TRANSPORT
Brussels to Tokyo in two hours
22 June 2016
by Jon Cartwright
Researchers are designing planes that can travel at eight times the speed of sound. Credit: Pixabay/ joelfotos
A typical flight from Brussels to Tokyo takes over 11 hours – but imagine if that time was shaved
to just two and a quarter.
That is the sort of possibility offered by hypersonic jets, which travel at many times the speed of sound
– and which researchers in Europe are trying to make a reality.
‘Getting in a couple of hours to the other side of the world is quite impressive and nearly unimaginable,’
said aerospace engineer Dr Johan Steelant of the European Space Agency in the Netherlands. ‘I’m still
amazed that classical aeroplanes weighing 500 tonnes are able to hang in the air travelling at 800 to
900 kilometres per hour – but just imagine if we could crank this speed up to seven to eight times
faster.’
The speed of sound – 1 200 kilometres per hour – has been broken by civilian aeroplanes before, albeit
only by two models: the Anglo-French Concorde and the Soviet Union’s Tupolev Tu-144, both of which
flew at about twice the speed of sound. Both are now retired.
But even those supersonic aircraft would be left well behind by the prototype being developed by Dr
Steelant and colleagues. Known as HEXAFLY, it is expected to travel at seven or eight times the
speed of sound.
Fast target
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Such speeds would not easily be reached. One problem will be generating enough thrust to overcome
air beating past at over 8 000 kilometres per hour, and even then there are issues of stability and
managing the thousand-degree temperatures generated by aerodynamic friction.
Fortunately Dr Steelant has had prior success: HEXAFLY’s precursor project, LAPCAT-II, saw the
researchers test a 1.2-metre physical model in a wind tunnel at 7.4 times the speed of sound. In
HEXAFLY, he and his colleagues want to test a 3-metre prototype at similar speeds in the open air.
The basic design of the aircraft is nearly complete, and they are now optimising its mass before the
proposed launch in 2018 or 2019. This particular prototype will not generate its own thrust and will be
launched from a rocket in order to test flight stability and other factors.
‘This test will demonstrate that we have mastered the different aspects of the design and the related
technologies,’ said Dr Steelant.
One of those related technologies has been developed as part of a project that Dr Steelant also
coordinated. Known as ATLLAS-II, it sought to create materials that could withstand the heat generated
at hypersonic speeds.
Lightweight
The result of that project was a range of composites called ceramic matrixes. They are similar to the
composite materials already used in aircraft, but are treated during manufacture so that the only
materials left over are those such as carbon or aluminium oxides which can survive high temperatures,
while still being sufficiently light to minimise fuel consumption.
Fuel itself is a consideration for hypersonic flight,
as the kerosene used by conventional airliners is
not only heavy but a potent source of greenhouse
gas emissions. Liquid hydrogen, liquid methane and
even liquid oxygen are prime alternatives, but have
to be stored at cryogenic temperatures of -200 to 250 degrees Celsius.
Dr Martin Sippel, an aerospace engineer at the
German Aerospace Centre (DLR) in Cologne,
coordinated a project called CHATT to investigate
fuel management on hypersonic aircraft. The
project is now finished, but the researchers believe
they got some way towards identifying the best
approach.
‘Just imagine if we
could crank speeds
up to seven to eight
times faster.’
Dr Johan Steelant,
European Space Agency
One of the problems with cryogenic fuels is that they take up a large volume, yet tend to slosh around
in large tanks which affects the stability of the plane. For this reason Dr Sippel and colleagues have
performed a lot of computer modelling to work out how to reduce sloshing.
The researchers have also built several different demonstrator tanks to see which was best able to
withstand cryogenic temperatures. A particularly promising one was made from a carbon-fibre thin-ply
material, which, unlike other carbon-fibre designs, did not need a protective internal liner to prevent the
propellants seeping through or reacting with the tank’s walls.
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Hypersonic planes could look significantly different from the aircraft we know today.
Challenges ahead
However, Dr Sippel says there is a still a lot left to do. ‘(We will only know that) all problems are solved
when a hypersonic vehicle is in safe and reliable routine operation,’ he said.
The next step is to develop a cryogenic tank demonstrating thermal protection and ‘health monitoring’
– that is, monitoring of the technical system’s condition over many cycles of filling and depletion.
That would be yet another step towards civilians travelling at eight times the speed of sound. Dr
Steelant believes commercial flights could become economically viable towards the middle of the
century.
But eight times the speed of sound may just be the start. Some of the concepts investigated in CHATT
would be suitable for planes such as DLR’s SpaceLiner, a rocket-propelled craft that is designed to
travel at 20 times the speed of sound, making Brussels to Japan in about an hour.
‘I think it's about the dream of creating something new and making a difference to today’s conventional
subsonic airliners,’ said Dr Sippel.
More info
HEXAFLY
LAPCAT-II
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ATLLAS-II
CHATT
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