Helicopter Systems – Pneumatics PDF B1-12d 2020

Student Resource Subject B1-12d: Helicopter Systems – Pneumatics Copyright © 2020 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold, or otherwise disposed of, without the written permission of Aviation Australia CONTROLLED DOCUMENT 2020-05-11 B1-12d Helicopter Systems – Pneumatics Page 2 of 6 CONTENTS CONTENTS............................................................................................................................................ 3 DEFINITIONS......................................................................................................................................... 4 STUDY RESOURCES............................................................................................................................... 5 INTRODUCTION.................................................................................................................................... 6 Topic 12.6.1 Air Supply Systems..................................................................................................... 6 Topic 12.6.2 Air Conditioning (ATA 21)........................................................................................... 6 Topic 12.16 Pneumatic/ Vacuum Systems (ATA 36....................................................................... 6 2020-05-11 B1-12d Helicopter Systems – Pneumatics Page 3 of 6 DEFINITIONS Define To describe the nature or basic qualities of. To state the precise meaning of (a word or sense of a word). State Specify in words or writing. To set forth in words; declare. Identify To establish the identity of. List Itemise. Describe Represent in words enabling hearer or reader to form an idea of an object or process. To tell the facts, details, or particulars of something verbally or in writing. Explain Make known in detail. Offer reason for cause and effect. 2020-05-11 B1-12d Helicopter Systems – Pneumatics Page 4 of 6 STUDY RESOURCES B1-12d Student Handout 2020-05-11 B1-12d Helicopter Systems – Pneumatics Page 5 of 6 INTRODUCTION The purpose of this subject is to familiarise you with basic helicopter Pneumatic and Vacuum systems and components. On completion of the following topics you will be able to: Topic 12.6.1 Air Supply Systems Describe the supply of air for helicopter air conditioning and component pressurisation from the following sources: Engine bleed air APU Ground cart Topic 12.6.2 Air Conditioning (ATA 21) Identify components of and explain the operation of helicopter air conditioning systems. Explain the operation of air cycle and vapour cycle machines. Explain the operation of the following air conditioning systems: Distribution Air flow control Temperature control Humidity control Identify protection and warning devices used in air conditioning systems and explain their purpose and operation. Topic 12.16 Pneumatic/ Vacuum Systems (ATA 36 Describe the system layout of typical helicopter pneumatic systems. Explain the supply of pneumatic and vacuum pressure from the following sources: Aircraft Engine / APU Compressors Reservoirs Ground Supply Explain the following elements of pneumatic and vacuum systems: Pressure Control Distribution Indications and warnings Interfaces with other systems 2020-05-11 B1-12d Helicopter Systems – Pneumatics Page 6 of 6 Table of Contents List of Figures....................................................................................................................................... 2 TOPIC 12.6.1: AIR SUPPLY SYSTEMS............................................................................................ 3 Air Supply Sources................................................................................................................................ 3 Heating and Ventilation....................................................................................................................... 4 Ventilation System............................................................................................................................... 4 Heating and Ventilation System (Sikorsky S76)........................................................................... 5 Heating and Ventilation System........................................................................................................... 5 Heating Mode - Blower De-energised............................................................................................. 6 Heating Mode - Blower Energised................................................................................................... 6 Ventilation Mode............................................................................................................................. 6 Components Operation........................................................................................................................ 7 Bleed-air Shutoff Valve.................................................................................................................... 7 Modulating and Shutoff Valve (Mixing Valve)................................................................................. 7 Pressure Regulator.......................................................................................................................... 7 Duct Temperature Limiter............................................................................................................... 7 Duct Temperature Sensor................................................................................................................ 7 BELL 412 HEATING AND VENTILATION SYSTEM........................................................................... 8 Bleed Air Sources................................................................................................................................. 8 2017-03-13 B1-12.6.1 Air Supply Page 1 of 12 Training Material Only List of Figures Figure-1. Air Supply Sources............................................................................................................. 3 Figure-2. Ventilation......................................................................................................................... 3 Figure-3. Heating and Ventilation..................................................................................................... 4 Figure-4. Sikorsky S76 Heating and Ventilation................................................................................ 5 Figure-5. Sikorsky S76 Heating and Ventilation Schematic.............................................................. 6 Figure-6. Bell 412 Bleed Air............................................................................................................... 8 Figure-7. Bell 412 Cabin Air Distribution........................................................................................... 9 Figure-8. Bell 412 Air Distribution................................................................................................... 10 Figure-9. Bell 412 Air Distribution Schematic................................................................................. 11 2017-03-13 B1-12.6.1 Air Supply Page 2 of 12 Training Material Only TOPIC 12.6.1: AIR SUPPLY SYSTEMS The purpose of the air supply is to provide both heating and cooling within the helicopter for the passengers, crew comfort and equipment cooling and/or ventilation Air Supply Sources Air is received from either the engines, the APU, a ground source or, on some helicopters it is as easy as opening a vent or window to admit fresh air for ventilation. Air from the engines may be from direct bleed air (gas turbine engines) or air provided by bleed air from the engine turbochargers (piston engines). Figure-1. Air Supply Sources If the helicopter has an APU, it is generally used for ground power or engine starting. On some helicopters air for cabin ventilation is obtained by opening the sliding windows in each of the entrance doors. Additional ventilation to the crew area may be obtained through ram air grilles located in nose of the helicopter. When this additional ventilation is required, it is gained by the pilot pulling the VENT control knob and positioning the DEFOG BLOWER switch on the overhead console to the ON position. Figure-2. Ventilation 2017-03-13 B1-12.6.1 Air Supply Page 3 of 12 Training Material Only Heating and Ventilation The heater system is a bleed-air system with bleed-air supplied by the main engines under flight conditions or the APU during ground operations. The heater system uses a bleed-air mixing valve to mix engine or APU bleed-air and ambient air at a cockpit selected mixture temperature. Heated air is distributed to the cockpit and cabin through a system of ducts. A mixture temperature sensor works along with the bleed-air mixture valve, regulating the bleed-air flow to match the mixture temperature selected at the cockpit heating control. Figure-3. Heating and Ventilation Ventilation System The ventilation system provides ventilated air to the cockpit and troop/cargo cabin. Air obtained from outside the helicopter by an air intake duct is then distributed by the blower unit through the heating system ducts. 2017-03-13 B1-12.6.1 Air Supply Page 4 of 12 Training Material Only Heating and Ventilation System (Sikorsky S76) Heating and Ventilation System The heating and ventilation system consists of engine bleed-air shutoff valves, low- pressure switches, a blower, blower control switch, blower relay, cockpit heating and ventilating controls, cockpit and cabin ducting with gaspers, cockpit door air inlets with controls, and a sound suppressor with duct temperature limiter, duct temperature sensor, mixing valve, pressure regulator, and modulating valve. The system has two basic modes of operation: the ventilation mode and the heating mode. The system may be operated in the heating mode with or without the blower energised. When operated in the heat mode, uses hot engine bleed-air mixed with outside (ambient) air for cabin heating at the desired flow and temperature. After bleed-air is permitted to flow by electrically operated bleed-air shutoff valves, pressures and temperatures are automatically controlled by pneumatic components. Figure-4. Sikorsky S76 Heating and Ventilation A blower connected into the system may be used to increase air flow. In the ventilation mode of operation, the blower provides outside air to the cabin distribution system. The air inlets, installed in the cockpit doors, can be manually opened by the crew to provide additional ventilation by outside ram air. 2017-03-13 B1-12.6.1 Air Supply Page 5 of 12 Training Material Only Figure-5. Sikorsky S76 Heating and Ventilation Schematic Heating Mode - Blower De-energised When the manual HEATER, ON-OFF selector valve on the HEATER CONTROL panel in the cockpit is placed ON for cabin heating and the BLEED AIR switch is ON, both No.1 and No. 2 engine bleed-air shutoff valves open, allowing hot compressed air to flow through the pressure regulator to the pneumatic control components, where cabin in- flow temperature is automatically controlled. Turning the TEMP CONT selector on the HEATER CONTROL panel clockwise increases cabin in-flow temperature. Turning the selector counter clockwise decreases it. In this mode of operation, the blower check valve is closed and the outside air check valve is open, permitting air to be drawn into the mixing valve where it is mixed with engine bleed-air. Heating Mode - Blower Energised Operation is the same as for heating with the blower de-energised, except that increased outside air-flow is provided by the fan and the outside air check valve is closed. Bleed air-flow is modulated by the mixing valve and added to the blower-induced outside air to provide the cabin in-flow temperature. Ventilation Mode To operate in the ventilation mode, the HEATER ON-OFF selector is placed to OFF, blocking regulated supply air to the mixing valve. This closes the mixing valve which stops bleed air-flow to the system. When the BLOWER switch is placed ON the blower energizes, opening its check valve and closing the outside air check valve, and supplying outside air to the cockpit and cabin distribution system. Air inlets in the cockpit doors, which can be manually opened as desired, provide outside ram air for additional cooling of the cockpit. 2017-03-13 B1-12.6.1 Air Supply Page 6 of 12 Training Material Only Components Operation Bleed-air Shutoff Valve The shutoff valve is a normally open pneumatic valve, solenoid controlled, with a spring- loaded- closed inline check valve. Two bleed-air shutoff valves are installed and functionally the same, but they are not physically interchangeable. The inlet of each shutoff valve is connected to its respective engine compressor. The outlet of each valve is connected to one common welded tube assembly which routes bleed-air to a mixing valve, where bleed-air and ambient air are mixed and pneumatically controlled. Modulating and Shutoff Valve (Mixing Valve) The modulating valve is normally closed. Increasing control pressure opens the modulating valve to supply the required amount of warm engine bleed-air for heater operation. As bleed-air flow through the modulating valve is increased, the poppet valve opens, increasing the ratio of warm, bleed-air flow to cool ambient air flow induced by the ejector. This results in increasing cabin inflow temperatures for increasing modulation valve position. For this mode of operation, the mixing valve ambient air check valve is open and the blower check valve is closed when the blower is off. Pressure Regulator The pressure regulator is preset to reduce and regulate engine bleed-air pressure to the pneumatic control components where automatic control of cabin inflow temperature is maintained. Duct Temperature Limiter The duct temperature limiter is preset to move the modulating valve to the fully closed position at a predetermined duct over-temperature limit. A bimetal sensing element exposed to the sound suppressor airstream becomes concave as its set point temperature of 210°F (99°C) is approached. This forces the poppet valve off its seat, causing control pressure to decrease to its minimum value. As duct temperature decreases below 190°F (88°C), the bimetal sensing element becomes flat again. This allows the poppet valve to reseat, and regulated air pressure returns to a normal control level. Duct Temperature Sensor The sensing element of the duct temperature sensor generates an increasing force as a function of increasing temperature. A calibration spring and a diaphragm pressurized by reference pressure oppose this force to position the diaphragm plate relative to the bleed- off nozzle. The nozzle-plate flow area relative to the flow area of the orifice in the restrictor T-assembly determines the value of mixing valve control pressure. Demand for an increase in duct temperature results in an increase in valve control pressure. 2017-03-13 B1-12.6.1 Air Supply Page 7 of 12 Training Material Only BELL 412 HEATING AND VENTILATION SYSTEM Heating and ventilation system provides: Cockpit and cabin heating (engine bleed air) Windshield and chin-bubble defogging/defrosting (bleed air) Fresh air ventilation and defogging (ventilating air) Bleed Air Sources Engine bleed air is taken after the last stage of axial compression. This bleed air is used as one of the motive forces of the engine fuel control. After regulation by the fuel control, the bleed air becomes governor reset pressure, or PG air, which controls automatic fuel control operation. Engine bleed air is also used as the source for the Bell 412 standard heating/defogging system. Compressor discharge bleed airflows through electrically actuated bleed air shut off valves from each power section, then through a common line to a solenoid operated valve in the heater variable control mixing valve. The shut off valves are normally controlled by the HEATER switch. The shut off valves are also automatically closed when the HEATER AIR LINE caution panel segment illuminates, or when the either power section FIRE PULL “T” handle is pulled. Figure-6. Bell 412 Bleed Air The cabin interior is ventilated with ambient ram air. The ram air enters an inlet duct located inside the forward pylon fairing on the cabin roof. Air is routed to three distribution plenums, forward, left and right. Each of the three plenums has individual adjustable outlet valves, two in the forward and five in each of the left and right. Air is also routed forward from both the left and right routed forward from both the left and right plenums to the crew compartment where two additional outlet valves are provided on each side. 2017-03-13 B1-12.6.1 Air Supply Page 8 of 12 Training Material Only The standard heating system will maintain a comfortable cabin environment [minimum 4°C (40°F)] down to an outside temperature of -18°C (0°F). The basic heating system uses bleed air from the compressor discharge pressure port of each power section. The bleed air is routed from the port on the gas generator case of each power section, to an electrically controlled bleed air shut off valve at the work deck, joining into a common line below the work deck. The bleed air is then directed to the variable air mixing valve on the right side of the helicopter, just forward of the tail boom attachment point. The temperature of the mixed air is controlled by a rheostat located on the right door post. Outside air is drawn in by the variable air mixing valve and mixed with the bleed air to maintain a preselected temperature. The mixed air is ducted through a noise suppressor and plenum chamber, then forward under the right fuel cell, below the cabin floor to the air distribution valve on the right side of the helicopter, and forward to the four outlets on center pedestal of the crew area, for heating, or into the upper window nozzles for defogging. The air distribution valve controls air to the four door post outlets. The aft outlet switch, located on the overhead console, permits even distribution of heated air to the passenger compartment. The Heat/Defrost lever closes off the centre pedestal outlets and directs all heated airflow to the windshield nozzles and lower nose window outlets. Figure-7. Bell 412 Cabin Air Distribution The systems are controlled by three switches located on the overhead console. These switches, labelled VENT BLOWER, AFT OUTLET, and HEATER each have an ON and OFF position. A DEFROST lever on the upper right corner of the centre pedestal provides control defrosting air to the windshields. A temperature selector located on the right cabin doorpost, controls heater and temperature. 2017-03-13 B1-12.6.1 Air Supply Page 9 of 12 Training Material Only Figure-8. Bell 412 Air Distribution The systems are controlled by three switches located on the overhead console. These switches, labelled VENT BLOWER, AFT OUTLET, and HEATER each have an ON and OFF position. A DEFROST lever on the upper right corner of the centre pedestal provides control defrosting air to the windshields. A temperature selector located on the right cabin doorpost, controls heater and temperature. 2017-03-13 B1-12.6.1 Air Supply Page 10 of 12 Training Material Only Figure-9. Bell 412 Air Distribution Schematic 2017-03-13 B1-12.6.1 Air Supply Page 11 of 12 Training Material Only This page intentionally blank 2017-03-13 B1-12.6.1 Air Supply Page 12 of 12 Training Material Only Table of Contents List of Figures....................................................................................................................................... 3 PHYSICS................................................................................................................................................ 4 Heat Transfer Terms............................................................................................................................ 4 General Gas Law................................................................................................................................... 5 Gas Law Application............................................................................................................................. 6 Air Conditioning Systems..................................................................................................................... 7 Ventilation and Defogging in Smaller Helicopters............................................................................... 8 Heating and Ventilation in Medium to Large Helicopters................................................................... 9 Ventilation System............................................................................................................................... 9 Air Cycle Machine (ACM) Operation.................................................................................................. 10 Air Cycle System – Components........................................................................................................ 11 Flow Control – Shutoff Valve............................................................................................................. 12 Primary Heat Exchanger..................................................................................................................... 13 Secondary Heat Exchanger................................................................................................................. 13 Environmental Control System - Sikorsky S70b – Seahawk............................................................... 14 ECS Operation.................................................................................................................................... 14 Auto Mode.................................................................................................................................................. 14 Manual Mode............................................................................................................................................. 14 Operation................................................................................................................................................... 14 Bell 222 Environmental Control System............................................................................................ 16 Operation of the ECU......................................................................................................................... 16 Components of the ECU.............................................................................................................................. 17 Vapour Cycle Air Conditioning........................................................................................................... 18 Transfer of Heat................................................................................................................................. 18 Refrigerant......................................................................................................................................... 18 Vapour Cycle Machine....................................................................................................................... 19 Operation................................................................................................................................................... 19 Components of a Vapour Cycle System............................................................................................. 21 Receiver-Dryer............................................................................................................................................ 21 Thermal Expansion Valve........................................................................................................................... 21 Evaporator.................................................................................................................................................. 23 Compressor................................................................................................................................................ 24 Condenser.................................................................................................................................................. 25 Heating and Ventilation System (Sikorsky S76)................................................................................. 26 Air Conditioning System..................................................................................................................... 27 Heating and Air-conditioning (Bell 430)............................................................................................. 28 Distribution System............................................................................................................................ 28 2017-03-13 B1-12.6.2 Air Conditioning Page 1 of 44 Training Material Only Environmental Control Unit....................................................................................................................... 28 Air-conditioning System..................................................................................................................... 29 Forward Vent and Defog System........................................................................................................ 29 Passenger Vent System...................................................................................................................... 30 Environmental Control System (Bell 222).......................................................................................... 31 Components....................................................................................................................................... 31 Temperature Control Selector................................................................................................................... 31 Temperature Control/Sensor...................................................................................................................... 31 Temperature Control Valve........................................................................................................................ 31 Check Valve................................................................................................................................................. 31 Pressure Regulator..................................................................................................................................... 32 Pre-cooler................................................................................................................................................... 32 Heat exchanger........................................................................................................................................... 32 Reheater/Condenser.................................................................................................................................. 32 Economy Solenoid Valve............................................................................................................................. 32 Primary Turbine Inlet Valve........................................................................................................................ 33 Secondary Turbine Inlet Valve.................................................................................................................... 33 Cooling Turbine........................................................................................................................................... 33 ECU Ducting................................................................................................................................................ 34 Airframe Distribution Ducts........................................................................................................................ 34 Control Switches......................................................................................................................................... 34 Overheat Switches...................................................................................................................................... 35 Heat/Defog Lever....................................................................................................................................... 35 Cooling Turbine Speeds...................................................................................................................... 35 Installation.................................................................................................................................................. 36 Heating and Cooling System (Bell 212).............................................................................................. 37 Heating and Ventilation System (Bell 412)........................................................................................ 39 Summary of the Two Different Types of Air Conditioning Systems.................................................. 42 2017-03-13 B1-12.6.2 Air Conditioning Page 2 of 44 Training Material Only List of Figures Figure-1. General Gas Law................................................................................................................ 5 Figure-2. Gas Law Application.......................................................................................................... 6 Figure-3. Ventilation and Defogging in Smaller Helicopters............................................................ 8 Figure-4. Heating and Ventilation System Medium to Large Helicopter.......................................... 9 Figure-5. Air Cycle Machine............................................................................................................ 10 Figure-6. Air Cycle System Components......................................................................................... 11 Figure-7. Flow Control Shutoff Valve.............................................................................................. 12 Figure-8. Air Flow Control Schematic............................................................................................. 12 Figure-9. Primary and Secondary Heat Exchangers........................................................................ 13 Figure-10. Sikorsky S70B ECS System Diagram................................................................................. 15 Figure-11. Components of the Bell 222 ECU.................................................................................... 17 Figure-12. Vapour Cycle Air Conditioning System............................................................................ 20 Figure-13. Receiver Dryer................................................................................................................. 21 Figure-14. Thermal Expansion Valve................................................................................................ 22 Figure-15. Evaporator....................................................................................................................... 23 Figure-16. Compressor..................................................................................................................... 24 Figure-17. Condenser....................................................................................................................... 25 Figure-18. S76 Heating and Ventilation System............................................................................... 27 Figure-19. Bell 430 Air Distribution.................................................................................................. 30 Figure-20. Bell 222 Environmental Control System.......................................................................... 36 Figure-21. Bell 212 Heating and Cooling System.............................................................................. 38 Figure-22. Bell 412 Air Distribution.................................................................................................. 39 Figure-23. Mixing Valve.................................................................................................................... 40 Figure-24. Mixing Valve – No Bleed Air............................................................................................ 40 Figure-25. Mixing Valve – Full Heat.................................................................................................. 40 Figure-26. Mixing Valve – Mixture of Bleed and Ambient Air.......................................................... 41 Figure-27. ACM Summary................................................................................................................. 42 Figure-28. Vapour Cycle Summary................................................................................................... 43 2017-03-13 B1-12.6.2 Air Conditioning Page 3 of 44 Training Material Only PHYSICS Before we can understand how an Air Conditioning system works, we will recap on some Physics terms. Heat Transfer Terms Adiabatic A temperature change without the addition or removal of heat. Conduction The transfer of heat from one object to another due to the physical contact of the two objects. Convection The process by which heat is transferred by bulk movement of a fluid. Radiation The transfer of energy between objects without the need for a medium. Latent Heat Heat that causes a substance to change its state with no change in temperature. Sensible Heat Heat, when applied, causes a temperature change that can be sensed. Super Heat The heat energy added to a gas after complete evaporation. E.g. Once water has boiled, it takes only 50 calories to heat one gram of steam from 100°C to 200°C. Humidity The amount of water vapour present in a volume of air. General Gas Law Combines both Boyle’s law, V1P1 = V2P2 and Charles’ law, V1/T1= V2 /T2 into one formula. This allows you to calculate pressure, volume or temperature, 2017-03-13 B1-12.6.2 Air Conditioning Page 4 of 44 Training Material Only General Gas Law If temperature is constant, pressure is inversely proportional to its volume. If a gas is forced into a smaller volume, its pressure will increase (and vice-versa). If volume is constant, pressure is proportional to temperature. If a gas increases in pressure, its temperature increases (and vice-versa). If pressure is constant, volume is proportional to temperature. If a gas is heated, its volume increases (and vice-versa). Figure-1. General Gas Law 2017-03-13 B1-12.6.2 Air Conditioning Page 5 of 44 Training Material Only Gas Law Application General Gas Law can be applied directly to the operating principles of air conditioning systems. Air is compressed in the compressor and expanded in the turbine. This compression and expansion adds and removes energy from the air. In addition, the turbine extracts energy to do work, driving the compressor. The expansion of the air over the turbine creates a temperature drop which is the primary method of supplying cool air to the aircraft cabin. Figure-2. Gas Law Application 2017-03-13 B1-12.6.2 Air Conditioning Page 6 of 44 Training Material Only Air Conditioning Systems The function of an air conditioning system is to maintain a comfortable air temperature within the aircraft fuselage. The system will increase or decrease the temperature of the air as needed to obtain the desired value. Most systems are capable of producing an air temperature of 21 C to 27 C o o with normally anticipated outside air temperatures. This temperature-conditioned air is then distributed so that there is a minimum of stratification (hot and cold layers). The system, in addition, must provide for the control of humidity, it must prevent fogging of windows, and it must maintain the temperature of wall panels and floors at a comfortable level. In a typical system the air temperature is measured and compared to the desired setting of the temperature controls. Then, if the temperature is not correct, heaters or coolers are set into operation to change the air temperature, and the air is mixed together to create a uniform temperature in the cabin. In summary, an air conditioning system is designed to perform any or all of the following functions: Supply ventilation air Supply heated air Supply cooled air There are basically two types of air conditioning systems: Air Cycle Machine (ACM) Vapour Cycle Machines 2017-03-13 B1-12.6.2 Air Conditioning Page 7 of 44 Training Material Only Ventilation and Defogging in Smaller Helicopters Air for cabin ventilation is sometimes, in helicopters, a case of opening the sliding windows in each of the entrance doors. Additional ventilation to the crew area may be obtained through ram air grills located in nose of the helicopter. When this additional ventilation is needed, it is gained by the pilot pulling the VENT control knob and positioning the DEFOG BLOWER switch on the overhead console to the ON position. Figure-3. Ventilation and Defogging in Smaller Helicopters 2017-03-13 B1-12.6.2 Air Conditioning Page 8 of 44 Training Material Only Heating and Ventilation in Medium to Large Helicopters The heater system is a bleed-air system with bleed-air supplied by the main engines under flight conditions or the APU during ground operations. The heater system uses a bleed-air mixing valve to mix engine or APU bleed-air and ambient air at a cockpit selected temperature. Heated or cooled air is distributed to the cockpit and cabin through a system of ducts. A mixture temperature sensor works along with the bleed-air mixture valve, regulating the bleed-air flow to match the mixture temperature selected at the cockpit heating control. The heater system gives a temperature of 40 F (4.4 C) when the outside ambient temperature is - o o 65 F (-53 C). o o Figure-4. Heating and Ventilation System Medium to Large Helicopter Ventilation System The ventilation system provides ventilated air to the cockpit and troop/cargo cabin. Air obtained from outside the helicopter by an air intake duct is then distributed by the blower unit through the heating system ducts. 2017-03-13 B1-12.6.2 Air Conditioning Page 9 of 44 Training Material Only Air Cycle Machine (ACM) Operation An air cycle cooling system consists of a centrifugal air compressor and an expansion turbine (cooling turbine) that drives the compressor, air-to-air heat exchangers, and various valves which control airflow through the system. When the heated bleed air passes through the primary heat exchanger, it loses some of its heat but almost none of its pressure. This air then enters the compressor of the air cycle machine (ACM), and its pressure is further increased. With the increase in pressure, there is some increase in its temperature, but this is removed by the secondary heat exchanger. Now the somewhat cooled high-pressure air flows into the expansion turbine where a large percentage of its remaining energy is used to drive the compressor. As this air expands across the turbine, there is a large decrease in pressure. The decrease in pressure, coupled with the energy extracted to drive the compressor, results in a very large decrease in temperature. There are two forms of cooling used in this system. Some is done by transferring heat to the ram air, but most of the heat is removed by expansion and converting it into work to drive the compressor. This type of cooling system is called a bootstrap system. Some of the hot bleed air from the engines can be bypassed around the ACM if warm air is needed in the cabin. A water separator is used to remove any water from the very cool air coming from the turbine. A refrigeration bypass valve is used to stop water freezing up in the water separator by mixing some bleed air into it. Temperature controllers are used to keep the desired setting by receiving signals from various sensors and giving signals back to open or close valves to mix hot or cold air to regulate temperature throughout the cabin. Figure-5. Air Cycle Machine 2017-03-13 B1-12.6.2 Air Conditioning Page 10 of 44 Training Material Only Air Cycle System – Components Figure-6. Air Cycle System Components 2017-03-13 B1-12.6.2 Air Conditioning Page 11 of 44 Training Material Only Flow Control – Shutoff Valve The air conditioning shutoff valve, often called the pack valve, is used to control the flow of engine bleed air into the system. It can either shut off the air flow or modulate the flow of air to provide that which is needed to operate the air conditioning package. Figure-7. Flow Control Shutoff Valve The shutoff valve, located in the bleed air supply duct to the refrigeration unit, controls the air pressure to that unit. It is also the main shutoff valve for the cabin air conditioning and pressurisation systems. The valve requires electrical power and minimum of 15 psi upstream to function. It will regulate the downstream pressure to 115 psi. Although this is an open/close valve, its major function is to regulate. This is accomplished by a spring-loaded valve in the airflow line which is controlled by a primary piston. Upstream pressure bleeds through a filter and acts upon the primary piston. This pressure on the piston forces the valve to open. When downstream pressure reaches 115 psi, pressure will act on a secondary piston which will mechanically open a bleed orifice. This will cause upstream pressure to be vented and therefore less pressure acts on the primary piston, causing its valve to close. When the cockpit switch is placed to OFF a solenoid valve opens to vent all upstream pressure overboard so it doesn’t act on the primary piston. Figure-8. Air Flow Control Schematic 2017-03-13 B1-12.6.2 Air Conditioning Page 12 of 44 Training Material Only Primary Heat Exchanger The primary heat exchanger is a radiator through which cold ambient ram air passes to cool the hot bleed air from the engines. As the cold ram air passes over the radiator’s fin-like tubes, bleed air passing through the tubes is cooled. The flow of ram air through the heat exchangers is controlled by moveable inlet and outlet doors, which modulate in flight to provide the required cooling. On many aircraft, the heat exchangers are sized to provide most, if not all, of the necessary cooling in flight. The air supply from the primary heat exchanger is controlled to a constant temperature of approximately 150oC by the heat exchanger mix valve. On the ground there is not enough air passing through the cooling doors, so fans called pack fans provide adequate air-flow to cool the heat exchangers. Secondary Heat Exchanger The function of the secondary heat exchanger is to partially cool the air for the air conditioning to a temperature which makes possible the efficient operation of the refrigeration unit. As cooling requirements increase, air exiting the primary heat exchanger is routed to the compressor side of the ACM. The compressor raises both the pressure and temperature of the air passing through it. The warmer, high pressure air is then directed to the secondary heat exchanger. The secondary heat exchanger operates in essentially the same manner as the primary heat exchanger. Cabin air that is to be further cooled is routed through the tubes in the heat exchanger core. Cooling air is forced through the secondary heat exchanger and returned to an engine air inlet or can be exhausted directly to the atmosphere. Air from the heat exchanger has been further cooled to approximately 50 C o Figure-9. Primary and Secondary Heat Exchangers 2017-03-13 B1-12.6.2 Air Conditioning Page 13 of 44 Training Material Only Environmental Control System - Sikorsky S70b – Seahawk ECS Operation Auto Mode With the ECS control panel set at AUTO, the ECS controller will compare the desired temperature (ECS Control Panel) with the actual temperature (Cabin Temperature Sensor) and the cabin temperature control valve position. The difference will produce an error signal. The error signal is processed to produce a drive signal to the Cabin Temperature Control Valve. Manual Mode With the ECS control panel set at MAN, the ECS controller now receives its commands from the HOT/COLD switch on the ECS control panel. The HOT/COLD switch provides drive to the cabin temperature control valve through the controller. The pilot can now manually select the cabin temperature. Operation When the Air Source ECS/START switch on the overhead console is set to ENGINE, it will energise (unlock) the cross bleed valves. Provided the engines are developing enough air pressure (>5 psi), the bleed-air shutoff valves will open. Now bleed-air is sent to the ECS Modulating Valve, which will control the amount of bleed-air supplied to the air-cycle machine. With the air source switch selected at APU, power is removed from the bleed air shut off valves. These valves close and shut off engine bleed air as the ECS air source. Power from the APU control SW is routed through the ECS temp control panel to the Aux Relay Panel, through a diode in the Aux Relay Panel to energise solenoid ‘A’. This keeps the modulating valve closed. Air source is now available at the modulating valve. With solenoid ‘A’ energized the valve is closed. With solenoid ‘B’ energized the valve is fully open. With solenoids A and B de-energized there is normal flow. If A is energised the valve is closed no matter what the state of B. Solenoid B is controlled by the Normal/High switch on the ECS control panel which locks the modulating valve into the open (high flow) condition operating the air cycle machine at full flow. If the ECS control panel mode switch is at AUTO or MAN, bleed-air from the Modulating Valve is sent to the flow limiting venturi. This in turn outputs airflow to the primary heat exchanger and the cabin temperature control valve. Airflow enters the primary heat exchanger and is partially cooled. This partially cooled air is sent to the turbine driven compressor. The compressor boosts the bleed- air pressure and temperature. Compressor output pressure is now sent to the secondary heat exchanger for additional cooling. Airflow from the secondary heat exchanger is routed to drive the turbine wheel of the air- cycle machine. The turbine expands and cools the airflow. This is sent to the water separator. Driving the turbine wheel also drives the compressor and the ram air fan. The ram air fan supplies ambient airflow through the heat exchanger assembly for bleed-air cooling. The Water Separator removes and collects moisture from the cooled airflow. The dry cool air is ducted into the cabin. Depending upon the cabin temperature desired warm air may bypass the heat exchanger via the Cabin Temperature Control Valve and mix with cool air from the turbine. 2017-03-13 B1-12.6.2 Air Conditioning Page 14 of 44 Training Material Only Figure-10. Sikorsky S70B ECS System Diagram 2017-03-13 B1-12.6.2 Air Conditioning Page 15 of 44 Training Material Only Bell 222 Environmental Control System The following ENVIRONMENTAL CONTROL SYSTEM (Bell 222) consists of reverse flow check valves, temperature selector, two Bleed Air Shutoff Valves, and an Environmental Control Unit (ECU). The ECU includes a cooling turbine (Item 2a), a pre-cooler (Item 2c), a combined primary heat exchanger and water condenser (Item 2b), an electronic temperature control/sensor (Item 2g), a temperature control valve (Item 2d), a jet-pump assembly (Item 2h), and two turbine inlet valves (Items 2e, 2f). Operation of the ECU High pressure bleed air, supplied by the two engines, passes through the engine bleed port flow limiting venturis and shutoff valves with reverse flow check valves. The air is ducted to the ECU compartment where the air enters the pre-cooler (Item 2c) and is reduced in temperature prior to entering the primary heat exchanger and water condenser. The heat sink for the pre-cooler is ambient air drawn from the compartment through the primary heat exchanger by the cooling turbine fan (Item 2a) and exhausted through the pre-cooler and then discharged overboard. In the primary heat exchanger (Item 2b), bleed air is cooled to near ambient air temperature. Additional cooling below ambient air temperature occurs in the reheater/condenser, where the bleed air is continually cooled by recirculated conditioned air. Because of the high pressure and moderate temperature in the reheater/condenser, the bleed air is usually cooled below its dew point and moisture condenses from the air. This condensed water is collected at the reheater/condenser outlet and is sprayed onto the inlet face of the heat exchanger where the liquid re-evaporates and depresses the effective ambient cooling air temperature into the heat exchanger. Cool high-pressure bleed air leaving the reheater/condenser is then expanded through the cooling turbine (Item 2a), where the air temperature is further reduced. Shaft energy produced in the turbine drives the fan, which induces cooling airflow across the primary heat exchanger (Item 2b) and exhausts the airflow through the pre-cooler (Item 2c). The cooling turbine nozzle is divided into two parts and operates with either one or both nozzles, depending on engine power, by opening or closing the secondary turbine inlet valve (Item 2f). At maximum bleed pressure the valve is fully closed and all the bleed airflow passes through the primary nozzle. At lower power settings, the valve is in the open position and the turbine passes the maximum amount of bleed airflow to obtain good performance at flat pitch power by using both nozzles. Air leaving the turbine enters the ejector nozzle of the jet pump, where recirculation airflow is induced from two sources. The first is across the cold side of the reheater/condenser. This condenser recirculation air is drawn from the conditioned air supply duct, and passes through the reheater/condenser. The condenser exhaust air mixes with the cold turbine discharge air in the Jet pump, and returns to the conditioned air supply duct. 2017-03-13 B1-12.6.2 Air Conditioning Page 16 of 44 Training Material Only The second source is air recirculated from the cabin, which mixes with turbine discharge air to provide the desired ventilation rate. These two secondary air sources also serve to heat the ejector nozzles to prevent icing. Figure-11. Components of the Bell 222 ECU Components of the ECU 2a - Cooling Turbine (Dual Nozzle) 2b - Heat Exchanger 2c - Pre-cooler 2d - Temperature Control Valve 2e - Primary Turbine Inlet Valve 2f - Secondary Turbine Inlet Valve 2g - Temperature Control/Sensor 2h - Jet Pump Duct Assembly 2017-03-13 B1-12.6.2 Air Conditioning Page 17 of 44 Training Material Only Vapour Cycle Air Conditioning Before understanding how a vapour cycle system works lets understand the principle behind the vapour cycle. Temperature is a measure of the effect of heat on a body or material, and is a convenient way of expressing this physical phenomenon numerically. While there is a relationship between heat and temperature, heat can be added to or removed from a refrigerant without changing its temperature. The heat put into a material as it changes its state without changing its temperature is called latent heat, and this heat will be returned when the material reverts to its original state. This process acts in a continuous cycle. A refrigerant changes state from a liquid into a vapour, and in doing so, it absorbs heat from the cabin. This heat is taken outside of the aircraft and is given off to the outside air as the refrigerant returns to a liquid state. Transfer of Heat Heat is a form of energy, and can neither be created nor destroyed. It can, however, be transformed or moved from one place or material to another. This energy continues to exist regardless of its form or location. Heat will flow from an object having a certain level of energy into an object having a lower level. Any material that allows this transfer easily is said to be a conductor of heat, while any material that impedes the transfer is called an insulator. The refrigerant used in an aircraft air-conditioning system is a liquid under certain conditions. When it is surrounded by air having a higher level of heat energy, heat will pass from the air into the liquid. As the liquid absorbs the heat, it changes state and becomes a gas. The air that gave up its heat to the refrigerant is cooled in the process. Refrigerant Almost any volatile liquid can be used as a refrigerant, but for maximum effectiveness, it must have a very low vapour pressure and therefore a low boiling point. The vapour pressure of a liquid is the pressure that will exist above a liquid in an enclosed container at any given temperature. For example, a particular liquid refrigerant in an open container boils vigorously as the liquid turns into a gas at a temperature of 21 C. If the container is closed, the liquid will continue to change into a o vapour and the pressure of the vapour will increase. When the pressure reaches 70.1 psi, no more vapour can be released from the liquid. The vapour pressure of this particular material is then said to be 70.1 psi at 21°C. Many different materials have been used as refrigerants in commercial systems, but for aircraft air- conditioning systems, dichlorodifluoromethane was almost universally used. It is a stable compound at both high and low temperatures and does not react with any of the materials in an air-conditioning system. It will not attack the rubber used for hoses and seals, and is colourless and practically odourless. Rather than calling this refrigerant by its long chemical name, it is just referred to as Refrigerant-12. A much more environmentally friendly refrigerant called R134A is used today. Boiling point (1.013 bars): -26.6°C and Vapour pressure (at 15°C): 4.9 bar where one bar is equal to 14.7 psi (atmosphere). 2017-03-13 B1-12.6.2 Air Conditioning Page 18 of 44 Training Material Only A volatile liquid is one which readily evaporates (vaporises) at normal temperature. The space above the surface of a volatile liquid is quickly occupied by the vapour given off by the liquid. In an open container this process will continue until all the liquid has evaporated. Gasoline, methylated spirits, and alcohol are typical examples. Any type of fuel is extremely volatile. So much so that you can actually see the fumes above a fuel pump at a gas station. You can also readily smell acetone as soon as a fingernail polish remover container is opened Vapour Cycle Machine Operation The system is divided into two sides, one that accepts the heat (High Side) and the other that rejects it (Low Side). Both the Low and High side of the compressor are pressurised, therefore the ‘suction’ or compressor inlet side is called the ‘Low Side’ (yellow)– The compressor outlet or discharge has a high pressure and is called the ‘High side’ (red) The side that accepts the heat is called the low side, because here the refrigerant has a low temperature and is under a low pressure. The heat is given up on the high side, where the refrigerant is under high pressure and has a high temperature. Notice in the figure below that the system is divided at the compressor where the refrigerant vapour is compressed, increasing both its pressure and temperature, and at the expansion valve where both pressure and temperature drop. The refrigeration cycle starts at the receiver-dryer which acts as a reservoir to store any of the liquid refrigerants that is not passing through the system at any given time. If any refrigerant is lost from the system, it is replaced from that in the receiver-dryer. Liquid refrigerant leaves the receiver-dryer and flows under pressure to the expansion valve where it sprays out through a tiny metering orifice into the coils of the evaporator. The refrigerant is still a liquid, but it is in the form of tiny droplets, affording the maximum amount of surface area so the maximum amount of heat can be absorbed. The evaporator is the unit in an air-conditioning system that produces the cold air. Warm air is blown through the thin metal fins that fit over the evaporator coils. This heat is absorbed by the refrigerant, and when the air emerges from the evaporator, it is cool. When heat is absorbed by the refrigerant, it changes from a liquid into a gas without increasing its temperature. The heat remains in the refrigerant in the form of latent heat. The refrigerant vapour that has the heat from the cabin is taken into the compressor, where additional energy is added to it to increase both its pressure and temperature. It leaves the compressor as a hot, high-pressure vapour. 2017-03-13 B1-12.6.2 Air Conditioning Page 19 of 44 Training Material Only The heat trapped in the refrigerant vapours in the condenser escapes into the walls of the coil and then into the fins that are pressed onto these coils. Relatively cool air from outside the aircraft flows through these fins and picks up the heat that is given up by the refrigerant. When it loses its heat energy, the refrigerant vapour condenses back into a liquid and then flows into the receiver- dryer where it is held until it passes through the system for another cycle. Figure-12. Vapour Cycle Air Conditioning System 2017-03-13 B1-12.6.2 Air Conditioning Page 20 of 44 Training Material Only Components of a Vapour Cycle System Receiver-Dryer The receiver-dryer is the reservoir for the system and is located in the high side between the condenser and the expansion valve. Liquid refrigerant enters from the condenser and is filtered and passed through a desiccant such as silica-gel to absorb any moisture that might be in the system. A sight glass is normally installed in the outlet tube to indicate the amount of charge in the system. Bubbles can be seen in the glass when the charge is low. A pickup tube extends from the top of the receiver-dryer to near the bottom where the liquid refrigerant is picked up. A filter is installed either on the end of the pickup tube or between the tube and the desiccant to prevent any particles getting into the expansion valve. It is of extreme importance that all moisture be removed from the system, as a single drop can freeze in the expansion valve and stop the entire air conditioning process. Water will also react with the refrigerant to form hydrochloric acid that is highly corrosive to the metal in the system. Thermal Expansion Valve Figure-13. Receiver Dryer The thermal expansion valve is the control device which meters the correct amount of refrigerant into the evaporator. The refrigerant should evaporate completely by the time it reaches the end of the coils. The heat load in the aircraft cabin controls the opening, or orifice, in the valve. There are two types of thermal expansion valves, the internally equalised valve, and the externally equalised valve. We will discuss the internally equalised valve as it is the most common in use today. The internally equalized thermal expansion valve is controlled by the amount of heat in the evaporator. A capillary tube to the evaporator connects the diaphragm chamber of the valve. The end of the capillary is coiled into a bulb and is held tightly against the discharge tube of the evaporator. Coiling this tube allows a greater area to be held in intimate contact with the tube, allowing for a more accurate temperature measurement. 2017-03-13 B1-12.6.2 Air Conditioning Page 21 of 44 Training Material Only If the liquid refrigerant completely evaporates before it reaches the end of the evaporator, it will continue to absorb heat and become superheated. It is still very cold to touch, but it is considerably warmer than it would be if it had not absorbed this additional heat. The expansion valve is adjusted to a given amount of superheat. When the pressure of the refrigerant vapour reaches this value, the diaphragm pushes down against the superheat spring and opens the valve, allowing more refrigerant to enter the evaporator. A balance between the vapour pressure on the diaphragm and the superheat spring controls the amount of refrigerant flow. These valves are calibrated at the factory and cannot normally be adjusted in the field. If there is a lot of heat in the cabin, the liquid refrigerant will evaporate quickly, and more superheat will be added to the vapour, so the valve will open and allow more refrigerant to flow into the evaporator. When the heat load is low, the liquid will use most of the evaporator length to evaporate. Little superheat will be added, and a smaller amount of refrigerant will be metered into the coils. Figure-14. Thermal Expansion Valve 2017-03-13 B1-12.6.2 Air Conditioning Page 22 of 44 Training Material Only Evaporator The evaporator is the actual cooling unit in a vapour-cycle air-conditioning system. An evaporator consists of one or more circuits of copper tubing arranged in parallel between the expansion valve and the compressor. These tubes are silver-soldered into a compact unit, with thin aluminium fins pressed onto their surface. The evaporator is usually mounted in housing with a blower. The blower forces cabin air over the evaporator coils. The refrigerant absorbs heat from the cabin air, thereby cooling it before it returns to the cabin. A drip pan is mounted below the evaporator to catch water that condenses out of the air as it cools. The capillary of the thermostat is placed between the fins of the evaporator core to sense the temperature of the coil, and it is this temperature that controls the cycling of the system. Figure-15. Evaporator 2017-03-13 B1-12.6.2 Air Conditioning Page 23 of 44 Training Material Only Compressor The compressor circulates the refrigerant through the system. Refrigerant leaves the evaporator as a low-pressure, low-temperature vapour and enters the compressor. The compressor provides the energy necessary to operate the system. The gas leaving the compressor is at a high temperature and pressure. Aircraft air-conditioning systems usually use reciprocating-type compressors, which have reed valves and a lubricating system that uses crankcase pressure to force oil into its vital parts. On small aircraft, these compressors are usually belt driven by the engine, very similar to the arrangement used in an automobile. The compressors in systems used on larger aircraft are driven by electric or hydraulic motors, or by compressor bleed air powered turbines. Engine-driven compressors are single speed pumps whose output is controlled by a magnetically actuated clutch in the compressor drive pulley. When no cooling is needed, the clutch is dc- energized and the compressor does not operate. When the air conditioner is turned on, and the thermostat calls for cooling, the magnetic clutch is energized, causing the drive pulley to turn the compressor and pump refrigerant through the system. Electric motor-driven compressors are controlled by a thermostat that turns the compressor motor on and off as required. Hydraulic motors are turned off and on by solenoid valves controlled by the thermostat. When the valve is opened, hydraulic fluid is directed under pressure to the motor. When the motor is not being driven, the output of the engine-driven hydraulic pump is returned to the reservoir. In all of these systems, the cabin blower operates continually, forcing the cabin air over the evaporator so heat from cabin air can be transferred into the refrigerant. Figure-16. Compressor 2017-03-13 B1-12.6.2 Air Conditioning Page 24 of 44 Training Material Only Condenser The condenser is the radiator-like component that receives the hot, high-pressure vapours from the compressor and transfers the heat from the refrigerant vapours to the cooler air flowing over the condenser coils. When heat is removed from the vapour, the refrigerant returns to a liquid state. The condenser is made of copper tubing with aluminium fins pressed onto it, formed into a set of coils, and mounted in housing. The condenser and the evaporator are similar in both construction and appearance, differing primarily in strength. Since the condenser is in the high side of the system, it must be capable of withstanding the high pressure found there. Condensers normally operate at a pressure of about 300 psi and have a burst pressure in excess of 1,500 psi. In larger aircraft the condenser is mounted in an air duct where cooling air can be drawn in from the outside and blown over the coils. In flight, ram air usually provides sufficient airflow over the condenser for proper operation. For ground operation, a fan must be used to supply the necessary cooling airflow. Figure-17. Condenser 2017-03-13 B1-12.6.2 Air Conditioning Page 25 of 44 Training Material Only Heating and Ventilation System (Sikorsky S76) The heating and ventilation system consists of engine bleed-air shutoff valves, low- pressure switches, a blower, blower control switch, blower relay K36, cockpit heating and ventilating controls, cockpit and cabin ducting with gaspers, cockpit door air inlets with controls, and a sound suppressor with duct temperature limiter, duct temperature sensor, mixing valve, pressure regulator, and modulating valve. The basic heating and ventilation system, when operated in the heat mode, uses hot engine bleed- air mixed with outside (ambient) air for cabin heating at the desired flow and temperature. After bleed-air is permitted to flow by electrically operated bleed-air shutoff valves, pressures and temperatures are automatically controlled by pneumatic components. A blower connected into the system may be used to increase air flow. In the ventilation mode of operation, the blower provides outside air to the cabin distribution system. The air inlets, installed in the cockpit doors, can be manually opened by the crew to provide additional ventilation by outside ram air. 2017-03-13 B1-12.6.2 Air Conditioning Page 26 of 44 Training Material Only Air Conditioning System The air conditioning system consists of a compressor pallet, filter/dryer/receiver, blower/evaporator, load shed box, air intake/exhaust ducting, air conditioning switch panel and the cabin and cockpit ducting and gaspers shared with the heating system. The vapour cycle air conditioning system, when in operation, cools the cabin and cockpit by extracting the moisture and heat from the air within the compartment. The cooled conditioned air is then recirculated through the distribution ducting to the cabin and cockpit gaspers. The extracted heated air is exhausted overboard through ducting on the right side of the helicopter tail cone. Moisture collected from the conditioned air is routed overboard through a drain line on each side of the fuselage. Figure-18. S76 Heating and Ventilation System 2017-03-13 B1-12.6.2 Air Conditioning Page 27 of 44 Training Material Only Heating and Air-conditioning (Bell 430) The heating and air conditioning provisions are the ducts installed below the floor and along the left and right side of the helicopter. The ducts are installed from FS 161 to 240. A cap is installed on all the openings if the helicopter does not have a heating or air conditioning system. You must remove the cabin floor to remove the ducts. Distribution System The heating provisions connect to the system. The ECU is thus connected to the vent and defogs system, the forward floor vents and the passenger vents. Environmental Control Unit The environmental control unit (ECU) supplies hot or cool air to the cabin area. The ECU also removes moisture from the air it supplies to the cabin. The system operates with bleed air from the engines. The temperature is manually controlled by the TEMP CONT knob on the overhead console. The environmental control system (ECS) provides either cool conditioned air or hot air for cabin comfort. The ECS consists of an environmental control unit (ECU), a temperature control panel in the overhead console, and distribution ducts and outlets. The ECU is driven by engine bleed air. The mixture ratio of hot bleed air to cooled air from the ECU is automatically varied to maintain the selected temperature. Immediately following engine start, the full range of conditioned air is available. A high volume of dry air is circulated by the system for quick cooling and steady cabin temperature. The ECU operation is quiet and permits full comfort with all windows and vents closed. There are two separate distribution systems. The cool air distribution system is located in the cabin roof. It has eight adjustable air outlets in the aft cabin and two adjustable and two fixed outlets in the forward cabin. The warm air distribution system is located under the cabin floor. This system has ten adjustable air outlets; four in each aft cabin door and one on each side of the centre console. The warm air system also defogs the front windshield and lower nose windows. All warm air is automatically diverted to the four windshield outlets when the pilot selects the DEFOG on the HEAT/DEFOG lever. In the DEFOG setting the valve is mechanically closed to divert the heated air from the fwd vents and at the same time the switch is tripped to control valves on the passenger vents and divert some of this heat to the defog system also. ECU conditioned air may be directed through the upper or lower distribution systems by two remotely operated diverter valves. The upper one is more effective for cooling and the lower one for heating. There are four "push to activate" buttons located on the overhead console. There is also a temperature control increase/decrease switch on the overhead console. The button labelled “ECS” controls bleed air from both engines to the environmental control system. Press the button to the ON position to allow bleed air from the engines to flow to the ECS and provide the appropriate cooling or heating. 2017-03-13 B1-12.6.2 Air Conditioning Page 28 of 44 Training Material Only The passenger door outlets button will either open or close outlets in the doors of the passenger compartments. The ECU flow button reduces the amount of bleed air delivered to the ECS (when selected to ECOM) and, as a result, the amount of air delivered by the system. This ECOM position should be used after the cockpit and cabin have reached the desired temperature, and only a low volume of air is needed to maintain the selected temperature. The NORM position should be used to facilitate rapid temperature change of the cockpit and cabin. The DISTR SYS button routes the air produced by the ECS to either the upper or lower outlets, depending upon the position selected. The A/C position will route ECS air to the upper vents, and the HTR position will route ECS air to the lower vents. The button position does not affect the function of the ECS, only the distribution of air. The temperature control dial determines the function of the ECS. The lower the temperature is set, the more dry cool air will be delivered. Conversely, the higher the temperature is set, the more warm air will be delivered by the ECS. In the event of an engine failure, the ECS will be automatically shut off to preclude power drain on the remaining engine. Air-conditioning System The air conditioning system has two forward vents and defogs systems and a passenger vent system. Two cables at each crew station control each forward vent and defog system. One control cable is used to open and close the plenum door. The other cable controls the flapper valve assembly and directs air to either the defogging nozzles or the cabin air outlet valves. The electric blower supplies air for ventilation and to defog the windows. A control lever, on the overhead console and adjustable outlet air valves, control the passenger vent system. Forward Vent and Defog System The forward vent and defog system has two identical vent and defog systems, one for each crew station. Each system has: A vent door A plenum A defog blower A flapper valve assembly A forward vent check valve assembly A defog nozzle Ducts An air outlet valve Two control cables The plenum is attached with rivets to the outboard cabin nose structure. The plenum door makes part of the outside skin when closed. 2017-03-13 B1-12.6.2 Air Conditioning Page 29 of 44 Training Material Only A control cable opens and closes the vent door. Vent air enters the plenum through the vent door and flows through the vent blower to the flapper valve assembly. A control cable operates the flapper valve. In the defog position the flapper valve moves air through the forward vent check valve to the defog nozzle. In the vent position the flapper valve moves air through the ducts to the air outlet valve below the instrument panel. For maximum defog, close the air outlet valves while the vent doors are open. The vent doors must be open when the defog blowers are on. The electric defog blowers supply air to defog or to ventilate when the helicopter is on the ground or in a hover. Passenger Vent System The passenger vent system has a plenum which is part of the cabin roof structure, duct hoses, air outlet valves, a vent door and a control linkage to actuate the door. There is a drain line to drain moisture from the plenum when the door is open. The control lever on the overhead head console operates the passenger vent door. The forward edge of the door moves up into the outside airflow when the lever is put in the aft position and air enters the plenum. The ducts, hoses and air outlet valves move air into the cabin. Each air outlet valve can be closed to stop local airflow. Figure-19. Bell 430 Air Distribution 2017-03-13 B1-12.6.2 Air Conditioning Page 30 of 44 Training Material Only Environmental Control System (Bell 222) The purpose of the environmental control system is to control air temperature within the helicopter for the passengers and the crews comfort. See Figure 20 Components Located in the bleed air lines between the engines and the bleed air shutoff valves, there are restrictors installed to limit the amount of bleed air to a maximum of 5% of the engines compressor discharge. Bleed air shutoff valves, which are located at the centre top on the aft side of the aft firewall, turn on and off the ECS system by the ECS switch on the overhead panel in the cockpit. When the ECS switch is pushed in to the on position, this will energize a solenoid on each bleed air shutoff valve. Pc air will flow around the solenoid valve allowing the bleed valve to open. Three things will cause the bleed air shutoff valve to close. Pressing the ECS switch to the off/de- energized position, either one of the fire switches in the armed position, or having one or both of the engines’ RPM fall below 55 ±2% Ng (speed). In the event that there is reverse flow in the ECS system, there is a check valve feature that will close the bleed air shutoff valve. Temperature Control Selector Mounted in the overhead panel is a temperature control selector switch. This rotary, variable resistor type switch, will allow the pilot (or co-pilot) to vary the temperature range from full counter clockwise to full clockwise an ECS discharge temperature of 35 F to 185 F (1.67 C to 85 C). o o o o Temperature Control/Sensor The temperature control sensor is mounted on the conditioned air plenum. Here the sensor probe is exposed directly to the mixed air flow. The control is an integral assembly consisting of a solid state electronic control and a probe. The probe contains two glass bead-type thermistor sensing elements that respond to temperature. The temperature control/sensor receives the desired temperature setting from the temperature control selector switch, senses the mixed airflow temperature, and positions the temperature control valve torque motor as required to maintain the desired cabin temperature. Temperature Control Valve The temperature control valve is found on the left side of the ECS unit as mounted in the aircraft. This valve normally in the closed position, will respond when voltage is applied via the temperature control/sensor. It can be described as an “electro-pneumatically actuated shutoff and modulating valve”. The valve contains a torque motor and flapper valve to control the regulated air pressure to the primary turbine inlet valve and the temperature control valve. Check Valve The check valve is located between the temperature control valve and the primary turbine inlet valve. The function of this check valve is to prevent reverse flow when the economy solenoid is open. 2017-03-13 B1-12.6.2 Air Conditioning Page 31 of 44 Training Material Only Pressure Regulator The pressure regulator, located downstream of the heat exchanger outlet, supplies 18psi regulated air pressure to the temperature control valve and the economy solenoid. Pre-cooler The pre-cooler is located between the bleed air shutoff valves and the heat exchanger. Pc air temperature between 550 F to 600 F (288 C to 316 C) is forced through the nickel and o o o o stainless pre-cooler. Air driven by the fan is forced through the pre-cooler’s cooling fins to reduce the temperature of the Pc air before entering the heat exchanger. The pre-cooler air is then vented overboard through an outlet under the left aft fuselage section. Heat exchanger The heat exchanger, located after the pre-cooler and cooling fan, contains the ambient heat exchanger, condenser and water collector within one aluminium heat exchanger core. The heat exchanger receives discharge air from the pre-cooler. Ambient air is drawn through the heat exchanger by the cooling turbine driven fan to further lower the temperature. Condensed moisture is collected from the reheater/condenser, and with the help of a little Pc air, sprayed onto the face of the heat exchanger for increased performance. Reheater/Condenser On the downstream side of the heat exchanger, but still part of the heat exchanger unit, is the reheater/condenser. A small portion of the cooling turbine air (temperature as low as 35 F (1.67 C)) is forced through the o o cooling fins of the condenser, dropping the bleed air temperature below ambient and below its dew point, causing condensation to collect on a screen. This condensation is collected in a sump and with the help of a little Pc air, sprayed onto the face of the heat exchanger. Economy Solenoid Valve Located between the pressure regulator and the primary turbine inlet valve is the economy solenoid valve. This valve, controlled by the ECU FLOW switch on the overhead panel, in the NORMAL position has the solenoid energized closed. When selected to the ECONOMY position, the valve is de-energized to the open position, allowing regulated air pressure to flow to the primary turbine inlet valve driving it to its 50% open position. 2017-03-13 B1-12.6.2 Air Conditioning Page 32 of 44 Training Material Only Primary Turbine Inlet Valve The primary turbine inlet valve is located between the condenser and the cooling turbine. The valve has two modes of operation; Normal mode – The valve senses the actuator pressure of the temperature control valve, and when maximum cooling is selected, this valve remains full open. When warmer cabin air is selected, the primary turbine inlet valve begins to close prior to the temperature control valve opening, thus reducing cold air flow out of the turbine before adding hot air and reducing total bleed air flow required for heating. When the temperature control valve is stroked to the full stop position, the turbine air flow is reduced by approximately 50%. Economy mode – Regulated air pressure passes through the economy solenoid valve to drive the primary turbine inlet valve to its minimum position. A check valve in the actuator air inlet line prevents feedback of actuator pressure to the temperature control valve. Bleed air flow is reduced by approximately 50% in the economy mode. Secondary Turbine Inlet Valve The secondary turbine inlet valve is located between the condenser and the cooling turbine. When the aircraft is at flat pitch on the ground, and not pulling much power, the bleed air pressure will be approximately 28psig. At this pressure, the primary inlet turbine will not have enough bleed air to operate the cooling turbine. So the secondary turbine inlet valve will remain open to aid in operation until the bleed air pressure rises to 30psig, when the secondary inlet turbine valve will begin to close. At 42psig bleed air pressure, the valve will be fully closed. During cruise flight, this valve will remain closed to prevent excessive bleed air flow from the engine. Cooling Turbine The cooling turbine is located between the primary and secondary valves and the cabin distribution system. The purpose of the turbine is to take the cool high-pressure bleed air leaving the reheater/condenser and expand it; causing its temperature to be reduced at the same time it flows through the turbine wheel and gives up energy driving the turbine shaft. Shaft energy is transmitted to a fan whose purpose is to load the turbine and induce ram airflow through the heat exchanger and across the pre-cooler. The cooling turbine assembly consists of a straight-bladed radial inflow turbine wheel mounted on a common shaft with an axial-flow fan. The rotating assembly is supported on ball bearings lubricated by wool felt wicks leading from a cotton packed oil sump to the shaft. Dual jet pump nozzles are located on the discharge of the cooling turbine. Action of the jet pump creates a low pressure area, drawing a flow of conditioned air across the reheat/condenser and cabin return air. The dual jet pump nozzles have fins which promote heat transfer between the cooling turbine discharge air (down to -40 F (-40 C)) and the reheater/condenser and cabin return o o air and prevent ice formation on the nozzles. When heat is selected, air from the temperature control valve enters the dual jet pump. 2017-03-13 B1-12.6.2 Air Conditioning Page 33 of 44 Training Material Only ECU Ducting The dual jet pump air is ducted through two ducts that contain internal noise suppressors. The ducts are connected to the left and right airframe ducting. A plenum is located under the ECS ducting and a small amount of cooling turbine discharge mixed with air is allowed to enter. This air flows across the temperature sensor and then to the condenser. Three airframe cabin return air inlets are located in the cabin; one is located on the left side of the parcel shelf, one located under the left armrest of the aft left passenger seat, and one found in the centre front of the aft bench seat. Cabin air is drawn in through these inlets by the cooling turbine dual jet pumps. Airframe Distribution Ducts The airframe distribution ducts receive conditioned air flow from the two ECS discharge ducts into the airframe ducts. From there, the air is routed to the diverter valves that are located in the left and right hand side behind the parcel shelf. When the diverter valves are in the “HTR” position by the Distribution System switch in the overhead panel, the valves are in the de-energized position and allow the flow of air to go to the heating ducts under the floor for maximum heating efficiency. When the diverter valves are in the “AC” position by the Distribution System switch in the overhead panel, the valves are electrically energized, pneumatically positioned to allow the ECS air to flow to the airframe overhead ducts for maximum cooling efficiency. (Pneumatic pressure for the valve operation is tapped off a pressure line on the left side of the ECS unit). Control Switches The Temperature Control switch (TEMP CONT), which is a rotary type switch found in the overhead panel, supplies a signal to the Temperature Control/Sensor which in turn supplies a signal to the Temperature Control Valve to select and control desired temperature. The Environment Control System switch (ECS) is a push on/off switch found in the overhead panel. This switch controls the normal operation of the Bleed Air Shutoff Valves. Passenger Door Outlets switch (OPEN/CLOSE) is a push on/off switch found in the overhead panel. This switch controls the normal operation of the passenger door outlet valves located in the vertical structure forward of the litter door, or door post of the litter door. The Environmental Control Unit Flow switch (NORM/ECON) is a push on/off switch found in the overhead panel. In the “NORM” position, the switch allows automatic operation of the primary turbine inlet valve, energizing the valve closed. In the “ECON” position, the switch will de-energize the valve to the open position. Regulated Bleed air pressure will drive the primary turbine inlet valve to its 50% open position. The Distribution System switch is a push on/off switch found in the overhead panel. Labelled “AC/HTR”, when selected to the “HTR” position, will cause the Diverter Valves to divert the conditioned air down to the lower ducts. In the “AC” position, will cause the Diverter Valves to divert the conditioned air up to the overhead vents. 2017-03-13 B1-12.6.2 Air Conditioning Page 34 of 44 Training Material Only Overheat Switches Overheat switches are located in different areas to protect the ducts, passengers, crew, and aircraft in the event of a possible overheat condition. Compartment Overheat Switches are located on the forward and aft side of the structural panel aft of the ECS compartment. These switches will detect a leak in the engine bleed air-line (if one should develop) and trip the 5 amp ECS power circuit breaker when the temperature in that area reaches 176-185 F (80-85 C), causing the bleed air shutoff valves to close. o o A Duct Overheat Switch is located in the left airframe duct just downstream of the ECS unit. If the ECS unit discharge air should reach a temperature of 215-228 F (101-109 C), the switch will trip the o o same ECS power circuit breaker. Heat/Defog Lever Located on the upper right side of the centre console, this lever is used to control warm air flow for normal heating operations in the forward cabin, or divert the heated air to the defog nozzles. In the normal operation, the lever is placed in the forward “HEAT” position which allows airflow to go to the outlets on either side of the centre console, and the passenger door outlets switch (located under lever in the centre console) to control operation of the passenger door outlet valves. In the aft “DEFOG” position, a flapper valve will manually block airflow to the console outlets, while the defog lever will contact a micro-switch which closes both passenger door outlet valves. Cooling Turbine Speeds Maximum Cooling 64,000 RPM Economy 53,000 RPM Maximum Heating 23,000 RPM Tested Maximum 90,800 RPM 2017-03-13 B1-12.6.2 Air Conditioning Page 35 of 44 Training Material Only Installation The ECS is located under the baggage compartment floor. It is mounted by seven mounting points; four under the heat exchanger, one under the plenum with a clamp, and two under the temperature control valve. NOTE The two under the temperature control valve must be shimmed to fit the airframe structure after the other five mounts have been installed. Figure-20. Bell 222 Environmental Control System 2017-03-13 B1-12.6.2 Air Conditioning Page 36 of 44 Training Material Only Heating and Cooling System (Bell 212) This system uses engine bleed air (hot) and ambient air (cold) mixed together in the mixing valve and then through the noise suppressor to the plenum and only then is it distributed into the cabin. In the mixing valve, bleed air is mixed with ambient air to obtain the desired temperature. Mixing of bleed and ambient air is accomplished by increasing or decreasing bleed air in response to a heat sensor in the plenum regulated by the temperature-selecting dial on the doorpost. An overheat switch is mounted in the outlet of the mixing valve which activates at 220 F (104 C) to close the o o bleed-air valves and also “pop” the “CABIN HTR” circuit breaker in approximately 30 seconds. Mixed air passes through a noise suppressor-muffler to the plenum and then through ductwork to the air distribution valve and the overheat switch mounted in the plenum, which activates at 220 F o (104 C) and illuminates the HEATER AIR LINE caution panel light. o At the air distribution valve, heated air is either totally distributed forward to the crew area or, if the AFT OUTLET switch is in ON, divides between the aft outlets on the rear side of the forward cabin doorposts and the crew compartment. Heated air to the crew compartment is further divided as follows: A portion of the air is routed directly to the lower chin bubble The remaining air is directed to the lower pedestal outlets as long as the DEFROST lever is in the OFF position If the DEFROST lever is in ON, part of the airflow is directed to the right and left windshield nozzles. Intermediate positions of the DEFROST lever between OFF and ON provide proportionate airflow between the pedestal outlets and the windshield outlets NOTE The heater should not be operated above 21oC to prevent damage to the chin bubbles. Heater operation causes changes in helicopter performance. 2017-03-13 B1-12.6.2 Air Conditioning Page 37 of 44 Training Material Only Figure-21. Bell 212 Heating and Cooling System 2017-03-13 B1-12.6.2 Air Conditioning Page 38 of 44 Training Material Only Heating and Ventilation System (Bell 412) Heating and ventilation system provides: Cockpit and cabin heating (engine bleed air) Windshield and chin-bubble defogging/defrosting (bleed air) Fresh air ventilation and defogging (ventilating air) The systems are controlled by three switches located on the overhead console. These switches, labelled VENT BLOWER, AFT OUTLET, and HEATER each have an ON and OFF position. A DEFROST lever on the upper right corner of the centre pedestal provides control defrosting air to the windshields. A temperature selector located on the right cabin doorpost, controls heater and temperature. Figure-22. Bell 412 Air Distribution Where there is no air conditioning unit, a mixing valve is used to mix engine bleed air and ambient air. The valve is controlled by a solenoid valve which controls the temperature (set in cockpit) by controlling how much bleed air is mixed with the ambient air. 2017-03-13 B1-12.6.2 Air Conditioning Page 39 of 44 Training Material Only Figure-23. Mixing Valve Mixing Valve – no bleed air Figure-24. Mixing Valve – No Bleed Air Full (Heat) bleed air flow Figure-25. Mixing Valve – Full Heat 2017-03-13 B1-12.6.2 Air Conditioning Page 40 of 44 Training Material Only Mixture of bleed air and ambient air Figure-26. Mixing Valve – Mixture of Bleed and Ambient Air 2017-03-13 B1-12.6.2 Air Conditioning Page 41 of 44 Training Material Only Summary of the Two Different Types of Air Conditioning Systems Figure-27. ACM Summary Try identify

Helicopter Systems – Pneumatics PDF B1-12d 2020

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