11.4 air con/cabin pressure Flashcards
where is an aircrafts pressurised air received from
engines, APU, Ground source
what happens to temperature as pressure increases
temperature increase
what stage in the engine is the compressed air taken from
compressor
when is low pressure air used
take off, climb, cruise
when is high pressure air used
low engine RPM
how many bleed ports will be open at a time
1
what is air pressure controlled by
pressure regulating valve or bleed air valve
if we use bleed air from the compressor what it there a reduction in
engine performance
what is used for cabin pressure to prevent usage of the engines air
independent cabin compressor
cabin compressors are divided into what 3 groups
positive displacement compressor, centrifugal compressor, turbo compressor
what does CAC stand for
cabin air compressor
to meet high demands for ground power when the engines arent running what is used
APU
what type of engine is a typical APU
small turbine engine
if an APU is used in flight what the bleed extraction limited to (height)
22,000ft
what is the ACP
air conditioning pack
if an aircraft doesnt have any engine on or APU running whats used for the air supply
pneumatic ground cart
what does ACS stand for
air conditioning system
whats the approximate cruising temp
-40 degrees celcius
whats the function of the air conditioning system
maintain comfortable air temperature in the aircraft
what range of temps can most ACS produice
21-27 degrees celcius
what are the 2 types of ACS system used on aircraft
air cycle machine, vapour cycle machine
where are air cycle machines commonly used
passenger aircraft
where are vapour cycle machines used
small and medium sized aircraft
what are the functions of the ACS
ventilation, heated air, cooled air, cabin pressure, equipment cooling
whats the size of the hose off the pneumatic cart
4 inch diameter
where does the air cycle conditioner get its air from
engine bleed air or APU
where is the air cycle conditioner usually located
lower fuselage or tail section
at extreme altitudes the bleed air is extremely hot, what does it use to cool the air
air cooling system
air arriving from the bleed air system and entering the heat exchange has an average psi of what and what temperature
30 to 40 psi, 150 degrees celcius
what does bleed air temp reduce to after passing the heat exchanger
100 degrees celcius
what temp is the bleed air after entering the compressor
30 to 40 degrees celcius
what temp is the bleed air after going through the secondary heat exchanger
60 - 70 degrees celcius
what does the pack or flow control valve do
regulates bleed air from the pneumatic manifold into the air cycle machine
how are pack flow and control valved controlled and operated
controlled electrically, operated pneumatically
what type of valve is the pack valve
venturi type butterfly valve
what is the main function of the pack valve
control the airflow into the cabin
at 8000 ft what is the mass air flow into the cabin
0.86 kg/s
on the ground what is the mass air flow into the cabin
1.1 kg/s
how are air conditioning systems able to save energy
adjusting their air output to number of passengers
what is the ACM
air cycle machine
what are the 2 types of ACMs used
oil lubricataed, air lubricated
what are the 2 functions of the condenser/reheater
cool air in AC pack, heat air in AC pack
whats the use of trim air valves
accurate temp controlled air
where is the RAM air door located
underside of aircraft
what are the 5 components of a vapour cycle machine
refrigerant, compressor, condenser, expansion valve, evaporator
what is the refrigeration process in order
compression, condensation, receiver dryer, expansion, evaporation, repeat
where is the receiver dryer located in a vapour cycle system
downstream of the condenser and upstream of the expansion valve
what are the majority of evaporators constructed from
copper or aluminium tubing
what is conditioned air distributed through
ducts
on modern turbine powered aircraft what is conditioned air also used for
cabin pressurisation
during long distance flights what is likely to happen to the air
becomes very dry after being repeatedly recycled
what do humidifiers do for the passengers
hydration, better taste, sleep quality, reducing jet lag
what percentage of the cabin air is normally filtered and recirculated
50%
whats the use of the cabin outflow valve
controls cabin pressure by controlling the release of air
what are the 2 safety valves
positive, negative
what is the use of the positive safety valve
relives positive cabin pressure when maximal is exceeded
when will the positive safety valve open (psi)
maximum between 8-10 psi
what do negative relief valves do
prevents excessive negative differential
what way do positive relief valves open
outward
what way do negative relief vales open
inward
simply describe negative/positive relief valves
negative - under pressure so puts more air in
positive - over pressure so reliefs
at what psi will negative relief valves open
0.5-1 psi
what valves are used to quickly dump air and air pressure from the cabin
dump valves
name the 3 pressurisation gauges/indicators
cabin altimeter, cabin rate of climb, cabin differential pressure
what are the 2 modes of pressurisation system operation
auto (1 and 2) and manual
how many controllers are in use at any time in the pressurisation system
1
during taxi what is the pressurisation GROUND/FLIGHT switch on
FLIGHT
during take off/climb what controls the amount of cabin pressure to altitude
outflow valve
in cruise does the cabin pressure change
no it stays constant
what does the cabin pressure controller do
controls cabin air pressure
what type of controls do modern aircraft use for cabin pressurisation control
pneumatic, electrical, electronic
on modern aircraft how many cabin pressure controller are there
two controllers, or 1 with a redundant circuitry
what is the ADC
air data computer
what is the FMS
flight management system
what is the best type of leak detector in air conditioning systems
electronic leak detector
the best leak detector of a air con system could detect what leakage per year
1/2 ounce
what leak detection methods other than a detector can be used
soapy solution, leak detection dye
what is R12
non-toxic and non-flammable gas, toxic to ozone layer
whats the main type of servicing equipment for vapour cycle air
manifold
on the manifold air vapour servicing machine whats the lower pressure/high pressure gauges psi range
low 0 - 150 psi
high 0 - 500 psi
what colour is the low pressure hose on the air vapour servicing manifold
blue
what colour is the high pressure hose on the air vapour servicing manifold
yellow
to ensure all water is removed from a vacuum pump how long is it help before use
15-30 mins
what is an aircraft bleed air leak
uncontrolled loss of bleed air from any system
what is a major concern with pressurisation and air con systems
temperature
if overheat was to happen at what temp will an OVERHEAT warning display
pack overheat - 260 plus
outlet temp - 230 plus
why is low cabin humidity good and bad
prevents bacteria and fungus, promotes fatigue and dehydration
on the central warning panel what do all 4 colours mean
red - warning
amber - caution
green - advisory
white - advisory
