Aircraft Systems 1 Flashcards
What is Dilution Air when referring to gas turbines?
Dilution Air is airflow injected through holes in the liner at the end of the combustion chamber to help cool air before it reaches the turbine stages. The air is used to produce the uniform temperature profile desired in the combustor.
What are the effects of icing on an aircraft?
Thrust will decrease.
Lift will decrease.
Drag and weight will increase.
What is a torque meter?
The torque meter comprises two concentric shafts. The inner shaft is connected to engine drive and the reduction gearbox. The outer shaft is connected to the engine drive only. It measures the twist applied to the shaft.
What are the key properties of AVGAS that influence engine design?
AVGAS
- Anti-knock value - the resistance a fuel has to detonation. A good value is one that combusts smoothly throughout the combustion chamber.
- Volatility
- Vapour locking tendency
- Stability
- Solvent and Corrosion properties
Describe the compression stroke of the Otto cycle.
Compression
This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C.
In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke. Both the intake and exhaust valves are closed during this stage.
What is the most suitable fuel for gas turbines?
AVTUR
What accessory systems can be drive by the gearbox?
Fuel control unit
High pressure fuel pump
Low pressure fuel boost pump
Oil Pumps
Scavenge pumps
Centrifugal breather
N1 Tachogenerator
DC Starter/Generator
Air Conditioning compressor
What is the purpose the jet pumps?
The jet pumps feed fuel from storage tanks to collector tanks. There are no moving parts, instead the jet pumps work using the ‘venturi’ principle.
Describe the function of a differential static pressure ice detector.
Differential static pressure ice detector.
The detector monitors the pressure differential between a series of holes on the leading and trailing edges. If holes become blocked, a pressure differential between the edges is created and an alarm is triggered.
What is Strain?
Strain is deformation caused by stress.
What is the optimum speed for turboprop operation?
Speeds up to 350kts, beyong which the efficiency of the propeller deteriorates rapidly because of shockwaves at the blade tips.
What is the purpose of stringers in a wing structure?
Wing Stringers allow the wing to react to bending movements and stiffen the wing skin,
What is thermal stress?
Rapid changes in temperature causes uneven expansion and contraction in a turbine blade which increases the stress in the blade. Minimising power changes and allowing temperature to stabilise before shutdown can reduce thermal stress and prolong blade life.
What parts of an aircraft require hot air for de-icing?
Inlet guide vanes
First stage of compressor blades
Nose cone
Nose cowling
During aircraft aerobatics what aircraft systems can prevent surging?
Hinge flip flop tube (flexible tube with weight)
Double entry LP fuel pump
Recuperator system
Describe the function of thermal (hot air) airframe anti icing?
Thermal airframe anti icing utilises hot air bled from the engine compressors. The hot air is fed through a system of valves, pressure regulators and mixing valves and then ducted to relevant areas.
Describe the function of a visual ice detector.
Visual ice detector
The unit is mounted outside the cockpit window in a location where ice build up can be observed. The probe is painted matt black and has a heater element if required.
What is the purpose of the fuel collector tanks?
The fuel collector tanks ensure the engine can be provided with an uninterrupted supply of fuel during turbulence and any aircraft attitude.
How does a centrifugal compressor work?
They accelerate the air mass by spinning the air. The amount of acceleration is dependent on the rotational speed of the compressor.
There is a stationary diffuser at the outer edge of the impellor and this converts kinetic energy to potential energy. The resultant airflow is now tangential to the flow at the intake.
What properties must AVTUR possess?
Ease of flow under all operating conditions.
Quick starting of the engine.
Complete combustion under all conditions.
A high calorific value.
Non-corrosive
Minimal fire hazard
Provide lubrication of the moving parts of the fuel system.
What is the difference between a scavenge and a pressure pump?
A scavenge pump has greater capacity thatn pressure pump to ensure complete scavenging of the bearings. They have to pump increased volume due to air leakage into bearing housing.
What is the purpose of frames in a fuselage structure?
The frames maintain the shape of the fuselage cross-section and improve the stability of the stringers.
What is the purpose of monitoring instruments in an oil system?
Monitoring Instruments
Sensors and switches feed cockpit display and central warning system (CWS) captions for engine monitoring.
What is the purpose of the oil tank?
Contains the lubricant.
May have sight glass or dipstick for measuring oil quantity.
What is turbine creep?
Turbine creep occurs when turbine blades are subjected to very high temperatures and centrifugal loads and tend to lengthen (creep) and then fail if RPM and temperature limits are exceeded.
What are the two distinct sub-systems of an aircraft fuel system?
Engine fuel system
Airframe fuel system
What the key components of the Air System?
Engine cooling
Blade cooling
Air sealing
Bleed air
Anti-icing.
What common cylinder layouts are there?
In-line
Inverted-in line
Flat Opposed
V
Radial
What is boundary lubrication?
Layer of oil is very thin.
Caused by high bearing loads, inadequate viscosity, oil starvation or loss of pressure.
Thin oil film can rupture which can increase wear, temperature and then lead to failure. Often occurs during starting conditions.
What is Volatility?
Not a single figure. A volatile liquid is one that can change from liquid to vapour when heat is applued or contact is made with a gas into which is can evaporate.
What is the purpose of spars in a wing structure?
Spars all the wing to react to shear forces (shear stress).
Spars are the principal structural members of the wing. They correspond to the longerons of the fuselage. They run parallel to the lateral axis of the aircraft, from the fuselage toward the tip of the wing.
What is a taileron?
Tailerons are control surfaces that combine the elevator and the aileron. They are often found on aircraft without traditional ailerons on the wing, they can provide control in both pitch and roll.
What are the uses of the air system?
Engine cooling
Blade cooling
Air sealing
Bleed air
Anti-icing
What is the purpose of the fuel filter in an engine fuel system?
Fuel filter
Very fine filter in the engine fuel sub system. In the event of blockage there is a bypass system to ensure a continuous supply of fuel, albeit unfiltered, reaches the engines in the event of filter blockage.
What are the symptoms of a compressor stall?
Indications of a compressor stall are an increase in engine vibration and increase in turbine gas temperature (TGT).
Describe the function of a frequency monitor ice detector.
Frequency monitor ice detector.
The change in resonant frequency of a probe when ice formed is detected. The probe is vibrated at its clean resonant frequency, the formation of an ice mass reduces this frequency and the detector senses the chnage and activated a cockpit alarm.
What types of tail configuration are there?
All flying tailplan
Taileron
Tailless
V Tail
Describe a monocoque fuselage structure.
A monocoque fuselage uses a stressed skin over a frame to support the load.
What are the two primary types of internal combustion engine?
Four-stroke cycle piston
Gas Turbine cycle.
What are Stringers?
Stringers accept some of the flight loading.
What is a fire wire?
Fire Wire - a sensing element in the form of a wire, 2mm in diameter (known as the continuous wire detection system). The electrical pulse can only pass through the central electrode as the filling material is an insulator. Extreme heat prevents insulation by the filling material and an alarm is triggered.
Central electrode with metal sleeve, insulation breaks down under heat creates circuit and alarm. (stainlesss steel)
Describe a semi-monocoque fuselage structure.
A semi-monocoque fuselage is a hybrid structure combining a tensile stressed skin and a compressive structure made up of longerons and ribs or frames.
How does a Halon fire extinguisher work?
Halon extinguishers stop the fuel, ignition and oxygen by chemically disrupting combustion.
What are the advantages of an electrical de-icing system?
Electrical de-icing systems are used when complex control arrangements are needed and when small areas require heating. The system comprises heater elements made from copper-manganese alloy built onto a backing material (heater mat) or deposited (spray mat) onto the backing.
What are the nine uses of oil in an aircraft?
Reduce friction
Reduce wear
Cleaning
Minimise corrosion
Cooling
Heating
Hydraulic
Chip detection
Engine Status
What is mixed lubrication regime?
Has qualities of both hydrodynamic and boundary lubrication regimes.
Generated lubricant film is not enough to separate the bodies completely, but hydrodynamic effects are present.
Why would an aircraft commander wish to jettison fuel?
To meet maximum landing weight.
What properties must AVGAS possess?
Anti-knock value
Volatility
Vapour Locking Tendency
Stability
Solvent and corrosion properties.
Briefly describe the operation of a turboprop.
A turboprop consists of a gas turbine driving a propeller. The turbine stages of the engine absorb the majority of the gas energy to drive the propeller, leaving only a small residual jet thrust at the propelling nozzle.
What is an all flying tailplane?
Such as C17, the entire tailplane’s angle of attack can be adjusted by trim actuators to compensate for increased nose down trim forces at high speeds and CoG changes.
What is the Brayton Cycle, and what are the four phases?
The Brayton cycle represents the operation of a gas turbine engine. The cycle consists of four processes, compression, combustion, exhaust and induction.
What is the purpose of magnetic chip detectors in an oil system?
Magnetic chip detectors
These collect ferrous debris from the bearing chamber and provide a CWS caption when chips are detected. They are permanent magnets that are inserted into the oil flow, retained in self sealing valve housings.
What are the key limitations of piston engines?
RPM
Increased RPM leads to increased stress on engine components, there are therefore RPM limitations for each engine type.
Temperature
High cylinder temperatures can lead to a breakdown of cylinder wall lubrication and cause failure. Oil shortage may cause inadequate lubrication and bearing failure.
What is the max speed of turboprop operation?
350 kts
At speeds greater than 350 kts and high altitudes, the efficiency of the prop deteriorates rapidly beuase of the development of shock waves on blade tips.
What is Design Limit Load?
Maximum load the designer would expect an airframe to experience in service.
How does thrust increase take off performance?
Increased thrust at low forward speeds results in better take off performance
What is blade cooling?
Blade cooling
Turbine blades require the most cooling, air is tapped from the compressor to provide cooling. Cooling is often convection cooling or film cooling.
What are the causes of a compressor stall?
Air flow impacts the compressorblades at the wrong angle.
Compressor blade stalls
All compressor blades in a stage are at the same angle/relative air flow; therefore the entire compressor stage stalls.
Air flow presented to the next compressor stage is distrupted.
What is volatility?
Volatility is a term for a liquid that can change to vapour when heat is applied.
What is Stiffness/Rigidity?
Ratio of stress over strain.
What are the three different lubrication regimes?
Hyrodrodynamic (fluid flim)
Boundary
Mixed
What is N1?
Fan speed
What is an aircraft’s empennage?
The empennage is the entire tail group and consists:
Fin, tailplane, elevator, rudder, trim tab, fixed tab.
What are the four fuels available for military use?
AVGAS - Piston Powered Aircraft
AVTAG - 50/50 Kersone Gasoline Blend Fuel
AVTUR - Aviation Turbine Fuel (Jet Fuel)
AVCAT - Aviation Carrier Turbine Fuel
What is wing loading?
Wing loading describes the g forces on the wing due to payload
What are the two types of thermal deicing systems?
Thermal (Hot Air)
Thermal (Electric)
What are the causes of an engine surge?
If all stages of the compressor stall, the pressure in the combustion chamber is high enough to force the flame forward.
Can be caused by over fuelling. Indications are intake banging, rise in turbine gas temperature, loss of thrust and possible catastrophic compressor failure.
What is viscosity?
Viscosity is the resistance to flow. Viscosity affects the atomisation of fuel and the ability of an aircraft to start at low temperatures.
What are the benefits of a high wing configuration?
High wing enables ease of cargo loading, greater visibility, greater ground clearance.
What is the purpose of an aircraft Bulkhead?
Bulkheads can be either a curved membrane and react to loads in tension, or flat and react to loads in bending.
What is a Tacho-generator?
Tacho-Generator
Fitted to the auxillary gearbox to measure the rotational speed of the compressor shaft.
What is thermal stress?
Thermal stress occurs when rapid changes in temperature cause uneven expansion and contraction in a turbine blade.
What type of compressor are there?
Axial compressor
Centrifugal compressor
What is AVGAS?
AVGAS
Used as a fuel in spark ignition internal combustion engines.
What are Holdover times (HOT) with regards to deicing?
The HOT is the duration of time at which deicing fluid is effective, during which the aircraft must get airborne or have deicing repeated.
What is AVTAG?
AVTAG is the combination of AVGAS and AVTUR
What fuel is often used in cold climatic conditions by military aircraft?
AVTAG - ‘Wide-cut’ Fuel
It has a lower freezing point than AVTUR.
What is an engine surge?
An engine surge occurs when all stages of the compressor stall, the pressure in the combustion chamber is high enough to force the flame forward.
This reversed flamae is the compressor surge. It can be caused by over fuelling.
What is convection cooling?
Convection cooling is a type of blade cooling is which cool air is passed through longitudinal holes or hollow blade sections.
What is a canard?
A canard is a small forewing that is placed forward of the main wing of a fixed-wing aircraft. The canard reduces trim drag at high speed.
The canards reduce the main wing loading, allow better control of the main wing airflow and can increase the aircraft’s maneuverability, especially at high angles of attack.
Briefly describe the structure of aircraft floors?
Aircrafy floors require robust construction as local loads can be high.
They are often made of composite honeycombs and designed in short sections and supported laterally off their frames.
What are the main elements of an oil system?
Oil tank
Oil Pump
Filter Assembly
Oil Cooler
Monitoring Instuments
Magnetic Chip detectors.
What is film cooling?
Film cooling is a type of blade cooling in which a film of cooling air is passed over the surface to protect it from hot gas flow, typically only applied to leading and trailing edges.
What is the purpose of an oil cooler in an oil system?
Oil Cooler
These can be air-cooled or fuel-cooled. The exchanged consists of a series of joined tubes with inlet and outlet ports. The bypass valve protects the oil cooler from excessive pressure build up from high viscosity during cold starting.
What is FSII?
Fuel system icing inhibitor (FSII)
All military aircraft should use fuel containing FSII. It inhibits fuel system icing and fungal growth.
When may boundary lubrication occur?
In starting conditions.
High bearing loads.
Inadequate viscosity.
Oil starvation, loss of oil pressure.
What are the four phases of the four-stroke cycle?
Induction
Compression
Power
Exhaust
List some devices used to monitor engine temperature.
Thermocouples
Hot junction mounted in exhaust gas, cold junction senses ambient air at reference point. Several devices are used to give an average temperature.
Pyrometer
Measures radiated energy (heat) from the source at which it is directed. A DC voltage is produced and amplified for the control and indication circuits.
What materials can be used in aircraft construction?
Aluminium alloys
Titanium alloys
Magnesium alloys
Steel
Carbon fibre composites
Glass reinforced plastics
Wood
What types of ice detector are there?
Visual detector
Differential static pressure ice detector
Frequency monitor ice detector.
What is the purpose of a filter assembly in an oil system?
Filter assembly
The filters and strainers prevent debris from circulating in the oil system. They include a filter, bypass, blockage indicator and non return valve. When there is differential pressure across the filter the bypass valve opens.
What component is the boundary between the engine and the airframe fuel systems?
Fuel cocks.
What are the purposes of the oil system in an aircraft?
To lubricate and cool the main bearings and other load bearing parts of the engine.
What is Stress Corrosion?
Stress corrosion occurs when materials are subjected to permanent tensile stress in corrosive environments. Cracking propogates around material grain boundaries. Aluminium alloys and steels are susceptible.
What are the three oil lubrication regimes?
Hydrodynamic (fluid film)
Boundary
Mixed
What is Fuel cross-feed?
Cross feed allows any engine to receive fuel from any tanks.
What are the two main types of turbine engine compressor?
Axial and Centrifugal
What are Longerons?
Heavy longitudinal members taking concentrated loads in direct tension and compression, accepting longitudinal loads due to fuselage bending.
What is Intermediate Air when referring to gas turbines?
Intermediate Air
Intermediate Air is the air injected into the combustion zone through the second set of liner holes (primary air goes through the first holes). This air completes the reaction process, cooling the air and diluting the high concentrations of carbon monoxide and hydrogen.
What is the Holdover Time (HOT) for de-icing procedures?
The HOT time refers to the time period at which de-icing fluids remain effective. If this time is exceeded the de-icing procedure must be repeated.
What types of gas turbine are there?
Turbojet
Turbofan
Turboprop
Turboshaft
What type of intake types are there?
Subsonic - Large open intake
Supersonic Intake - to slow air down
What are the two main fire detection systems on an aircraft?
Thermal Switch - as temperature rises the cylinder expands more than the bow and allows the contacts to spring together. A warning light and an aural alarm will warn the flight crew that an overheat condition exists in a particular area.
Fire Wire - a sensing element in the form of a wire, 2mm in diameter (known as the continuous wire detection system). The electrical pulse can only passthrough the central electrode as the filling material is an insulator. Extreme heat prevents insulation by the filling material and an alarm is triggered.
How does a turbofan differ from a turbojet?
A turbofan has an additional fan at the front of the engine, which accelerates air in a duct bypassing the core gas turbine engine. Turbofans are the dominant engine type for medium and long-range airliners.
Describe a truss fuselage structure.
A truss fuselage consists of longerons, verical and diagonal web members, a bulkhead and stringers.
The structure is still used in many lightweight aircraft.
What types of Ice Detection devices are there?
Visual ice detector
Differential static pressure ice detector
Frequency monitor ice detector.
What is flash point?
Flash point is the lowest temperature at which fuel begins to form a combustible vapour.
What are the disadvantages of an axial compressor?
Expensive to produce
Difficult to manufacture
High maintenance and running costs
What is the purpose of the low pressure cock (LP) in an engine fuel system?
Low pressure (LP) cock
Delineates between airframe fuel and engine fuel.
Fitted as the final component in the airframe system.
What are the causes of a compressor stall?
A compressor stall is a local disruption of airflow through the compressor that causes a failure of the system. A compressor stall occurs when it operates outside its limits.
Airflow impacts the compressor blades at the wrong angle causing the blades to stall, which are all at the same angle to RAF. The airflow then presented to the next compressor stage is disrupted which causes subsequent stalls.
What is an electronic tacho-generator?
An electric tachometer system makes use of a small AC generator mounted to the accesory drive section of a turbine engine.
As the engine turns, so does the generator. The frequency output of the generator is directly proportional to the speed of the engine.
What are the bleed air services?
Airframe anti-icing
Cabin pressurisation and heating
Fuel tank pressurisation
Pneumatic services
Air blow flight control services
What are the ideal properties of materials used in aircraft construction?
High strength and stiffness
Lightness
Low Cost
Ease of construction and production.
What is hydrodynamic (fluid film) lubrication?
Layer of oil between surfaces is relatively thick.
Keeps the two surfaces apart.
The amount of friction generated is very small.
What are the advantages of a centrifugal compressor?
Cheap to produce
Easy to manufacture
Low running costs
What are the four types of tailplane?
All flying tailplane
The entire tailplane’s angle of attack can be adjusted by trim actuators to compensate for increased nose down trim forces at higher speed.
Taileron
Slab tailerons can be actuated independently of eachother and provide aircraft primary control in both pitch and roll.
Tailless
Control power is provided by trailing edge elevators or elevons.
V Tail
Twin fins, perform the functions of conventional horizontal and vertical tail surfaces
What is Stress?
The load unit per unit area of cross-section.
Which aircraft areas are most prone to icing?
Aerofoil surfaces
Engine intakes
Engine internal surfaces
Rotor blades and props
Windscreens
Probes and vanes
Weapons and pylons.
What is the purpose of an oil pump in an oil system?
Oil Pump
Provides pressurised oil to lubricate engine components. Driven through reduction gears from external gearbox. Usually mounted in a ‘pack’ with one pressure pump and several scavenge pumps.
What principle is behind the function of jet pumps?
Jet pumps work on the ‘venturi’ principle. Fuel bled from the LP pumps provides the motive force.
What types of oil filter are there?
Fine pressure filter.
Thread type.
Scavenge filter.
What is fuel cross-feed?
Fuel cross-feed allows fuel tanks to feed the opposing engine. Cross feed valves are opened. This system ensures engine operation should fuel system blockage occur.
What design features can help prevent engine stalls?
Variable inlet guide vanes
Multi-spool compressors
Compressor bleeds.
What are the main differences between a turbofan and a turbojet?
A turbofan has less ground clearance than a turbojet. A turbofan has increased noise level reduction, reducing the need jet noise suppression. A turbofan engine is a turbojet with and added fan at the initial stage of compression.
What is the purpose of the high pressure (HP) fuel pump in an engine fuel system?
High pressure (HP) fuel pump
Driven by the engine, which provides a sufficient supply of fuel for engine operation. There are two types of HP fuel pump used on gas tubrines, the piston-type variable stroke Lucas pump and the gear-type pump.
Describe the power stroke of the Otto cycle.
Power/Combustion
This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
What effects can icing have on engine performance?
Thrust will decrease because engine efficiency will be reduced. Drag and weight of aircraft will increase, increasing engine demand.
What are the uses of a turboshaft engine?
Helicopters
APUs
What is a fuel recuperator system?
The fuel recuperator system is found on many combat aircraft. If the LP pump pressure drops due to surging in a manoeuvre, fuek from the recuperator is forced into the system.
What are the differences between air-cooled and fuel-cooled oil coolers?
Air-cooled
Sufficient for turboprop engines but impractical at high speed aircraft because of the drag penalty incurred.
Fuel-cooled
Incorporates a spring-loaded bypass valve that protects the matrix from excessive pressure build up due to high viscosity during cold starting.
How does a vibrating/frequency monitor ice detector work?
The device utilises the changes in resonant frequency of a prove which occurs when ice forms on it.
The probe is vibrated at its clean resonant frequency. If ice forms, the resonant frequency on the probe will be reduced and a detector alarm triggered.
What is the purpose of pressure bulkheads in a fuselage structure?
Pressure bulkheads within the fusleage are the front and rear component of the pressure seal in all aircraft that cruise in a tropopause zone in the earth’s atmosphere.
It helps maintain pressure when stratocruising and protects the aircraft from bursting due to the higher internal pressure.
Describe the exhaust phase of a gas turbine jet engine cycle.
Exhaust
Exhaust gases are used to provide jet thrust in a turbojet engine. In a turboprop engine the gases drive a propeller through reduction gearing via an additional turbine.
What is the role of longerons in a fuselage structure?
Longerons are heavy longitudinal members that take concentrated loads in direct tension and compression.
What is the purpose of the LP fuel cock?
LP fuel cock, stops fuel travelling the engine.
What is an axial compressor?
An axial compressor is a rotating, aerofiol based compressor, in which the gas flows parallel to the axis of rotation. Axial compressors produce a continous flow of compressed gas, and have the benefits of high efficiency and large mass flow rate. They are complex due to the requirement of several rows of aerofoils to create a large pressure rise.
Briefly describe the gas turbine jet engine work cycle.
Air is compressed by the fan blades as it enters the engine, and it is mixed and burned with fuel in the combustion section.
The hot exhaust gases provide forward thrust and turn the turbines which drive the compressor fan blades.
- Intake
- Low pressure compression
- High pressure compression
- Combustion
- Exhaust
- Hot section
- Turbines Low and High pressure
- Combustion chambers
- Cold section
- Air inlet
What is the purpose of an oil tank in an oil system?
Oil tank
Contains the lubricant, may have a sight glass or dipstick to measure oil quantity.
What is DLL?
Design Load Limit
What properties should a gas turbine fuel (AVTUR) possess?
- Ease of flow under all operating conditions
- Quick starting of the engine
- Complete combustion under all conditions
- A high calorific value
- Non-corrosive
- Minimal fire hazard
- Provide lubrication for the moving parts of the fuel system.
What is torque?
Twisting moment of the prop on the engine
What fuel is used in naval carrier operations?
AVCAT - High flash kerosene
To prevent vapour build up within confined spaces.
What is the purpose of the HP shut-off valve in an engine fuel system?
HP shut-off valve
Normally part of the throttle system, shuts off fuel to the engine burners.
What are the nine uses of oil in an aircraft?
Reduce friction
Reduce wear
Cleaning
Minimise corrosion
Cooling
Heating (oil to fuel heat exchange)
Hydraulic Fluid
Chip Detection
Engine Status
Describe the exhaust stroke of the Otto Cycle.
Exhaust
During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve.
What services can bleed air provide?
Bleed air can be used for:
Airframe anti icing
Cabin pressurisation and heating
Fuel tank pressurisation
Pneumatic services
Air blow flight control services.
Describe the combustion phase of a gas turbine jet engine cycle.
Combustion
Fuel is injected and ignited by igniter pumps. Some of the compressed air provides cooling by bypassing the burner section. The fuel/air mixture is burned in a continous combustion process at a very high temperature. The hot air and gases expand and force the turbine to rotate, which drive the compressor. The high velocity gases exit via the exhaust.
What are the components of an oil system?
Oil tank
Oil pump
Filter assembly
Oil Cooler
Monitoring instruments
Magnetic chip detectors.
What is Primary Air when referring to gas turbines?
Primary Air is highly compressed air from the high-pressure compressor (often decelerated by the diffuser). The air is fed through the main channels in the dome of the combustor and the first set of liner holes. The air is mixed with fuel to allow combustion.
What is the purpose of the magnetic chip detector?
Collects ferrous debris from the bearing chamber that can be analysed to monitor bearing performance and assess engine life.
What is Stress?
Load per unit area (cross section)
What is a centrifrugal compressor?
A centrifugal compressor accelerates the air mass by spinning the air. The amount of accelleration is dependent upon the rotational speed of the compressor.
What is the role of the skin in a fuselage structure?
The aircraft’s skin is the primary structural component of the fuselage. Its thickness is determined by the loads imparted to it during flight.
Describe the induction stroke of the Otto cycle.
Induction
The piston begins its downwards travel at top dead centre (TDC) as the inlet valve opens and the fuel/air mixture is drawn into the cylinder by producing vacuum pressure through its downwards motion, the piston ends at bottom dead centre (BDC).
What wing configurations are there?
High Wing - Enables easy cargo loading.
Mid Wing - Presents a smaller radar signature.
Low Wing - Shorter undercarriage, crash protection.
What is Flash Point?
The lowest temperature at which the fuel begins to form a combustible vapour. At temperatures below the flash point, fuel will not vapourise enough to provide vapours capable of combustion.
What are the advantages of Thermal (Electric) deicing systems vs hot air?
Electrical heating systems are widely used for anti icing when complex control arrangments are needed or only small areas require heating.
What are the advantages of axial compressors over centrifugal?
They are more efficient (95% vs 86%).
Higher compression ratio due to multistage.
Small frontal area.
What are the symptoms of a compressor surge?
A compressor surge results in intake banging, a large ruse in TGT, loss of thrust and possible catastrophic compressor failure.
What are AL41, AL61, AL48 and TEL?
These are all aviation fuel additives.
How are turbine blades cooled?
Turbine blades require significant cooling.
Air is tapped from the compressor to provide cooling.
Convection cooling - passing cooling air through longitudinal holes or hollow blade sections.
Film cooling - passing a film of cooling air over the surface to protect it form hot gas flow, typically only applued to leading and trailing edges.
Why is boundary lubrication not desirable?
Boundary lubrication is not desirable as rupture of the exceedingly thin film causes wear, increases bearing surface temperature and can cause seizure.
What are the advantages of centrifugal compressors over axial?
Centrifugal compressors are:
Cheaper to produce.
Easy to manufacture.
Cheap to run.
What is the purpose of the fuel cooled oil cooler (FCOC) in an engine fuel system?
Fuel cooled oil cooler (FCOC)
Its primary function is to remove heat from the engine oil, its secondary function is to remove ice crystals and increase volatilty for more efficient fuel ignition.
What is N2?
The power turbine
What is a thermal switch in a fire protection system?
A thermal switch is a heat-sensitive system in which under fire conditions a cylinder expands and triggers an alarm.
What is a fire tetrahedon?
The fire triangle (fuel, oxygen, ignition) with the addition of the ‘chain reaction’ due to the invention of the HALON fire extinguisher.
Name and describe the two basic phases of lubrication.
Hydrodynamic (film) lubrication
Where the surfaces concerned are separated by copious amounts of oil and there is a thick layer of oil between the surfaces.
Boundary lubrication
Where the oil film is exceedingly thin and may be caused by high bearing loads, inadequate viscosity, oil starvation or loss of oil pressure
What is turbine creep?
The expansion of turbine blades when subjected to very high temperatures and centrifugal loads. They will ultimately fail if RPM and temperature limits are exceeded
