11.4 Flashcards
Whats the 3 thing which provide the aircraft with pressurised air ?
Engines
APU
Ground source
What part of the engine takes in air to pressurise the cabin ?
Compressor
Whats the three types of compressors ?
Positive displacement compressor
Centrifugal compressor
Turbo compressor
How is air pressure adjusted ?
Pressure regulating valve or
Bleed air valve
When is low pressure air used ?
During take-off climb and cruise.
( high pressure bleed air is used at low engine RPM speeds during decent )
What lowers the hot air which is bled from the engine ?
Pneumatic system
What happens to the engines power when air is bled from the compressor ?
Power will drop
( this decreases the engine efficiency as the compressor is resulted to work harder )
- individual cabin compressors are designed to minimise the disadvantages which follow from bleeding the air from the engines compressor )
Explain a positive displacement blower ?
Two rotors rotate at the same speed in which air travels around the outside of the case and is deposited.
Explain centrifugal cabin compressor ?
Takes air from atmosphere into a supercharger, where it is compressed by the high-speed impeller and delivered to a distribution
What does the supercharger have in a centrifugal cabin compressor which produces optimal airflow regardless of the engine speed ?
Variable - ratio drive
How does the turbo compressor work ?
Bleed air from engine drives a turbine, which directly drives a compressor. Hot air produced is blended with cooled decompressed bleed air.
What is the cabin air compressor powered by ?
Three-phase motor
What does the APU compressor supply ?
Bleed air to a load compressor
If the APU is designed to provide bleed air extraction in flight, what altitude is the bleed air extraction normally limited to ?
22,000 ft
Whats the two APU outputs ?
Electrical
Pneumatic ( compressed air )
What does a ground cart air supply consist of to supply air ?
Small jet engine inside soundproof steel unit which carry’s conditioned air through ducks from the pack where it is required on the aircraft.
Whats the two types of air conditioning systems used on aircraft ?
Air cycle machine - used on large aircraft
Vapour cycle machine - used on small aircraft
Whats the two types of air conditioning systems used on aircraft ?
Air cycle machine
Vapour cycle machine
Whats the range that an air conditioning system is capable of maintaining ?
21 - 27 degrees
Whats the use of a pack ?
To drop air down to around 0 degrees
What two things are found in an air con pack ?
Heat exchanges
Air cycle machine
How is conditioned air distributed to the cabin ?
Trough ducts
( conditioned exits through ceiling vents where it circulates )
What are distribution ducts constructed of?
Light fibreglass coated to prevent moisture damage
( ducts must be able to expand and shrink without loss of the pressure tight properties )
Where are temperature monitoring valves located ?
Electronics compartment
Whats a thermistor ?
Resistor that changes with its exposure to heat and has a shut off control.
( its not a on/off switch. It’s resistant changes as temperature changes )
What do on board humidifiers do ?
Help passengers stay hydrated
How much of the cabin air is filtered and recirculated ?
50%
( this means engines only need to supply the other 50% of cabin air which saves fuel )
When the air is supplied to cabin and circulates around, how is it discharged out of the cabin ?
Through air grilles located on the sidewalls near the floor.
*Cannot mix r12 And r134a
Whats a gaspo fan ?
Air conditioning outlet in the cabin
What fan is found in packs ?
ACU fans
Above what altitude does there be a lack of oxygen and cabin pressurisation be needed ?
Above 10,000 ft
What happens to the outside pressure as the altitude increases ?
It decreases
What high is the cabin pressure when at cruise ?
8,000 ft
How much is 1 atm in psi and Hecto pascal ?
14.7 psi
1013.2 hPa
In the terms of passenger comfort, why do we pressurise the cabin ?
Depressurised cabin would make it have for passengers to breathe
Whats hypoxia ?
Becoming unconscious due to a depressurised cabin.
Whats the airframe subjected to when the aircraft’s being pressurised in a high altitude ?
Differential pressure
Calculation- (cabin psi - outside psi)
Whats the maximum anticipated loads called ?
Limit load
( limit load x safety factor = ultimate load )
Whats cabin altitude ?
Cabin pressure inside of aircraft in terms of altitude above sea level.
( Normally maintained around 8,000 ft )
How is the cabin pressurisation controlled in light ?
Through an outflow valve which regulates the amount of air that flows out of the cabin. This is controlled from the flight deck.
If cabin altitude increases, what happens to the cabin pressure ?
It decreases.
If you want to increase cabin pressure, should the outflow valve be open or closed ?
Closed.
Whats the three pressurisation mode ?
Isobaric mode - maintains cabin altitude no matter the altitude change.
Differential mode. - maintains cabin pressure
Manual mode ( emergency ) - used if isobaric control is faulty so it controls cabin pressure manually.
Explain a positive safety valve ?
Outwards pressure relief valve fitted to relive positive pressure in cabin when maximum pressure differential is exceeded.
( if its exceeded by 8 - 10 psi )
Explain a negative safety valve
Inwards relief valve which is fitted to prevent excessive negative differential pressure which will open if pressure outside the aircraft exceeds that inside the aircraft by 0.5 - 1 psi.
( allows air to enter cabin )
- to much air entering can cause difficulties opening the cabin door or structural damage.
Explain the leak detector methods for air conditioning ?
- Held close to component with a hose connection and an audible and visual alarm will signal.
- Apply soapy solution to fittings and inspect for bubbles.
- Injecting special leak detection dyes.
How do you find cabin differential pressure ?
Inside cabin pressure - outside ( ambient ) pressure
Explain he difference between a positive and negative negative safety pressure valve ?
Positive - opens outwards
- let’s excessive differential pressure out of
Cabin.
Negative - opens inwards
- allows ambient air to enter cabin
Whats a dump valve used for ?
Quickly remove air from the cabin and operates automatically or by a switch in the flight deck.
What is used to allow the flight crew to warn about a bleed air leak or monitor the systems function ?
Flight deck gauges
Overheat detectors
Bleed air monitoring systems
