M11.4 Flashcards
What ata chapter is air conditioning and cabin pressure?
ATA chapter 21
Where does an aircraft receive its pressurised air?
Engines
Auxiliary power unit (APU)
Ground source (Air Cart)
Which engine stages is pressurised air taken from?
Bled off Compressor stage
(5th) and nine (9th) depending on the engine type
Part of bleed air system
When is low pressure air used?
11.4
during take-off, climb and cruise conditions
5th stage
When is high pressure used?
11.4
High-pressure bleed air is used at low engine RPM speeds during descent ananytime the low-pressure air supply is inadequate.
9th stage
Where is the LP stage?
Bleed air system
11.4
Fan on front of engine
What is air pressure adjusted by?
Pressure Regulating Valve (PRV) or the Bleed Air Valve (BAV)
What are the three groups of cabin compressor?
Positive displacement compressors (Roots-type blower)
Centrifugal compressors
Turbo Compressors
What is the disadvantages of engine driven compressors?
Not free power or efficient
Every time air is bled from the engine compressor, there is an equal amount of reduction in power output due to the reduced amount of air available for combustion
Engine works harder and burns more fuel and will increase engine temperature
Why are cabin compressors used?
disadvantages associated with pressurising sources. independent cabin compressors are designed to prevent an increase in fuel consumption.
What is a positive displacement (root type) blower and how does it work?
Roots-type blower is similar to the action of a gear pump as it takes a predetermined volume of air, compresses it, and then delivers it to the cabin duct.
Rotors mounted in an airtight casing, on parallel shafts, rotate at the same speed. Air then travels around the outside of the case and is deposited into the plenum at the exit.
What is a centrifugal cabin compressor?
Super charger
It has a centrifugal impeller, similar to a turbo-supercharger, in the induction system of a reciprocating engine.
Outside air at atmospheric pressure is let into the supercharger, where it is compressed by the high-speed impeller, and delivered to a distribution system.
What does CAC stand for?
Cabin air compressor
What is the outside air temperature during cruise?
-40 f and c
What does adiabatic mean?
Adiabatic - Temperature change without the addition or removal of heat.
What does conduction and convection mean?
Conduction - Transfer of heat from one object to another due to the physical contact of the two objects.
Convection - Process by which heat is transferred by bulk movement of a fluid.
What is super and sensible heat?
Sensible Heat - Heat, when applied causes a temperature change that can be sensed.
Super Heat - Heat energy added to a gas after complete evaporation.
What is the function of the acs?
Air Conditioning System
The function of the ACS is to maintain a comfortable air temperature inside the aircraft.
Majority of acs 21 to 27c or 70 to 80 f
Can also control humidity
Supply ventilation air
Supply heated air
Supply cooled air
Cabin Pressurisation
Equipment Cooling
What are the two types of acs?
Air Cycle Machine – Used mainly in larger passenger aircraft
Vapour Cycle machines – Used mainly used in small and medium-sized aircraft
What does the pack or flow control valve do?
Air cycle system
regulates bleed air from the pneumatic manifold into the air cycle air conditioning system. The valve is controlled with a switch on the air conditioning panel in the flight deck.
valve opens, closes and modulates, to allow the air cycle air conditioning system to be supplied with a predetermined volume of hot, pressurised air
How are Most pack or flow control valves controlled?
What happens in an abnormal event?
electrically controlled and pneumatically operated.
When an overheat, or any other abnormal condition is detected, the pack or flow control valve is commanded by a signal to close.
What type of valve is a pack or flow control valve?
The pack valve is a venturi-type butterfly valve controlled by a solenoid. It is pneumatically operated and spring-loaded to closed.
