Scramjets Could Rocket Australia Into 21st Century
Source: Space Daily
January 6, 2001
Dr. Allan Paull and his crew at the University of
Queensland’s Centre for Hypersonics are about to make the first test
flight of their brand new toy - the world’s first operational
scramjet.
Sydney - Dr. Allan Paull and his crew at the University
of Queensland’s Centre for Hypersonics are about to make the first
test flight of their brand new toy - the world’s first operational
scramjet. If the thing works, the UQ scramjet will be the fastest
air-breathing engine ever built, capable of pushing aircraft along at
up to ten times the speed of sound.
This sounds fast, and it is fast - faster by a factor of three than
any existing military plane. The current speed record is held by the
Lockheed SR-71, an American high-altitude surveillance machine with a
top speed of Mach 3.6, or around 3,500 kilometres per hour.
This is about as fast as it’s been possible to go for
quite some time - the SR-71 first flew as long ago as 1965. An F-18
Hornet fighter/bomber, the frontline aircraft of the RAAF, has a top
speed of Mach 2.5.
Allan Paull has spent the last fifteen years trying to
break this speed limit. To smash it to pieces, in fact. And now, after
countless tests in the University’s remarkable T4 shock tunnel (the
windiest wind tunnel on earth), the Hypersonics crew will finally haul
their gadget to Woomera next March and let her rip.
"We were the first group in the world to show that you
could make these things work - that we could actually get net thrust
out of a scramjet engine," says Paull.
"We developed techniques which allowed us to measure the
thrust performance and be able to see what was going on inside the
engine. I joined the team as an applied mathematician way back in
1985, and now we’re finally going to flight test the thing."
So what is a scramjet, and how is it that they come with
so much grunt? In essence, a scramjet is the simplest jet there is,
but that hasn’t meant that building one is a simple job.
A scramjet is a supersonic ramjet, and a ramjet is
basically a turbojet stripped down to its bare essentials. Turbojets
are the engines that power commercial airliners. They use a compressor
fan - those big windmill blades at the front - to shove air into a
combustion chamber, where it’s combined with fuel and ignited. The
exhaust gases are forced out the back, and on their way they power the
compressor, which forces more air into the front of the engine, and so
on.
The beauty of this arrangement is that it allows the
engine to be fired up while it’s stationary - essential for any
commercial application.
A ramjet is much simpler, in that it dispenses with the
compressor. The downside is that the engine must be moving through the
air at high speed to generate the pressure required to compress the
air and fuel in the combustion chamber.
What this means is that a ramjet must be brought up to a
certain critical speed before it can be turned on, typically by
piggybacking the ramjet to a turbojet or a rocket engine until
ignition speed is reached.
A scramjet works on the same principle, except that
unlike a ramjet, the combustion takes place while the gases are moving
at above the speed of sound.
And at the Centre for Hypersonics, they’ve been forcing
air at enormous speeds and pressures though countless configurations
of scramjets, dreaming that one day they could unbolt their monster
from the bench, strap it to a rocket and see what the hell would
happen in a real live atmosphere.
Unfortunately, there was a small matter of money to be
sorted out. Wind tunnel tests are a lot cheaper than flight tests, and
when you want to test an engine at Mach 8, they’re much, much cheaper.
"The problem was that a test launch would have cost us a
minimum of about $10 million, which was out of the question. Then we
got very lucky."
Paull heard that British aerospace company Astrotech had
been given approval to test-launch their new breed of sounding rockets
from Woomera, and after some complex negotiations his group was able
to hitch not one, but two free rides for their scramjet. At last the
first flight tests, dubbed HyShot, were on.
After lift-off in late March or early April, HyShot will
reach an altitude of over 300 kilometres before plunging back into the
desert. On the way down, around 25 kilometres above the middle of
nowhere, the scramjet will kick in, hopefully sending back a torrent
of data before it is incinerated or pulverised.
The main purpose of the tests is to establish that
sustainable combustion actually takes place in the howling maelstrom
inside the engine.
Paull admits that the forthcoming launch has put him "on
the steepest of learning curves". When it became clear that the launch
was actually going to happen, he soon realised how little he knew
about some of the finer points of sub-orbital space flight. He has had
to re-invent himself, transforming from applied mathematician into
payload specialist in short order.
"We’ve had to learn about things like turning rockets
around in space, we’ve had to develop new sensing equipment,
thrusters, the lot. These are tough problems."
The window of opportunity to glean information from the
flight is terrifyingly narrow. The correct test conditions for
combustion occur for only five seconds as the engine screams through
the atmosphere on re-entry.
"It’s a big step, a lot different to doing tests in the
wind tunnel. This thing’s got to work; you’ve got to get it right.
It’s a very big change moving from academic life to something that’s
very, very real."
And he’s had to make an almighty leap from lab to launch
on a budget that would be considered laughable in the United States or
Europe. Paull is eloquent on the subject of research funding in
Australia, and has a dim view of accountants who insist on short-term
results from long-term projects. It is a familiar gripe, one that can
be heard in just about every lab in the land, but if nothing else,
financial adversity has necessitated inspired improvisation.
"We’re doing this for a tenth of the price that anyone
else could do it for. At the core of the project, it’s just two or
three dedicated people, working non-stop on dozens of different
problems.
"We’ve had to build all sorts of ancillary equipment,
and do it on the cheap. For instance, one of things we had to do is
ensure that the payload’s spin was correct. To get the spin balance
right we bought a second-hand car tyre balance from Bob Jane. It works
beautifully!"
Paull knows that the flight is experimental by its very
nature - no one really knows what’s going to happen - and he’ll be
happy just to get the scramjet into the air. Data is data, and in that
sense, any results will be good results.
"We’ve obviously got to crawl before we walk, and this
test will be our first chance to get supersonic combustion results in
the real world.
"But you have to remember that everything we do on this
project - the equipment, the people, the physics - is pushed right to
the limit. It’s the nature of the game. But if you take risks and ask
new questions you get new information - there’s no point in asking the
same old questions and getting the same old answers.
"The way I see it, even if we get the payload to the
platform we’ve already succeeded. The chances are about 1 in 5 that
the thing’s going to work. and we’ve got two goes at it. I’ll let you
work out the odds!"
For the sheer hell of it, maybe. Knocking together a
Mach 10 jet engine in the backyard has a Boys’ Own, Airfix appeal that
cannot be denied. But if these things prove to be practical, they will
indeed have their practical side.
They’re bloody fast, that’s for sure. In terms of
getting from A-to-B in next to no time, they’ll be hard to go past.
They also burn hydrogen, which is renewable and non-polluting (the
only exhaust gas is steam), and with no moving parts, scramjets are
simple and efficient.
They may well power the next generation of supersonic
airliners and low earth orbit boosters, and it’s in this role that
Paull sees a big future for scramjet technology.
Unlike the rocket engine, which caries both fuel and
oxygen, the scramjet only has to carry fuel, as it takes its oxygen
from the atmosphere. This cuts the launch weight by almost half, and
while there’s no oxygen in space, a scramjet-powered plane would be
capable of taking a satellite at very high speeds to an altitude of
over 15 kilometres. After that a small rocket engine could take the
payload the rest of the way.
"The possibility of cheaper satellite launches is the
main commercial aspect of the research, and I think that’s where it
will be used first."
But there is a darker side to the scramjet. There had to
be a dark side to something this powerful.
"Naturally there are serious military implications as
well. You wouldn’t want an unfriendly overseas country having one of
these things. The Defence Department people seem to think that this
technology is too far in the future to worry about, but I think they
should be taking it very seriously indeed.
"If we as a university can undertake a flight test,
imagine what a country determined to develop these engines could do if
they put their minds to it."
It’s true that a scramjet fighter would make the F-18
look extremely pedestrian, and scramjets could power an armada of
low-cost, long-range missiles.
But the potential uses of scramjet technology extend
well beyond simply pushing payloads around at mind-boggling speeds.
When they were invented back in the 60’s, no one expected that the
biggest use of laser beams would be in domestic stereos, and Paull
expects that his group’s work with high temperature supersonic gases
will have ramifications that he hasn’t even thought of.
"This technology already has a lot of really diverse
applications. One application we’re looking at is working with the
Japanese on the chemical analysis of constituents of volcanic plumes,
which could lead to much better early warnings of major eruptions."
So what happens next if the Woomera tests are
successful? Planning is already well advanced for HyShot 2, which
Paull hopes will conclusively show not only that combustion takes
place, but that the engine generates more thrust than drag in the real
world. Once that’s established, he’s got a fair-dinkum scramjet on his
hands. Demonstrating that the engine works outside the wind tunnel
might be the easy part. Convincing the aerospace industry to invest
billions in developing commercial scramjet aircraft could prove to be
the biggest hurdle of all.
But convincing Boeing or Airbus to build a Mach 10
airliner is the last thing on Allan Paul’s mind right now, and anyway,
he doesn’t really see that as being his department.
"It will happen one day. It could take as long as sixty
years. When you think about it, this is how long it took to get from
the Wright brothers to the 747. But I suspect it will happen a lot
sooner than that."
But for now Allan Paull just wants to get to Woomera and
watch his baby fall out of the sky at 8,600 kilometres an hour.
After that, who knows?
Center for Hypersonics:
http://www.mech.uq.edu.au/hyper/
by Pat Sheil
http://www.spacedaily.com/news/future-01a1.html