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.

 
 
 
 

The Fire Brigades Union’s statement on Theresa May’s resignation is completely damning

Grenfell Tower. Image: Getty.

Just after 10 this morning, Theresa May announced that she would resign as Britain’s prime minister on 7 June. A mere half an hour later, a statement from Royal Institute of British Architects president Ben Derbyshire arrived in my inbox with a ping:

“The news that Theresa May will step down as Prime Minister leaves the country in limbo while the clock ticks down to the latest deadline of 31 October. While much is uncertain, one thing remains clear – a no deal is no option for architecture or the wider construction sector. Whoever becomes the next Prime Minister must focus on taking the country forward with policies beyond Brexit that tackle the major challenges facing the country such as the housing crisis and climate change emergency.”

I was a bit baffled by this – why would the architecture profession try to get its thoughts into a political story? But then Merlin Fulcher of Architects Journal put me right:

Well you know construction is a larger contributor to GDP than financial services, and most of the work UK architects do is for export, and at least half of the largest practice (Foster + Partners) are EU, so there's a lot at stake

— Merlin Fulcher (@merlinfulcher) May 24, 2019

So, the thoughts of the RIBA president are an entirely legitimate thing to send to any construction sector-adjacent journalists who might be writing about today’s big news, and frankly I felt a little silly.

Someone else who should be feeling more than a little silly, though, is Theresa May herself. When listing her government’s achievements, such as they were, she included, setting up “the independent public inquiry into the tragedy at Grenfell Tower” – a fire in a West London public housing block in June 2017 – “to search for the truth, so nothing like it can ever happen again, and so the people who lost their lives that night are never forgotten”.

Matt Wrack, general secretary of the Fire Brigades Union, is having precisely none of this. Here’s his statement:

“Many of the underlying issues at Grenfell were due to unsafe conditions that had been allowed to fester under Tory governments and a council for which Theresa May bears ultimate responsibility. The inquiry she launched has kicked scrutiny of corporate and government interests into the long-grass, denying families and survivors justice, while allowing business as usual to continue for the wealthy. For the outgoing Prime Minister to suggest that her awful response to Grenfell is a proud part of her legacy is, frankly, disgraceful.”

A total of 72 people died in the Grenfell fire. At time of writing, nobody has been prosecuted.

Jonn Elledge is editor of CityMetric and the assistant editor of the New Statesman. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.

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