Aircraft Systems 1 Flashcards
What is the load per unit area of a cross-section?
Stress
What is the deformation caused by stress?
Strain
What is the maximum load the designer would expect an airframe to experience in service?
Design Limit Load
What are the two types of heating of an airframe?
Local and Kinetic
What are the 2 types of corrosion?
Chemical
Stress
What 5 factors are taken into consideration when choosing a material?
Strength Stifness Lightness Cost Ease of construction/production
What are the advantages of using composite materials over metals?
Readily engineered, designed and manufactured to complex shapes
What are the primary and secondary considerations when designing the fuselage?
Primary: accommodate the payload
Secondary: Aerodynamic
What are the three fuselage structures?
Truss
Monocoque
Semi-Monocoque
What is the function of the frames in a fuselage?
Maintain shape
improve stability of stringers
What type of bulkhead reacts to loads in tension?
Curved pressure bulkhead
What is the primary structural part of a modern fuselage?
The skin
What loads do longerons support?
Direct tension and compression
What loads do longerons support?
Direct tension and compression
Longitudinal loads due to fuselage bending
What function do stringers have?
Stabilise and reinforce the skin by accepting some of the flight loading
What are the 4 components of a wing?
Skin
Stringers
Ribs
Spars
What is an advantage of a high wing?
Ease of cargo (un)loading
What is an advantage of a mid-wing?
Small RCS / stealth
What advantages are there of a low wing?
Shorter undercarriage
Crash protection
In what direction do the tips of anhedral wings point?
Downwards
In what direction do the tips of dihedral wings point?
Upwards
Why do some aircraft have dihedral wings?
Roll stability
Why do some aircraft have dihedral wings?
Roll stability
What makes up an aircraft’s empennage?
Tailplane, fin and associated control surfaces
What is the only ground adjusted surface on an empennage?
Fixed tab (yaw trim)
What are the moveable surfaces on an empennage?
Elevator
Rudder
Trim Tab
What is an advantage of an all flying tailplane?
Trim control for changing CoG with minimal increase in trim drag
What is a control surface which is attached to the tailplane and provides both pitch and roll control?
Taileron
How are tailless aircraft controlled about the lateral axis?
Elevons
trailing edge elevators
How does a V-Tail cause Yaw?
Both control surfaces are moved in equal magnitude and opposite directions.
How does a V-Tail cause pitch?
Both control surfaces are moved equally in the same direction.
Describe the advantage of a canard.
Reduces trim drag at high speeds.
What 4 factors need to be taken into consideration for the design of a Combat Aircraft?
Powerplant
Payload (fuel, undercarriage, weapons)
Aerodynamics (low frontal area and smoothing of cross-section)
Stealth
What 4 main factors determine the fuselage size of a Transport aircraft?
Cabin length
Cabin width
Freight Volume
Passenger and Freight distribution to correct CoG
What are the two primary types of aviation internal combustion engines?
Piston
Gas Turbine
What cycle describes how a Piston engine produces torque?
Otto cycle
What cycle describes how a Gas Turbine engine produces Thrust?
Brayton Cycle
Briefly describe the 4 stages of the Otto cycle in a piston engine.
Suck - Fuel/air mix drawn into the cylinder
Squeeze - Inlet valve closes, the piston compresses fuel/air mix
Bang - Ignition forces the piston downwards
Blow - The exhaust valve opens, gasses are expelled
Briefly describe the 4 stages of the Otto cycle in a piston engine.
Suck - Fuel/air mix drawn into the cylinder
Squeeze - Inlet valve closes, the piston compresses fuel/air mix
Bang - Ignition forces the piston downwards
Blow - The exhaust valve opens, gasses are expelled
Which limitation of a piston engine causes increased stress and wear on engines if exceeded?
RPM limit
Which limitation of a piston engine causes a breakdown of cylinder wall lubrication and distortion if exceeded?
Temperature limit (CHT)
What are the 4 types of Gas Turbine Engines?
Turbojet
Turbofan
Turboprop
Turboshaft
List the stages in a Gas Turbine Engine.
Intake Compression Combustion Turbine Exhaust
In a Gas Turbine Engine, what is the function of the Intake?
Direct air into the compressor at the correct velocity (subsonic, 0.5M)
What is the function of the compressor stage in a Gas Turbine Engine?
Air is compressed, increasing temperature and decreasing volume then delivered to the combustion chamber.
What is the function of the combustion stage in a Gas Turbine Engine?
Fuel is added and burned, further increasing the temperature and volume of the gases.
What is the function of the Turbine stage in a Gas Turbine Engine?
The hot gases from the combustion chamber are directed to the turbine, forcing the turbine sections to rotate, which in turn drives the compressor by means of a direct shaft.
What is a rotating, aerofoil-based compressor in which the gas or working fluid principally flows parallel to the axis of rotation?
Axial compressor
What is a rotating, aerofoil-based compressor in which the gas or working fluid principally flows parallel to the axis of rotation?
Axial compressor
What is a compressor which accelerates the air mass by spinning the air, causing the resultant airflow to be tangential to the flow at the intake?
Centrifugal compressor
What are the 3 advantages of a centrifugal compressor?
Cheap
Easy to manufacture
Low maintenance/running costs
What are the 5 advantages of an Axial compressor?
Large mass flow rates Small frontal area Air flows parallel to axis of shaft High compression ratio High efficiency
What is the purpose of a diffuser in a combustion chamber?
Slow the high speed air to a velocity suitable for combustion
What is highly compressed air from the high-pressure compressor, that is fed through the main channels in the dome of the combustor and the first set of liner holes, to be then mixed with fuel to allow combustion?
Primary air
What is the air which is injected into the combustion zone through the second set of liner holes to complete the reaction process, cool the air and dilute the high concentrations of CO and Hydrogen?
Intermediate air
What is airflow injected into the combustion chamber through holes in the liner at the end of the combustion chamber to help cool the air before it reaches the turbine stages, so that the temperature profile is uniform?
Dilution air
What is the name of the mechanism which describes the failure of turbine bladdes when subjected to excessively high temperatures and centrifugal loads due to the RPM and Temperature limits being exceeded?
Turbine Creep
What is the name of the mechanism which describes what happens to Turbine blades when a rapid change in temperature causes an uneven expansion and contraction in a turbine blade?
Thermal stress
What is the name of the mechanism which describes what happens to Turbine blades when a rapid change in temperature causes an uneven expansion and contraction in a turbine blade?
Thermal stress
In a Turbofan, what drives the Fan and low pressure compressor?
The low pressure Turbine
LP Turbine is always behind the HP Turbine
In a Turbofan, what drives the high pressure compressor?
The high pressure Turbine
HP Turbine is directly after the combustion chamber
What are the advantages of a Turbofan?
Increased Thrust at low forward speeds (TO performance)
By-pass air can be used for cooling
Better ground clearance than turboprop
Increased operating economy over Turbojet
What type of Gas Turbine Engine uses the vast majority of the energy in the exhaust gases to drive a propellor?
Turboprop
What type of Gas Turbine Engine is most efficient at low/medium altitudes and less than 350kts?
Turboprop
What type of engine uses all useful exhaust gas energy to drive a shaft?
Turboshaft
What is a free-wheel turboshaft engine?
The gas turbine which drives the compressor is seperate to the turbine which drives the shaft
What are the advantages of a free-wheel turboshaft engine?
No clutch
more versatile load bearing
What is the disadvantage of a free-wheel turboshaft?
slight loss of thrust due to exhaust stream being recirculated
What causes a compressor stall?
Airflow impacts a compressor blade at the wrong angle
What does an increase in engine vibration and an increase in Turbine Gas Temperature (TGT) indicate?
Compressor stall
What causes an engine surge?
If all stages of the compressor stall, the pressure in the combustion chamber is high enough to force the flame forwards
What does intake banging, a large rise in Turbine Gas Temperature (TGT), and a loss of THrust indicate?
Engine Surge
What 3 design features on a Gas Turbine Engine help to prevent stalls and surges?
Variable inlet guide vanes and variable stator vanes
Multi-spool compressors
Compressor bleeds
What are the 9 uses for oil in an aircraft?
Reduce friction Reduce wear Cleaning Minimise corrosion Cooling Heating Hydraulic fluid Chip detection Engine status
Describe Hydrodynamic lubrication.
Layer of oil between surfaces is relatively thick
Keeps two surfaces apart
Very small amount of friction generated
Describe Boundary lubrication.
Layer of oil is very thin
Caused by high bearing loads, inadequate viscosity, loss of oil pressure.
Often occurs during starting conditions.
What are the 6 components of an engine oil system?
Tank Pump Filter assembly Cooler Monitoring instruments Magnetic chip detectors
What part of an engine oil system contains the lubricant, and may have a sight glass or dipstick for measuring oil quantity?
Oil Tank
What part of the oil system provides pressurised oil to lubricate engine components?
Oil pump
What part of the oil system prevents debris from continuously circulating through the system?
Filter assembly
What part of the oil system collects ferrous debris from the bearing chambe that can be analysed to monitor bearing performance and assess engine life?
Magnetic chip detector
What part of the fuel system deliniates between airframe fuel and engine fuel?
Low pressure cock
What part of the engine fuel system removes heat from the engine oil?
Fuel cooled oil cooler
What part of the engine fuel system delivers fuel to the fuel control unit?
High pressure fuel pump
What are the 5 components of the air system?
Engine cooling Blade cooling Air sealing Bleed air Anti-Icing
What do Thermocouples measure in a Gas Turbine Engine? Briefly describe how they work.
Monitors temperature to prevent overheating of the turbine/engine components.
‘Hot junction’ mounted in the exhaust gas, ‘cold junction’ mounted to measure the ambient air temperature as a reference point.
What device measures the engine speed?
Tacho-Generator
What device measures Engine Power?
Torque meter
What is the effect of icing on an aircraft?
Thrust and Lift will decrease
Weight and Drag will increase
Name the 3 types of ice detection devices
Visual Ice Detector
Differential Static Ice Detector
Frequency Monitor Ice Detector
Describe how a visual ice detector works.
An illuminated probe that is viewable from the cockpit. Ice buildup is observed by the crew.
Describe how a differential static ice detector works
A probe, which has static vents on the leading and trailing edges. When Ice builds up, it blocks the leading edge static ports and causes a pressure differential which alerts the cockpit.
Describe how a frequency monitor ice detector works
The probe is vibrated at its resonant frequency in clean air. When ice builds up, the resonant frequency of the probe changes, and the detector senses this and alerts the cockpit.
Briefly describe an anti-icing system.
Anti-icing systems prevent the formation of ice in critical areas, where the formation of ice cannot be tolerated.
Briefly describe a de-icing system.
De-icing systems work to remove ice that has already formed on the aircraft surfaces. De-icing is the process of removing frozen contaminants, ice, and/or slush from a surface.
The majority of airframe anti-/de-icing systems use hot air, where does this hot air come from?
Bleed air from the compressor.
How are propellor blades and rotary blades kept free of ice?
Electrical heating of the edges.
Briefly describe the windscreen anti-icing system.
A thin film of gold between the glass is electrically heated to de-ice and de-mist the windscreens.
What are the 5 types of aviation fuel that can be used?
Avgas, Avtur, Diesel, Avtag, Avcat
What is Avtag a combination of and when is it used?
Avgas and Avtur
Cold climates because it has a lower freezing point
What is Avcat a combination of and when is it used?
Avtur and Diesel
Used on carriers because it has a lower flashpoint.
What is a FSII and what does it do?
Fuel System Icing Inhibitor
Inhibits fuel icing and suppresses fungal growth
What is the Anti-Knock value?
The resistance a fuel has to detonation. A good anti-knock value fuel will combust smoothly throughout the combustion chamber and provide a regular rise is pressure on the piston.
What is in a typical engine fuel system?
High pressure pump
Final filtration
Fuel control unit
Carburation device
What is in a typical airframe fuel system?
Tanks Collector tanks Low pressure pump Low pressure fuel cock Pressure control valve
Briefly describe how a recuperator tank works.
Fuel enters the tank via gravity, and stops flowing when there is a negative g event. As the tank rotates, the flip flop valve opens, allowing fuel in via a lower pipe but preventing air entering the system via a top valve. When the aircraft returns to positive g, the tank refuells.
What does a fuel cross-feed valve do?
Allows either tank to fuel either engine.
What does a fuel transfer valve do?
Transfers fuel between tanks to restore the balance of the aircraft.
What are the two functions of a fire detection system?
Fire and overheat detection
Fire extinguishing
What are the 3 most common causes of fire in an aircraft?
Fuel leaks in vicinity of hot equipment
Hot gas leaks impinging on flammable materials
Electrical or mechanical malfunctions in equipment
What are the two types of thermal sensors?
Thermal switch Continuous element (firewire)
