Aerospace Systems

Aircraft Hydraulics Auxiliary Power Units Environment Control Systems RAM Air Turbine Electrical Power Systems Integrated Pneumatic System Integrated Cabin Pressure control Systems Wheels & Brakes Integrated Flight safety equipment Lighting Systems Power Generation & Distribution systems Bleed Air control systems Engine Fuel controls

Aircraft Hydraulics Hydraulic Systems provide hydraulic power generation, control and distribution to the specific consumers. Components involved are typically pumps, valves and manifolds.

Auxiliary power unit

The APU exhaust at the tail end of an Airbus A380An auxiliary power unit (APU) is a device on a vehicle whose purpose is to provide energy for functions other than propulsion. Different types of APU are found on aircraft, as well as some large ground vehicles. Aircraft APIC APS3200 APU for Airbus 318/319/320/321An aircraft APU is a relatively small, selfcontained generator used to start the jet engines, usually with compressed air, and to provide electricity, hydraulic pressure and air conditioning while the aircraft is on the ground. In many aircraft, the APU can also provide electrical power in the air. A gasoline piston engine APU was first used on the Pemberton-Billing P.B.31 Nighthawk Scout aircraft in 1916. The Boeing 727 in 1963 was the first jetliner to feature a gas turbine APU, allowing it to operate at smaller, regional airports, independent from ground facilities. Although APUs have been installed in many locations on various military and commercial aircraft, they are usually mounted at the rear of modern jet airliners. The APU exhaust can be seen on most modern airliners as a small pipe exiting at the aircraft tail. In most cases the APU is powered by a small gas turbine engine that provides compressed air from within or drives an air compressor (load compressor). Recent designs have started to explore the use of the Wankel engine in this role. The Wankel offers power-to-weight ratios better than normal piston engines and better fuel economy than a turbine.

APUs fitted to ETOPS (Extended-range Twin-engine Operations) are a critical safety device, as they supply backup electricity and compressed air in place of the dead engine or failed main engine generator. While some APUs may not be startable while the aircraft is in flight, ETOPS compliant APUs must be flight-startable at up to the aircraft service ceiling. Recent applications have specified starting up to 43,000 ft (≈ 13,000 m) from a complete cold-soak condition. If the APU or its electrical generator is not available, the airplane cannot be released for ETOPS flight and is forced to take a longer route. APUs are even more critical for space shuttle flight operations. Unlike aircraft APUs, they provide hydraulic pressure, not electrical power. The space shuttle has three redundant APUs, powered by hydrazine fuel. They only function during powered ascent and during re-entry and landing. During powered ascent, the APUs provide hydraulic power for gimballing of shuttle's engines and control surfaces. During landing, they power the control surfaces and brakes. Landing can be accomplished with only one APU working. On STS-9, two of Columbia's APUs caught fire, but the flight still landed successfully. A typical gas turbine APU for commercial transport aircraft comprises three main sections: Power section Load compressor Gearbox The power section is the gas generator portion of the engine and produces all the shaft power for the APU. The load compressor is generally a shaft-mounted compressor that provides pneumatic power for the aircraft, though some APUs extract bleed air from the power section compressor. There are two actuated devices, the inlet guide vanes that regulate airflow to the load compressor and the surge control valve that maintains stable or surge-free operation of the turbo machine. The third section of the engine is the gearbox. The gearbox transfers power from the main shaft of the engine to an oil-cooled generator for electrical power. Within the gearbox, power is also transferred to engine accessories such as the fuel control unit, the lube module, and cooling fan. In addition, there is also a starter motor connected through the gear train to perform the starting function of the APU. Some APU designs use combination starter/generator for APU starting and electrical power generation to reduce complexity. With the Boeing 787 being an all electric airplane, the APU delivers only electricity to the aircraft. The absence of pneumatic system simplifies the design, but the demand for hundreds of kilowatts (kW) of electricity requires heavier generators and unique system requirements. Two main corporations compete in the aircraft APU market: United Technologies Corporation, through its subsidiaries Hamilton Sundstrand and Pratt & Whitney Canada, and Honeywell International Inc. In case of APU failure an air start unit (ASU) and ground power unit (GPU), respectively is needed. Armor APUs are also fitted to some tanks to provide electrical power when stationary, without the high fuel consumption caused by running the main engine. Commercial Vehicles Some commercial vehicles now mount auxiliary power units of their own. A typical APU for a commercial truck is a small diesel engine with its own cooling system, generator, and air conditioning compressor, mounted to one of the frame rails of a semi-truck. This unit is used to provide climate control and electrical power for the truck's sleeper cab and engine block heater during downtime on the road.

In the United States, federal Department of Transportation regulations require 10 hours of rest for every 11 hours of driving. During these times, truck drivers often idle their engines to provide heat, light, and power for various comfort items. Although diesel engines are very efficient when idling, it is still financially and environmentally costly to idle them like this, from a fuel consumption and an engine wear perspective. The APU is designed to eliminate these long idles. Since the generator engine is a fraction of the main engine's displacement, it uses a fraction of the fuel; some models can run for eight hours on a US gallon (≈ 4 litres) of diesel. The generator also powers the main engine's block and fuel system heaters, so the main engine can be started easily right before departure if the APU is allowed to run for a period beforehand. An APU can save five gallons (≈ 19 litres) of fuel a day, and can extend the useful life of the main engine by around 100,000 miles (≈ 160,000 kilometres), by reducing nonproductive run time. Some vehicle APUs can also use an external shore power connection for their heating and cooling functions, thus eliminating fuel consumption during rest periods altogether. Many truck stops already provide shore power connections in their parking areas. On some older diesel engines an APU was used instead of an electric motor to start the main engine. These were primarily used on large pieces of construction equipment. As an alternative to the diesel units, APUs using an auxiliary battery system or hydrogen fuel cells as a source of power have also been designed. Freightliner has shown a demonstration model of a fuel cell APU, run on a tank of liquid hydrogen mounted to the truck, on one of their Century Class S/T road tractors.

Environment Control Systems Control system on a Boeing 737-800The Environmental Control System of an airliner provides air supply, thermal control and pressurization for the passengers and crew. Avionics cooling, smoke detection, and fire suppression are also commonly considered part of the Environmental Control System. Overview The systems described below is specific to current production Boeing airliners, although the details are essentially identical for passenger jets from Airbus and other companies. Air supply On most jetliners, air is supplied to the ECS by being "bled" from a compressor stage of each turbine engine, upstream of the combustor. The temperature and pressure of this "bleed air" varies widely depending upon which compressor stage and the RPM of the engine. A "Pressure Regulating Shutoff Valve" (PRSOV) restricts the flow as necessary to maintain the desired pressure for downstream systems. This flow restriction results in efficiency losses. To reduce the amount of restriction required, and thereby increase efficiency, air is commonly drawn from two bleed ports (3 on the Boeing 777). When the engine is at low thrust, the air is drawn from the "High Pressure Bleed Port." As thrust is increased, the pressure from this port rises until "crossover," where the "High Pressure Shutoff Valve" (HPSOV) closes and air is thereafter drawn from the "Low Pressure Bleed Port." To achieve the desired temperature, the bleed-air is passed through a heat exchanger called a "precooler." Air from the jet engine fan is blown across the precooler, which is located in the

engine strut. A "Fan Air Modulating Valve" (FAMV) varies the cooling airflow, and thereby controls the final air temperature of the bleed air. On the new Boeing 787, the bleed air will instead be provided by electrically driven compressors, thereby eliminating the inefficiencies caused by bleed port system. Air conditioning pack The air conditioning package, or "A/C pack" is usually an air cycle machine (ACM) cooling device. Some aircraft, including early 707 jetliners, used vapor-compression refrigeration like that used in home air conditioners. An ACM uses no Freon: the air itself is the refrigerant. The ACM is preferred over vapor cycle devices because of reduced weight and maintenance requirements. On most jetliners, the A/C packs are located in the "Wing to Body Fairing" between the two wings beneath the fuselage. On some jetliners (Douglas Aircraft DC-9 Series) the A/C Packs are located in the tail. The A/C Packs on the McDonnell Douglas DC-10/MD-11 and Lockheed L-1011 are located in the front of the aircraft beneath the flight deck. Nearly all jetliners have two packs, although larger aircraft such as the Boeing 747, Lockheed L-1011, and McDonnellDouglas DC-10/MD-11 have three. The quantity of bleed air flowing to the A/C Pack is regulated by the "Flow Control Valve" (FCV). One FCV is installed for each pack. A normally closed "isolation valve" prevents air from the left bleed system from reaching the right pack (and v.v.), although this valve may be opened in the event of loss of one bleed system. Downstream of the FCV, the bleed air enters the primary "Ram Air Heat Exchanger", where it is cooled by ambient air. The cold air then enters the ACM compressor, where it is re-pressurized, which reheats the air. A pass through the secondary "Ram Air Heat Exchanger" cools the air while maintaining the high pressure. When this cool, high-pressure air is expanded through the ACM turbine, the expanding air can be chilled to sub-zero temperatures. Similar in operation to a turbo-charger unit, the compressor and turbine are on a single shaft. The energy extracted from the air passing through the turbine is used to power the compressor. The air is then sent through a Water Separator, where the air is forced to spiral along its length and centrifugal forces cause the moisture to be flung through a sieve and toward the outer walls where it is channeled toward a drain and sent overboard. Then, the air usually will pass through a Water Separator Coalescer or, The Sock. The Sock retains the dirt and oil from the engine bleed air to keep the cabin air cleaner. This water removal process prevents ice from forming and clogging the system, and keeps the cockpit and cabin from fogging on ground operation and low altitudes. The temperature of the Pack Outlet Air is controlled by the adjusting flow through the "Ram Air System" (below), and modulating a "Temperature Control Valve" (TCV) which bypasses a portion of the hot bleed air around the ACM and mixes it with the cold air downstream of the ACM turbine. Ram Air System The "Ram Air Inlet" is a small scoop, generally located on the "Wing to Body Fairing." Nearly all jetliners use a modulating door on the ram air inlet to control the amount of cooling airflow through the primary and secondary ram air heat exchangers.

To increase ram air recovery, nearly all jetliners use modulating vanes on the ram air exhaust. A "Ram Air Fan" within the ram system provides ram air flow across the heat exchangers when the aircraft is on the ground. Nearly all modern fixed-wing aircraft use a fan on a common shaft with the ACM, powered by the ACM turbine. Air distribution The A/C Pack exhaust air is ducted into the pressurized fuselage, where it is mixed with filtered air from the recirculation fans, and fed into the "mix manifold". On nearly all modern jetliners, the airflow is approximately 50% "outside air" and 50% "filtered air." Modern jetliners use "High Efficiency Particulate Arresting" HEPA filters, which trap >99% of all bacteria and clustered viruses. Air from the "mix manifold" is directed to overhead distribution nozzles in the various "zones" of the aircraft. Temperature in each zone may be adjusted by adding small amounts of "Trim Air", which is low-pressure, high temperature air tapped off the A/C Pack upstream of the TCV. Pressurization Airflow into the fuselage is approximately constant, and pressure is maintained by varying the opening of the "Out Flow Valve" (OFV). Most modern jetliners have a single OFV located near the bottom aft end of the fuselage, although some larger aircraft like the 747 and 777 have two. In the event the OFV should fail closed, at least two Positive Pressure Relief Valves (PPRV) and at least one Negative Pressure Relief Valve (NPRV) are provided to protect the fuselage from over- and under- pressurization. Aircraft cabin pressure is commonly pressurized to a "cabin altitude" of 8000 feet or less. That means that the pressure is 10.9 psia (75 kPa), which is the ambient pressure at 8000 feet (2,400 m). Note that a lower cabin altitude is a higher pressure. The cabin pressure is controlled by a "Cabin Pressure Schedule," which associates each aircraft altitude with a cabin altitude. Since jetliners do not always fly at their maximum rated altitude, the cabin altitude is also generally lower than the maximum permitted. For example, domestic flights rarely exceed a 5500 ft cabin altitude. The new airliners such as the Airbus A380 and Boeing 787 will have lower maximum cabin altitudes which help in fatigue reduction during flights. Myths Do crews turn off one A/C Pack during flight to save fuel? When one A/C Pack fails or is turned off, the other pack increases flow to ~185% of normal. This is required for safety reasons to maintain cabin pressurization. This may actually increase fuel consumption because the bleed flow is taken asymmetrically from the engines. Is there a switch for the crew to provide less air to the cabin unless the passengers complain? One of the oldest 747s has a feature to turn off one of the three packs. No recently produced jetliner has this feature. Jetliners are designed to operate with all packs operating at all times. The bleed air comes from the engines - is there fuel vapor or jet exhaust in the cabin air? The air is "bled" from the engine upstream of the combustor. Air cannot flow backwards though the engine except during a compressor stall (essentially a jet engine backfire), thus the bleed air should be free of these contaminants from the aircraft's own engines. The bleed air has the same composition as the outside air, thus, when the aircraft is on the ground, you are breathing the same air, and the same outdoor contaminants, as the ground crew on the runway.

On rare occasions, jet engine bearing seals can leak oil into the bleed air, but this is generally dealt with quickly since failed seals will reduce the engine life. Is the air in first class better? Airbus and Boeing jetliners supply constant flow per unit length of the cabin. The seats in first class are spaced farther apart, resulting in more air per seat, but the nozzles provide the same amount of air at all locations. Since all the air in the main cabin comes from the same manifold, first class receives 50% outside air and 50% filtered recirculated air just like the rest of the cabin. Is the air in the flight deck better? Most jetliners supply 100% outside air to the flight deck. This is because the flight deck has the highest concentration of avionics and the most glass per unit volume, making the flight deck very hard to keep cool on hot days. By providing 100% outside air to the flight deck, the air supply temperature can be near freezing if required, much cooler than if the air was mixed with recirculated air. A drawback is that the air in the flight deck is much drier on these aircraft. Some jetliners provide 50% recirculated air to the flight deck, to increase pilot comfort by raising the humidity. Are the cargo compartments pressurized? The cargo compartment is generally pressurized to the same level as the cabin and the temperature may be controllable. Some aircraft have crew controlled commands for cargo compartment pressurization and temperature control.

Ram air turbine

Ram air turbine on F-105 Thunderchief fighter-bomber Ram air turbine on Boeing 757 commercial airlinerA ram air turbine (RAT) is a small propeller and connected hydraulic pump, or electrical generator used as an emergency power source for aircraft. In case of the loss of both primary and auxiliary power sources the RAT will power vital systems (flight controls, linked hydraulics and also flight-critical instrumentation). Some RATs produce only hydraulic power, that is then used to power electrical generators. Modern aircraft generate power through the main engines or an additional fuel-burning turbine called an auxiliary power unit, which is often a small tail-mounted turbine engine. The RAT

generates power from the airstream due to the speed of the aircraft, and if aircraft speeds are low the RAT will produce less power. In normal conditions the RAT is retracted into the fuselage (or wing), deploying automatically in emergency power loss. In the time between power loss and RAT deployment, batteries are used. RATs are common on military aircraft, where sudden and complete loss of power is more likely. Fewer civilian aircraft are fitted with them, although most commercial airliners are (since the 1960s on the Vickers VC-10). The Airbus A380 has the largest RAT propeller in the world at 1.63 m in diameter, but around 80 cm is more common. A typical large RAT on a commercial aircraft can be capable of producing, depending on the generator, from 5 to 70 kW. Propellers started as two-bladed or four-bladed models but military (and increasingly commercial) models now use ducted multi-blade fans. Smaller, low airspeed models may generate as little as 400 watts. In another military use, pod-fitted units such as the M61A1 Vulcan or electronic systems (e.g. the AN/ALQ-99 TJS) can be powered by a RAT in standard operation. In non-military use, RATs have been used to power centrifugal pumps to pressurize the spray systems on aircraft that are used as crop dusters to deliver liquid agents to cropland. The major reason for choosing a RAT is safety; using a RAT allows the FAA-certified engine and power systems on the aircraft to remain unmodified. There is no need to use an engine power takeoff to drive the pump, and the pump can be placed low or below the exterior of the airframe greatly simplifying plumbing, and being the lowest point in the plumbing, it will have gravity feed from the spray tanks and never need to be primed. In the event of a pump failure that could result in seizure, there is no effect on the flying ability of the aircraft or its systems apart from the obvious fact that the spray systems are non functional. Honeywell and Hamilton Sundstrand are the main US suppliers of RAT systems.

Integrated Pneumatic System

Integrated Cabin pressure systems Cabin Pressure Control Systems control automatically cabin pressure to ensure passenger and crew comfort. Key components are electric or pneumatic, or electro-pneumatic outflow valves. Cabin pressurization Cabin pressurization is the active pumping of air into an aircraft cabin to increase the air pressure within the cabin. It is required when an aircraft reaches high altitudes, because the natural atmospheric pressure is too low to allow people to absorb sufficient oxygen, leading to altitude sickness and ultimately hypoxia. Unpressurized flight A lack of sufficient oxygen will bring on hypoxia by reducing the alveolar oxygen tension. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 1500 m (5000 ft) above sea level, although most passengers can tolerate altitudes of 2500 m (8,000 ft) without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level.[1]

Passengers may also develop fatigue or headaches as the plane flies higher. As the operational altitude increases, reactions become sluggish and unconsciousness will eventually result. Sustained flight operations above 3,000 m (10,000 ft) generally require supplemental oxygen (through a nasal cannula or oxygen mask) or pressurization. Pressurized flight Aircraft that routinely fly above 3000 m (10,000 ft) are generally equipped with an oxygen system fed through masks or canulas (typically for smaller aircraft), or are pressurized by an Environmental Control System (ECS) using air provided by compressors or bleed air. Bleed air extracted from the engines is compressively heated and extracted at approximately 200 °C (392 °F) and then cooled by passing it through a heat exchanger and air cycle machine (commonly referred to by aircrews and mechanics as 'the packs system'). Most modern commercial aircraft today have a dual channel electronic controller for maintaining pressurization along with a manual back-up system. These systems maintain air pressure equivalent to 2,500 m (8,000 ft) or less, even during flight at altitudes above 13,000 m (43,000 ft). Aircrafts have a positive pressure relief valve in the event of excessive pressure in the cabin. This is to protect the aircraft structure from excessive loading. Normally the maximum pressure differential between the cabin and the outside ambient air is between 7.5 and 8 psi (51.7 and 55.2 kPa). If the cabin were maintained at sea level pressurization and then flown to 35,000 feet (10.7 km) or more, the pressurization differential would be greater than 9 psi (62 kPa) and the structural life of the airplane would be limited. The traditional method of bleed air extraction from the engine comes at the expense of powerplant efficiency. Newer aircraft such as the Boeing 787 are using electric compressors to provide pressurization. This allows greater propulsive efficiency. As the airplane pressurizes and decompresses, some passengers will experience discomfort as trapped gasses within their bodies expand or contract in response to the changing cabin pressure. The most common problems occur with gas trapped in the gastrointestinal tract, the middle ear and the paranasal sinuses. Note that in a pressurized aircraft, these effects are not due directly to climb and descent, but to changes in the pressure maintained inside the aircraft. It is always an emergency if a pressurized aircraft suffers a pressurization failure above 3000 m (10,000 ft). If this occurs, the pilot must immediately place the plane in an emergency descent and activate oxygen masks for everyone aboard. In most passenger jet aircraft (such as the Boeing 737[2]), passenger oxygen masks are automatically deployed if the cabin altitude is above 14,000 feet.[3] History and usage of cabin pressurization While the piston fighters of World War II often flew at very high altitudes, they were not pressurized; instead pilots used oxygen. However, in a larger bomber where crew moved about the cabin, this was considerably less practical. Therefore, the first aircraft with cabin pressurization (though restricted to crew areas), was the B-29 Superfortress. Post-war piston airliners such as the Lockheed Constellation brought the technology to civilian service, and as jet airliners were always designed for high-altitude operation every jetliner features the technology. Most turboprop aircraft also feature cabin pressurization due to their medium to high altitude operation. A very few piston-engined small private planes also do so; most do not routinely fly high enough to justify such a system.

Loss of pressurization One consequence of cabin pressurization is that the pressure inside the airplane might be 70 kPa (10 psi), while the pressure outside is only 15 kPa (2 psi). An otherwise-harmless pinhole under these pressure differences will generate a high-pitched squeal as the air leaks out at supersonic speeds[citation needed]. A hole a metre and a half (5 feet) across will depressurize a jetliner in a fraction of a second. Gradual or slow decompression is dangerous because it may not be detected. Rapid decompression is a change in cabin pressure where the lungs can decompress faster than the cabin. Explosive decompression is a change in cabin pressure faster than the lungs can decompress (less than 0.5 seconds). This type of decompression is potentially dangerous and often results in lung damage and unsecured items / debris flying around the cabin.[citation needed] Rapid decompression of commercial aircraft is extremely rare, but dangerous. People directly next to a very large hole may be forced out or injured by flying debris. Floors and internal panels may deform. Hypoxia will result in loss of consciousness without emergency oxygen. Onset of hypoxia-induced unconsciousness varies depending on the altitude. Additionally, the air temperature will plummet due to expansion, potentially resulting in frostbite. Contrary to Hollywood myth, as seen in the James Bond film, Goldfinger, people just a few feet from the hole are more at risk from hypoxia than from being forced out. Effects of cabin pressurization on an aircraft fuselage As the airplane is pressurized and depressurized, the metal skin of the airplane expands and contracts, resulting in metal fatigue. Modern aircraft are designed to resist this compression cycle, but some early jetliners (see De Havilland Comet) had fatal accidents due to underdesign for fatigue. Effects of cabin pressurization on the human body Ear and paranasal sinuses - One needs to adjust to the pressurized cabin air from the beginning. 1 in 3 passengers suffer ear discomfort, pain and temporary hearing loss on takeoff or landing, called "aerotitus" by the House Ear Institute in Los Angeles. Rapid changes in air pressure cause the air pocket inside the ear to expand during takeoff and contract during descent, stretching the eardrum. To equalize pressure, air must enter or escape through the Eustachian tube. "If a passenger has serious congestion, they risk ear drum damage", says Sigfrid Soli, Ph.D., head of the HCSD Department at the HSI.[citation needed] Tooth - Anyone with intestinal gas or gas trapped in an infected tooth may also experience Barodontalgia, a toothache provoked by exposure to changing atmospheric pressure. Pneumothorax - Anyone who has suffered a pneumothorax is recommended not to fly (even in a pressurised cabin) for at least 1 month and should obtain an x-ray prior to travelling. As well as the more acute health effects experienced by some people, the cabin pressure altitude of 2,500 m (8,000 ft) typical in most airliners contributes to the fatigue experienced in long flights. The in-development Boeing 787 airliner will feature pressuration to the equivalent of 1,800 m (6,000 ft), which Boeing claims will substantially increase passenger comfort. The A380 will go even further, pressurising to 1,500 m (5,000 ft). Some people may still experience symptoms of altitude sickness despite the cabin pressure.

Wheels & Brakes Air brake (aircraft) Airbrake on a British Buccaneer naval strike aircraftIn aeronautics air brakes are a type of flight control used on aircraft to reduce speed during landing. Air brakes differ from spoilers in that air brakes are designed to increase drag while making little change to lift, whereas spoilers greatly reduce lift while making little change to drag. Often, both characteristics are desirable and are combined - most modern airliner jets feature combined spoiler and airbrake controls. On landing, the deployment of these spoilers causes a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding. In addition, the form drag created by the spoilers directly assists the braking effect. Reverse thrust is also used to help slow the aircraft after landing. The British Blackburn Buccaneer naval strike aircraft designed in the 1950s had a tail cone that was split and could be hydraulically opened to the sides to act as a variable air brake. It also helped reduced the length of the aircraft in the confined space on an aircraft carrier.

Lighting control system Lighting control system consists of a device, typically an embedded processor or industrial computer, that controls electric lights for a building or residence. Lighting control systems usually include one or more keypads or touch panel interfaces. These interfaces allow users the ability to toggle power to lights and fans, dim lights, and program lighting levels. A major advantage of a lighting control system over conventional lighting is the ability to control any device from any interface. For example, a master touch panel might allow the user the ability to control all lights in a building, not just a single room. In fact, any light might be controlled from any location. In addition, lighting control systems provide the ability to automatically power a device based on programming events such as: Chronological time (time of day) Astronomical time (sunrise/sunset) Room occupancy Events Alarm conditions Program logic (any combination of events) Chronological time is a time of day or offset from a time. Astronomical times includes sunrise, sunset, a day, or specific days in a month or year. Room occupancy might be determined with motion detectors or RFID tags. Events might include holidays or birthdays. Alarm conditions might include a door opening or motion detected in a protected area. Program logic can tie all of the above elements together using constructs such as if-then-else statements and logical operators. Many companies offer lighting control systems for sale. Major competitors in the industry include Lutron, Clipsal, Smarthome, Crestron, Dynalite, iLight, Vantage Controls, Intellibus, Control4, and Leviton.

Power Generation & Distribution systems

Bleed air control system Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage(s) and before the fuel is injected in the burners. While in theory bleed air could be drawn in any gas turbine engine, its usage is generally restricted to jet engines used in aircraft. This compressed air can be used within the aircraft in many different ways, from de-icing, to pressurizing the cabin, to pneumatic actuators. However, bleed air is quite hot and when being used in the cabin or other low temperature areas, it must be cooled or even refrigerated. Bleed air is valuable in an aircraft for two properties: Its high temperature and its high pressure. Newer aircraft rely more on electricity, reducing the need for compressed air. Since most gas turbine engines use multiple compressor stages, some newer engines have the bleed air inlet between compressor stages to reduce the temperature of the compressed air.

Merits of bleed air In civil aircraft, its primary use is to provide pressure for the aircraft cabin by supplying air to the Environmental Control System. Additionally, bleed air is used to keep critical parts of the aircraft (such as the wing leading edges) ice-free. When used for cabin pressurization, the air from the engine must first be cooled (as it exits the compressor stage at temperatures as high as 300°C) by passing the bleed air through an air-toair heat exchanger cooled by cold outside air. It is then fed to an air cycle machine unit which regulates the temperature and flow of air into the cabin, keeping the environment comfortable. A similar system is used for wing de-icing. In icing conditions, water droplets condensing on a wing's leading edge can freeze at the ambient temperatures experienced during flight. This build-up of ice adds weight and changes the shape of the wing, causing a degradation in performance, and possibly a critical loss of lift. To prevent this, warm bleed air is pumped through the inside of the wing's leading edge. This heats up the metal, preventing the formation of ice. Alternatively, the bleed air may be used to inflate a rubber boot glued to the leading edge, breaking the ice loose. Recent developments in civil aircraft Bleed air systems have been in use for several decades in passenger jets. Recently, Boeing announced that its new aircraft, the 787 would operate without use of bleed air (and the two engines proposed for the aircraft, the General Electric GEnx and the Rolls-Royce Trent 1000, are designed with this in mind). This represents a departure from traditional winged aircraft design, and proponents state that eliminating bleed air improves engine efficiency, as there is

no loss of mass airflow and therefore energy from the engine, leading to lower fuel consumption. Additionally, eliminating bleed air may reduce the aircraft's mass by removing a whole series of pumps, heat exchangers and other heavy equipment. Lastly, advocates of the design say it improves safety as heated air is confined to the engine core, as opposed to being pumped through pipes and heat exchangers in the wing and near the cabin, where a leak could damage surrounding systems. Skeptics point out that eliminating bleed air creates a requirement for another source of energy for cabin heating, anti-ice/de-ice systems, and other functions previously covered by bleed air. The other source can be a "dummy engine" - which can require electrical energy from the main engine(s). Therefore, from a complete system point of view, this approach can be less efficient than might initially be thought. The dummy engine has an inlet, a compressor, a turbine, an exhaust, an electric motor. Instead of a combustion chamber it has much like a turbocharger connections to deliver and take back air. A reverse flow heat exchanger can be used to lower energy requirements for the cabin ventilation. Airbus does not currently (as of November 2004) have any plans to eliminate bleed air from its 787 competitor, the A350, while Boeing is actively pursuing this technology, touting it as one of the main advantages of its design.