Final Exam Flashcards
Difference between soft & hard magnets?*
Soft readily susceptible not good at retention (steel/iron)
Hard iron opposite.
What 6 ways can electricity be generated?
Friction Pressure (piezo electric) Heat Light Chemical Magnetism
What are the 3 requirements for electromagnetic induction?
A magnetic field
A conductor
Conductor move through magnetic field
Describe the basic principal of an alternator
Stator encloses a rotating bar (rotor) to generate AC, which slip rings or silicon diodes rectify to DC.
Magnetic field lies in rotor.
Current produced in armature (stator)
Describe the basic principal of a generator
Stationary magnetic field and rotating conductor (armature)
AC is rectified to DC using split rings commutator and carbon brushes.
Current produced in armature (rotor).
What is the purpose of the electrical system?
Generate, regulate and distribute electrical power.
How many electrical systems are on board a large a/c? Of what type?
At least 2 for redundancy of a mix of AC/DC.
AC more common, largely due to lightweight alternator attached to each engine and greater power demands. They also have smaller gauge wire. Will have an alternator attached to each engines to drive AC circuit.
What is a bus bar?
Power is supply is routed off a common bar, which several components are connected too. This breaks the electrical system into channels which can be prioritised.
What 3 types of bus bar are there?
Parallel, split bus, split parallel
What type of power is supplied from a battery?
Can this type be isolated from the other?
DC.
Yes it can be using it’s own bus.
How to convert AC - DC and DC - AC?
AC-DC: AC is rectified using full wave rectifier to DC.
DC-AC: static inverter
What purpose is a CSD?
Output of electrical generators must produce power at a constant frequency.
A constant speed drive is required to produce a constant frequency power supply of approx 400hz.
An alternator output frequency is determined by rotation of armature which is driven by the engine, which does not operate at a constant speed. Hence the need for a CSD (works of CFF flyweights balanced by springs).
What is the most common type of CSD
Hydro mechanical.
Mechanical governors maintain rotation speed for this type.
Is the oil in the CSD the same as the engine?
They are independent. Oil inlet and outlet temp, low oil px are monitored.
Describe the principal of operation of the CSD
Integral to generator/alternator.
Input from engine on a cog, attached to 2 cogs of same size, one attached to fixed displacement. The faster it spins the more charge oil is entered and enters the control cylinder which provides a braking action to variable displacement cog. This spins a similar sized cog attached to an output shaft maintaining RPM. Governor maintains a stable oil px.
Is there an option to disconnect the CSD? Why/why not?
Yes, in the event of a gearbox or generator failure (overheat/mechanical), as rotation must be stopped before serious damage would occur.
A guarded switch “GEN DISC” activated a solenoid switch which pulls a dog clutch breaking the connection between the engine gearbox and CSD. Once disconnected, it can’t be reset inflight.
What is a CSD a called on Boeing/Airbus?
Integrated drive generators (Boeing)
Integrated constant speed drive (Airbus)
What advantages are there to 3 phase AC over single phase?
Any disadvantages?
Increases the amount of current available.
Connection to phase sensitive devices (motors/transformers) is essential to be correct otherwise the incorrect phase will cause motor to spin in the opposite direction. Connecting these devices in parallel with incorrect phase can cause burn out.
What areas other than the cabin are air conditioned and/or pressurised? Why?
Air con to A/C equipment compartment (avionics) to prevent condensation due heat build up.
Air con/pressurised to cargo compartment as animals often carried.
What a/c systems make the PAX environment?
O2, pressurisation, air con, heating, pressure cell.
Main purpose is to control pressure and temp to ensure comfort and sufficient O2/safe px.
What is pressure differential? What the normal cabin altitude?
How is this cabin altitude controlled?
PD: difference between internal cabin px and ambient outside px.
8000ft.
Controls outflow rate to be less than the inflow from the aircon by a rate controller. Once desired PD met outflow rate increases. VS in cabin is also controlled by rate controller to ensure pax comfort.
Compare a flight profile of the internal cabin px compared with ambient outside px.
What control this?
Both are initially the same on the ground. As altitude increases, pressure decreases. Both the a/c and outside px will “inc in altitude/dec in px” but the a/c will at a slower rate that is comfortable to PAX.
This rate is controlled the outflow valve, which is controlled by crew settings (in 0000’s of ft/min) to ensure safe PSID.
What is the purpose of an air conditioning system?
Maintain comfortable cabin temp within the a/c fuselage. Will utilise an automatic control system so that the crew set a temperature and the system will automatically maintain this temp.
What are the requirements of an air conditioning system?
A pressure cell designed to withstand pressure differential.
Ability to respond to rapid changes to ambient temp and pressure.
Air supply capable of providing sufficient air for cabin pressurisation and air conditioning.