact of altitude
Compressor fitted to intake manifold, driven by the crankshaft, maintains manifold pressure at higher altitudes.
Turbocharged engine
Compressor fitted to intake manifold, driven by turbine running on exhaust gases, maintains manifold pressure at high altitudes.
Setting manifold pressure on super/turbo charged engines
There will be a power table showing power output at different rpm and manifold pressure settings.
Should aim for lowest rpm and highest manifold pressure to achieve the required power level.
Ohms Law
V = IR
V: Voltage - potential difference
I: Current - rate of flow
R- Resistance
Power
- Definition
- Calculation
The rate of doing work
P = F x d (force x distance)
AC wavelength, phase and amplitude
Ao is amplitude, lambda is wavelength
Typical electrical system setup (charging)
Alternator produces AC current which needs to be rectified (using diodes) to DC to charge battery and run equipment.
Bus Bar
Electrical conductor which distributes power to all components.
Typically a primary bus and an avionics bus.
How are components earthed?
The bus bar is earthed which provides earth to all components
Impact of wiring batteries in parallel or series
Series - add voltage together
Parallel - add amp hours together
Generator
- How it works
- Issues
Generator uses a metal loop (armature) rotating within a magnetic field (N & S magnets) which generates a current.
Heaver than an alternator and not good at low rpm.
Alternator
- How it works
Some power required to generate initial magnetic field.
Left-zero ammeter
Measures alternator or generator output.
High reading when starting and battery is being recharged.
Will be just above zero with electric items off and rise as more items are switched on.
Zero means there is a problem.
Centre-zero ammeter
Current into the battery (charge) moves needle to the right.
Draw from the battery (discharge) moves needle to the left.
Bonding wires
Connect different components of aircraft body to ensure static electricity in all components can be discharged easily.
Static wick
Positioned at trailing edge of wings. Dissipate static charge into the atmosphere.
Main conduction of static charge
Tyres constructed of conductive material so static charge is earthed on landing.
Vacuum system (standard)
Engine driven suction pump requires 3 to 5 inches of mercury pressure to create vacuum in gyro buckets on outside of gyroscope.
Airflow then rotates gyroscope at around 20k rpm.
Vacuum system (alternative)
Can use venturi tube for a vacuum, but it can get blocked by icing and doesn’t work well at low speeds.
Vacuum system issues and how to identify them
i) Blocked air filter (lower suction reading)
ii) Vacuum pump failure (zero reading)
iii) Excessive pressure (pressure release valve exists to prevent damage
Strut wheel system
Oleo-pneumatic wheel system
Strut & brace wheel system
Torque link system
Maintains alignment of nose wheel with airframe
Nosewheel shimmy
- prevention
Nosewheel shimmy is when the nosewheel vibrates and moves side to side.
Can be prevented with a shimmy damper.
How does IAS indicator work?
Total pressure from pitot and static pressure (from static source) deducted to determine dynamic pressure.
A gearing system translates this to knots of IAS.
How does IAS display TAS?
Optional dial to set temperature and altitude so that TAS can be displayed
Altimeter accuracy requirement
+/- 50ft at runway
How does VSI work?
A metered leak in a static pressure source allows a change in pressure over time to be detected.
Alternate static source
Situated in cockpit as a backup.
Will have a slightly low reading due to cockpit protection.
Properties of a gyroscope
i) Rigidity in space - Tendency to maintain same absolute direction in space despite what goes on around it.
ii) Precession - If a force is applied to it, the change in direction is displaced 90 degrees further on in direction of rotation.
Requirements of strong gyroscope
i) High spin speed
ii) High mass
iii) Mass distributed towards edge of gyroscope
Turn indicator vs turn coordinator
Coordinator has a picture of an aeroplane, turn indicator just has an arrow.
They work (mostly) the same.
How do turn indicators work?
Responds to rate of turn, not bank angle.
Gyro converts yaw motion to a rotation in 90 degree plane. A spring resists the rotation so it settles at a position where the rotational force is at a certain level - which then indicates the turn rate (i.e. rate 1 or 2).
How do turn coordinators work?
Similar to turn indicators but mounted at 30 degree tilt which means it also provides a response to the roll rate.
How does attitude indicator work?
Rigidity characteristic of a gyro maintains the alignment of the horizon, the plane moves around it.
How does heading indicator work?
Rigidity characteristic maintains direction card relative to true magnetic directions.
Should be realigned every 10 to 15 minutes as rotation of the Earth will affect the gyro.
Swinging the compass
When engineers position aircraft at a specific point on aerodrome to determine deviation of the compass on board.
2 types of stall warning
- Electric switch which is lifted by turbulent air
- Hole with a reed which makes a noise when airflow goes over it
AHRS
Attitude Heading Reference System
Solid state system with accelerometers and magnetometers (+ GPS) to display attitude to pilot without gyros.
ADC
Air data computer
Receives static and pitot pressure and temperature to calculate precise IAS, TAS, OAT.
IAU
Integrated Avionic Unit
Interface unit between other items to display information to pilot
What backups are required for glass cockpit aircraft?
IAS
Altimeter
AI
Where to find out if MoGas is suitable for a given aircraft or engine?
CAA Airworthiness Notices
Action in case of alternator failure
Switch off unnecessary electrics and land as soon as practical and safe - not emergency or pan pan
Worst conditions for icing
- Low engine power
- 0 to 15 degrees C (or -5 to 20)
- High humidity
Best pressure gauge for low pressure systems
Aneroid
Is an earthed magneto’s primary circuit closed or open?
Closed
Requirements for AVGAS fuel check
- Evaporates readily
- Blue colour
- No debris
- No water
- Smells like avgas
Canard wing
Small wing at front of aircraft.
Effect of spark plug gap being too small
Reduced spark
What is a stall strip?
Small strip attached to leading edge of one or both wings to alter behaviour in stall (perhaps prevent wing drop) or ensure wing roots stall first.
Where is air for cabin heat routed?
Via engine exhaust system, thus the risk of carbon monoxide.
Is synthetic or mineral oil used in modern aircraft?
Synthetic is common in newer aircraft, mineral in older.
Rough running during magneto check
Likely problem with a spark plug. Each magneto is connected to a different spark plug so this will be masked when both sets are running.
Structure of a sandwich material
Two thin layers surrounding a light core layer.
Is light, stiff, stable and strong.
Effect if magnetos are disconnected from cockpit switch
They will not be earthed and continue to be live
Suggested action during running in period of engines
First 25-50 hours, basically normal operation - full power climb & TO, >65% power cruise. Need to get engine up to normal running temp.
Components of wood and metal plane structures
Formers and stringers (formers make the shape like ribs or frames, stringers join them).
Hysteresis
Error that can occur in altimeter due to deformation of the capusle
What is QNE?
Altitude above 1013.25 hPa pressure level.
Correction on magnetic compass when turning through north/south in NH
UNOS
Under-read turning through north
Over-read turning through south
Depends on the heading at the end of the turn
Correction on magnetic compass when accelerating west/east in NH
ANDS
Accelerating - shows turn to north
Decelerating - shows turn to south
What speeds does the white Arc of ASI cover?
V(S0) to V(FE)
Attitude director indicator
Combination of attitude indicator and flight director
Horizontal situation indicator
Combines directional gyro and radio aids (VOR/DME)
Which instrument to break glass on if static port lost
VSI - This is the least critical indicator and will be lost on breaking the glass, but will allow static air to enter other connected indicators (e.g. altimeter)
Which factor impacts bank angle required for a rate 1 turn?
TAS
Gyroscope directions
Horizontal for everything except AI (which is vertical)
