Future Commercial Aviation Trends S. Tsach*, A. Tatievsky† and L. London‡ Israel Aerospace Industries (IAI), Ben Gurion Intl. Airport, 70100, Israel In December 2003, the world celebrated a century of powered flight. Leaps in technological progress through the years have led aviation from small, fragile wooden biplanes that barely took off the ground, to modern carbon fiber, transonic jet airliners. New advanced subsystems and structural materials, design concepts, manufacturing and assembly methodologies – all allow further improvement in aircraft efficiency and reduction in costs. It's hard to foresee future trends of aviation, but careful analysis of the sum of the trends in each aspect of civil aircraft development, can allow a glimpse into the future of commercial aviation. I. Introduction In 1903 the world witnessed the first flight of a powered aircraft – the Wright brothers' Flyer I. The fragile biplane aircraft, made of wood and fabric, leaped for a short distance, rising barely several feet above the ground. This leap signalized the start of the aerospace era – a period in which the human race finally was able to conquer the sky. Once out, the progress of aviation, fueled by economical, demographical and technological development galloped forward with full steam. The Wright brothers' powered flyers were soon to be replaced by much more robust and capable biplane aircraft, used for mail and packages deliveries, which later played an operational role over the battlefields of the WWI. The early wooden design was practical for the low-and-slow biplanes, but soon aircraft structures required a new, stronger and more lightweight materials and aluminum alloy structures became more and more common in aircraft design. Advances in internal combustion engines development provided more power than ever, while reducing weight. Concurrent with the development of the military aircraft, passenger aircraft started to appear in the mid 1910's. Metallic aircraft design offered more comfortable closed cabin with additional systems, which were incorporated for smoother and more comfortable flight. Over the next decades the world witnessed tremendous progress in the area of aviation. Piston engines for commercial aircraft were gradually replaced by jet and turboprop engines in the mid-century. Increased altitude and flight speed led to the creation of insulated, pressurized cabins, with the all needed amenities for prolonged flight. Material and structural concepts had gradually matured, leading to safer and more reliable airframes, allowing lower maintenance costs and longer lifecycles. Advancing design, analysis and manufacturing techniques produced more efficient aerodynamic design. As aviation became more reliable and accessible for larger portions of the population, the aircraft became a widespread and common sight. Modern commercial airliners are state-of-the-art machines, incorporating the latest achievements of science and technology. They usually use advanced, high bypass-ratio, efficient turbofan (or, in some cases, turboprop) engines, made in sophisticated manufacturing processes from advanced aluminum alloys and carbon fiber materials, and incorporate mechanical and electronic equipment, needed to transport several hundred passengers and crew comfortably, at nearly *
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the speed of sound. The question one might ask is what is to be expected next? Will the airplane of the future resemble the current aircraft or maybe some other radical ideas will lead aviation in a new path. Careful examination of historical trends, may suggest that every direction of development have had a history of slow and gradual maturing of technologies and step-by-step evolution. It may seem that aircraft development had progressed in giant leaps from early biplanes to modern jets, but the way of progress has always had a solid scientific and experimental base. Thus, it can be assumed that future of aviation will lead to comply with the future stricter environmental requirements regulations, and provide more efficient and more comfortable flight than ever, using the concepts and technologies being developed and evaluated today.
Figure 1. Advanced in aerostructure materials over the history of aviation [1]
II. Future Market Trends The future commercial aviation market can be summarized shortly as continuous and constant growth in all segments and sizes. Some segments may grow faster than others, some will loose their relative weight, but when value and quantities are concerned, all the numbers are on the rise. An important trend which already visible today, and which is expected to become even more prominent in the future, is the gradual shift of commercial aviation centers from developed countries like the United States and Europe to the emerging world economies in Asia, mainly to China and to a lesser extent - India. This growth shows that aviation's environmental impact (2% of the total man-made CO2 emissions nowadays), will significantly increase in the next decades, considering the fact that air travel expected to grow for about 5% annually for the next 20 years, more than doubling itself.
Figure 2. Air travel is expected to continue its historic trend, with average annual growth of 4.8% for the next 20 years, doubling in size in the next 15 years (Global Market Forecast 2011-2030, Airbus) [2]
Figure 3. Given current trends, emerging economies are expected further increase their share in global air travel (Global Market Forecast 2011-2030, Airbus) [2]
III. Future Environmental Requirements Goals Aviation has a vital part in modern society and as such, is subject to both local and international policies and regulation, supervising its safety and its environmental impact. Aircraft use non-renewable and polluting fossil fuels, as well as a source of noise pollution and are therefore subject of various standards and regulation by both local and international authorities. Due to the growing detrimental environmental impact of modern industrialized society, "green" considerations have become highly important. This is perhaps the most
important driving factor for the development trend of the future aircraft – lowering global atmospheric pollution and improving the life quality of the residents who live in proximity to airports, by lowering aircraft induced noise. The added benefit of such improvements could be the reduction in fuel consumption and as a result – the reduction the operational costs and oil dependence. More radical concepts for the future, suggest the use of alternative fuels and innovative propulsion concepts, like electric or hybrid propulsion. Additional improvement might come from new and improved aerodynamic configurations, more sophisticated onboard systems and air traffic control management. One of the main international institutions, constantly researching and planning for the technologies of tomorrow, is NASA. As part of NASA's Fundamental Aeronautics Program, the agency began in 2007 an extensive study, divided into three phases, or "generations", of the Subsonic Fixed Wing (SFW) future aircraft. The program's goals are summarized in table below (Fig. 4).
Figure 4. Subsonic Fixed Wing Project requirements, NASA Fundamental Aeronautics Program, 2011 [3,4]
NASA's activities in the field on promoting future aviation are complemented with the American Federal Aviation Authority's (FAA) CLEEN (Continuous Lower Energy, Emissions, and Noise) program. It is intended for investment and research of the technologies needed for reducing aviation noise and pollution in the near future. Its goals are coordinated with NASA's N+1 goals. NASA's and FAA's goals suggest that commercial aviation would have to undergo radical changes to comply with future regulation. It will require a considerable reduction of the noise level, much lower exhaust pollution and fuel use, and a drastic improvement in take-off and landing performance (ESTOL – Extremely Short Take-Off and Landing). These steps are necessary in order to reduce commercial aviation's footprint, despite the expected growth in global air travel in the foreseeable future. Europe launched its own future aviation environmental program in 2008, the Clean Sky JTI (Joint Technology Initiative). It is aimed to advance and coordinate European aircraft manufacturers' efforts to comply with the EU's ACARE (Advisory Council for Aeronautics Research in Europe) environmental goals, by reducing aviation pollution and fuel consumption. Its main goals are reducing CO2 emissions by 50%, NOx by 80% and noise by 50%, by the year 2020. The full figures can be seen in Fig. 5 below:
Figure 5. The goals of the Clean Sky program by ACARE for the year 2020 (compared to 2000) [5]
The Clean Sky program goals are to be met through advances to various fields of research (Fig. 6). The program's goal is to mature emerging technologies to reach a sufficient technology readiness level (TRL) required for implementing them in commercial aircraft, as well as fundamental scientific research, with the aid of universities and research institutes. Future development of commercial aviation is fully directed for more environmentally friendly and efficient flight. The ambitious future goals facing aircraft manufacturers are the catalyst for further development of advanced technologies. Summation of the contribution in each of the fields of development, may lead aerospace to this future path. In the following chapter we will try to give more detailed prospective of some of the most promising directions in each of the major technological fields, that we believe can make these environmental goals become a reality. Additionally, some other prospective directions, like supersonic flight, will be discussed briefly.
Figure 6. Contributing factors for achieving the demanding goals of the European Clean Sky initiative [5]
IV. Future Technologies Future technologies are the gateway to the future of aviation. In this chapter we will briefly review some of the most promising directions in the fields of propulsion, materials and structure, aerodynamics, systems and avionics. A. Propulsion One of the most promising directions for improving aircraft performance is its propulsion system. Most of today's commercial aircraft use turbofan engines, with less common use of turboprops, usually in smaller aircraft. In the near future, most research will on improvements to existing powerplants and usage of alternative fuels, but eventually new engine concepts will take their place, like new hybrid and electrical propulsion systems. Proposed jet engine improvements range from extended use of advanced materials, improved impellers and combustors for higher combustion temperatures, resulting in more efficient combustion, to novel engine concepts. These concepts include mainly ultra high bypass ratio engines, like the Geared Turbofan (GTF), developed by Pratt & Whitney and NASA, and the Open-Rotor engine, also known as Unducted Fan (UDF), developed by General Electric and NASA. Geared Turbofan engines use a reduction gear between the fan and the compressor, allowing each of them to revolve at its respective optimal speed, unlike a regular turbofan engine. The optimized fan and core operation allows a reasonable engine and core size and offers a significant improvement in fuel burn efficiency, noise and emissions. Open-Rotor engines offer a different approach to achieving improved engine performance. The uniquely shaped, high-speed propellers are specially designed to allow the aircraft to reach higher speeds, approaching those of turbofan propelled aircraft, much faster than aircraft equipped with turboprop engines. While the counter-rotating propellers increase fuel efficiency, they also increase the noise levels. Thus, a lot of effort is put in to decrease noise while maintaining engine efficiency.
Figure 7. Open Rotor engines offer better fuel performance, whereas Geared Turbofan engines offer lower noise levels [6]
Other propulsion concepts include hybrid and electric engines, which are already in use in some general aviation aircraft and are envisioned to power even large airliners, in the class of the Boeing 737. Recent studies, like the Boeing/NASA SUGAR Volt, have shown great potential for gas-generator (jet engine) / battery-powered electric engine hybrid propulsion.
Another concept that was studied recently is EADS' all-electric aircraft concept, the Voltair. Both hybrid and electric propulsion concepts require major advanced in battery energy density to become commercially viable, such as the Lithium-Air (Li-Air) battery concept, with a theoretical energy density that rivals that of gasoline.
Figure 8. Lithium-Air batteries would offer energy density as high as gasoline [7]
Another area of great interest in future propulsion, is the use of alternative fuel sources, which have the potential for reducing aircraft emissions of as well as reduce aviation dependency on foreign fuel. These alternative fuels include the following three types. Fischer–Tropsch synthesis produces synthetic diesel and jet fuel from coal and natural gas, diversifying fossil fuel sources and reducing dependence on oil. Biomass fuel can reduce dependency on fossil fuels in favor of renewable fuel sources, such as plants and algae. Finally, liquid hydrogen (LH2) fuel, one of the most energetic fuel types, used today mostly in space applications, such as satellite launchers, could propel future supersonic or hypersonic commercial aircraft. B. Materials and Structures Since the 1980's, civil aviation has rapidly adopted the use of composite materials, with general aviation (GA) aircraft approaching 100 percent composite structures. Commercial aviation adopted composite materials slower than military and general aviation, due to a more conservative approach.
Figure 9. Steep increase in structural composite material use in commercial aircraft since the 1980's
[8]
Composite materials offer higher strength-to-weight ratios than most aviation graded materials, such as aluminum, thus reducing weight and consequently fuel consumption. Composite materials also allow a significant part count reduction, thus lowering manufacturing and assembly complexity and costs. For example, some general aviation aircraft already feature a single-part fuselage. Future advanced aero-structures material development will introduce such exotic materials as carbon nanotubes, which will offer unparalleled strength along with tailored thermal and electrical properties.
Figure 10. Potential application of nano-composites in an aircraft [9]
Other advanced materials already entering into service include aluminum-lithium (Al-Li) alloys, which offer improved strength-to-weight ratio, lower costs and better corrosion resistance, compared to conventional aluminum alloys. Recent technological breakthrough in aerostructures, already introduced to some extent in modern aircraft, include "smart structures". These include Structural Health Monitoring (SHM) systems embedded in the aircraft's structure, which would alert the pilot and ground crew of any structural cracks and reduce the need for periodical preventive maintenance. Further improvements might include Self Healing Structures – a vascular-like system of healing resin in sandwich structures, which would instantly repair structural cracks. These systems are expected to become an integral part of future commercial aircraft. Additional "smart structures" concepts include morphing and adaptive materials that would optimize the aircraft's geometry to changing flight conditions in real-time and resist dents and impacts. These structures will mainly employ piezoelectric and shape-memory alloys. C. Aerodynamics Aerodynamics research deals with drag reduction for improved fuel consumption, increased lift for superior takeoff and landing performance, and noise reduction. Several methods are being evaluated for application in future aircraft. Among the leading research directions for more efficient aerodynamic configurations are lifting bodies and blended wing-body configuration (BWB). These configurations play a significant role in improving performance by aerodynamically shaping the fuselage to create lift, thus improving lift-to-drag ratio, and improving fuel consumption. Another concept under evaluation is that of vertical tail Active Flow Control (AFC) actuators, which will enable on-demand increased rudder efficiency, allowing a reduction in tail size and
thus, in structural weight and friction drag. Aft fuselage AFC could reduce pressure drag as well. Friction drag is a major contributor to the total aircraft drag. Many of the current aerodynamic research programs include laminar flow maintenance. Laminar flow can significantly reduce friction drag, improving fuel consumption. Whereas Natural Laminar Flow (NLF), which relies on shaping and surface finish can be used in small aircraft with low swept wing, in larger aircraft that usually fly in higher Reynolds numbers and employ highly swept wings, suction has to be applied. Types of laminar flow which require suction include Laminar Flow Control (LFC) and Hybrid Laminar Flow Control (HLFC). Whereas all laminar flow methods offer a significant improvement in skin friction drag, they also take a toll in the form of increased weight and cost, due to constrains they impose on the aircraft geometry, and high requirements for surface finish. Special coatings and finishes are under development to maintain the required surface finish even in icing conditions and insects impact.
Figure 11. Laminar flow improves fuel consumption drastically [10]
Boeing proposed the trailing edge variable camber method for its future aircraft, which allows loads distribution optimization and cruise drag reduction by tailoring the trailing edge camber to flight conditions. D. Avionics and Systems Avionics and systems are the brains and guts of the modern aircraft. Avionics include pilot-machine interface and computerized control of the aircraft, whereas systems allow aircraft operation and keep environmental control for its occupants. Future improvements would include more electric systems, such as flight control actuators, landing gear and landing gear brakes, Environmental Control System (ECS), anti-icing systems, etc. Reduction in the engine air bleed requirements will also reduce the required engine thrust, turbine temperature and jet velocity, resulting in reduced engine noise and emissions.
Figure 12. All-electric systems aircraft and its benefits
Future avionics would utilize miniaturized, light-weight computers and employ touch-screen interface. Further improvements in artificial intelligence would ultimately make the pilot redundant.
Figure 13. Projected development of computing capacity through 2100 showing Million Instructions Per Second (MIPS) and the development of inter-process communications (IPC) as compared to various animals [11]
Using advanced reliable and affordable avionics and flight control systems a new generation of aircraft will eventually emerge – the autonomous aircraft. The autonomous aircraft's roots are planted in today's Unmanned Aerial Vehicles (UAV) which is mainly used today for military applications. These UAV are gaining more and more autonomous capabilities, from automatic take-off and landing to autonomous aerial refueling and in the future are expected to perform complex military missions without remote operator interference. The removal of the human element, combined with advanced computers and sensor suites, would lead to improved flight safety and reduction in operating costs. Although the technology maturity level for autonomous commercial aircraft is near, the greatest challenges to overcome will be psychological and regulatory. To address these intermediary issues, a pilot might remain in
the airplane as an operator or supervisor in case of an emergency. Another solution might be the gradual integration of autonomous aircraft into the national airspace (NAS), first as cargo freighters, leading to small jets, personal aircraft and business jets, and finally – large regional jet and airliners. A concept for an autonomous commercial cargo aircraft studied by IAI is depicted in figure 14.
Figure 14. IAI Commercial Autonomous Air Cargo Vehicle concept
V. Future Configurations A. Subsonic Airliners Since the dawn of commercial aviation, the "tube-and-wing" aircraft configurations have ruled the sky. Although significant improvements in performance had been achieved due to advances in aerodynamics, propulsion and structural technologies, the basic shape of the airliner remains relatively unchanged.
First delivery: 1970
First delivery: 1976
First delivery: 1989
First delivery: 2012 (planned)
Figure 15. Boeing 747 airliner configurations, basic shape nearly unchanged after 40 years [12]
Whereas in the near future conventional configurations are expected to retain their dominance, a new generation of radical designs and innovative configurations is necessary to comply with stricter environmental regulation, increasing oil prices and overcrowded airports due to continuing growth in commercial air travel. Both American and European aircraft manufacturers, research institutes and governmental agencies are conducting studies on futuristic designs for the airliner of tomorrow.
EU “Clean Sky” Concepts
NASA/Bowing
NAAS / Boeing
NASA/MIT
Airbus
NASA / Lockheed Martin
Future Airliner Study
NASA / Northrop Grumman
EADS
Figure 16. Different future airliner concepts
B. Supersonic Flight Supersonic aircraft is a separate field of future development, since it is performanceoriented and can't be categorized as an efficient or environmentally friendly mean of transportation. The golden age of supersonic commercial air travel began in the late 1960's and continued through the 1980's, with the development and later introduction of two competing supersonic airliner projects – the French-British Concord and the Soviet Tu-144. Both were neither efficient nor affordable, and despite widespread publicity didn't gain much popularity. Despite its drawbacks, a small number of Concord aircraft remained operational until the early 2000's. Since then, the focus of developing supersonic aircraft shifted towards much smaller business jets, with a variety of different concepts and designs. The main challenges of supersonic aircraft are the strict FAA and ICAO regulations about supersonic boom over populated areas, lack of suitable civil engines and the overall technical complexity of such an endeavor. The problem of silencing of the supersonic boom is a major challenge which will have to be dealt with, along with general high noise and emissions related to supersonic flight. It remains the main challenge for the developers of future supersonic business jets. On the other hand, the market for supersonic jet seems favorable, and though it is much more expensive than conventional subsonic flight, it is appealing to many high wealth individuals, for whom time equals a lot of money. Although there are somewhat hesitant attempts by leading aerospace companies for commercial supersonic aircraft development, as well as research institutes like NASA and JAXA, there is only one small company active in this field (Aerion). Nevertheless, it can be foreseen that with further research and development of suitable effective technologies, supersonic aircraft will become a reality as well and even mature enough for the creation of a truly efficient supersonic airliner.
Figure 17. Design goals by NASA for the next steps of supersonic aircraft development [13]
VI. IAI Future Commercial Aviation Concepts IAI is one of a few members of international aircraft manufacturers, owning full capabilities of developing, manufacturing and certifying commercial aircraft. Consequently, IAI is investing in research and development of promising technologies and new concepts of the prominent future directions in aviation. Markets and pivotal technologies are analyzed constantly, sifting the most promising directions to follow, be it in the business core of IAI products or even beyond. The most promising ideas are further analyzed and studied, with final proposal for the potential design points for each product segment. Each concept is a candidate for full scale development, dependent on the best timing for its introduction. Several such promising directions studied recently include; very light and personal jet general aviation aircraft, supersonic business jets, ESTOL (Extremely Short Take-Off and Landing) regional aircraft, next-generation propulsion for regional aircraft, cargo airships and many more. These directions fully comply with the market's needs and trends, allowing best implementations of IAI's unique capabilities and allowing it to offer the best competitive solution. Future requirements and goals, as being charted by US and EU regulatory authorities' future aviation studies, are fully taken into account, with its nearest implementation in IAI product portfolio, as one of the main objectives for its future development. IAI is a leading world-class aerospace corporation and is already at work creating the world of tomorrow's aviation.
Figure 18. Some of the concepts of IAI future directions in the regional aviation segment (depicted with ultra-high bypass ratio turbofan, open rotor engine or electric propulsion configurations, from left to right)
VII. Conclusion The amazing technological development from the basic Flyer I to ultra-sophisticated Boeing 787, in only a century, allows us to only wonder of what the future directions civil aviation might take. On the other hand, from the more rational point of view, future trends of aviation can be tracked to some extent, by understanding the technologies development trends and the basic goals of this mean of transportation. The use of civil aviation will grow and introduce an unprecedented number of aircraft, several times their current number, with the accompanied ease and access to this medium of long distance travel. With such growth, there is no doubt that environmental issues would be the major catalyst for civil aviation development. This will spur related technologies development, and influence aircraft configuration and implementation principles. Aircraft configurations will become more efficient, both environmentally friendly and more capable. Propulsion technology will further push the boundaries of turbofan performance, the main directions being Geared Turbofan and Open Rotor concepts. In the more distant future we might even see other, more exotic types of propulsion. Aircraft structure will be lighter yet stronger, with higher content of carbon fiber and other advanced materials, including the use of carbon nanotubes super-strong materials in the more distant future. The structure itself will become "smarter", with self-curing and health-monitoring features. Life supporting and aircraft operational systems will continue to become more efficient, with transition toward more electric aircraft. Avionics will be based on smaller and more sophisticated computers, with easier pilot-machine interface, eventually transforming the commercial aircraft to pilot-less and autonomous. Technology, therefore, is the cornerstone of building the future aviation, thus we can anticipate its future development, based on our best knowledge and experience. Conservatism that is common in the business of commercial aviation allows us to assume that recognizable tube and wing designs will stay with us at least in the near future, with small yet constant increments in its performance. Eventually, though, new requirements and environmental regulation along with changing market conditions will lead to innovative concepts that will succeed them. There is no doubt; we are on the footsteps of a new world of aviation.
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