{"id":32636,"date":"2023-08-18T08:00:00","date_gmt":"2023-08-18T06:00:00","guid":{"rendered":"http:\/\/6158de27-4ad6-4fb3-8eef-a64cb8bf7617"},"modified":"2023-08-18T09:38:38","modified_gmt":"2023-08-18T07:38:38","slug":"supersonic-passenger-flights-are-making-an-unlikely-return-heres-why","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/rss_feed\/supersonic-passenger-flights-are-making-an-unlikely-return-heres-why\/","title":{"rendered":"Supersonic passenger flights are making an unlikely return. Here\u2019s why"},"content":{"rendered":"

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By Stephen Dobie\n <\/p>

Published: Friday, 18 August 2023 at 06:00 AM<\/p>

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November will mark the 20th anniversary of Concorde\u2019s retirement. And with it, a lengthy pause on regular, paying airline passengers (albeit those with healthy bank accounts) travelling faster than the speed of sound \u2013 343 metres per second, or 761mph (1,224km\/h).<\/p>

Many still mourn the distinctive, dart-shaped aircraft\u2019s loss, deeming its costly tickets, urgent fuel use and thunderous sonic booms when it breached the sound barrier as acceptable prices to pay for being propelled across the Atlantic at Mach 2 (over 1,500mph or 2,400km\/h).<\/p>

Supersonic travel looks to be on its way back, though, and in a cheaper, cleaner and quieter form. \u201cConcorde was a technical marvel and well ahead of its time,\u201d says Ben Murphy<\/a>, vice president of Sustainability at Boom. \u201cBut it was a nationalistic project that hadn\u2019t been built around a viable economical model.\u201d<\/p>

Boom is an American company aiming to fly passengers supersonically by the end of the decade on its new Overture aircraft.<\/p>

\u201cWe can build on Concorde\u2019s legacy with nearly 60 years of advancement in aerodynamics, materials and propulsion systems,\u201d Murphy says, \u201cwith the use of sustainable aviation fuel (SAF)<\/a> enabling the return of supersonic travel in an economical and environmentally sustainable manner.\u201d<\/p>\n

The XB-1, due for its first test flight later this year, is blazing a trail for the next-generation of supersonic passenger aircraft – Image credit: Boom Supersonic<\/figcaption><\/figure>\n

SAF is seen as the most viable route to reduce the carbon footprint of aviation and can cut a plane\u2019s lifetime carbon dioxide emissions by 80 per cent. It can be made by recycling waste materials from landfill and food production, or produced synthetically by carbon capture from the air.<\/p>

SAF can also be mixed in a 50\/50 ratio with regular aviation fuel to partially decarbonise the airline fleets operating right now.<\/p>

The viability of supersonic travel<\/h2>

Overture\u2019s propulsion is based entirely around SAF, with Murphy and his team all too aware that the aircraft\u2019s green credentials are vital to the project winning favour.<\/p>

\u201cConcorde was famously loud and dirty, [powered by] afterburning military-derived engines that produced a lot of particulate matter. That\u2019s the image people have in their mind,\u201d says Murphy.<\/p>

\u201cWe\u2019ll travel twice as fast as a regular subsonic passenger plane over water [around 1,300mph or 2,090km\/h] and 20 per cent faster over land [just shy of 700mph or 1,100km\/h], meaning we\u2019ll burn up to 2.5 times as much fuel per flight, but with SAF giving us a net zero carbon footprint.\u201d<\/p>\n

\"The
Measuring almost 20m (65ft) long, with a 5m (17ft) wingspan, the XB-1 is powered by three jet engines and has a carefully shaped nose designed to ensure stability over a wide range of airspeeds – Image credit: Boom Supersonic<\/figcaption><\/figure>\n

In the early stages of the project, the team at Boom purchased old Concorde seats \u2013 \u201cthey\u2019re basically an economy-class seat today\u201d \u2013 to work out how to arrange the 64-80 business-class seats that\u2019ll sit in each Overture.<\/p>

The thinking behind the smaller seats is that the faster journey times Overture will offer, makes the luxury of bigger, fully reclining, \u2018lie-flat\u2019 seats, as found in the more premium classes of today\u2019s long-haul flights, unnecessary.<\/p>

Overture\u2019s longer range \u2013 4,250 nautical miles [approx 6,850km] versus Concorde\u2019s 3,900 [6,270km] \u2013 opens up more than 600 economically viable routes and much greater variety than its forebear, with LA to Sydney possible with a fuel stop.<\/p>

Its top speed of Mach 1.7 (1,304mph or 2,098km\/h) lags a little behind Concorde\u2019s Mach 2, but also negates the need for noisy afterburners, a fuel-guzzling solution usually found on military jets to increase the thrust of an engine.<\/p>

London to New York in around four hours (versus Concorde\u2019s three hours and 20 minutes) is still significantly quicker than a business-class flight at subsonic speeds.<\/p>

Overture\u2019s expected routes will largely be over water, with supersonic travel currently prohibited over land to save those of us on the ground from the disruption of sonic booms. \u201cWe\u2019ve made a software set that predicts where the sonic booms will propagate to find the fastest route,\u201d says Murphy.<\/p>

Benchmark flights<\/h2>\n
\"Aerial
The Overture aircraft will use four Symphony jet engines, which are currently being developed to produce 35,000lb of thrust and run on sustainable aviation fuel – Image credit: Boom Supersonic<\/figcaption><\/figure>\n

Overture won\u2019t be the first Boom aircraft to fly, however. The company\u2019s XB-1 experimental craft is set to make its first test flight in Mojave\u2019s supersonic corridor, in California, later this year.<\/p>

Overture\u2019s debut flight is scheduled for 2027, with passengers due to travel by the end of the decade (with tickets expected to cost a little more than those of business-class prices). By the early 2030s, Boom hopes to be making 66 Overtures a year at its North Carolina plant.<\/p>

Given those ambitions, what does Murphy have to say to anyone scaling back their air miles in pursuit of a greener planet? \u201cSometimes it gets lost that travel brings a lot of benefits,\u201d he says.<\/p>

\u201cA more connected world has brought huge economic growth and cultural exchanges lead to a more peaceful planet. We want to make people feel good about travelling. You can both travel and protect the planet. It\u2019s not an \u2018either\/or\u2019 situation with the technology we\u2019re working on today.\u201d<\/p>

It\u2019s a view echoed by Mike Bannister<\/a>, British Airways\u2019 chief Concorde pilot from 1995 until the aircraft\u2019s retirement in 2003 and an occasional advisor on the Overture project.<\/p>

He clocked 9,000 flight hours on the legendary passenger jet before its final flight, with 7,000 of them above the sound barrier, likely making him the most frequently supersonic human who isn\u2019t an astronaut.<\/p>\n

\"An
Production of the Overture, illustrated here, is due to start in 2025, ahead of its maiden flight, expected in 2027 – Image credit: Boom Supersonic<\/figcaption><\/figure>\n

\u201cI\u2019m an optimist \u2013 I think humans never take a backward step for too long,\u201d says Bannister. \u201cMy daughter is a commercial pilot on a 737. She was 10 when Concorde retired and she said, \u2018But dad, I really wanted to fly supersonically\u2019. I think she now has a chance.\u201d<\/p>

Bannister\u2019s career-high came as he flew in formation with the Red Arrows for Queen Elizabeth II\u2019s golden jubilee in 2002 (Her Majesty and two million spectators waving up at the cockpit as he buzzed the capital at 1,000ft\/300m) little over a year before he landed Concorde for the final time. \u201cWe didn\u2019t know at that point,\u201d he admits.<\/p>

The reasons for the aircraft\u2019s retirement were numerous, but ultimately financial. \u201cIn the 1990s we looked at modernising the controls,\u201d Bannister says. \u201cBy this point, Concorde was making \u00a31m profit per round trip per day, so the cost of grounding one [of British Airways\u2019 fleet of seven] for a year of recertification was too high.\u201d<\/p>

He estimates the plane could have soldiered on to 2015 with enough money behind it.<\/p>

\u201cThe seats might have been small, but they were built to 1960s standards,\u201d says Bannister. \u201cAnd the short time you spent on board, actually sitting in them, more than compensated.<\/p>

\u201cEven though you flew at 60,000ft [approx 18,000m \u2013 20,000ft \/ 6,000m higher than a subsonic plane] its cabin was pressurised for a lower effective altitude than regular flight. Crossing the Atlantic, you\u2019d basically spend three hours and 20 minutes up a 5,000ft hill [in terms of cabin pressure] rather than eight hours up an 8,500ft mountain.\u201d<\/p>

The draws of travelling aboard Concorde didn\u2019t end there, though. \u201cAt supersonic speed, you travel so quickly you go faster than Earth rotates,\u201d explains Bannister. \u201cSo the Sun appears to go backwards, which scientists tell us resets the body clock. To all intents and purposes, it eliminated jet lag<\/a>.\u201d<\/p>\n

\"A
NASA is working on the design of its X-59 aircraft, which it hopes will reduce the loud booms produced when breaking the sound barrier to a level that will enable the ban on supersonic flight over land to be lifted – Image credit: NASA<\/figcaption><\/figure>\n

A smaller bang<\/h2>

\u201cOverture looks a lot like Concorde, but that\u2019s understandable,\u201d says Bannister. \u201cThe issues of aircraft heating expand exponentially as you travel faster and there\u2019s probably only one optimal solution.<\/p>

\u201cI flew the first generation of supersonic travel and Boom is launching the second. But the third is when we can reduce the impact of the sonic boom to allow supersonic travel over land. That\u2019s the Holy Grail.\u201d<\/p>

And it\u2019s a target firmly in the sights of the engineers behind X-59 QueSST<\/a>, a Mach 1.4 experimental aircraft produced by Lockheed Martin as part of NASA\u2019s pursuit to suppress the aural impact of the sonic boom.<\/p>

X-59 QueSST\u2019s first flight is due by the end of 2023, two years later than initially planned. It\u2019ll conduct what are dubbed \u2018community flight tests\u2019, amassing US residents\u2019 views on its suppressed \u2018sonic thump\u2019, which aims to reduce Concorde\u2019s 110-decibel sonic boom<\/a> (about the same perceived loudness as thunder) to around 75 decibels (equivalent to a car door being shut).<\/p>

The trick is to separate the shockwaves caused by the plane pummelling the air beyond the sound barrier. It\u2019s thought you can do that by refining the shapes and inlets of an aircraft\u2019s nose, wings and tail so that those waves don\u2019t coalesce before they reach the ground.<\/p>\n

\"A
The shockwaves produced as an aircraft passes through the air at supersonic speeds are what cause the loud booms heard by people on the ground – Image credit: NASA<\/figcaption><\/figure>\n

Adjustable bodywork could allow pilots \u2013 or, indeed, algorithms \u2013 to react to flight data to ensure a supersonic plane\u2019s acoustic signatures remain quiet during a journey. Planes flying faster than the speed of sound currently drop sonic booms to the ground the entire time they\u2019re supersonic.<\/p>

Available to the public<\/h2>

\u201cThe X-59 is just one critical step in the process of making supersonic travel commercially viable,\u201d says its programme director David Richardson. \u201cIt proves to the general public and to regulators that quiet supersonic flight is achievable, thereby making supersonic commercial flights practical if they can now go over land.\u201d<\/p>

He sees 2037\/2038 as a target for a passenger jet being both technologically and legally capable of doing so. \u201cWe\u2019re very excited about the potential change this could have for everyone, including me and you. It\u2019ll likely always be more expensive than an economy ticket on a large subsonic airliner \u2013 but remember, you\u2019ll get there twice as fast.\u201d<\/p>

Keeping things below Mach 1.8 (and so foregoing afterburners) reduces fuel costs and simplifies servicing, a cost saving that ought to make its way to the passengers buying and sitting in the seats.<\/p>

All told, the new supersonic era looks a lot more democratic than the old one. The fate of whether it\u2019s truly cleaner and quieter now lies in some very enthusiastic hands.<\/p>

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