science
10279 Concorde – How We’re Planning to Travel Faster Than the Speed of Sound

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It often feels like there just aren’t enough hours in the day to do what we aim to do, and for businesspeople, travelling all over the world from meeting to meeting, cutting down on travel time would seem like a tempting idea.

The world-famous Concorde was developed in the 70s as a very high-speed passenger plane to do just this, able to fly London to New York in under 4 hours. Let’s examine the technology and science behind Concorde which allowed it to perform such amazing feats, and then at the future of speedy travel.

Reducing Drag

Just looking at Concorde, you can immediately see differences from a standard plane. The extremely pointed nose and swept-back wings both help to streamline the plane, to reduce the air resistance (also called drag) and so reduce the fuel consumption of the Concorde.
The shape of the wing, called a “delta wing” also helped to stabilise the plane during flight, removing the need for stabilisers on the tail of the Concorde. This was helpful as added horizontal stabilisers would have further increased the drag on the plane.
The shape of the wing also helps create enough lift for the Concorde to fly.
Lift is the upward force created by wings as air flows over them, and is explained by Bernoulli’s principle.

Lift

Bernoulli’s principle is easiest to understand by considering a tiny parcel of air travelling along a straight streamline. If the parcel of air encounters a decrease in pressure, the back of the parcel will be subject to a higher pressure than the front. This means there will be a net force pushing from the back of the air parcel towards the front, and therefore causing the air to accelerate forwards.

This little example shows a very important result – when pressure decreases, speed increases and vice versa.

Now we consider our same parcel, this time travelling around a curved streamline. When travelling on a curved path, the direction of travel is constantly changing. Newton’s First Law tells us that there must be some force applied to the air to cause this change in direction (Newton’s Law says that a body will carry on travelling in a straight line at a steady speed unless some force is applied to it). So we can see there must be some force acting on the parcel of air.

Where is this force coming from? There is nothing actively poking this air parcel to force it to go in a different direction so we can conclude this force must be another pressure force, caused by a pressure gradient.
This second example tells us that when air travels on a curved path, there must be some pressure gradient present.

These examples have given us 2 really important results:
When pressure decreases, speed increases (and vice versa). This is Bernoulli’s principle.
When air travels on a curved path, there must be some pressure gradient present

Now we can think about a wing. When air meets a wing travelling through it, the air has to curve to get around it. This tells us that there must be some sort of pressure gradient across the wing.
If we imagine a wing with high-pressure air on the bottom and low-pressure air on top, we can imagine that this will cause a net force upwards to be felt by the wing – this is lift!

Returning to Concorde, the shape of the wings and the angle they meet the air at was chosen to maximise the amount of lift force created, while not making too much drag.

Engines

A key part of any vehicle is the engine. The location and type of engines on the Concorde’s was different from on other jets. Usually, engine struts are used to attach the engine to the body of the plane. In Concorde, the engines were attached directly to the underside of the wings. This was for two reasons. When flying at supersonic speeds, the high velocity of the air flowing past the plane can cause damage and stress to the outside of the plane, therefore the struts would be likely to break if they were used.
The second reason is to do with the flow of air around the plane. By not using struts and keeping the engines close into the body of the plane, the flow of air around Concorde is less disturbed, so the plane experiences lower drag force.
There was something else special about Concorde’s engines. They used afterburners to generate maximum thrust from the engines. The afterburners would take the exhaust gases from the initial engines and burn them for a second time along with added extra fuel. This meant the engines could produce huge amounts of thrust, allowing Concorde to reach its mind-blowing speeds.

Fuel

Where there are engines there is, of course, fuel. Concorde had a number of fuel tanks but, unlike other planes, they were used for more than storage. The fuel tanks were actually used to help achieve aerodynamic stability.

We need to introduce the idea of the aerodynamic centre of an object. When a wing flies through the air, a number of different forces act on it, like pressure, lift and drag. These won’t all act at the same point – they might be spread over a large area, like pressure forces, or act away from the centre of the wing. When forces are applied to an object away from its centre, these forces create “moments” which cause the wing to tilt or tip.
If you imagine pushing a cube along on a table, if you pushed in the centre you’d expect it to move in a straight line without turning or tipping. However, if you applied your force at one side, you’d expect the cube to turn as well as move. This is because you would’ve applied a moment (defined by the equation Moment=Force x Distance from Centre of Mass) as well as a force. The aerodynamic centre of an object is the location where the moments created by the forces acting on that object are constant, so even if you change the angle of the wing, the moments won’t change. Due to the differences between subsonic (below the speed of sound) and supersonic (above the speed of sound) flight, the aerodynamic centre of Concorde can shift backwards as it speeds up from subsonic to supersonic.

This shift unbalances the aircraft and could cause the nose to tip downwards. To counteract this, fuel is pumped from tanks at the front of the plane to tanks at the back, to rebalance the craft. The opposite can be done when the plane slows down, so the fuel can actually be used for stabilising, as well as powering the jet engines.

Reflective Paint

If you picture Concorde in your head, you imagine a gleaming white aircraft punching through the air. It turns out that the choice of white paint for the outer surface of Concorde was no coincidence. The white paint was, in fact, a very high reflectivity material, chosen to keep Concorde cool. As the plane moved through the air at high speed, the friction with air particles caused a heating effect – even the inner walls of the plane became warm to the touch.

The white paint was chosen to help Concorde reflect this heat away from itself. It’s well known that black objects emit and absorb radiation best, while white is the best colour for reflection – this was used to the plane’s advantage in this situation.

Sonic Boom

There were significant problems with Concorde and its flight, one of which was the “sonic boom” it made.

When a plane flies, it pushes on the air in front of its nose and compresses it. This makes waves of compressed air which travel forward at the speed of sound. However, if the plane is travelling at supersonic speeds, the waves of air are travelling slower than the plane, so new waves get in the way of old ones and they are forced together into a single shock wave.
This fast-moving air can cause damage to buildings, break glass and be loud and startling. This lead to Concorde only being allowed to fly at supersonic speeds over oceans, meaning it only had a small number of routes open to it.

The Future

Concorde had its last flight in 2003 and since then supersonic flight has been at a standstill. But China had recently revealed plans for a hypersonic aircraft (hypersonic flight is defined as flight at 5 times the speed of sound).

China’s craft, the I plane, earned its name from its shape – when viewed from the front it looks like a capital letter I, due to its 2 pairs of wings, one on top of the other.

Using two pairs of wings means the plane can create more lift, meaning it has enough upward force to carry more passengers than a single-winged plane would. The second pair of wings can also disrupt the sonic boom waves by redirecting them.

So is hypersonic flight the wave of the future? Nothing can stop the sonic boom shockwaves from being created when you fly above the speed of sound, so these will always remain a problem. However, in an ever-faster-moving and more hurried world, it seems likely that sonic boom will soon just be an unfortunate consequence of our need for speed.

Concorde Categories: Articles Tags: , , 10100 Smaller Than an Ant, Big Enough to Change Your Life

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This month, Tokyo will host the 17th edition of Nano Tech – an international exhibition and conference on nanotechnology. This year’s exhibition will feature research covering subjects from AI to cancer research, and aerospace to the environment. So what is nanotechnology, and how can it be a part of this wide variety of fields?

Nanotechnology is technology of very small things, typically on the scale of 1-100 nanometres. To give you an idea of how small this is, if a marble were a nanometre, then one metre would be the size of the Earth.

It’s quite a recent technology – before we had scanning electron microscopes (the kind of microscopes which can view things on an atomic scale) we couldn’t see things on a nanoscale, let alone make them.

How did it begin?

In 1959 Richard Feynman, the famous physicist, gave a talk entitled “There’s Plenty of Room at the Bottom”, where he put forward the idea of manipulating individual atoms and molecules, and talked about the possibilities this would present. At this time, it was just an idea, and it stayed this way until the scanning electron microscope was invented in 1981.

This signalled a huge change in our abilities to do things on a tiny scale, and soon we were making astonishing creations.

In 1985, a joint research project between the University of Sussex and Rice University was taking place, aimed at identifying interstellar matter. As part of their experiments, the scientists were vaporising a carbon rod, and noticed that C60 (a molecule made of 60 carbon atoms) was forming, in spherical shapes.

This completely rewrote the current understanding of the chemistry of carbon. Previously, it had been thought and taught that carbon can take two forms – it’s either found as graphite or as diamond. These scientists had just discovered a whole new form of carbon, completely by accident.

The structures they’d found are commonly known as “Buckyballs” and were the first “fullerenes” to be created. Now, many more have been made – tubes, ellipsoids and loads of others.

Buckyballs have lots of uses – the hollow shape of the balls means they can encase other atoms which can be useful as a delivery system. There are hopes they could be used to carry radioactive elements into the body and deliver them to cancerous tumours.

Fullerenes have also been used in lubricants, electronics, superconductors and countless other applications.

Where next?

Nanotechnology is a really new science, still taking its first baby steps. No one can really say where it will go next although there have been a range of predictions – maybe we’ll be able to make pencils into diamonds, or maybe self-replicating nanorobots will take over the world! However, there are some exciting developments happening as we speak.

Electronics

A team of researchers from the University of Southampton made headlines recently after making a highly successful alternative to a transistor, called a memristor, using nanotechnology.

Transistors are the building blocks of all computing, found in huge numbers on circuit boards called chips in every digital device. Over the years, transistors have been getting smaller and smaller, allowing us to improve our technology time and again by putting more transistors on each chip. However, we are now reaching the physical limit of how small we can go – you can’t make anything smaller than an atom.

The memristor heralds a new step forward – whereas a transistor can either be on or off, a memristor can hold up to 128 different states at once! This could allow future computers to reach blistering speeds we can only dream of.

The team managed this amazing feat by layering metal-oxides on the nano-scale and experimenting with different combinations of metals within the memristor.

Sensors

One of the most interesting areas nanotechnology has been applied to is medicine. As technology improves, there is a drive (and an ability) to move towards regular tracking of patients with ongoing conditions to help them manage their health over the long term.

Diabetes is a condition where the body can’t control the levels of sugar in the blood and affects millions in the UK alone. Diabetics have to check their blood sugar levels regularly to make sure they don’t get too high or low. At the moment, this involves pricking the skin and drawing blood, which can be unpleasant and time-consuming. People often avoid checking their blood sugar levels because of this – which can lead to them getting seriously ill.

A study on a wearable blood glucose sensor was recently published in the journal ACS Nano – the sensor could be part of a contact lens or watch and could detect levels of blood sugar through the sweat or tears.

Using nanoribbons of indium oxide, the researchers made a biosensor by trapping an enzyme in the nanostructure. When glucose was present, the enzyme would react with the glucose and make a tiny electrical signal. The intensity of the overall signal, gives the sensor a good idea of how much glucose is present, and can be used to continually and painlessly track a patient’s levels.

The sensor has been found to be sensitive enough to pick up data from tears, sweat and saliva, in people with and without diabetes. It is also hardy – it can cope with being bent back and forth 100 times.

This incredible technology could change the lives of many diabetics, and lead to fewer people needing emergency treatment.

An exciting future

It will be interesting to see where nanotechnology takes us next – it really is the stuff of Sci-Fi. There are still some worries about the safety of nanoparticles, as it is such a new technology with research still ongoing. However when these concerns are allayed, we can expect big growth in this sector – as Richard Feynman said “There’s plenty of room at the bottom”.

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