11.4 Flashcards
35000ft where is air pressure greater
Inside is greater then outside
On ground what is air pressure like
Equal inside and outside the aircraft
1 atmospheric pressure = what in psi and hpa
14.7 & 1013.2
What are the pressurised areas in the aircraft
Cockpit & fwd/aft cabins
Fwd/aft cargo holds
Cabin differential Pressure at 40000 ft
10.92-2.72 = 8.2psi
Cabin differential Pressure at 24000
10.72 - 5.7 = 5.22 psi
What is cabin vertical speed
The rate of change of air pressure inside a cabin
What is normal cabin pressure value
Maintained around 8000 ft for passenger safety and comfort
What do we use to establish an airtight pressure vessel
Compressible door seals , grommets and sealants
What does an outflow valve do
Opens , closes and modulates to maintain the correct amount of air pressure in the cabin
How do outflow valves operate
Pnuematically
What does isobaric mode do
Maintain cabin altitude at a single pressure even if altitude changes
What is differential mode
Keeps pressure to a constant difference between air pressure in the cabin and ambient pressure
What is manual mode
Isobaric mode can be turned off and cabin pressure is controlled manually
Why is manual mode used
Trouble shooting when systems occur
What happens with an increase in cabin altitude
Decrease in cabin pressure
What happens with a decrease in cabin altitude
Increase in cabin pressure
When does a positivity saftey able valve open
Pressure rises to max differential between 8-10 psi and
What is the name of a positive safety valve and what does it do
Excessive differential pressure relief valve
Relieves positive pressure when max pressure differential is exceeded. This prevents structural maximum differential from being exceeded
What way does a negative relief valve open
Inwards
What does a negative relief valve do
Prevents excessive negative differential pressure
When will negative relief valve open
Pressure outside exceeds inside by 0.5-1 psi
What can a loss of bleed air cause
Damage to aircraft wing
Components to overheat
Damage to aircraft structure
Fire
What is red warning
Immediate action
What is amber light
Caution which needs timely attention
What is a green indication
Advisory or indication
What’s a white/blue indication
System in use
Low pressure gauge range
0-150 psi
High pressure gauge range
0-500 psi
Where does low pressure gauge connect to
Low side fitting which is blue
Where does high pressure gauge connect to
High pressute side which is red
Colour of centre house
Yellow
What is a dump valve
Saftey valve that is operated automatically or manually in the flight deck
What does a dump valve do
Remove air and air pressure quickly from the cabin usually in abnormal , maintenance or emergency situations
When does air pressure switch from ground to flight
When being taxied
When would discharge valves be closing
As differential pressure increases
When would discharge valves be opening
Differential pressure is decreasing
When does the discharge valve not move
When differential pressure is constant
Air condition system range
21-27 degrees c
2 types of aircraft systems
Air cycle machine and vapour cycle
What system is used to cool bleed air from the engines in extremely cold temperatures?
An air-cooling system
Example sentence: During extremely cold temperatures, experienced at high altitudes, bleed air from the engines is too hot to be used, and so requires cooling using an air-cooling system.
What is the average pressure and temperature of the air entering the primary heat exchanger?
30 to 40 psi and 150 °C (300 °F)
No additional information provided.
What is the temperature rise of the air passing the compressor section?
Approximately 30 to 40 °C (85 to 105 °F)
No additional information provided.
What is the temperature drop of the air passing the secondary heat exchanger?
About 60 to 70 °C (140 to 160 °F)
No additional information provided.
What is the purpose of the water extractor duct?
To remove condensed moisture after it passes through the secondary heat exchanger
The secondary heat exchangers use the centrifugal effect of swirling the air through vanes to separate the water particles and direct the moisture to a water collector.
What is the purpose of the re-heater in the air cycle machine?
To warm the air that goes to the turbine, to increase turbine efficiency
No additional information provided.
What is the pack or flow control valve?
The valve that regulates bleed air from the pneumatic manifold into the air cycle air conditioning system.
Most pack or flow control valves are electrically controlled and pneumatically operated. They are also referred to as the supply shut-off valve.
How is the pack or flow control valve controlled?
With a switch on the air conditioning panel in the flight deck.
The pack or flow control valve opens, closes and modulates to allow the air cycle air conditioning system to be supplied with a predetermined volume of hot, pressurized air.
What happens when an overheat or abnormal condition is detected?
The pack or flow control valve is commanded by a signal to close.
What is the pack valve?
A venturi-type butterfly valve controlled by a solenoid.
The pack valve is pneumatically operated and spring-loaded to closed. It also contains a shut-off function which is controlled to close from the fire handle, during engine start, and from the pack switch.
What happens when a pack switch is operated?
The pack valve solenoid is de-energized, and if there is bleed air available, the pack valve opens.
Because of the fail-safe philosophy, the pack valve also opens when the electrical power supply is broken.
What causes the pack valve to close if pneumatic power is not available?
The actuator spring closes the valve.
The pack valve has a built-in micro-switch to indicate if it is fully closed or in the open position.
Main function of pack valve
Control airflow into cabin
Pack flow selector positions and percentages
Normal - 100%
High - over 100%
Low - 80%
What are primary and secondary heat exchangers?
Devices that allow heat transfer between two fluids, in this case air. Cold ram air is used to cool the hot bleed air passing through fin-like tubes in the heat exchangers.
How is the flow of ram air controlled over the heat exchanger?
The flow of ram air is controlled with modulating inlet and exit doors, which modulate in flight to provide the required cooling effect.
How is the air supply from the primary heat exchanger controlled?
The air supply from the primary heat exchanger is controlled to a constant temperature by a temperature sensor controlling the flow of air from the pack or flow control valve.
What is used on the ground to induce adequate airflow through the ram inlet doors?
A fan is used to induce adequate airflow through the ram inlet doors on the ground. The fan can be driven by engine bleed air, mechanically by the ACM drive shaft, or by an electric motor.
What is the purpose of the secondary heat exchanger?
The secondary heat exchanger is added to further cool the air to a more acceptable temperature before it enters the compressor of the ACM.
What does ACM stand for?
Air Cycle Machine
ACM consists of a centrifugal compressor and an expansion turbine.
What is the purpose of the expansion turbine in an ACM?
To drive the compressor and provide a decrease in temperature
The expansion turbine uses the remaining energy of the high pressure air to drive the compressor.
What is the cooling system called in an ACM?
Bootstrap system
Cooling system in ACM involves transferring heat to the ram air and converting heat into work to drive the compressor.
What are the two types of ACMs used?
Oil Lubricated and Air Lubricated
Oil Lubricated ACMs have oil slingers for lubrication, while Air Lubricated ACMs are oil free and use air bearings.
What is the purpose of a slinger in an ACM?
To pump an oil/air mist through the bearings for lubrication
Slingers in ACMs provide lubrication by pumping an oil/air mist through the bearings.
What are the two functions of the condenser/reheater in an air cycle machine?
- To cool the air in the air conditioning pack before it goes through the water collector.
- To heat the air conditioning pack air to add energy to the air. The heated air helps operate the turbine in the air cycle machine.
Example sentence: The condenser/reheater in an air cycle machine plays a crucial role in both cooling and heating the air for efficient operation.
Why are separators used in the cabin air conditioning system?
Separators are used to remove excessive moisture from the air to prevent freezing and avoid passenger discomfort or corrosion in the cabin and distribution lines.
Additional information: Separators help maintain a comfortable and safe environment inside the aircraft cabin.
How does a water separator work in an air cycle machine?
A water separator removes water from the saturated air by forcing it through a fibreglass sock that condenses and combines the mist into larger water drops. The water collects on the sides of the separator and drains out of the unit.
Example sentence: The efficient operation of the water separator ensures that the air sent to the aircraft cabin is free from excess moisture.
Why do we need air cycle machine bypass air
Keep the tempted of air exiting acm form become too cold and ice forming
What is the function of a mix chamber/manifold in an air cycle machine?
A mix chamber/manifold collects the temperature-controlled, clean and conditioned air from the packs. Then distributes the warm/cool air to the flight compartments in the aircraft.
In the diagram above the temperatures in blue show the crew selectable desired temperature, in green are the duct temperatures and in white, the actual zone (cockpit/forward and aft cabin) temperatures.
What is the purpose of a ram air door/valve in an aircraft?
The ram air inlet is a small scoop or door on the underside of an aircraft. They are also frequently located on the wing to body fairing.
The majority of aircraft use a modulating door, controlled by actuators on the ram air inlet. These control the quantity of the outside ambient air that flows through the primary and secondary heat exchangers. When bleed air goes through the primary and secondary heat exchangers, the purpose of the ram air is to remove some of the heat. The ram air system helps control the air cycle machine (ACM) compressor discharge temperature. Maximum ram air is available on the ground and during take-off. During flight the doors/louvers modulate to reduce both the ram air flow and drag. The deflector doors are extended when the aircraft is on the ground. To increase ram air recovery, modulating vanes are used on the ram air exhaust. A ram air fan, within the ram system, provides ram air flow across the heat exchangers when the aircraft is on the ground. The majority of modern fixed-wing aircraft use a fan on a common shaft with the ACM, powered by the ACM turbine.
What is the Refrigerant?
A working fluid that undergoes repeated phase transition from a liquid to a gas and back again.
Example sentence: The refrigerant in a vapour cycle machine is responsible for absorbing and releasing heat.
What is the Compressor?
This component pressurizes the refrigerant gas, causing its temperature to rise significantly.
Additional information: The compressor plays a crucial role in increasing the energy level of the refrigerant.
What is the Condenser?
In this part, the high-temperature, high-pressure refrigerant releases heat to the external environment, often aided by the flow of ambient air or a separate cooling system.
Additional information: The condenser helps in transferring heat from the refrigerant to the surroundings.
What is the Expansion Valve?
The high-pressure liquid refrigerant passes through an expansion valve, causing it to rapidly expand and decrease in pressure. This results in a drop in temperature.
Additional information: The expansion valve is crucial in controlling the flow of refrigerant within the system.
What is the Evaporator?
Inside the cabin, the low-pressure, low-temperature refrigerant evaporates, absorbing heat from the surrounding air.
Example sentence: The evaporator is responsible for cooling the air inside the cabin by absorbing heat.
Evaporator material
Copper or alluminim
Describe the distribution systems.
The distribution of conditioned air into the cabin of an aircraft is achieved with a system of ducts leading from the pressurisation source into and throughout the cabin. The conditioned air exits through ceiling vents, where it circulates and flows out through floor level vents. The air then flows aft and exits the aircraft through the outflow valve(s) mounted on, or near the aft pressure bulkhead. Ducting is hidden below the cabin floor and behind walls and ceiling panels depending on the aircraft type and system design. Temperature sensors, overheat switches, and check valves monitor the flow of the conditioned air through the system. On the majority of turbine-powered aircraft, temperature controlled conditioned air from the air conditioning system is also used to pressurise the cabin as well. The final regulation of the temperature of that air is sometimes considered part of the distribution system. Mixing conditioned air with bleed air in a duct or a mixing chamber allows the flight crew to select the exact temperature desired for the cabin. The valve for mixing is controlled in the flight deck or cabin by a temperature selector. Centralised manifolds from which air can be distributed are common. The distribution ducts for different zones are usually of different shapes and sizes. Their construction varies according to the temperature of the air that can pass through them but, they are generally constructed of a light fibreglass material coated to prevent damage from moisture. It is important that the ducts be permitted to expand and to shrink again when the air cools down. This expansion and contraction must take place without loss of the pressure-tight integrity of the ducts.
Source: https://www.resourceiacademy.com/Files/Private/Shared/Lessons/eb5ab331-5465-467f-a07a-ce32649293f/xs4ztkf2/Content/11-13-… A
How much air in the cabin is filtered and recycled
50%
