Blink and you'll miss them, but you'll definitely hear them. Hypersonic
aircraft may look similar to the jet planes we're familiar with, but these
engineering marvels are completely different beasts. Able to attain speeds
that would literally tear conventional passenger jet apart, hypersonic
aircraft possess unique engines, are built from advanced materials and are
packed full of intelligent tech.
So just how fast are hypersonic jets? By definition,
supersonic vehicle can move faster than the speed of sound or Mach 1- which is 1,235 kilometers per hour, or 343 meters per second. But to
be classed as hypersonic, planes must
fly at least five times this speed 6,175 kilometers per hour, or 1,713
meters per second. And their speed isn't limited to Mach 5; that's just the beginning.
We've already created aircraft that can reach Mach 20 that's nearly seven
kilometers per second! As long as these vehicles can withstand the pressure in
the atmosphere, they can keep moving faster and faster. For over 30 years we
were able to use Concorde to fly at supersonic speeds. It broke through the
sound barrier and revolutionized air travel. But now the aim is to go faster
than ever, with jets and commercial airliners capable of reaching even greater
speeds. This is, of course, no simple task, but we're still building new
and innovative aircraft.
This technology reveals new realms of possibility that would make air travel
more efficient and convenient than ever before. Imagine travelling halfway
around the world in just few hours, or seeing spacecraft climb into the upper
atmosphere without gigantic rocket. The most exciting part is that this isn't
the stuff of science fiction
we've already flown vehicles at hypersonic speeds, and researchers are now
developing hypersonic planes suitable for public use.
Hypersonic vs Supersonic
For many years experts believed it was simply impossible to fly faster than
the speed of sound. But that all changed
in the 1940s, when US test pilot Chuck Yeager flew faster than Mach the
speed of sound for the first time in human history. Onlookers below heard the sonic boom as the pressurized air gave way to the
Bell X-1 rocket plane, and they realized that supersonic aircraft were dealing
with new extremes. But although supersonic aircraft have to overcome many
obstacles to break the sound barrier, these factors are compounded when moving
at hypersonic speeds. At Mach and above, the air does more than just form
shock waves. At such high speeds, the air heats the surface of the aircraft to
very high temperatures enough to melt steel and the engines have to cope with
huge pressures.
Below Mach 1: The aircraft compresses the air in front as moves
forward and emits noise from its engines, forming waves that move away at
the speed of sound.
At Mach 1: When the aircraft reaches the speed of sound, the air
being compressed cannot move away fast enough, so the waves accumulate at
the nose of the plane.
Above Mach 1: As the plane exceeds the speed of sound, overtakes the
waves. This causes change in air pressure, or shock wave, which is heard as
sonic.
Building hypersonic vehicle:
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Supersonic aircraft such as
Concorde differed greatly from their subsonic counterparts. They had adapted wing
designs and advanced engines. These changes allowed Concorde to smash through
the sound barrier, which is something subsonic commercial jets were simply
unable to do.
The difference between supersonic and a hypersonic aircraft is even
more striking, because at hypersonic speeds the rules change completely. The
previously benign air starts to become serious problem, as aircraft moving at
hypersonic speed generate huge amounts of friction. This results in
temperatures hot enough to melt the frame of standard jet, so hypersonic
aircraft must be built from robust heat-resist materials such as
ceramics. And they can't stop there, because even if they are able to
withstand the heat, the pressure at low altitudes is simply too great to fly
at hypersonic speeds.
Hypersonic vehicles need to climb high up into the atmosphere, where the air
is much thinner, in order to lessen the strain on the aircraft. Perhaps the
biggest consequence of the intense airflow is that
hypersonic vehicles can't even use the same engines as subsonic
aircraft. Air moving through supersonic plane engines does so at subsonic speeds
(the supersonic airflow is slowed by an engine inlet), but if you tried
using similar setup when travelling at hypersonic speeds, it would melt or
simply explode before your eyes. But rather than rely on rocket engines
the only proven systems to power hypersonic vehicles engineers asked
themselves more ambitious question: could we take what we've learned about
the jet engine and design an equivalent that works at high supersonic, and
even hypersonic, speeds?
This led to the invention of the
supersonic combustible ramjet, or scramjet. Taking the principles of a jet engine and stripping away all of the
unnecessary components for hypersonic travel such as a turbine and a
compressor allows air to move through much more quickly. With few moving
parts, these simple-looking engines produce enough thrust for an aircraft to
soar at incredible speeds; and in doing so, have started to bring the future
of air travel to life.
If there's one lesson that engineers have learned about hypersonic flight so
far, it's that heat, weight and power are all major obstacles.
Too much weight, and you can't reach the desired speed. Too much heat,
and your aircraft will melt mid-flight. And then there's the question of how we can power our machine to hypersonic
speeds and keep it there. Fortunately, solutions for each of these critical
problems have been suggested and some seriously cool aircraft have been
designed in the process.
Innovative engineers such as
Charles Bombardier
have been at the forefront of these endeavors. His envisioned aircraft,
called
Skreemr, would take to the skies with the help of an electrical launch system such
as a
railgun-so we could be bidding farewell to runways one day. A
railgun is an electromagnetic strip that uses electricity to launch
projectiles at incredible speeds, and could be used to fire the Skreemr into the air. This would eliminate
the need for tons of extra rocket fuel for take-off, reducing the aircraft's
weight considerably. Another design by Bombardier, known as the
Antipode, could tackle the heat problem as well as the menacing sonic
boom. By using counter flowing jets of air that move outwards in front of
the aircraft, the temperature generated from aerodynamic friction and the
sound produced by the sonic shock waves would be significantly reduced. And
these features would help Antipode fly up to Mach 24, equivalent to
29,500 kilometers per hour! These designs are still some time away from
being realized, but Airbus and Reaction Engines have recently generated two
concepts that could have us cruising at hypersonic speeds that much sooner.
Sooner or later we will be traveling using hypersonic planes.
Frequently Asked Questions: Hypersonic
Question No. 1: What is the speed of hypersonic vehicles?
Answer: Hypersonic planes must fly at least five
times the speed of sound 6,175 kilometers per hour, or 1,713 meters per
second. And their speed isn't limited to Mach 5; that's just
the beginning.
Question No. 2: Do we have hypersonic planes?
Answer: Yes, we do have hypersonic planes such as Concorde etc. but
we are trying to built hypersonic passenger planes.
Question No. 3: What engines does hypersonic planes use?
Answer: Hypersonic planes use combustible ramjet, or scramjet.
Taking the principles of a jet engine and stripping away all of the
unnecessary components for hypersonic travel such as a turbine and a
compressor allows air to move through much more quickly. With few moving
parts, these simple-looking engines produce enough thrust for an aircraft to
soar at incredible speeds; and in doing so, have started to bring the future
of air travel to life.
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