Aircraft Maintenance Technology

JUN-JUL 2018

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8 JUNE/JULY 2018 AIRCRAFT MAINTENANCE TECHNOLOGY MANUFACTURING INNOVATIONS are resolved, generating costs and inconvenience for operators and passengers alike. MEA — A Solution to Traditional Problems Well-designed electrically powered systems do not suffer from many of the shortcomings inherent to hydraulic, pneumatic, and mechanical systems described above. Electrical systems are relatively flexible and lightweight, and have higher efficiency. Over the years and decades more electric power was designed in and used in commercial aircraft. A milestone in the trend toward the MEA was the introduction of the fly-by-wire in the Airbus A320 in the late 1980s, soon followed by the Boeing 777 in 1994. The MEA technology significantly reduced weight, creating additional space for other aircraft components. The electrical transmission of steering inputs from the cockpit to the flight control surfaces eliminated mechanical linkages. Boeing set another — probably the most important — milestone with the 787. It was the very first large commercial aircraft with an electrically powered environmental control system, which additionally featured electrically actuated brakes and electrical deicing. Although the 787 still has a relatively conventional hydraulic system, the pressure in the system is generated by electrically powered hydraulic pumps. Boeing, the MEA Pioneer The development of small electric aircraft has been accompanied by technological upgrades to larger commercial aircraft in which electrically powered systems have been used to replace equipment previously powered by bleed air from the engines, including cabin pressurization, air conditioning, and deicing. Electric power is also being used to replace pneumatic and hydraulic systems, such as flight controls, brakes, and landing gear. Electric motors can also be used to power wheels to enable an aircraft to perform its own pushback and taxiing without the need for an external tug. One of the major pioneers of these ‘more-electric aircraft’ systems has been the Boeing 787 which uses electric systems to replace those previously powered by hydraulics or bleed air from the engines. 787 No-Bleed Systems The Boeing 787 Dreamliner introduced a unique no-bleed systems architecture that eliminated a traditional pneumatic system and bleed manifold, converting the power source of most traditionally powered bleed air functions to electric power. According to Boeing, using electrical power is more efficient than engine-generated pneumatic power systems. This architecture extracts as much as 35 percent less power from the engines on the 787. Bleed air is only used for engine cowl ice protection and pressurization of hydraulic reservoirs. Because the 787 uses more electricity than other Boeing airplanes, the 787 generates more electricity, using six generators: two on each engine and two on the APU in the tail section. On the ground, the 787 can be started without the use of ground power. The APU battery starts the APU generators, which start the APU to power the engine generators, which then start the engines. In flight, the four engine generators are the primary sources of electrical power; the APU generators are secondary. Power runs from the generators to four alternating-current (AC) buses, where it is either distributed for use or converted to what other systems need. Other power sources for the 787 include the main battery, used primarily for brief ground operations and braking; the APU battery, which helps start the APU; and ground power, which can connect through three power receptacles. The main battery, APU battery, and ram air turbine also are available as backup power in flight. Batteries and Battery Safety The 787 includes many layers of redundancy for continued safe operation. Boeing designed the systems so that no single failure will cause an accident by including redundant systems, separating systems in space and functions, and providing standby and protective systems. The 787 Dreamliner has two primary rechargeable batteries — the main ship and APU. While identical part numbers, they serve separate purposes. Boeing selected the lithium-ion type battery because it is capable to deliver a large amount of power in a short period of time. The 787 completed 5,000 hours of flight testing and an equal amount of test time on the ground prior to entering service. No battery-related incidents occurred before January 2013, when the airplane experienced two events and lessons learned improved the aircraft health. A Different Approach to E-Flight The two industry giants in the commercial aviation world took somewhat different approaches toward E-Flight. Airbus started this E-Flight journey a decade ago with single seat aircraft and is investing strongly in Urban Air Mobility field (see the March 2018 issue). Boeing has chosen a different approach by investing its venture capital arm HorizonX in finding promising startups to invest often along with partners, including the Zunum regional aircraft programs. Zunum Aero, a Seattle-based startup backed by Boeing and JetBlue Technology Ventures, announced in October 2017 plans for its first hybrid-electric plane, a 19-seater, which is optimized for a 700-nm range claiming a competitive price of about 8 cents per seat mile, or $250 an hour. The prototype should fly by 2020 and be certified under the revamped FAR Part 23 rules. The company hopes it can disrupt the regional airline industry, which it says is worth $1 trillion worldwide. Zunum has been working since 2013 but in April 2017 announced hybrid or electric air travel on airplanes from 10 to 50 seats by the early 2020s. The company says it will start with the 19-seater, which could be reconfigured to a six- or nine-seat (jet-alike) aircraft. Zunum hopes to bring a first hybrid-electric commuter aircraft to market

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