Could the planes of the future fly at hypersonic speeds?

Concorde, of course, was merely supersonic. Here it is back in 1975. Image: STF/Getty.

When Concorde entered service 40 years ago, it more than doubled the speed of air travel at a stroke. Following Concorde’s retirement, airliners today fly once more at subsonic speeds, but engineers worldwide are looking to a future in which high-speed flight is an everyday occurrence. Except they want to go one better: not at supersonic, but hypersonic speeds.

Aerospace giant Airbus was last year awarded a patent that details how a future hypersonic aircraft, with delta wings reminiscent of Concorde, could travel at Mach 4.5 – fast enough to carry passengers between Paris and Tokyo in just three hours.

But inevitably, technology that has reached the commercial realm will already have been investigated by the military. The US, Russia and China have all carried out test flights of hypersonic vehicles – those which travel at around five times the speed of sound – with varying degrees of success. Each also has plans for weapons systems that could be developed from them.

Because while these are often referred to as “fighter jets”, in truth the machines are more similar to missiles. Without pilots, they sit atop rockets which boost them to high supersonic speeds (Mach 4 and above), at which point they start up their own engines (if equipped) and accelerate to even faster cruise speeds. But they'd don't maintain them for long, as they usually run out of fuel quickly, and most of their flight time is spent in a glide, albeit an extremely fast one.

Current missiles have operated in this fashion for decades. Intercontinental ballistic missiles (ICBM) and some shorter-range versions use the same sort of flight path, with the missile formed of multiple rocket stages to provide enough power to arc high into the atmosphere, only flying faster and higher. The now retired US AIM-54 Phoenix air-to-air missile had a top speed of Mach 5. What makes the current generation of hypersonic aircraft designs different is their capability to manoeuvre, making them harder to intercept.

An X-43 rocket plane dropped from a B-52, seconds before igniting its scramjet engines and reaching a world record-holding 10,000km/h (Mach 9.8). Image: NASA.

Why bother? There are two main reasons for the fresh interest shown by the military in hypersonic aircraft. The first is that a very fast, highly manoeuvrable weapon is not easy to counter: it can be difficult to detect and its speed means that there is little time for defences to react, much less to actually take any action to stop it.

This makes it a threat to supposedly heavily defended targets – and most discussion of the Chinese hypersonic craft, dubbed Wu-14, and the Russian equivalent, the Yu-71, mention penetrating US missile defence systems as a primary aim.

The second relates to a requirement that has become more urgent in recent years, namely to shorten response time and to attack mobile targets. While drones, satellites and the like can locate them easily enough, highly mobile enemy units – anything from terrorist groups to Scud missile launchers – will not hang around waiting for the inevitable airstrike to be called in. A very fast weapons platform with the ability to manoeuvre means that once found, a target will have little time and less opportunity to escape.


The need for speed

Of course, to create a workable hypersonic vehicle, engineers have to overcome, or at least cope with, the severe environment encountered by something moving that fast. The main problem (from which most if not all the others stem) is heat – heat from air friction and from the shock waves generated by moving faster than the speed of sound.

The temperatures a hypersonic vehicle encounters are so high that conventional materials can’t withstand them and maintain their strength. There are materials that can insulate a structure from the heat, but they tend not to be very strong in themselves, and so any breach of insulation can quickly lead to catastrophic failure – as demonstrated by the tragic loss of the space shuttle Columbia in 2003, and also of some current test vehicles. Research into new heat-resistant materials and suitable manufacturing techniques is therefore a priority.

High air temperatures also reduce the thrust of an air-breathing jet engine, so new propulsion concepts are also needed – relying on rocket engines tends to lead to overly large and heavy aircraft. Among the companies leading the way on propulsion technology is British company Reaction Engines, which is testing the revolutionary Sabre variable-cycle engine.

Travelling at very high speeds will also require advanced sensors and controls. New materials will be needed again, as conventional radomes and antennae would never withstand the heat. Conformal antennae – where the craft’s fuselage skin is used as the transmitter and receiver – are a possibility, though this is not guaranteed to work. Depending on just how fast the vehicle is designed to travel, ionisation of the air around it could interfere with radio-frequency sensors and communications.

Whether it’s possible to create a crewed or passenger hypersonic aircraft is still up for debate. But producing any sort of hypersonic vehicle is a long-term project that will take a lot of time and effort – and a whole lot of money. Patents mark the ground as to where some may follow. But who out there has the will, the persistence and the funds to do so?The Conversation

Phillip Atcliffe is senior lecturer in aeronautical engineering at the University of Salford.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Coming soon: CityMetric will relaunch as City Monitor, a new publication dedicated to the future of cities

Coming soon!

Later this month, CityMetric will be relaunching with an entirely new look and identity, as well as an expanded editorial mission. We’ll become City Monitor, a name that reflects both a ramping up of our ambitions as well as our membership in a network of like-minded publications coming soon from New Statesman Media Group. We can’t wait to share the new website with you, but in the meantime, here’s what CityMetric readers should know about what to expect from this exciting transition.  

Regular CityMetric readers may have already noticed a few changes around here since the spring. CityMetric’s beloved founding editor, Jonn Elledge, has moved on to some new adventures, and a new team has formed to take the site into the future. It’s led by yours truly – I’m Sommer Mathis, the editor-in-chief of City Monitor. Hello!

My background includes having served as the founding editor of CityLab, editor-in-chief of Atlas Obscura, and editor-in-chief of DCist, a local news publication in the District of Columbia. I’ve been reporting on and writing about cities in one way or another for the past 15 years. To me, there is no more important story in the world right now than how cities are changing and adapting to an increasingly challenging global landscape. The majority of the world’s population lives in cities, and if we’re ever going to be able to tackle the most pressing issues currently facing our planet – the climate emergency, rising inequality, the Covid-19 pandemic ­­­– cities are going to have to lead the way.

That’s why City Monitor is going to be a global publication dedicated to the future of cities everywhere – not just in the UK (nor for that matter just in the US, where I live). Our mission will be to help our readers, many of whom are in leadership positions around the globe, navigate how cities are changing and discover what’s next in the world of urban policy. We’ll do that through original reporting, expert opinion and most crucially, a data-driven approach that emphasises evidence and rigorous analysis. We want to arm local decision-makers and those they work in concert with – whether that’s elected officials, bureaucratic leaders, policy advocates, neighbourhood activists, academics and researchers, entrepreneurs, or plain-old engaged citizens – with real insights and potential answers to tough problems. Subjects we’ll cover include transportation, infrastructure, housing, urban design, public safety, the environment, the economy, and much more.

The City Monitor team is made up of some of the most experienced urban policy journalists in the world. Our managing editor is Adam Sneed, also a CityLab alum where he served as a senior associate editor. Before that he was a technology reporter at Politico. Allison Arieff is City Monitor’s senior editor. She was previously editorial director of the urban planning and policy think tank SPUR, as well as a contributing columnist for The New York Times. Staff writer Jake Blumgart most recently covered development, housing, and politics for WHYY, the local public radio station in Philadelphia. And our data reporter is Alexandra Kanik, whose previous roles include data reporting for Louisville Public Media in Kentucky and PublicSource in Pittsburgh, Pennsylvania.

Our team will continue to grow in the coming weeks, and we’ll also be collaborating closely with our editorial colleagues across New Statesman Media Group. In fact, we’re launching a whole network of new publications this fall, covering topics such as the clean energy transition, foreign direct investment, technology, banks and more. Many of these sectors will frequently overlap with our cities coverage, and a key part of our plan is make the most of the expertise that all of these newsrooms combined will bring to bear on our journalism.

City Monitor will go live later this month. In the meantime, please visit citymonitor.ai to sign up for our forthcoming email newsletter.


As for CityMetric, some of its archives have already been moved over to the new website, and the rest will follow not long after. If you’re looking for a favourite piece from CityMetric’s past, for a time you’ll still be able to find it here, but before long the whole archive will move over to City Monitor.

On behalf of the City Monitor team, I’m thrilled to invite you to come along for the ride at our forthcoming digs. You can already follow City Monitor on LinkedIn, and on Twitter, sign up or keep following our existing account, which will switch over to our new name shortly. If you’re interested in learning more about the potential for a commercial partnership with City Monitor, please get in touch with our director of partnerships, Joe Maughan.

I want to thank and congratulate Jonn Elledge on a brilliant run. Everything we do from here on out will be building on the legacy of his work, and the community that he built here at CityMetric. Cheers, Jonn!

In the meantime, stay tuned, and thank you from all of us for being a loyal CityMetric reader. We couldn’t have done any of this without you.

Sommer Mathis is editor-in-chief of City Monitor.