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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Serie: Frontiers in Aerospace Science
- Sprache: Englisch
Conceptual Design of Green Transport Airplanes presents key information, methodologies, and modern tools for the conceptual design of airliners that comply with requirements to minimal environmental impact. The book is comprised of eight chapters that address relevant subjects such as airplane technological evolution, feasibility studies, design framework for conceptual design, and flight operations. Important issues and methods for an in-depth feasibility study are presented to facilitate the decision-making process of aircraft programs. These include examples of business plans for a 50-seat and 78-seat regional jets, description of design phases, market strategy, competition among manufacturers, regulatory requirements, and technology assessment.
Readers will also be introduced to modern methodologies used in the conceptual design process of transport airplanes, such as configuration study, aerodynamics, flight stability and control, performance, certification requirements and the role of flight operations. Thus, the design process is explained in an integrated manner which paves the way towards a better understanding of an optimized aeronautical design environment where noise and emission constraints are taken into consideration.
Conceptual Design of Green Transport Airplanes is an essential reference work for aeronautical engineering students and technicians as well as industry professionals involved in the aviation and environmental protection/regulation industry.
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Veröffentlichungsjahr: 2018
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PREFACE
Aircraft manufacturers and aviation are very important industries, both in social and economic aspects. According to the International Air Transport Association (IATA), aviation transported around 6.6 billion passengers in 2015 and provides approximately 62.7 million related jobs worldwide. Aircraft boost local and global growth with its civil and defense sector activities.
In particular, aircraft design has also a major impact on the society due to its safety record that inspires other industrial segments and technological spin-off effects. On the environmental side, in times of global warming, efficient aircraft will insert considerably fewer pollutants into the atmosphere and will consume less trip fuel. Most aircraft development programs make use of extensive and intensive research performed by academy as well as with the help of investments of the private sector in innovative technology. Few countries can develop, certify, market and support medium-to-large commercial airliners. This exemplifies the high level of effort, knowledge, and money involved in the aircraft manufacturing industry. Recycling of decommissioned aircraft and proper handling of the industrial processes to avoid environmental damage is part of the aircraft industry nowadays.
It is unfortunate that in the academic world few universities worldwide have a dedicated chair in airplane design, and even fewer in rotorcraft design. Most universities consider only basic disciplines such as aerodynamics, aeronautical structures, flight physics and space technologies as the fundamentals to provide higher education to aeronautical engineering undergraduate students. They disregard aircraft design as a specific discipline worthy of creating a specific chair. However, aircraft design enables the proper integration and practical application of all aeronautical disciplines. The authors of the present book have together over 60 years of experience working for one of the largest aircraft manufacturers in the world, major airlines and institution of superior education.
The present work is not intended to be or become a textbook, but to be complementary to the existing ones while highlighting environmental aspects on aircraft design. There are already several good books that were written with this purpose. Although these books have established some design practices and offer considerable data and information, most of them were mainly issued in the years 1980 to 1990. Also at that time, aircraft design was a sequential process starting with aerodynamics, followed by weight breakdown, load calculation, defining wing and tailplane areas and checking stability and controllability. Some of the methodology of these books is simple due to the lack of computer power in the past. However, aircraft design in the aircraft industry evolved from a sequential process in the past to the current utilization of high-fidelity multi-disciplinary design and optimization frameworks, where all disciplines are considered simultaneously and where everything depends upon everything. Therefore, today´s aircraft manufacturers are aware of the fact that modern engineers need to understand the whole aircraft as one complex system. There is a necessity for understanding the multi-disciplinary aspects of aircraft design also considering environmental aspects. Aircraft design disciplines are the best way to incorporate this philosophy. Books written in the past were unaware of these aspects. In the meantime, aircraft systems have evolved considerably. For instance, fly-by-wire systems have changed the way commercial and military aircraft are designed and flown. Aircraft with fly-by-wire systems are safer, more reliable, easier to fly, more maneuverable and fuel efficient with reduced maintenance costs. A fly-by-wire command and control system is already present in 9-seat business jet airplanes. All these new systems must be taken into consideration during the
conceptual design phase, where the aircraft sizing is carried out as well as other important tasks.
The proper understanding of the aviation and manufacturing business is very important for engineers. In this context, the present work provides the process and information for the elaboration of a business plan for a transport airplane project that includes information on how to conduct a market survey, undertake technological assessments as well as financial and risk analysis, and shows establishment of requirements. It is very important that the aeronautical engineer not restrict himself/herself to his/here discipline where he/she carries out his work but that, he/she can also understand the context of the aeronautical industry.
The continuous increase in computer speed and capacity has allowed finite-element methods for all structural layout, cabin configuration, and CFD methods to be incorporated in the conceptual design phase already. It is possible to integrate the different design boundaries, such as high speed and low-speed aerodynamics, and as a follow-up step, today the multidisciplinary methods permit an aircraft to be designed by integration of aerodynamic, structural and flight mechanics design constraints and by using multidisciplinary optimization methodologies. Multi-disciplinary design and optimization is the modern design methodology for many aircraft design features and aspects and nearly all papers on aircraft design now use some sort of multidisciplinary optimization approach.
Future airplanes need to comply with new and more stringent environmental rules. New challenges with regard to performance and energetic efficiency may reshape the today’s airplanes entirely. The exploration of new business opportunities for aviation, which may also affect airplane configuration, is addressed. This book presents emission and noise models that were employed for optimal design airliners of distinct categories. There is a trend to power ground vehicles with electric engines. This will change the share of aviation in emissions and the way public deals with it.
Finally, post design techniques and devices to improve aircraft performance and efficiency by improved and rethought aircraft operations are presented. Mitigation of design flaws are analyzed and discussed.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The authors declare no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENTS
We thank Financiadora de Estudos e Projetos (FINEP) a support technology agency belonging to Brazilian federal government for the Project CAPTAER II, which provided resources and equipments utilized in the present work.
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We thank institutions like NASA and United States Air Force Museum that release to the public domain, a large photo collections. This kind of initiative contributes enormously to widespread aerospace knowledge and help to inspire young hearts.
Part of the computations used in the present work were carried out with hardware and software purchased with support of the Brazilian federal agency Financiadora de Estudos e Projetos (FINEP) through the project CAPTAER II.
Aviation and the Environment
Bento Silva de Mattos,José Alexandre T.G. FregnaniAbstract
The present chapter contains information about the impact of aviation on global warming and describes the industry commitments to reduce greenhouse gas emissions. This chapter also analyses ICAO’s efforts in establishing goals and timeframe - carbon neutral by 2020 and 50% reduction on 2005 baseline - to states and industry to reduce aviation pollution. A solid “Four Pillar” initiative was set by the industry with the objective to address such a target, considering investments in operational procedures, infrastructure, technology and market-based measures. According to the recent studies, operational procedures and improvements in infrastructure may not be sufficient to accomplish the ICAO goals with current technological state of art. Innovative technological developments, mainly related to new airframe and engine designs and concepts are indeed considered the most effective and promising measures with potential to lead to fuel efficiency improvements up to 25% when compared with 2005 levels. With this perspective, fuel efficiency is becoming more and more relevant in aircraft design techniques. Electrical vehicles may be a considerably, if not entirely, a part of the ground transportation fleet in coming decades. A study was undertaken in the present work to estimate the percentage of aviation in CO2 emissions and noise levels considering a steadily increasing fleet of electrical vehicles over time. The evident conclusion is that even when introducing biofuels in aviation operations, their share in pollution compared to present levels will still steadily increase and take up a huge percentage of all transportation pollution. This will be an ongoing process up to the year 2050 despite the overall emission reductions. In other words, there is considerable evidence that aviation will be more and more in focus (and social-political pressure) throughout the years regarding the GHG emissions. This fact obviously reinforces the necessity for improvements in aircraft/engine designs, alternative motorization, and other sources of energy to empower aircraft systems and improve operational efficiencies.
AVIATION AND ENVIRONMENT
The Climate Change and Air Transport
Transportation plays a vital role for world economy. Within the transportation sector, commercial aviation has evolved from the 1960s to present days into the fastest, safest means of transport and a global transportation mode. Nowadays,
over 3 billion people, nearly half the world’s population, use the regular air transport, whose industry generates on a worldwide scale 56 million jobs, both direct and indirect [1]. Aircraft carry only 0.5% of the world trade shipments, which represents about 35% of the value of all world trade. This productivity is achieved by consuming just 2.2% of the world energy [1].
Regardless of the world’s dependency on air transport, the pollution it causes just as much as other means of transportation, is a matter of great concern, especially in view of increasing global warming [2] and major concerns for the impact on people’s health. Aircraft, cars, trucks, and other vehicles operating at airports create emissions because of the combustion of fuel. Aircraft engines produce carbon dioxide (CO2), which comprises about 70% of their exhaust, and water vapor (H2O), which comprises about 30% [1]. Less than 1% of the exhaust is composed of pollutants like nitrogen oxides (NOx), oxides of sulfur (SOx), carbon monoxide (CO), partially combusted or unburned hydrocarbons (HC), particulate matter (PM), and other trace compounds. In general, about 10 percent of pollutant emissions by aircraft take place close to the surface of the earth (less than 1000 meters above ground level), the remaining 90 percent of aircraft emissions are released at altitudes above 1 km. The pollutants CO and HCs are exceptions to this rule as they are produced when aircraft engines are operating at their lowest combustion efficiency (aircraft ground switch is on), which makes their split about 30 percent below 1000 meters, and 70 percent above 1000 meters [1].
Significant efforts of the aviation and aeronautical community have been made to lower aviation-related emissions. Alternative fuels, improved airplane designs, new aircraft concepts, and fuel-saving operational procedures are among them. The International Civil Aviation Organization (ICAO) proposed a “Four Pillar” initiative to the aviation and aeronautical industry with the objective to address some targets of emission reduction [3]. This initiative considers investments as well as efforts on operational procedures, infrastructure, technology and market-based measures.
Besides ICAO, there are several governments that have been issuing policies to address pollution caused by aircraft. In 2011, the European Commission established several goals concerning the protection of the environment intended to be accomplished by 2050 [4]. According to these targets, technologies and procedures available by 2050 are supposed to enable a 75% reduction in CO2 emissions per passenger-kilometer and a 90% reduction in NOx emissions; the perceived noise emission of flying aircraft is supposed to be reduced by 65%; in addition, aircraft movements are supposed to be emission-free when taxiing. All these targets are relative to the capabilities of typical new aircraft in 2000.
However, according to the recent studies, operational procedures, improvements on infrastructure, and biofuels may not be sufficient to accomplish the ICAO and European Commission goals with the current technological state of art. New, innovative radical designs may be needed to accomplish the envisaged emission reductions that were set by governments of several nations. In addition, aviation share of overall pollution could change significantly if electric road vehicles gain a more widespread use. There are only few studies on the impact of electrical road vehicles in the emission picture on the transport sector, and they disagree significantly with each other regarding their conclusions on the subject.
Electrical car serial production is not new; an article from the 1904 Motor Age Magazine published a conservative estimate of the probable output of the different factories for that year. A total production of 30,000 cars was estimated that was supposed to be divided roughly as follows: Licensed gasoline cars, 16,000; unlicensed gasoline cars, 8,000; electric cars, 3,000; steam cars, 2,000; miscellaneous, 1,000. Columbus Electric from Ohio was one of the electric car manufacturers. Its 1905 electric car weighed 635 kg and had a range of 75 miles before requiring battery recharge [5].
Many researchers claim that the electrical road vehicles will not contribute to lower emission levels in the whole chain, considering that the energy necessary to produce batteries and to power those vehicles will be higher than the current levels. However, a recent report from Electric Power Research Institute (EPRI) and Natural Resources Defense Council (NDRC) affirms that the electrical vehicle emission levels are far lower than the pollution caused by conventional vehicles, and could be even lower if the electric power sector cleans itself up over the next few decades [6]. In addition, cities will become cleaner, avoiding billions of money being spent on health care of people affected by pollution.
For the EPRI-NRDC study, some potential scenarios for the electricity sector in the future and the potential emission impact of widespread electrification displacing petroleum consumption in the transportation sector were well considered. To address the first issue, two potential greenhouse gas scenarios of the future electric power sector were considered: namely the “Base GHG” and “Lower GHG” scenarios. Both revealed that grid emissions will decrease over time, in part because of existing and potential regulations and plausible economic conditions. In the Lower GHG scenario, an increasing price on carbon is supposed to further reduce carbon emissions, as it could result in faster deployment of low-emission generation technologies [6]. In the Base GHG scenario, the study estimates that, by 2050, the electricity sector could reduce annual greenhouse gas emissions by 1030 million metric tons relative to 2015 levels, which represents a 45% reduction. In the Lower GHG scenario, the study estimates that, by 2050, the electricity sector could reduce annual greenhouse gas emissions by 1700 million metric tons relative to 2015 levels, representing a 77% reduction.
The EPRI-NDRC report also analyzed electric sector and transportation sector emissions with and without widespread utilization of electric road vehicles to determine the effect of electrification of light-duty personal vehicles, some medium-duty commercial vehicles like local delivery trucks and certain non-road equipment, like forklifts. It was found that electrification could displace emissions from conventional petroleum-fueled vehicles for each scenario:
In the Base GHG scenario, carbon pollution is reduced by 430 million metric tons annually in 2050 -equivalent to the emissions from 80 million of today's passenger cars [6].In the Lower GHG scenario, carbon pollution is reduced by 550 million metric tons annually in 2050 -equivalent to the emissions from 100 million of today's passenger cars [6].Independent from these results, there are good perspectives that the electrification of road vehicles will change the emission panorama of the transportation sector. This will turn the cities less polluted and quieter, changing the public standard for acceptable noise and emission levels. The present work therefore performs an analysis of the increasing electrification of road vehicles on the CO2 emission and how this could change aviation and redirect the efforts to comply with future emission reduction policies.
Aviation in a Global Warming Environment
The Climate Change and Air Transport
Pollution generated since the industrial revolution is changing dramatically the average global temperature (Fig. 1.1). Global warming and climate change can both refer to the observed century-scale rise in the average temperature of the Earth's climate system and its related effects [2]. Multiple lines of scientific evidence show that the climate system is warming [7]. More than 90% of the additional energy stored in the climate system since 1970 has gone into ocean warming; the remainder has melted ice, and warmed the continents and atmosphere. Many of the observed changes since the 1950s are unprecedented over decades to millennia [7]. Despite emission reductions from automobiles and more fuel-efficient turbofan and turboprop engines, the rapid growth of air travel registered from the 1978 Deregulation Act to the present contributed to an increase in total pollution attributable to aviation. In the European Union,
greenhouse gas emissions from aviation increased by 87% between 1990 and 2006 [8].
Fig. (1.1)) Atmospheric CO2 concentration and global air surface temperature (Source: NASA Goddard Institute for Space Studies, Graph released to public domain).Ice cores provide evidence for greenhouse gas concentration variations over the past 800,000 years. Both CO2 and CH4 vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature (Fig. 1.2) [9-11]. Direct data does not exist for periods earlier than those represented in the ice core record because the earth internal heat melts the ice. Data indicates CO2 mole fractions stayed within a range of 180 ppm to 280 ppm throughout the last 800,000 years, until the increase of the last 250 years.
The power stations presented in 2000 the bigger contribution in world energy use and emissions of greenhouse gases (GHGs) with the transport sector coming into third place (Table 1.1). In 2004, transport energy use amounted to 26% of total world energy use and the transport sector was responsible for about 23% of world energy-related GHG emissions [12]. The 1990–2002 growth rate of energy consumption in the transport sector was highest among all the end-use sectors. Road vehicles account for more than three-quarters of a total of 77 exajoules (EJ) of total transport energy use, with light-duty vehicles and freight trucks having the lion’s share. Virtually all (95%) of transport energy comes from oil-based fuels, largely diesel (23.6 EJ, or about 31% of total energy) and gasoline (36.4 EJ, 47%). One consequence of this dependence, coupled with the only moderate differences in carbon content of the various oil-based fuels, is that the CO2 emissions from the different transport sub-sectors are approximately proportional to their energy use.
Fig. (1.2)) 700 thousand years of ice core data indicates a strong correlation between temperature and CO2 concentration [9, 11].In fact, aviation contribution to world’s pollution is controversial. Contrails represent one of these controversies. Contrails are clouds formed when water vapor condenses and freezes around small particles (aerosols) that exist in aircraft exhaust (Fig. 1.3). Some of that water vapor comes from the air around the plane; and, some is added by the exhaust of the aircraft. The exhaust of an aircraft contains both gas (vapor) and solid particles. Aircraft contrails can spread into cirrus-like clouds high in the atmosphere. Like natural clouds, they are thought to have an overall warming effect on the planet. But they can also moderate daily temperature extremes by trapping heat that escapes from the ground and reflecting sunlight [14]. This raises the lowest overnight temperatures and, to a lesser degree, reduces the higher recordings during daylight hours.
Noise disturbance is a complicated issue to evaluate, as it is open to subjective reactions. Its impact is not a lasting one on the actual environment, but it can have significant adverse effects on people living close to an airport, including: interference with communication, sleep disturbance, annoyance responses, learning acquisition, performance effects and cardiovascular and psycho-physiological effects.
Fig. (1.3)) Airplane contrails (Photo: courtesy of Paulo Eduardo Cypriano).The October 2006 report by Nicholas Stern [15] states that the largest contributor to human-induced CO2 is power generation (24%), mostly produced in electricity stations burning gas and coal. Land use hits 18%, then agriculture, industry and transport at 14% each (aviation contribution is in the 2-2.5% range). Buildings (8%), other energy related activities (5%) and waste (3%) make up the rest.
Carbon dioxide is not the only greenhouse gas emitted by aircraft, however. The exhaust from aircraft engines is made up of: 7% to 8% CO2 and water vapor; around 0.03% nitrogen oxides, unburned hydrocarbons, carbon monoxide and Sulphur oxides; traces of hydroxyl family and nitrogen compounds and lesser amounts of soot particles, despite of the industry has managed to eliminate soot emissions over the past few decades. Between 91.5% and 92.5% of aircraft engine exhaust is normal atmospheric oxygen and nitrogen.
The International Civil Aviation Organization has defined a set of conditions for the assessment of local emissions, termed Landing-Takeoff (LTO) cycle, which covers NOX (NO+NO2), CO, UHC, and smoke emissions. These conditions are detailed in the volume II (Emissions) of the Annex 16 (Environmental Protection) to the Convention on International Civil Aviation [16]. The LTO cycle considers the airplane engine operating at the takeoff, climb, approach and taxi (idle) settings. These settings are defined as a percentage of the rated engine thrust (F∞): 100% F∞ (takeoff), 85% F∞ (climb), 30% F∞ (approach) and 7% F∞ (idle). The engine is supposed to operate at each setting for a definite time as follows: 42 s (takeoff), 132 s (climb), 240 s (approach) and 1,560 s (idle/taxi). Fig. (1.4) shows the scheme of the LTO cycle.
Fig. (1.4)) LTO-cycle for evaluation of engine emissions.Based on the LTO cycle, the ICAO Committee on Aviation Environmental Protection (CAEP) sets forth the limits for engine certification [16]. These limits consider the total pollutant emission parameterized by the total reference engine thrust (F∞) which enables the comparison of engines of varied sizes. Table (1.1) provides values of emissions and fuel used in the LTO phase for aircraft types frequently operated for domestic and international routes [16]. Concorde figures lays well above those of the other airplanes. The values for CO2 and NOx emissions per passenger for the aircraft of Table (1.2) are displayed in Table (1.3).
The impact of NOx emissions from aircraft, which, although representing only 1–2% of the total emissions of NOx from human and natural sources in the early 1990s [17] may have a pronounced impact on the chemical composition of the atmosphere. Numerous studies have focused on the different implications of NOx emissions from aircraft [18-22]. Most importantly, NOx emissions from aircraft are expected to increase ozone in the upper troposphere and lower stratosphere region [22].
Emission Control Policy
The mitigation of environmental impact is one of the key challenges for aviation and a main driver for research and technology in the sector. While the focus in the past was on noise and pollutant emissions, aviation greenhouse gas emissions have become the predominant environmental topic for the aviation community in the last years. Modern airliners are powered by turbofan or turboprop engines burning kerosene, which is a mixture of hydrocarbons and contains a large variety of carbon chain molecules, generally with chain lengths of nine to sixteen atoms. This is the case with JET A-1, fuel produced according to international standard specifications for use in civil aviation. Engine emissions can be divided into two basic groups: those proportional to engine fuel burn and those proportional to engine thrust setting. The fuel-burn proportional emissions as seen before are essentially carbon dioxide (CO2), water vapor (H2O), and sulfur oxides (SOX), whereas those proportional to thrust setting comprise carbon monoxide (CO), unburnt hydrocarbons (UHC), nitrogen oxides (NOX), soot, and smoke. From all these combustion products, carbon dioxide (CO2) is the main greenhouse gas that occurs naturally in the environment and the single most important waste product of industrialized economies. It is produced in the engine at a rate of approximately 3.15 grams per kilogram of fuel burnt in the engine. It is relatively abundant and has a very long life in the atmosphere, having, therefore, a leading importance in the global climate system. Per Intergovernmental Panel on Climate Change (IPCC) in 2007 [23], the CO2 emissions from global aviation were increased by a factor of about 1.5, from 330 MtCO2/year in 1990 to 480 MtCO2/year in 2000, and accounted for about 2% of total anthropogenic CO2 emissions. Considering also other relevant exhaust emissions from aircraft engines including contrails and cirrus, the contribution of air transport to the total anthropogenic greenhouse effect has been estimated at around 3%. IPCC [23] also concluded that, in the absence of additional measures, projected annual improvements in aircraft fuel efficiency of the order of 1–2% are likely to be overlapped by traffic growth of around 5% each year, despite of political and economic turmoil, leading to a projected increase in emissions of 3–4% per year. IPCC also forecasts that by 2050 aviation contribution to global anthropogenic carbon emissions could grow to 3%, representing 5% of the total greenhouse effect [23]. While aviation is a relatively small contributor of greenhouses gases, the scientific findings of the IPCC [24] indicate a clear urgency for action from all sectors to achieve their medium and long-term objectives. Therefore, emissions reduction measures were perceived by the industry as a real need for compensation of the effect of the traffic growth forecasted.
The Aviation Industry Initiatives
Considering the above scenario, at the United Nations Climate Conference in Copenhagen in 2009 (two years after the IPCC report), the aeronautical and aviation industry (airlines, manufacturers, airports and air navigation service providers) finally announced its commitment to a global approach to mitigating aviation greenhouse gas emissions, setting the following objectives [25]:
Improvement in fuel efficiency of 1.5% per year from 2009 to 2020 (measures under industry control, linked to operational procedures and basic infrastructure improvements).Carbon-neutral growth at 2020 (fuel CO2 emissions are neutralized).Reduction in CO2 emissions to 50% of 2005 levels by 2050.It was noticeable that this is a very ambitious roadmap where the aviation industry would invest hard and continuously on innovative technologies. Focus on fuel efficiency turned therefore the main goal for the industry, not only driven by fuel prices, but now in the environmental impact. Opportunities continue to exist for addressing aviation emissions through further air traffic management and operational measures, but clearly not sufficient to push the ambitious 50% reduction by 2050. From Fig. (1.5) it is widely perceived by the aviation industry has and must continue to pursue a range of opportunities in new areas [26].
Fig. (1.5)) Emissions reduction roadmap.Advances on new aircraft design technologies as well as the development of “drop-in” bio fuels to replace fossil-based fuels could offer further gains in the future to reach the targets. In addition, a range of market-based measures (MBM), including purchase of offsets from other sectors could further mitigate the climate impact of CO2 emissions from international civil aviation. Based on this industry commitment, to achieve the above high-level goals, the aviation industry, led by the International Air Transport Association (IATA), announced the so-called “Four-pillar Strategy” [26] with the objective to commit the industry stakeholders on such emissions reduction goals, which are resumed in Table (1.4)
In fact, at the Third Aviation and Environment Summit in Geneva (April 2008) a global declaration was signed across the air transport industry (ACI, CANSO, IATA, ICCAIA, Airbus, Boeing, Bombardier, CFM International, EMBRAER, General Electric (GE), Pratt and Whitney (PW), Rolls Royce (RR), ATAG) which committed the industry to a four-pillar strategy based on technological progress, infrastructure enhancements, operational improvements and suitable economic instruments to work towards the vision of zero net carbon emissions.
Following such initiative, at the 36th Session of the International Civil Aviation Organization (ICAO) Assembly in 2009, Contracting States adopted the statement of continuing ICAO policies and practices related to environmental protection. Under this scope, the Group on International Aviation and Climate Change (GIACC) formalized ICAO Council these initiatives from the industry commitment and recommendations, mostly based on the Four Pillars proposal. GIACC was therefore tasked with developing and recommending to the Council an aggressive program of Action on International Aviation and Climate Change and a common strategy to limit or reduce greenhouse gas emissions attributable to international civil aviation. The group has recommended the following potential areas of development and investments to Contracting States defined as follows [27]:
Investment in innovative technologies: Measures in this category may include purchase of new aircraft, retrofitting and upgrade improvements on existing aircraft, innovative designs in aircraft/engines, fuel efficiency standards and alternative fuels. Some of these measures have the potential for very high gains in fuel efficiency/emissions reduction but the costs are likely to be high with a long timeframe for implementation.Development of efficient operations: These measures include minimizing weight, improving load factors, reducing speed, optimizing maintenance schedules, and tailoring aircraft selection to use on routes or services. This area is essentially a matter for aircraft operators who will make their decisions based on commercial factors in their operational scenarios.Investment on effective infrastructure: These measures mean more efficient air traffic management planning, ground operations, terminal operations (departure and arrivals), en-route operations, airspace design and usage, and air navigation capabilities are measures with potential for relatively short to medium-term gains although the scale of potential relative gains is low to medium. In addition, more efficient planning and use of airport capacities, construction of additional runways and enhanced terminal facilities, and clean fuel operated ground support equipment to be implemented in the short to medium-term, but potential emission reduction gains are likely to be low. Increased airport capacity may also encourage increased emissions from aircraft unless appropriate actions are taken to address the emissions.Positive economic measures: These measures include voluntary carbon offsetting, emissions trading schemes (MBM, Market Based Measures), emissions charges and positive economic incentives. Measures in this category have potential for achieving gains in term of reductions in net emissions.Regulatory and others: Measures that include regulatory enforcements on carbon emissions reduction (i.e. aircraft movement caps/slot management) and other initiatives such as enhanced weather forecasting, transparent carbon reporting and education/training programs.Finally, the governmental meeting at ICAO in its Climate Change Resolution 17/2 at the 37th General Assembly in October 2010 set out a fuel efficiency goal to 2% per year (from former 1.5%) and reinforced the carbon-neutral growth to the 2020 goal, which represents a real challenge for the aviation industry. This new goal now considers comprehensive government controlled measures at State Level, such the development of Air Traffic Management programs, mainly focused on Performance Based Navigation (PBN) implementation. In this session, the Assembly also decided to develop an ICAO aircraft certification standard for CO2 emissions, like the existing standards for noise and engine emissions (nitrogen oxides, carbon monoxide, unburned hydrocarbons and smoke). With this ICAO would foster development and use of fuel-efficient technologies and designs by aircraft and engine manufacturers. With ICAO’s engagement, all levels of the industry and States were finally committed with the new emissions reductions targets the focus turned significantly to fuel efficiency programs.
Historically, the development of aviation has always been driven by fuel efficiency (fuel burn per seat), and over the last 50 years the fuel burn (and the carbon emissions) per passenger kilometer has been reduced by over 70%. Fuel is the most important single cost element for airline operators; and the high and strongly volatile oil prices of the last years have even more increased their need for more fuel-efficient aircraft. In addition, an aircraft certification standard limiting carbon emissions is currently being developed under ICAO, which is intended to drive forward the development and encourage the use of more low-emissions aircraft.
The fuel efficiency of civil aviation can be improved by a variety of means including the incorporation into airplanes of innovative technologies, operations techniques and air traffic management. Per IPCC [24], technology developments might offer a 20% improvement in fuel efficiency over 1997 levels. By using data from Ref [28], a graph containing fuel efficient of transport airplanes was elaborated (Fig. 1.6). This graph contains some airplanes due to enter service in the next coming years like the Boeing 737MAX. It is noticeable that over the past 40 years, since the first generation of jet transport aircraft, fuel efficiency has improved considerably, considering the 4th generation of jet engines and airplanes made of CFRP (Carbon-fiber Reinforced Polymer).
The development of new operational procedures and techniques are relevant, but limited to the current technological limitations. Fuel conservation programs are widely se by airlines and improvements are set observed on the magnitude of 5% to 10% at most. This represents a significant improvement with relatively lesser amounts of investments and airlines are constantly encouraged to optimize their operations on Fuel Conservation initiatives.
However, the first of the four pillars (innovative technologies) is considered nowadays as the main potential contributor for achieving the desired ICAO objectives in emission reduction. Its achievement strongly depends on the development and implementation of innovative technologies by aircraft, engine and equipment manufacturers, using higher fidelity aircraft design tools. The principal areas have direct impact on fuel efficiency are envisioned to be airframe (aerodynamics, structures, equipment systems and new configurations) and engines technologies. Nowadays, many individual technologies are under consideration for implementation in future aircraft and engines. For example, a study conducted in 2013 by IATA [26], the German Aerospace Center (DLR) and the Aircraft System and Design Laboratory (ASDL) of the Georgia Institute of Technology launched the Technology Roadmap for Environmentally Sustainable Aviation (TERESA) [27]. The objective was to quantify the expected benefits of the implementation of individual technologies in an operational framework, considering a typical world fleet. Current NASA's readiness levels [29] are considered to estimate the availability of each proposed technology. Tables (1.5) and 1.6) contain the list of proposed technological improvements (airframe and engines related) and their associated fuel efficiency reduction. It is noticeable that up to 30% reduction on 2005 levels on fuel efficiency may be achievable after 2020, most of them related to engines technologies.
Fig. (1.6)) Fuel efficiency gain since the early jet age [28].Finally, it is valuable to mention that environmental benefits of innovative technologies (through a better fuel efficiency and thus lower carbon emissions) will become effective through airline fleet modernization and, to a minor degree, retrofits to in-service aircraft. There is an underlying challenge to select the appropriate technologies as this selection are driven by uncertain factors such as their current development status, benefits, risk and their research and development costs.
In summary, aircraft design techniques under the environmental perspective became significantly relevant throughout the last decade, driven by the industry commitment on emissions reductions set by ICAO goals. The inclusion of fuel efficiency focus on the design framework is a key parameter on the next aircraft generations.
AERONAUTICAL INDUSTRY FACING THE ENVIRONMENTAL CHALLENGES
The Clean Sky Project
Within Europe, public and governmental positions increasingly point towards a desire to regulate the climate impacts caused by aircraft. The report by the UK Royal Commission on Environmental Protection (RCEP) noted that without regulatory control, the rapid growth of air transport would proceed in fundamental contradiction to the British government’s stated goal of sustainable development [30]. Europeans have a great concern with sustainable growth. The UK position on climate regulation is shared with many others European countries. In 2001, the report of the Group of Personalities “European Aeronautics: A vision for 2020” pioneered an integrated vision of the European Air Transport System for the next 20 years. It established, as its top-level objectives, the need to respond to society needs and to secure European leadership in the aeronautics, encompassing significant reductions in pollution and noise emission levels. The report also recommended the creation of the Advisory Council for Aeronautics Research in Europe (ACARE).
ACARE is the first European technology platform, which produced a set of strategic research objectives (SRA1) in 2002 and a second updated edition (SRA-2) in 2004. SRA-1 is built around five challenges for technology development. It has been used as a reference guide for several national and institutional bodies for establishing their research programs. SRA-2 describes six high-level target concepts (HLTCs) and their associated technologies with respect to different socio-economic scenario. Each HLTC stresses an aspect of the Air Transport System. The Clean Sky project was created to address of ACARE HLTCs. In fact, Clean Sky is one of the most ambitious aeronautical research program ever launched in Europe. Its mission is to develop breakthrough technologies to reduce environmental impacts of aircraft and aerial vehicles developing aircraft that are quieter and more fuel-efficient. CS1 was created as a public-private partnership. Clean Sky 1 (CS1) started in 2008. Clean Sky 2 (CS2) will enable a natural continuation to the progress achieved in the first Clean Sky Program launched under the EU’s 7th Framework Program for Research and Technological Development (FP7), which will end in 2017. CS2 extends the public-private partnership to 2024, and expands it to encompass large-scale high-bypass propulsion, hybrid laminar flow control, integrated cabin systems and structures, and next-generation cockpits. The program will fly both compound and tiltrotor high-speed rotorcraft, and show technologies for a 90-seat turboprop and a 19-seat transport.
The Clean Sky project intends to investigate key aircraft technologies:
Large Passenger Aircraft: This Clean Sky component includes new propulsion systems and their integration in future aircraft; advanced fuselage and aircraft systems concepts for possible next generation cabin architectures; and innovative cockpits. Large-scale demonstrators, test rigs and flight test demonstration are planned activities.
The Green Regional Aircraft (GRA): The future green regional aircraft features considerably less empty weight, more energy efficiency, lower drag, and higher level of operative performance. All this must be in pace with reduced pollutant emissions and lower noise signature.
The Fast Rotorcraft initiative: consists of two separate demonstrators, the NextGenCTR tilt-rotor and the LifeRCraft compound helicopter. These two fast rotorcraft concepts aim to deliver superior vehicle productivity and performance.
Airframe: Investigation of advanced and innovative airframe structures like a more efficient wing with natural laminar flow, optimized control surfaces, control systems and embedded systems highly integrated in metallic and advanced composites structures. It will also test novel engine integration strategies and investigate innovative fuselage structures.
Engines: Clean Sky will build on the work done in the Sustainable and Green Engines activity to validate more radical engine architectures.
Systems and equipment are crucial for aircraft operation, flight optimization and air transport safety. Thus, the Clean Sky project will investigate innovative aircraft architectures, such as more electrical aircraft and bleed-less engines rely on new system technologies to improve global aircraft performance.
The Small Air transport represents the research and technology for small aircraft in the 19-passenger category or for freight transport. This component of Clean sky project aims to develop, validate and integrate key technologies on demonstrators that can revitalize an important segment of the aeronautics sector that can bring key new mobility solutions.
Eco-Design will coordinate research geared towards high eco-compliance in air vehicles over their product life. It will heighten the stewardship in intelligent Re-use, Recycling and advanced services. This activity is critical to obtain excellence in materials, processes and resources; supporting the manufacturing base and supply chain competitiveness and sustainability.
The ERA initiative
The United States has also established a policy for improvement of airplanes considering environmental aspects. Created in 2009, as part of NASA's Aeronautics Research Mission Directorate's Integrated Systems Research Program, the Environmentally Responsible Aviation (ERA) Project explores and documents the feasibility, benefits and technical risk of vehicle concepts and enabling technologies to reduce aviation’s impact on the environment. ERAs goals include slashing aircraft level fuel burn by 50%, drag by 8%, weight by 10%, emissions by at least 70% and noise by up to 42 EPNdB. The main grounds for starting ERA are [31]:
Fuel Efficiency
In 2008, North American major carriers burned 19.6 billion gallons of jet fuel. Department of Defense alone burned 4.6 billion gallons. Considering an average price of US $3.00/gallon, fuel cost amounted US$ 73 billion. Even small reductions in fuel burn would result in significant lesser money spending.Emissions
Majority of U.S. airports are in non-attainment areas that do not meet Environment Protection Agency (EPA) local air quality standards for particulate matter and ozone.The fuel consumed by U.S. commercial carriers and Department of Defense releases more y than 250 million tons of CO2 into the atmosphere each year.Noise
Aircraft noise continues to be regarded as the most significant hindrance to airspace capacity growth.FAA made several attempts to reconfigure New York airspace, which resulted in 14 lawsuits by 2010.Since 1980, FAA has invested over US$ 5 billion in airport noise reduction programs.Market outlook from airplane manufacturers and forecasts from U.S. governmental agencies predict that the air transportation system will expand significantly within the next decades. Considering that such an expansion will bring negative environmental impacts, it makes imperative neutralize or reduce them. This is the goal of the ERA Project and its focused research. The project is organized to [31]:
Mature promising technology and advanced aircraft configurations that meet mid-term goals for community noise, fuel burn and nitrogen oxides (NOx) emissions as described in the National Aeronautics Research and Development Plan and;determine the potential impact of these advanced aircraft designs and technologies if successfully implemented into the air transportation system.To mature technologies and study vehicle concepts ERA Project is working on technologies in these research areas, called integrated technology demonstrations (ITC):
Innovate Flow Control Concepts for Drag Reduction.Advance Composites for Weight Reduction.Advance UHB Engine Designs for Specific Fuel Consumption and Noise Reduction.Advance Combustor Designs for Oxides of Nitrogen Reduction.Advance Airframe and Engine Integration Concepts for Community Noise and Fuel Burn Reduction.The ERA Project is comprised of three subprojects: Airframe Technology, Propulsion Technology and Vehicle Systems Integration. Work within the project is coordinated with research performed by other programs within NASA's Aeronautics Research Mission Directorate as well as other federal government agencies. NASA has also put mechanisms in place to engage academia and industry, including working groups and technical interchange meetings; Space Act Agreements for cooperative partnerships; and the NASA Research Announcement process that provides for full and open competition for the best and most promising research ideas. The ERA Project disseminates all its research results to the widest practical extent. Teams from The Boeing Company in Huntington Beach, Calif., Lockheed Martin in Palmdale, Calif., and Northrop Grumman in El Segundo, Calif., have spent time and effort studying how to meet NASA goals to develop technology to meet ERA’a targets (Fig. 1.7).
A modified 757 is being employed as technology demonstrator by Boeing to investigate AFC. The airplane is called ecoDemonstrator. The airplane was fitted with devices that will blow jets of air on the vertical tail (VT) and the other involves non-stick coatings to help repel bugs from the leading edge of wings.
The first technology that was tested is called the Active Flow Control Enhanced Vertical Tail Flight Experiment. NASA worked with Boeing to install 31 tiny jets called sweeping jet actuators that can manipulate, on demand, the air that flows over the ecoDemonstrator 757's vertical tail and rudder surfaces [32]. An aircraft’s vertical tail is primarily used to add stability and directional control during takeoff and landing, especially in the event of an engine failure. But when the aircraft is cruising at altitude the same large, heavy tail is less utilized. If the size of the VT the size of the vertical tail by using the sweeping jets to generate the same side force during takeoff and landing that a larger tail does. That would reduce the weight and drag of the airplane and decrease its fuel consumption.
Fig. (1.7)) Unusual configurations proposed by Boeing (Blended wing body at right), Lockheed-Martin (joined wings twinjet), and Northrop-Grumman for the ERA Project (Illustration: Courtesy NASA).
