B1-11d Aircon, pneumatics

Air Supply (11.4.1)

• Goal is to describe the operation of air supply sources, including engine bleed, APU, and ground cart.

Aeroplane Air Supply

• The pneumatic system delivers compressed air (low to medium pressure, high flow) to various aircraft systems.
• Pneumatic power is used by; engine start, air conditioning, pressurisation, nitrogen generation, engine inlet cowl, wing anti-ice, water tank pressurisation, and hydraulic reservoir pressurisation systems.

Air Supply Sources

• Engine bleed air and auxiliary power units are common air supply sources.
• Electric cabin air compressors, centrifugal cabin compressors and turbo chargers are less common.
• Jet pumps and ground supply carts are also air supply sources.

Engine Bleed Air

• In turbine engine aircraft, compressed air is drawn from the engine compressor for air conditioning and cabin pressurisation.
• Air is bled from the low-pressure (LP) and high-pressure (HP) stages of the compressor.
• LP bleed air is used at medium to high engine power settings like takeoff, climb and cruise.
• HP bleed air is for low engine RPM, providing airframe systems with adequate pressure and flow during low-power engine operation.
• Changeover between LP and HP is automated with both ports never being open at the same time
• After the HP bleed valve opens, a downstream check valve of the LP port closes to prevent HP air from re-entering the LP stages.
• A Pressure Regulating and Shut Off Valve (PRSOV) downstream from the LP and HP bleeds can act as a shutoff valve to prevent overpressure or overheat, controlled by a cockpit switch.
• Jet transport aircraft use large quantities of pneumatic air for engine starting.
• An APU compressor can supply the air to start the first engine; the APU starts with electricity from the battery.

Auxiliary Power Unit

• Turbine-powered transport aircraft require large amounts of power for starting and operation
• APUs are ground power sources when engines are off if airport lacks a medium-pressure, high-volume pneumatic air source.
• A typical APU is a small turbine powerplant driving an electric generator.
• APUs feed all pneumatic systems and have gas turbine engines, also bleed air loads generally place the greatest demand on an APU.
• Most APUs extract bleed air only on the ground
• APUs designed for bleed air extraction are normally limited up to specific flight altitude only.
• An example is the Honeywell 131-9B, which can only supply pneumatic power alone up to 17,000 feet.
• The APU is typically in the tail section, supplying air through bleed air duct that runs under the passenger floor to the wheel and air conditioning bays.
• A check valve prevents reverse flow from engine bleed air into the APU.

Emergency Ram Air

• In the event of dual-pack failure, an emergency ram air inlet flap can open for A/C ventilation or smoke removal.
• In case of smoke removal or both packs being lost, the ram air selector switch must be set to "on".
• The emergency ram air inlet flap opens if ditching is not selected for the "on" setting.
• The air is supplied from the other side via a flap installed between the low-pressure ground connection and ram air inlet that closes one duct side, and the check valve stays closed.

Electrically Driven Compressors

• Recent electrical technology improvements enable jet transport to save fuel by minimising air bled from engines ie, Boeing 787.
• Bleed air is only for engine cowl ice protection and hydraulic reservoir pressurisation.
• By feeding ram air to electric motor-driven cabin air compressors there is improved efficiency.
• Advantages include improved fuel consumption and no regulation of supplied compressed air since compressed air is produced by adjustable speed motor cabin air compressors at the required pressure.
• No-bleed architecture simplifies the pneumatic system through the elimination of the pneumatic system, pre-coolers, control valves and pneumatic ducting
• The number of installed parts reduces maintenance and aircraft weight significantly.

Smaller Turbo-Prop Aircraft

• Aircraft utilize air bled directly from the engine compressor.
• Smaller turboprop aircraft combine engine bleed air and turbo compressors or jet pumps.

Turbo Compressors

• Pressurising aircraft or driving a turbo compressor are means for using engine compressor bleed air.
• The turbo compressor provides compressed air for cabin pressurisation by drawing a smaller amount of high-pressure air with bleed air.
• In the turbo-compressor system, bleed air from the engine drives a turbine, which cools so the air at the output of the turbine is actually quite cold.
• Outside air compresses in the turbo-compressor, which heats the act itself.
• Outside air is mixed with cooled, decompressed bleed air for temperature and pressure before it enters the cabin or environmental system.

Jet Pumps

• Certain aircraft employ a jet pump flow multiplier to increase the amount of cabin air.
• A jet pump is venturi inside a duct connected to ram air.
• A nozzle stream of high-velocity compressor bleed air flows into the venturi throat, which induces a low pressure that draws in a larger mass of ram air.
• The air mixes with the compressor bleed air for temperature and pressure within the aircraft cabin enters the cabin or environmental system.

Ground Supply Cart

• Aircraft without a serviceable APU need a ground cart source of pneumatics for ground operations.

High-Pressure Ground Connection

• A ground cart supplies medium-pressure compressed air to the entire aircraft pneumatic system, directly connecting to the pneumatic manifold.
• The use is normally for main engine-starting and short-duration maintenance checks since the air conditioning system isn't normally designed to cope with the demands of a medium-pressure supply.

Low-Pressure Ground Connection

• Low-pressure ground connector connects to the ram air ducting for a low-pressure ground air conditioning supply.
• The ground-conditioned air connector lets an external source of conditioned air supply the airplane air conditioning ducting system.

Air Conditioning (11.4.2)

• This section will cover the purpose and describe common configurations of aeroplane air conditioning systems.
• The characteristics and operation an aeroplane air cycle machine and its components will also be covered.
• We will explain of aeroplane vapour cycle mahcines and their components
• We will learn the purpose and operation of aeroplane air conditioning distribution systems and components
• We will lean the purpose and operation of aeroplane air conditioning flow, temperature and humidity control systems.

Air Cycle System

• Flights might begin on the ramp at 35 °C and then climb to cruise at a temperature of up to 56 °C
• Climate systems must provide comfortable cabin temperatures, regardless of outside air temperature plus it must be free contaiminants, fumes, odours or other factors that might affect the health or comfort for passenges and crew.
• Function of air conditioning system is to maintain comfortable air temperature of supply air in the cabin.
• Most systems are capable of producing air temperature of 21° to 27 °C with normally anticipated outside air temperatures.
• The temperature-conditioned air is distributed to minimize stratification (hot and cold layers).
• An air conditioning system also control humidity, and must prevent fogging of windows, while maintaining the temperature of wall panels and floors at a comfortable level.
• Designed to supply ventilation and heated or cool the air.
• In a typical system the air temperature is measured and compared to the desired setting of the temperature controls and changes if the air temperature isn't what is desired.
• There are two types of air conditioning systems: air cycle machine (used in larger passenger aircraft) and vapour cycle machines (used mainly in small and medium-sized aircraft).

Air-Cycle System – Location

• Most commercial aircraft have two to three air cycle systems installed in the wing root area, forward of the landing gear bay that supply air for air conditioning, ventilation and pressurisation.
• A primary component of each pack assembly is the air cycle machine which consists of an expansion turbine (cooling turbine), air-to-air heat exchangers and various valves which control airflow through the system.

Air-Cycle System - Operation

• The Flow Control Shut-Off Valve (FCSOV) gets hot bleed air from the pneumatic manifold, contorlling the flow of hot bleed air to the primary heat exchanger and air mixing valve.
• A hot air connection downstream of the FCSOV supplies hot bleed air to the turbine case to prevent ice in the turbine case.
• Ram air removes heat when bleed air goes through the primary heat changer.
• Partially cooled bleed air then goes to air mix valve while preserving pressure until the comrpessor in the air cycle mahcine (ACM) increases pressure and temperature
• Air goes through the secondary heat exchanger for more ram air removal.
• Turbine section uses rapid expansion to decrease the temperature of the bleed air.
• The cold bleed air then goes into the water separator which removes moisture, which then goes into the ram air duct by the water spray nozzle.
• If the temperature of the cold bleed air in the water separator decreases towards freezing, the low limit system adds partially cooled bleed air to cold this stream via the low limit valve, upstream of the water separator.
• After the water separator, the cold bleed air goes to the mix chamber, where there hot bleed air from the hot side of the air mixing valve is added.

Air-Cycle System – Temperature Control

• The temperature control valve controls the discharge temperature of the air conditioning pack.
• Systems use temp control valves to mix hot or cold air to regulate temperature in the cabin and Temperature controllers are used to keep the desired setting and receive signals from sensors to control the on/off valves.
• The system also use the standby temperature control valve, giving backup control for the discharge temperature of the pack and increases the temperature to melt ice in the condenser.

Air Cycle System Components

• The Flow Control Shut-Off Valve (FCSOV) controls and adjusts air flow into the air conditioning pack by shutting off flow or modulating as needed to operate.
• The flow control shut-off valve typically is in in the air conditioning compartment and requires electrical power and upstream pneumatic pressure to open being electrically controlled and pneumatically actuated to regulate downstream pressure and flow.

FCSOV Valve Operation

• Upstream bleed air pressure acts through a filter acts on the primary piston to open the valve.
• Downstream overpressure acts as moduration and release ont he secondary piston release control pressure and modulate the valve to the closed position.
• An energized dump valve solenoid, opens to vent control pressure to ambient, and ensures that the valve closes under action of the spring acting on the piston.
• The pack valve failsafe is open in electrica power failure or de-energizing of the dump valve solenoid, and closes pneumatic pressure is applied.
• If downstream pressure is too high, the secondary piston will move opening bleed orifice allow air to in the primary piston to escape and move the shut-off valve towards the closed position.
• The result of low air flow re-balanced downstream to a pressure.

Primary and Secondary Heat Exchangers

• Primary and secondary heat exchangers are air-to-air plate fin cross-flow-type heat exchangers where isolated airstreams flow through thin-walled channels made up of plates and fins that increase surface area.

Primary Heat Exchanger

• Primary heat exchanger air passes from cold ram air, and the hot bleed air passes form the engine.
• Air from the flow control shut-off valve travels though and and a crossflow removes heat air before the air enters the ACM compressor inlet.
• Cooling of the flow of rain air is modulated via moveable inlet and exit doors, providing most of the cooling is modulated
• Temperature is controlled by the heat exhcnage by the heat exchanger mixing valve at about 150°C.
• Pack fans provide adequate air-flow on the goond, but ram air pressure opens the banpass and checks for valving cooling.

Secondary Heat Exchanger

• The function removes heat from bleed air the is from the compressor section of the air cycle machine (ACM) and cools partially to make the efficent operation of ACM pack possible.
• Primary heat exhcnager, compressor and ACM increases both peessue and temperature
• Warm, high-pressure air goes to the secondary heat exchanger in the sane manncer as Primary ehcat exchanger with Cooling air forced out at 50°C.

Air Cycle Machine Turbine Unit

• Also known as ACM at the heart of air systems.
• High speed rotating assembly with comprenssor driven by an expansion of turbine
• Air passed from primary heat exhanger from compressor, ise re-heated and through the secondary for cooling
• Air is cooled significanlt via the turbien and passes through to water seperator and mix champber enterng teh cabin.

Air-Cycle Machine Turbine Operation

• ACMs run at very high speeds, normally supported by air bearings or oil lubricated roller bearings.
• The Air-Cycle Machine (ACM) is made up of a centrifiugal air conprenssor and expansion turbine that drives the conprenssor.
• After hear is reduced via heat loss in the primary heat exchange, this loss prevents large pressure loss.
• Next stage of turbine: enrergy goes here to drive a comprimssor for a large decrease of pressure from energy extraction
• The amount of work needed to be done by transferring heat and converting it as work to drive turbinve.
• Can theoretially decrease to below freezing point

Air-Cycle Machine Construction

• The main housing assembly provides mounting for the two scroll assemblies and support for the two shaft bearings, and has an oil reservoir from which oil feeds bearings by wicks.
• A filler cap that has stick is mounted near an outboard of each shaft bearings that carry and pump lubrication. and air seals for wheels.

Air-Bearing Air Cycle Machine

• These are oil free, use air bearing to support on high speed friction, and eliminate contamination.

Low-Limit Anti-Ice Valve

• Uses temp valve to keep air exiting ACM becoming too cold, generally kept at 2 °C (35°F) by passing warm bleed air arond ACM.
• Prevents wate freeze form outlet

Cabin Temperature Control Valves

• Cabin temp control valves are primary for contrelling dischangre of ACM with hot and cold with mix via air mix valve.

Air-Cycle Machine Temperature Control Valve

• When cooling is low, so hot can be bypassed with the ACM turbione

Temperature Control Valve Operation

• Electrically controlled and operation is for a sign from down, and it can be applied open, but pressure to open valves.
• Electric is applie,d coild enerzises and closes and forces piston that for duct to be open and is safde to close.

Air-Mixing Valve

• Adjusts proportions of hot and cold to each ACM

Air-Mixing Valve Opertation

Valve that controls park otuputs tempeature is direct with airflow thought to chamnber.

Air-Mixing Valve Visual Position Indicator

For cold or hots and transmitters signals to poistion on pane.

Water Seperator

• The large reduction in temperature causes the moisture in the air to condense
• The water temperature is used to collect apart in the cabin. is installed in thr discharge duct of cooling tubine

Water Seperator Operation

• After cold in air cycles, then through to water seperator and contempature is fine. this is atomzied, the water superate and is collection to remove extra moisture is distribution

High Pressure Water Extractor

• type of water extraction than fitted to newer types
• ineritaly and centrifugral and flow fluid from swisl

Mixing Chamber

or plan, allows that or Bypasser, coor mixing and allws unlimit from air or circulation

Ram Air Door

• the rAM control system qunaity of outer ambluent to heater exchange.

The ram air actuator moves the ram

• Air inlet modulation panel sections When the sytem sense the air craft is in under actuator , at fully open the deflection exntes unwanted ateria

Emergency Ram Valve or Door/Flap

• valves can open from ouside or during pressure the system suppily 100

Air Distribution System

• Cabin air supply sources distribute cabin managed with air duct that supply into cabinet from vents

Calin Distribtuion

• The contioners and the maduct fo tow thr aircraft

Distribution Ducts

• Ducts are form alumunium allow and stell The temperature does noy exceed