Systems PT1 Flashcards
what is the function of the electrical system on a large transport aircraft?
generate, regulate and distribute electrical power throughout the aircraft
how many electrical systems are there
there is usually more than one system and comprise of a mixture of AC and DC circuits
what is the normal config of a electrical system
will have a separate AC circuit powered by the alternator fitted to each engine and each circuit will feed a specific bus
why is AC more common in use than DC
AC alternators are more light than DC generators of similar capacity
explain the basic bus system
power supply is routed to a common bar, off which several components or services can be powered.
this splits the electrical system into channels so that some parts can be prioritized in the event of a supply breakdown
what are the different types of bus system
parallel type
split bus type
split parallel type
how is DC power provided on an aircraft
AC power is rectified using a full wave rectifier
(AC can be produced from DC using an INVERTER also)
DC circuits have their own bus system isolating them from the AC bus
what must be determined before AC generators are connected in parallel
output voltage, frequency, and phase rotation are the same
how does emergency lighting work in an aircraft
it’s armed and will automatically activate after the failure of primary lighting power
explain how the CSD works
the AC alternator requires power at a constant 400hz. the frequency is determined by the rotation speed of the armature, which is driven by the engine. The engine however doesn’t output a constant speed so a constant frequency can’t be delivered unless a device (CSD) is installed so that no matter what the speed of the engine is, the alternator can still output 400hz.
explain the implications of generator failure
in an electrical fault, the circuit breakers protect the system, however a mechanical failure can cause serious engine damage is rotation is not stopped
The GEN DISC switch disconnects the engine drive from the gearbox and CSD using a DOG CLUTCH and cannot be reset after broken
what are CSDs that are built into generators called
IDG (Boeing) integrated drive generator
ICSD (airbus) integrated constant speed drive
what purposes do air conditioning and pressurisation have on an aircraft
- conditioned air for heating/cooling cabin/cockpit
- prevent condensation on a/c equipment and protect avionics
- provide conditioning for cargo as animals sometimes stored
what is PD
pressure differential, the difference between pressure inside the hull and the ambient pressure.
the system maintains a cabin alt of 8,000ft regardless of the altitude the aircraft is flying. if the a/c climbs beyond 8,000ft then PD will increase
how is PD controlled
controlling outflow of air from the fuselage. as air con flows in, the outflow is regulated at a lesser rate by a a rate controller. it also controls cabin VS.
when desired PD is achieved, outflow is increased again at a rate that will maintain the desired PD level
how does the outflow valve work?
outflow valve position is controlled by a cabin pressure controller either automatically or manually w a target of 8.9 PSI diff.
how is the environmental system controlled from the cockpit
simple systems have a OFF-NORMAL-RAM setting
most modern aircraft have a panel where individual temps can be set in the cabin and cockpit.
- also will have individual pressure controls on the panel incl. emergency controls and warning lights
what are the safety features of the environmental system
- pressure control valve
- pressure relief valve (used to ensure pressure does not build up beyond max operating pressure)
- negative pressure valve ( ensures pressure outside cabin never exceeds pressure inside the cabin and operates automatically
- emergency depressurisation valve (activated by WOW switch)
- emergency cabin altitude control
explain how vapor cycle air conditioning works
on the principle of latent heat
the refrigerant changes state from liquid to vapor, and in doing so absorbs heat from the cabin. this heat is sent outside the aircraft as the refrigerant returns to a liquid state.
explain the requirements and behavior of refrigerants
almost any liquid can be a refrigerant
for max effectiveness:
- low vapor pressure and boiling point
how does the continuous flow oxygen system work
- used in the cabin where it is automatically actuated and a flow of oxygen is immediate and continuous
how does the pressure demand oxygen system work
has a diluter demand regulator, which delivers oxygen to persons lungs when person sucks in to breathe.
oxygen is automatically diluted in regulator with some atmospheric air which only takes place below 34,000ft
found on the flight deck where it is more essential for the crew to be functioning than the cabin until the aircraft gets down to a safe altitude
when is 100% oxygen used?
in the event of smoke or other contaminants in the cockpit
what is the requirement for oxygen supply on large transport aircraft
enough for the aircraft to descend from cruising altitude to 14,000ft in less than 4 minutes without exhausting the oxygen supply
what are the advantages and disadvantages of chemical oxygen systems
advantages:
- lightweight
- less equipment
- less maintenance
disadvantages:
- fire hazard higher
- not tamperproof
- won’t turn off
what systems protect an aircraft from fire
overheat, smoke and fire protection systems
a complete fire protection system includes:
fire detection and fire extinguishing systems
what are the characteristics of automatically fired extinguishing systems? where are they found?
usually found in toilets
- the fire bottle is fitted with a squib which melts at 70-75 degrees, allowing the extinguishing agent to exit the bottle
what are the 4 types of extinguishing agents
- Water (cools fire and excludes oxygen)
- carbon dioxide (displaces surrounding oxygen)
- dry chemical (smothers the fire excluding oxygen)
- halogenated hydrocarbons (chemically interferes with combustion)
how does the pneumatic fire protection system work
a gas inside tube inside a cylinder expands when heated. when the trigger temp is reached, the gas pressure moves the tube (check valve) which hits the alarm contact causing the alarm to sound.
when the temp falls below the trigger temp, the valve will move back into place and can be used again.
how does the smoke detector work
uses photoelectric cells with a light beam directed toward them. if enough smoke is present, the light beam refracts light to the cells causing the alarm to sound.
how does fire extinguishing work inside the engine nacelle
- bottle is powered at 500-600psi.
- has a relief valve that will rupture if the bottle were to overheat
- the bottle is discharged from the cockpit by an electrical current applied to contactor which detonates an explosive cartridge and shatters a disk at the bottle outlet letting the agent flow
what speed do turbine engines spin at
7,000-10,000 rpm
why is halon 1301 the ideal agent used for fire extinguishing in the air
- low concentration and very effective
- may be used in occupied personal compartments
- effective on all 3 fire types
- no residue remaining after use
how does fire extinguishing work in the engine nacelle
- fire bottle pressurized to 500-600 psi
- relief valve is a fusible disk that will rupture if bottle overheats
- electrical current is applied to contactor which detonates an explosive cartridge which shatters a disk in the bottle outlet, allowing the agent to flow
what callouts are there for lockout system failures
- rudder ratio
- all lock
- EICAS
when are high lift devices employed
only at low speeds
form part of aerofoil when not in use
what are the common lift augmentation devices
- slot, slat flaps (LE and TE), fowler flaps
what is the problem of the power boosted control system
during transonic flight, shock waves form on control surfaces causing buffeting
how are buffeting forces dampened
power operated irreversible control system
cockpit controls actuate control valves which direct hydraulic fluid to control surface actuators (PCU)
- artificial load is built into the system so pilot has more control feel
how does the fly by wire system work
crew command inputs are translated into electrical signals
signals go to actuator control electronics
signals converted to digital format and sent to primary flight computer
inputs are analyzed, and if outside flight control envelope the signals are modified so they stay inside
can be operated with IFS providing auto flight control and feed flight control data to the FDC
