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.