With no sign of our appetite for air travel diminishing, we need to create quieter aircraft that are easier to live with. In fact, while those living near airports may beg to differ, data included in the Airports Commission report into a new runway for London shows a very significant reduction in aircraft noise over several decades. The noisiness of an individual aircraft at departure and approach is described by its Effective Perceived Noise Level (EPNL). This is measured when the aircraft enters service, and is used to track noise improvements between successive generations of aircraft. As this Airports Commission report chart shows, EPNL has fallen since modern turbojet and turbofan engines were first introduced – roughly a halving of radiated acoustic energy per decade. This is a remarkable technical achievement – a 95% reduction in the sound power generated by aircraft jet engines since their introduction. However, over the same period there has been an explosion in air travel and the number of flights and passengers has risen exponentially. The issue then is not whether aircraft are getting quieter, but whether they are doing so sufficiently quickly to compensate for the fact that there’s so many more of them. The answer also depends upon how quickly older, noisier aircraft are retired from service. In the UK, the net effect has been positive – aircraft are becoming quieter at a rate that outweighs the increase in traffic and the Airports Commission expects this trend to continue. When air is too loud Aircraft noise is generated by turbulent flows of air over and around surfaces. This includes air going into and out of the engine, and air flowing around the airframe – fuselage, wings and other aerodynamic surfaces such as flaps, slats and landing gear. What has brought about the continuing reductions in aircraft noise since the 1970s? The largest factor driving down aircraft noise has been a move towards higher and higher “bypass ratios” – originally sought after for greater engine efficiency, but which fortunately generate lower noise too. The bypass ratio is the proportion of the air which enters the engine inlet but bypasses the turbojet and exits at low speed, in comparison to the hot, high-speed jet coming from the engine core. This ratio has risen – all the air entering turbojet engines of the earliest airliners passed through the engine. In the turbofan designs of the 1960s and early 1970s this fell to around a third, while the engines powering large modern aircraft today such as the Airbus A380, Boeing 787 and Airbus A350 draw only a tenth of the air into the engine core. These engines have larger, more slowly-rotating fans with fewer blades – all features that reduce the aircraft’s noise profile. Quieter engines This process still has some way to run. Turbofan engines in smaller aircraft have lower bypass ratios than those in larger, wide-bodied aircraft, but development of new engines is underway for the venerable Airbus A320 and Boeing 737 families, and newer jets such as the Bombardier CSeries and the Mitsubishi MRJ. Such narrow-bodied jets constitute 70% of the commercial fleet, so this will have a profound impact on noise levels as they replace older jets. Better engines for larger aircraft are coming too, based on the same turbofan technology. Using a gearbox to uncouple the fan and the low pressure turbine will improve performance and reduce noise. A market leader here is the Pratt and Whitney PW1000G geared turbofan developed over the last decade and due to enter service, is anticipated to lead to larger, quieter and more fuel-efficient engines with bypass ratios approaching 15:1. Other techniques to quieten engines include acoustic liners on the inner walls of the intake and bypass ducts which absorb acoustic energy, and improved aerodynamic fan design and outlet vanes. Both of these have been made possible by the power of modern computers to accurately simulate airflow dynamics – there is scope for further advances in this area. Quieter airframes Reducing airframe noise is more challenging. The use of flaps and slats and deploying of landing gear at approach are necessary to slow the aircraft while maintaining lift, but they all create additional noise. It’s hard to have one without the other. Perhaps the most effective means to ensure both will come from new, improved aerodynamic aircraft designs that can provide better low-speed performance without sacrificing fuel efficiency at cruise. In the longer term, after 2050, completely new aircraft geometries that use blended wing designs, and even morphing geometry – aircraft that change shape – will potentially lead to major reductions in airframe noise, greater efficiency and improved environmental impact. All just as well, as by then there’ll be many more people still wishing to fly.

  _This article is a part of The Conversation’s series on unique courses. For other articles in this series, read here and here. _ Today’s college students may benefit from an exciting array of subjects to study. But they seem to miss the most important education of all: how to relate their specialization to others in an increasingly interconnected world. The National Academy of Engineering has categorically stated that today’s engineers need to be more than individuals who simply “like math and science.” They must be “creative problem-solvers” who help “shape our future” by improving our “health, happiness, and safety.” And in 2001, the engineering accreditation body ABET added a new criterion so as to ensure that students get “the broad education necessary to understand the impact of engineering solutions in a global, economic, environmental, and societal context.” The point is that the connections between humanities and science have been lost in today’s separation of disciplines. Indeed, a recent report by the American Academy of Arts and Sciences discovered that humanities and STEM (Science, Technology, Engineering and Mathematics) training majors largely dwell in different silos. So, where and how did we lose our way? And how can educators and institutions change things? Separation of disciplines The founders of the National Endowment for the Humanities (NEH) were well aware of the critical nature of this interdependence. When the NEH and the National Science Foundation (NSF) were established in the 1950s and ‘60s, the NEH founders wrote: If the interdependence of science and the humanities were more generally understood, men would be more likely to become masters of their technology and not its unthinking servants. These founders, hailing from leading universities as well as the US Atomic Energy Commission, IBM Corp and New York Life Insurance, knew that connecting the humanities and sciences helps us make informed judgments about our control of nature, ourselves and our destiny. But, since the 1980s, political rhetoric has emphasized the need for less humanities and more STEM education. STEM is painted as a more profitable investment, in terms of job creation and research dollars generated. A notable example is the Obama administration’s “Race to the Top” initiative, which both isolates and prioritizes the STEM disciplines from the humanities, arts and social sciences. This rhetoric is also evident in the creation of separate political education organizations such as the bipartisan STEM Education Caucus founded several years ago by congressional representatives to strengthen STEM education from kindergarten to the workforce. This separation of disciplines actually hurts education, and it also hurts our ability to innovate and solve big problems. Connecting STEM with humanities doesn’t just provide the well-rounded education today’s employers want. As the American Academy of Arts and Science’s 2013 “The Heart of the Matter” report observes, connecting these fields is necessary to solve the world’s biggest problems such as “the provision of clean air and water, food, health, energy, universal education, human rights, and the assurance of physical safety.” So, separating and prioritizing STEM from humanities ignores the fact that we live in a complex social and cultural world. And many different disciplines must combine to address this world’s needs and challenges. Bringing the disciplines together To address this gap, four years ago the faculty from materials engineering and liberal arts at the University of Florida began working with the Materials Research Society. We wanted to put together a new course on “materials.” Why did we choose materials? Because everything is made of them, every discipline studies them and they are tangible (quite literally) to the average freshman. After all, grade school students still learn about the Stone, Bronze, and Iron ages. The Industrial and Information revolutions revolved around new uses for steel, aluminum and silicon. The human past has been shaped by harnessing and consuming materials and energy. Materials will be important for our collective future as well. So, we thought, this is the future for which we should be preparing students. And thus our course, The Impact of Materials on Society (IMOS), was born. Taught by a team of nine faculty from engineering, humanities and social sciences, the course explores the close connection between the “stuff” in our lives and our experiences as social beings. Students discuss how materials benefit global trade and communication but also risk resource exploitation and political conflict. For example, we depend upon rare earths for our cellphones, iPads and wind farms, but accessing these rare earths from limited sources is not sustainable. So, some of the questions that the course raises are: what materials do we depend upon in our daily lives? Does this dependence have social consequences? What social relationships form around the production and use of these materials? And how do our current uses of materials affect our ability to discover new uses for them? Students also discuss the ethical and social aspects of using certain materials. college.library, CC BY Students are also asked to consider how our values shape our willingness to adopt new technologies. For example, Earl Tupper may have invented Tupperware, but it was Brownie Wise and her home parties with other women who first made his polymer famous! Each week covers a different material (eg, clay, glass, gold, plastic), its scientific properties, demonstrations, and its past and present impacts. Working together in multidisciplinary groups, students then contemplate the development of future materials. These include flexible electronic materials that can be used to create wearable sensors that can transmit important information, such as body hydration levels during athletic training. New polymer (plastic) materials  made from renewable sources instead of petroleum may have fewer health risks and are more sustainable than today’s plastic cups and bottles. At the same time, they discuss the ethical and social considerations that might affect the successful production and adoption of these new materials in different contexts. Gap in education The course is different from other freshman-oriented courses. It is not a “history course for engineers.” And it is not an “engineering course for humanists.” It is an interdisciplinary