[{"command":"openDialog","selector":"#drupal-modal","settings":null,"data":"\u003Cdiv id=\u0022republish_modal_form\u0022\u003E\u003Cform class=\u0022modal-form-example-modal-form ecl-form\u0022 data-drupal-selector=\u0022modal-form-example-modal-form\u0022 action=\u0022\/en\/article\/modal\/7369\u0022 method=\u0022post\u0022 id=\u0022modal-form-example-modal-form\u0022 accept-charset=\u0022UTF-8\u0022\u003E\u003Cp\u003EHorizon articles can be republished for free under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence.\u003C\/p\u003E\n \u003Cp\u003EYou must give appropriate credit. We ask you to do this by:\u003Cbr \/\u003E\n 1) Using the original journalist\u0027s byline\u003Cbr \/\u003E\n 2) Linking back to our original story\u003Cbr \/\u003E\n 3) Using the following text in the footer: This article was originally published in \u003Ca href=\u0027#\u0027\u003EHorizon, the EU Research and Innovation magazine\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003ESee our full republication guidelines \u003Ca href=\u0027\/horizon-magazine\/republish-our-stories\u0027\u003Ehere\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003EHTML for this article, including the attribution and page view counter, is below:\u003C\/p\u003E\u003Cdiv class=\u0022js-form-item form-item js-form-type-textarea form-item-body-content js-form-item-body-content ecl-form-group ecl-form-group--text-area form-no-label ecl-u-mv-m\u0022\u003E\n \n\u003Cdiv\u003E\n \u003Ctextarea data-drupal-selector=\u0022edit-body-content\u0022 aria-describedby=\u0022edit-body-content--description\u0022 id=\u0022edit-body-content\u0022 name=\u0022body_content\u0022 rows=\u00225\u0022 cols=\u002260\u0022 class=\u0022form-textarea ecl-text-area\u0022\u003E\u003Ch2\u003EBack with a boom? Supersonic planes get ready for a quieter, greener comeback\u003C\/h2\u003E\u003Cp\u003E24 October 2003 was the end of an era. On that day Concorde, the legendary supersonic airliner, made its final commercial flight, flying from London Heathrow to New York City\u2019s John F. Kennedy airport. Since then no commercial supersonic airliners have operated \u2013 the regulatory, technological and commercial problems being too much to overcome. The futuristic dream of a three-hour flight between London and New York, that Concorde offered, seemed shattered.\u003C\/p\u003E\u003Cp\u003ENow, however, almost 20 years later, we might be returning to that supersonic dream. New technological advances allow designs to succeed where Concorde failed and a range of companies and research institutes are heavily investing in a new generation of civilian supersonic aircraft. The US company \u003Ca href=\u0022https:\/\/spectrum.ieee.org\/aerospace\/aviation\/boom-supersonics-xb-1-test-aircraft-promises-a-new-era-of-faster-than-sound-travel\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EBoom\u003C\/a\u003E wants to fly a scale model of its supersonic airliner, called the Overture, in 2021, and has already raised $196 million to do it. NASA has pioneered the \u003Ca href=\u0022https:\/\/www.nasa.gov\/specials\/X59\/\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EX-59\u003C\/a\u003E, an experimental supersonic aircraft that lowers noise levels of the infamous sonic boom. And \u003Ca href=\u0022https:\/\/en.wikipedia.org\/wiki\/Aerion_AS2\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EAerion\u003C\/a\u003E\u003Cu\u003E,\u003C\/u\u003E in cooperation with Boeing, is developing a supersonic business jet, which could fly by 2025.\u003C\/p\u003E\u003Cp\u003E\u2018This is not just a dream anymore,\u2019 said Professor Nicole Viola of the Polytechnic University of Torino in Italy, where she works on supersonic airliners. \u2018Everywhere people are working on this.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ESonic boom\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EOne important boost behind the resurgence of civilian supersonic aircraft is that they could produce less noise and reduce the problem of a sonic boom.\u003C\/p\u003E\u003Cp\u003EWhen an immobile object, such as a stereo, produces sound, its sound waves spread in all directions. If they were visible to the naked eye, these waves would look similar to what happens when a stone is dropped in a pond, with little waves spreading in concentric circles.\u003C\/p\u003E\u003Cp\u003EWhen an aeroplane goes supersonic, however, it moves ahead of the sound it produces. This leads to its soundwaves trailing behind the aircraft in a cone-like shape, similar to the waves trailing behind a boat. An approaching supersonic aircraft is inaudible, but when it crosses the observer, they get hit by a sudden, boom-like sound of concentrated sound waves that is quite uncomfortable. In some cases these booms can cause damage to buildings and supersonic military jets flying over land have \u003Ca href=\u0022https:\/\/news.sky.com\/story\/brazil-jets-shockwave-shatters-court-windows-10476929\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003Eeven been known to break windows\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003EThis means that in most countries, routine supersonic flight is banned over land, severely limiting the potential routes of a civilian supersonic plane. For this reason, Concorde only flew routes that were largely over water.\u003C\/p\u003E\u003Cp\u003ENew designs, however, are pioneering so-called low-boom technology.\u003C\/p\u003E\u003Cp\u003E\u2018The (intensity) of the sonic boom is mainly dependent on the aerodynamic shape of the plane,\u2019 explained G\u00e9rald Carrier, senior aerodynamicist at French aerospace lab ONERA. He was involved in a project called \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/id\/769896\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003ERUMBLE\u003C\/a\u003E, which gathered evidence around the noise emitted by sonic booms and low-boom aircraft for regulatory authorities.\u003C\/p\u003E\u003Cp\u003ECarrier notes that, by shaping the geometry of the plane, the loudness of the boom can be reduced from more than 100 decibels for Concorde, similar to listening to a jackhammer, to 70-80 decibels for the new designs, about the sound of a vacuum cleaner.\u003C\/p\u003E\u003Cp\u003E\u2018Proper shaping of the aircraft with characteristics like a very long front nose can reduce noise. By mastering this we can sculpt the sound signature of the aircraft and make the boom less annoying.\u2019\u003C\/p\u003E\u003Cp\u003EFor now, low-boom civilian aircraft are still theoretical, although they\u2019re getting closer to launch. Boom hopes to fly a one-third scale model of their design in 2021 and NASA wants to start flight tests of the X-59 in 2022. Carrier compares the noise new low-boom designs would make to very distant fireworks. People would still hear it, but it\u2019s not window-breaking loud.\u003C\/p\u003E\u003Cp\u003ELow-boom became possible because of advances in tools and research. New computers programs make it easier to simulate the properties of an aircraft and experiment with 3D-shapes. And since the 1960s, when Concorde was designed, we know much more about sonic booms. \u2018We benefit from decades of new research and developments,\u2019 said Carrier.\u003C\/p\u003E\u003Cp\u003EYet even this new generation of supersonic aircraft will still produce noise, and regulation needs to be crafted for these low-boom designs. The RUMBLE project simulated how much sound these new aircraft would produce and what the effect would be on buildings, measured sonic booms with Russian military aircraft and even studied the effect on humans.\u003C\/p\u003E\u003Cp\u003E\u2018We looked at how people reacted to different levels of sonic booms, so called psycho-acoustic studies,\u2019 said Carrier. Specifically, they put speakers next to a house in which test subjects were located. From time to time these speakers produced sounds similar to a sonic boom. The test subjects then had to report how this affected their wellbeing, capacity to do tasks and ability to sleep. Based on \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/id\/769896\/results\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003Ethese results\u003C\/a\u003E, governments can decide how much noise is acceptable from these new aircraft.\u003C\/p\u003E\u003Cp\u003E\u2018We want to help define regulations that can limit the sonic boom of new aircraft to an acceptable level for humans,\u2019 said Carrier. These regulations might then allow supersonic aircraft to fly over land, dramatically expanding the routes they can service.\u003C\/p\u003E\u003Cp\u003E\u003Cblockquote class=\u0022tw-text-center tw-text-blue tw-font-bold tw-text-2xl lg:tw-w-1\/2 tw-border-2 tw-border-blue tw-p-12 tw-my-8 lg:tw-m-12 lg:tw--ml-16 tw-float-left\u0022\u003E\n \u003Cspan class=\u0022tw-text-5xl tw-rotate-180\u0022\u003E\u201c\u003C\/span\u003E\n \u003Cp class=\u0022tw-font-serif tw-italic\u0022\u003E\u2018Proper shaping of the aircraft with characteristics like a very long front nose can reduce noise.\u2019\u003C\/p\u003E\n \u003Cfooter\u003E\n \u003Ccite class=\u0022tw-not-italic tw-font-normal tw-text-sm tw-text-black\u0022\u003EG\u00e9rald Carrier, senior aerodynamicist, ONERA\u003C\/cite\u003E\n \u003C\/footer\u003E\n\u003C\/blockquote\u003E\n\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMach\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EIn Torino, Prof. Viola will be exploring another way to test sonic boom in her project \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/id\/101006856\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EMOREandLESS\u003C\/a\u003E, which has just kicked off and will run for four years. In one experiment, researchers will shoot small projectiles in the shape of planes out of a gun on a large, outdoor testing track. The projectiles achieve a sonic boom, which is then measured by microphones situated around the track to see what different designs will do for the noise. \u2018We will investigate a wide range of speeds, from Mach 2 to 5,\u2019 said Prof. Viola.\u003C\/p\u003E\u003Cp\u003EMach is the unit of speed for supersonic aircraft. Mach 1 means that the aircraft goes as fast as the speed of sound at that location, which can differ based on the local temperature, which, in turn, is mainly dependent on altitude (the higher up in the atmosphere, the lower temperatures are). At sea level, with a temperature of 15\u00b0C, Mach 1 is located at 340.3 metres per second or 1225.08 km per hour. At an altitude of 11,000 metres, that becomes 295 metres per second or 1062 km per hour. Supersonic is generally designated as the area between Mach 1 and 5, or 1 to 5 times the speed of sound. The Boom Overture, for example, is planned to maintain a Mach 2.2 speed, similar to the cruising speed of Concorde.\u003C\/p\u003E\u003Cp\u003EProf. Viola is also studying fuel options - another key issue that new supersonic civilian aircraft will face. One of the reasons why Concorde was uneconomical was its high fuel consumption, especially during low-speed phases of flight. And although the new generation of supersonic aircraft designs have reduced fuel use through interventions like more economical engines and better aerodynamics, they would still spend more than a regular, subsonic jet, producing problems of pollution and climate impact.\u003C\/p\u003E\u003Cp\u003EA key way to reduce this is new forms of fuel. \u2018Emissions of course depend on the type of engine,\u2019 said Prof. Viola. \u2018But they also depend on the fuel, and the chemical processes at the basis of combustion.\u2019\u003C\/p\u003E\u003Cp\u003EFor Prof. Viola, two candidates for more sustainable fuels spring out: biofuels and liquid hydrogen. Hydrogen is \u2018candidate number 1\u2019, said Prof. Viola, because it doesn\u2019t produce CO2 emissions. But biofuels, which are derived from biomass such as plants or waste, are also still in the running, possibly mixed in with regular jet fuel.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EEconomics\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EBut for all the new technology, what will make or break the new generation of supersonic is economics. \u2018The last straw for Concorde was that the economics just weren\u0027t viable,\u2019 said Dr Turab Zaidi, who jointly leads the \u003Ca href=\u0022https:\/\/umi2958.gatech.edu\/research\/aerospace-asdlgtl\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EAerospace Systems Design Lab at Georgia Tech Lorraine\u003C\/a\u003E, which is located in Metz, France. \u2018British Airways and Air France just couldn\u0027t stand the amount of money they were losing.\u2019\u003C\/p\u003E\u003Cp\u003EDr Zaidi investigated whether that situation will shift in the future for the project \u003Ca href=\u0022https:\/\/cordis.europa.eu\/project\/id\/864521\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003EOASyS\u003C\/a\u003E, and whether airlines can profitably operate these new aircraft. In the project they developed two scenarios for supersonic airliners in the period between 2035 and 2050, and their conclusion seems cautiously optimistic.\u003C\/p\u003E\u003Cp\u003E\u2018Across the scenarios we found that a market does exist,\u2019 said Dr Zaidi. \u2018It\u0027s not as high as some of the manufacturers are projecting. But granting certain assumptions, there is a market.\u2019\u003C\/p\u003E\u003Cp\u003ETheir \u003Ca href=\u0022https:\/\/link.springer.com\/article\/10.1007\/s13272-020-00486-3\u0022 target=\u0022_blank\u0022 rel=\u0022noopener noreferrer\u0022\u003Estudy\u003C\/a\u003E starts from the current aviation market and projects how it will evolve, taking into account economic growth, which will most likely produce an increase in the use of airlines. It then calculates the size of the group of consumers who would take these supersonic aircraft, such as business passengers wanting fast connections or tourists who now pay for the premium offerings of airlines.\u003C\/p\u003E\u003Cp\u003EHowever, this potential market relies on a range of assumptions on how supersonic aircraft will evolve, such as fuel efficiency and regulation.\u003C\/p\u003E\u003Cp\u003E\u2018For the high-demand scenario, we assumed land overflight is permitted,\u2019 said Dr Zaidi. \u2018That is one of the big constraints on a high-demand scenario. When you don\u0027t allow land overflight, you severely limit the amount of destinations and force planes to fly slower when over land, reducing fuel efficiency.\u0027\u003C\/p\u003E\u003Cp\u003ENevertheless, in general, Dr Zaidi seems optimistic. \u2018A lot of the things that ended Concorde have shifted,\u2019 he said. \u2018The demand for fast airline connections never went away since then and we might see a resurgence now.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cfigure role=\u0022group\u0022 class=\u0022@alignleft@\u0022\u003E\n\u003Cimg alt=\u0022Graphic credit - Horizon magazine\u0022 height=\u00223624\u0022 src=\u0022\/research-and-innovation\/sites\/default\/files\/hm\/IMCEUpload\/topsupersonic_1200x.png\u0022 title=\u0022Graphic credit - Horizon magazine\u0022 width=\u00223001\u0022\u003E\n\u003Cfigcaption class=\u0022tw-italic tw-mb-4\u0022\u003EGraphic credit - Horizon magazine\u003C\/figcaption\u003E\n\u003C\/figure\u003E\n\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe research in this article was funded by the EU. 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