Illustrations of the Tempest (Picture: BAE Systems).
Technology

Frontline Tech: How Could The RAF Go Hypersonic?

The RAF has set out plans that could see the production of hypersonic planes.

Illustrations of the Tempest (Picture: BAE Systems).

Illustrations of the concept fighter jet, Tempest (Picture: BAE Systems).

By David Hambling, technology expert

This week, Sir Stephen Hillier, the outgoing Chief of the Air Staff, announced plans to give a tremendous boost to Britain’s jet fighters, in every sense of the word.

A new £10m program will explore engine technology which could see aircraft flying at hypersonic speeds.

What does 'hypersonic' mean?

Hypersonic means in excess of Mach 5 or over 4,000 mph. This is more than three times as fast as current aircraft, or, to put it another way, more than a mile per second.

There is currently something of an arms race going on in the field of hypersonics.

Ballistic missiles, like the Trident-II D5 missiles carried by the Royal Navy’s Vanguard submarines, already reach much higher speeds, but most of their trajectory is in space where there is no air resistance.

Ballistic missiles reach altitudes of hundreds of miles so they can be detected from long ranges, and they follow a predictable path, making them relatively easy to intercept.

By contrast, hypersonic missiles and aircraft fly on much lower trajectories and can change course in flight.

Flying at high speed inside the atmosphere presents several challenges for aerodynamics, control, management of the high temperatures causes by air friction – and propulsion.

The Tempest (Picture: BAE Systems).
Could the Tempest concept be a candidate for hypersonic engines in the RAF? (Picture: BAE Systems).

How do you achieve hypersonic speeds?

Most hypersonic projects are based on rockets.

These are a simple, known technology, but they have a big disadvantage.

A rocket has to carry both rocket fuel and the oxidizer to burn it, and the oxidizer can weigh far more than the fuel.

For example, each space shuttle launch consumed only 100 tons of hydrogen fuel but 600 tons of liquid oxygen. 

By contrast, “air breathing” engines do not need any oxidizer because they get their oxygen from the air like normal jet engines.

The new programme is being carried out by Rolls-Royce Plc, BAE Systems and a much smaller partner, Reaction Engines Limited from Oxfordshire.

It is Reaction Engines who have developed the SABRE, or Synergistic Air Breathing Rocket Engine, a design which aims for the best of both worlds.

At high altitudes, it is a rocket, but, at lower altitudes, it works like a jet engine - sucking in and compressing air.

SABRE’s unique feature is a precooler which reduces the temperature of the incoming compressed air. This means the engine does not need to cope with extreme temperatures which requires special materials.

Engineering the pre-cooler has been quite a challenge.

A computer generated image of Synergistic Air Breathing Rocket Engine (SABRE) (Picture: Reaction Engines).

After years of development, Reaction Engines have arrived at a design made from thousands of thin-walled tubes with joints bonded so thoroughly that the escape of coolant is measured in molecules.

Reaction Engines was started some 30 years ago, and what once looked like an unlikely prospect has started to appear increasingly feasible in recent years.

The company has had investment from both Boeing and Rolls Royce as well as the UK government, suggesting their ideas have not been accepted by the mainstream.

Reaction Engine’s long-term goal is a hypersonic vehicle which becomes a rocket at high altitude and is capable of launching payloads into space. But in the shorter term, their technology could be used to improve the efficiency of existing jet engines.

What jets could go hypersonic?

One suggestion is that the SABRE inlet precooler could be applied to the Rolls-Royce EJ200 engine on existing Eurofighter Typhoons.

As Sir Hillier says, hypersonic speeds are extremely unlikely, but it could give a significant performance boost - and hence a major advantage over competitor aircraft.

Looking further ahead, the programme will also explore how the technology could be applied to the RAF’s next-generation fighter jet, the Tempest.

While there is not yet an explicit requirement for a hypersonic fighter, some have suggested that aspects of its mission may require “more than supersonic” speeds.

At the same time as the jet propulsion programme, the RAF also announced it was looking into an "affordable" hypersonic missile which might be fielded in the near term.

“I have challenged my team - and we are working on this with some other people at this moment in time - to see whether or not we can generate a Mach 5 capability in four years,” Air Vice Marshal Simon Rochelle stated in a speech at the Air and Space Power Conference in London.

Could new technology make the Typhoon go even faster? (Picture: MOD).
Could new technology make the Typhoon go even faster? (Picture: MOD).

How much would hypersonic technology cost?

The focus on affordability is significant.

The hypersonic weapons being developed by other countries are ‘silver bullets,’ highly capable but expensive weapons for specific targets.

Some of them, like Russia’s Avangard, are purely intended as nuclear delivery systems, while others, such as those being developed by China, are likely to be aimed neutralizing American aircraft carriers or air defence sites.

An affordable British hypersonic weapon could be procured in large numbers - Air Vice Marshal Rochelle talked about firing “thousands” of them.

This could be used not just against high-value items but battlefield targets like tanks and bunkers. Their high speed means that targets such as artillery and rocket launchers using “shoot and scoot” tactics would have no chance to get away.

In the longer term, the RAF may end up with hypersonic aircraft armed with hypersonic missiles.

With everything moving at more than a mile a second, the pace of future wars promises to be very rapid indeed.

Hypersonic missile
Firing of the hypersonic Russian missile called 'Avangard' (Picture: Russian MOD).

This could be used not just against high-value items but battlefield targets like tanks and bunkers. Their high speed means that targets such as artillery and rocket launchers using “shoot and scoot” tactics would have no chance to get away.

In the longer term, the RAF may end up with hypersonic aircraft armed with hypersonic missiles.

With everything moving at more than a mile a second, the pace of future wars promises to be very rapid indeed.