The Science of Flight

This week on the Naked Scientists Radio Show and podcast we will be looking at flight - in terms of both animals and how they fly and the machines that people fly in. Cameras...
25 March 2007
Presented by Chris Smith, Helen Scales


This week we explore the science of flight. Dr Graham Taylor from Oxford University talks about the aerodynamics of insect flight and how video camera back-packs allow him to see how eagles fly, and Jenny Goodman describes how future aircraft might be flying at six times the speed of sound while withstanding temperatures hot enough to melt stainless steel in 5 seconds! In Kitchen Science, Ben Valsler sticks with the flight theme and finds out how a hot air balloon works.

In this episode

Marine diatoms as seen through a microscope. These tiny phytoplankton, which are encased within a silicate cell wall, were found living between crystals of annual sea ice in McMurdo Sound, Antarctica.

03:01 - How increased carbon dioxide levels affect shellfish

Rising carbon dioxide levels usually make us think about the atmosphere, but new research shows that carbon dioxide dissolving in the ocean could have devastating effects on shellfish and...

How increased carbon dioxide levels affect shellfish
with Frederic Gazeau from the Netherlands Institute of Technology

Chris - Now we're going to start off with something a little bit different this week, and that's with two emails. The first is from Simon in Burwell who says, 'I'm a great believer in trying to alleviate climate change and I even have solar water heating fitted to my house. I've recently watched a programme called the Great Global Warming Swindle. The main thrust of the programme was that although scientific studies have shown that there is a close relationship between rising CO2 in the atmosphere and an increase in planetary temperature. The relationship is that the planet warms first and then the CO2 rises. This could be accounted for by the increase in plants and animals. The programme therefore alleges that the CO2 man creates is not only insignificant compared to volcanic emissions, animal emissions and sea emissions, but CO2 doesn't appear to cause any increases in planetary temperature anyway. They blame it on the activity of the sun. Now I don't really know what to think.'Diatoms - a key Phytoplankton group

I've also got an email here from Steven who writes about Al Gore. He's had a documentary called An Inconvenient Truth. Steven says 'for the past few years I've taken for granted that global warming is happening. After doing a lot more reading recently and talking to someone who's interested in this and done a lot of research, I'm now unsure. I feel that humanity pumping CO2 and other greenhouse gases into the atmosphere must be doing damage, but is it as bad as is feared?' The important thing here is that both of these emails focus on one aspect of CO2, which is the impact we think it might have on global temperatures. But that's not the whole story necessarily because CO2 could also be having dire consequences for our oceans. Someone who's got evidence of that and is about to publish an important paper on it in the near future is Frederic Gazeau. Tell us about your research.  

Frederic - What we did was to try to estimate the impact of increase in CO2 in the ocean on the calcification of shellfish and molluscs. The calcification of molluscs is the growth of a shell.

Chris - So in other words things like mussels, oysters or anything that has a shell.

Frederic - Exactly. We did our experiments on mussels and oysters, which are the most important in terms of aquaculture so it has an economical impact. So that's why we chose these species.

Chris - So why should CO2 in the atmosphere have anything to do with the sea?

Frederic - What you have to know is that the CO2 that is released by human activities such as the consumption of petrol, gas and coal, one third of this CO2 is pumped by the ocean. If you pump CO2 in the ocean, you will decrease its pH.

Chris - So in other words the sea is soaking up carbon dioxide that we've put into the air.

Frederic - Exactly. One third is taken by the ocean. That's what we estimated. So if you have more CO2 in the ocean you will have a stronger acidity of the ocean. The problem is that this acidity can damage organisms that grow skeletons or shells made of calcium carbonate.

Chris - This is the same stuff that builds up as limescale in the kettle and we add acid to remove it.

Frederic - Yeah exactly. The thing is that CO2 in the ocean has three different species: the CO2 by itself, bicarbonate and carbonate. If you decrease the pH, you will shift the equilibrium between these three species towards more CO2 and less carbonate ions.

Chris - The thing is that it's all very well saying that Frederic, but how much CO2 does it take to make a big difference in the ocean? Have we got any evidence that the CO2 that we make does make a difference to the ocean and how are you proving that it actually makes a difference in the long run to animals in the ocean?

Frederic - We first have evidence that in some places on Earth in the ocean we had a decrease in the oceanic pH in the last decade. That's a fact.

Chris - So the sea genuinely has got more acidic in recent years. Frederic - They are more acidic, they are not acid of course. They are still basic but the pH is lower, so they are more acidic, yes.

Chris - And how do you know that this has an impact on animals?

Frederic - The thing is, it's just a chemical reaction. If you want to build a calcium carbonate shell or skeleton, you need carbonate ions. If you decrease the pH, you will decrease the concentration of carbonate ions, so that's a chemical fact. The thing is, now we're thinking that some organisms are able to adapt and acclimatise to the new environment and that's now what I'm going to do in the next month. I'm going to try and see if the organisms are able to adapt themselves.

Chris - What experiment did you do to prove that there is a problem in the first place?

Frederic - We incubated in a chambers in an aquarium two populations of the mussels and oysters. One population of mussels was incubated with a CO2 concentration which is what we have now. Another population was incubated with increased CO2 concentrations in the water. What I did was to measure the rate of production of their shells and I saw that if you increase the CO2, you decrease the rate of shell formation.

Chris - Now when you said you incubated them with increased CO2, how much increase? Is it within the realms of what we expect to see in the atmosphere within, say, the next fifty or one hundred years?

Frederic - Yes. I went further than these limits but I covered the range that is expected in the next one hundred years.

Chris - Now obviously the problem won't just be confined to shellfish, so what other animals might be affected?

Frederic - A lot of different animals. For instance the most famous ones are the coral reefs as they are made from calcium carbonate. Also we have small planktonic organisms that we call pteropods. You also have small planktonic algae, and you have species like sea urchins for instance. We have evidence for several of these species that if we increase the CO2 of the ocean then we will threaten and decrease their ability to produce their skeletons or their shells.

Chris - So irrespective of what CO2 does to the weather or to the temperature of the earth, it will definitely have this effect on the oceans and therefore there could be quite serious repercussions.

Frederic - That's what we think and that's what the first experiments have shown already. But now what we have to do is to see whether these different organisms are able to acclimatise first or also genetically adapt to an increase in CO2, and that's something that will be done in the next years, but we can't really answer this question now.

Chris - Sobering words there from Frederic Gazeau who's at the Netherlands Institute of Technology.

The main transmitter of the West Nile virus in the southeast is the mosquito species C. quinquefasciatus

A bit of bug spit could be a good thing

New research out this week hints at a ray of hope in the battle against malaria - and it seems the answer could be a rather simple ingredient - mosquito spit.  Every year somewhere between one and three million people die of malaria and the search for an effective vaccine is a huge challenge facing medical researchers today.Culex quinquefasciatus Mosquito

Scientists had already discovered that the saliva of sand flies can help protect against an insect-borne skin disease called leishmaniasis. And now a new study by Mary Ann McDowell and her team at the National Institute of Allergy and Infectious Diseases in Maryland in the US has shown that mice pre-exposed to mosquitoes that don't carry malaria have better protection against the disease when they are later bitten by infected mosquitoes.  Mice with uninfected mosquito saliva in their blood were found to have lower levels of the malaria parasite.  The non-infected saliva stimulated the immune systems of the mice to produce infection-fighting chemicals called cytokines which are mostly associated with immune cells called T-helper 1 cells.

Of course it's early days and we are a way off seeing a new anti-malaria vaccine based on mosquito spit, but McDowell and her team are already on to the next step and are hunting for the particular protein that is responsible for this immune response in mice - when they find it they will need to test whether the protein is also effective in humans.

Attractive way to pinpoint cells

US researchers have found a way to non-invasively track the movements of cells around the body, a discovery which could help scientists to better understand how some cancers spreadand how the immune system works. MRI machineAssaf Gilad, from Johns Hopkins in Baltimore, developed a way to entice cells to produce a natural contrast that could be picked up by MRI (magnetic resonance imaging), enabling thelocation of the cells to be pinpointed. To achieve this the researchers created an artificial "reporter gene" which, when inserted into a cell causes it to produce a hydrogen-rich protein (containing multiple lysine amino acid building blocks). This makes the cell visible to an MRI scanner,which works by zapping cells in a magnetic field with a pulse of radiowaves. This temporarily knocks hydrogen atoms off kilter, which the scanner detects. Using the technique as proof of principle, the researcherswere able to detect tumour cells that had been transplanted into animals brains. In the future the team hope to come up with an array of different tracers which can be simultaneously and independently tracked around thebody, non-invasively, with MRI.

Can curry reduce parasites?

There was a bit of research done on this. In 2004 some people looked at coriander, the thing that you use to perk up a curry. They managed to find a molecule in there called dodecanal, which is a 12-carbon hydrocarbon with an oxygen on the end. They found that it's very good at punching holes in the membrane of bugs like salmonella, so it works a bit like a detergent. It's got this long oily chain that it sticks into the membrane of the bacterium and then this water-loving bit at the other end that opens up a hole in the bug's wall. The hole allows the contents of the cell to leach out and the bug dies. So how much coriander would you need to achieve that effect? Well when they got an amount of coriander greater than the amount of curry you would eat, then you could get enough of this dodecanal to get approximately the same effect as the antibiotic gentamicin. So it can work but not at the concentration that we're seeing in curries.

Why do men have nipples?

It's an evolutionary thing. If you look at how we develop in utero, for the first few weeks male and female babies look absolutely identical. It's only subsequently that you start, under the power of the hormones pumped out, to change and alter your anatomy. But because you develop a lot of these surface structures and appearances when you're very early on in development, you've got them whether you need them or not. There is one example that I've managed to find that's a male and uses it's breasts to potentially breast feed as they certainly lactate. That's a Dayak fruit bat and they live in Indonesia. The male produces about a tenth of the amount of milk that the female does.

The Georgia Aquarium, USA

22:00 - Whale communication, musical aquariums - Science Update

Bob and Chelsea hear about the music of the ocean, including scientists that listen to whale communication, and how the Blue Danube is helping the visually impaired to see the magic of...

Whale communication, musical aquariums - Science Update
with Bob Hirshon and Chelsea Wald, Science Update, AAAS

Bob - This week for the Naked Scientists, while you've been busy with flight, we've been diving under the water. I'm going to talk about public aquariums and how scientists are making them accessible to people who can't see. But first, Chelsea's going to talk about oceanographers who are listening to the world's largest animals.

Chelsea -  The fascinating songs of humpback whales are familiar to scientists and the public, but those of blue whales - the largest animals on Earth - are much less known. Now scientists from Scripps Oceanography in California have linked these endangered whales' sounds to their behaviours by tagging them with suction-cup recorders. Team leader Erin Oleson sped up this one sound made by feeding whales to make it easier for us to hear.

Erin - So they'll be feeding and then they talk a little bit - it's kind of like eating at a diner where you chat a little but and then you go back to eating for a while and then you chat a little bit.

Chelsea - Since sound travels vast distances in water, thanks to this research scientists will be able learn more about blue whales around the world just by eavesdropping.

Bob - Thanks, Chelsea. If this version of The Blue Danube seems strange, it's because it's being played by fish. It's part of a new project to make public aquariums more accessible to the blind. Psychologist Bruce Walker of Georgia Tech says his team assigned each fish in a virtual demo to a different instrument in the song. The instruments get louder and pan right or left as the fish move around the tank. Walker says it can convey where the fish are, and a whole lot more.

Bruce - We want to make sure that the "ooh" and the "aah" experience that a sighted person has when they stand in front of a massive wall of glass and see fish behind is communicated to our visually impaired visitors. So choosing the right kind of music is crucial to sharing that emotional experience.

Bob - Besides well-known pieces of music, Walker's team is experimenting with other sounds, including more abstract tones and rhythms. Ultimately, they'd like to represent not only where the fish are, but also how fast they're moving and what activities they're doing. The team also hopes that the audio-enhanced aquariums will add to the experiences of sighted people.

Chelsea - Thanks, Bob. Next time we'll talk about a computer program that knows how you want to die - at least it can take a really good guess. Until then, I'm Chelsea Wald.

Bob - And I'm Bob Hirshon, for AAAS, The Science Society. Back to you, Naked Scientists...

Should coffee be stored in the freezer?

The main reason you want to freeze it is to keep in all the volatile chemicals and aromas. If you keep it in a warm place then the volatile chemicals come out of the coffee and it won't taste as good.

Could you return nuclear waste to the mines it came from?

I think there are a number of problems. One of the problems is making sure that when you're putting stuff in the ground you don't build a bomb by accident. This is in the sense that this stuff would be in a reasonably active state and so if you put everything together you might get reactions propagating. The second question is whether a mine is the best geological place to put something that could potentially have major health implications. If it gets into water and then into people, it could have major implications for human health and the environment. You may need a more stable geological site. This is why scientists have not really decided how to make the best repository. There is one site, which is over in America, but I don't think anything's in it yet. People are putting a lot of thought into this because you don't want to make the wrong decision. Some of this stuff remains radioactive for 250 000 years, so the place you put it must also be stable for 250 000 years. Putting it back in a mine might be dodgy if you want my personal opinion.

31:10 - Flying Planes at Mach 6

If you thought Concorde was fast, think again. Scientists are looking to make hypersonic engines that could travel from London to Syndey in a few hours.

Flying Planes at Mach 6
with Jenny Goodman from the University of Oxford

Chris - Now we're very pleased this week to welcome Jenny Goodman who's a researcher at Oxford University and works on getting us all to the other side of the planet much more quickly. So tell us about your research. A plane wingJenny - What I work on is something called the Sustained Hypersonic Flight Experiment. It has the rather unfortunate acronym of SHiFE.Chris - Which could be mistaken!Jenny - It's being done by a company called QinetiQ and the aim is to build something called a ramjet engine, which is a special kind of jet engine. This is going to fly on a rocket up to four times the speed of sound. It's then going to launch itself and accelerate up to six times the speed of sound, which is two to three times the speed of Concorde.Chris - So that's two kilometres a second isn't it?Jenny - Yes that's right. Then it's going to fly along at Mach 6, six times the speed of sound, for 100 seconds before running out of fuel and crashing to the ground. But 100 seconds, Mach 6, ramjet, is all very exciting and never been done before.Chris - How's it actually work and why does it need to be launched off a rocket? Why doesn't it just take off?Jenny - A ramjet engine works just the same as a jet engine that you get on your standard jumbo jet. What happens is that it needs to suck in air and it needs to compress it so it increases the pressure before it gets to the combustion chamber. You then squirt in some fuel, you combust that fuel and just exhaust it out of a nozzle. You get really high-speed air coming out the back, which creates the forward motion of the engine. Now a ramjet engine isn't like a jet engine because what happens is instead of having that big spinning set of blades you have in front of a jet engine, in a ramjet engine you can carefully shape the intake so that it does all the compression through something called the ram effect. That's why it's called a ramjet. You compress your air without this enormous lump of metal spinning at the front, so it's much lighter. Fantastic!Chris - It must be quieter I imagine.Jenny - Not necessarily quieter because you've got all that air coming out the back so it still makes a bit of a noise. Bu the trouble with it is that in order to get the ram effect to work, you need to be flying fast and creating something called shock waves in the intake. This means that you need to be flying at more than Mach 2 really for them to work effectively. In our case, our ramjet is only going to work at Mach 4 to 6, so in that case you have to get it there first of all with a rocket. Chris - So how is this different from what rockets already do?Jenny - The thing with a rocket is that it has to carry its fuel and its oxygen on board. With a ramjet engine it sucks in the oxygen in the form of air from the atmosphere, which reduces a lot of weight because you don't have to carry all that oxygen around with you. Chris - And once it actually gets going, how far are we away from seeing this being able to be plugged on to an aeroplane? One could see how you could apply this: you would need something that would go pretty fast to get it up to that threshold speed and then these things could kick in and then take you much much faster.Jenny - Well we've actually already got it on an aeroplane. The Blackbird SR71 actually has a turbo ramjet engine. So it uses a normal jet engine to get it up to around Mach 1 or Mach 1.5 and then it changes into a ramjet engine, but it only flies at around Mach 2 to 2.5, so our one is going to go faster. Chris - Does it use the same fuel as a normal aircraft engine? Jenny - Our one is actually using diesel, but it can also use the same fuel, kerosine, that we use in a normal engine. Chris - Because that's important because you don't want to be carrying two loads of fuel aloft, do you?Jenny - No, you wouldn't. If you then go faster still into something that's called a scramjet, which a supersonic combustion ramjet engine, they tend to use hydrogen because it's got different properties to diesel.Chris - So what are the major constraints with getting this going? Jenny - One of the major constraints is that once you go that fast, so above Mach 5 which we call hypersonic, things get very hot. If you can imagine the friction forces just on the outside, inside our combustion chamber we've got 2400 Kelvin, so that's about 2200 degrees Centigrade, so you're talking 1000 times hotter than your normal room.Chris - But things run hot anyway, I mean your average jet engine must be pumping out gases that are 1000 degrees or hotter at least.Jenny - They are hot but they're not as hot as that for sustained periods. The other thing is that you want to keep the whole thing light. So your standard jet engine or gas turbine engine is cooled by leading some of the air that goes into it through complicated passages, and that keeps the turbine blades at the back cool enough by film cooling and things. We don't want to anything as complicated as that when we're that hot and trying to keep the weight down, so that's complicated. Chris - And is that surmountable? I mean if we can put a probe so that it can slam into the atmosphere of Titan, Saturn's largest moon, at 13 000 miles an hour, get to 2000 degrees, withstand that and then plummet into a bath of liquid methane, surely it's not beyond the realms of possibility that we can design something that's light enough for what you need it to do.Jenny - Of course not, that's what we're doing. We're going to fly this thing in two years or so. We can do it! We're using something called carbon silicon carbide, which is a really fancy sort of composite material that's worth its weight in gold. That can withstand these kind of temperatures pretty much indefinitely. It's great stuff but you can see how it gets pretty expensive. You fly a probe to Titan and you can do it once. It costs millions and billions of pounds. You want to fly continually from London to Sydney, do you really want your air fare to be that high?Chris - No, of course not. Now what sort of altitude will these things run at? Presumably they would be able to go much much higher. If they're using that kind of approach they would probably being going twice as high as we fly at at the moment wouldn't they?Jenny - Our one's going to fly at 30 000 metres, so 30 kilometres, which is a lot higher than normal. We're usually at about 32 000 feet, I think.Chris - Yes because aeroplanes go along at about the height of Everest don't they. This would be three times that wouldn't it?Jenny - Yes it would be. That adds additional challenges for when you're designing your plane and things. Chris - But I would think that at those kinds of altitudes, because the air is so much thinner there will be much less resistance and it should be quite economical as far as flying goes.Jenny - I guess it is. Would you get less drag? I'm not sure. Drag goes against an aeroplane to stop it going along. I think there are an awful lot of challenges with going high because the pressure outside is lower, which means you have to pressurise your aeroplane a lot more, which means it needs to be stronger and therefore heavier. So there are a whole load of pros and cons to flying high. Chris - How long have people been trying to develop this? When I was little I swear I heard people talking ten or fifteen years ago about how notionally this technology could be used, and they were saying that in a couple of years they'd be able to build it. Here were are fifteen or perhaps even twenty years later and although it's taking to the air in a prototype form, it's still pretty prototype.Jenny - Well ramjets have been around for a very long time. I'm struggling with my history here but I'm tempted to say around the 1930s or 40s we actually had ramjet planes flying. The thing is that to be able to fly this fast, were talking hypersonic speeds, and to make it reliable and safe, now that is something that we're really grappling with. We've only just got there with subsonic flight, so moving up to supersonic and then hypersonic flight - we've had supersonic flight and let's face it, people weren't prepared to pay. Putting this extra amount of money in the get to these higher flight speeds is a challenge in itself.Chris - And my last question for you Jenny, what would be the sonic boom you would get from one of these things? Because Concorde upset quite a few people in Surrey if it went a bit too fast and they all got these sonic boom effects. Will this do the same thing and will we have a noisy future if we plug this into aeroplanes?Jenny - You will still get a sonic boom as far as I'm aware because at some point you will have to create that shockwave as you go over people. I believe these days if they created a new supersonic, a Concorde 2, they can make the sonic boom a lot less by the way they shape the actual aeroplane. So probably by the time you're taking off over people you're probably going at Mach 5 anyway, so we can actually do that better now, so it's probably going to better for people than Concorde.

40:25 - Mechanics of Insect and Bird Flight

Bird and insect flight is still not fully understood. So scientists are now using video backpacks for eagles and virtual flight simulators for flies to work out exactly what's going on...

Mechanics of Insect and Bird Flight
with Graham Taylor from the University of Oxford

Chris - Now it's time to talk to Graham Taylor, another Oxford University guru, on the science of flight. You actually take a slower and more sedate approach to flight than Jenny does, not travelling at Mach 6 obviously. So how do you study the science of flight?

Graham - Nothing close to Mach 6 but perhaps not sedate if you look at it close up. If you've ever looked at the way dragonflies are dancing over a pond or perhaps how a hoverfly hangs in a woodland in a shaft of light, then you must have wondered how they're able to control themselves so well. That's what I'm interested in understanding; both how they're so manoeuvrable and so stable at the same time.

Chris - Sounds easy when you listen to it but actually how do you manipulate and watch and study a tiny insect to see how it does these tiny things. Their wings are beating at 800 times a second some of them, aren't they?

Graham - Yeah that's right. And you've put your finger on the really difficult thing there, which is that they're tiny. In fact most insects are actually much smaller than those which you're familiar seeing, and that poses real problems with how you can go about studying them experimentally. So what we do is to pin them down. Now the problem with pinning an insect down and then trying to understand how it flies is you need to convince it that it's flying. And so what we've done is to build a virtual reality flight simulator, a bit like the thing you might have sat in at a science exhibition. We put the insect inside of that and it allows us to simulate exactly how it would be experiencing things as it's flying through the air.

Chris - So you're showing it pictures as though it were flying and then you're seeing how it changes in response to things you show it.

Graham - Yeah that's right. But that in itself poses more problems because an insect is, unlike us, able to see all the way around itself. So for a start you have to immerse it in a sphere that has video projection the whole way around it, so that poses problems. And on top of that, flies are also able to see extremely quickly. So whereas you and I are sitting in this studio here don't see the fluorescent lights as a problem, for a fly that was sitting on the wall it would see the lights flickering on and off. So we have to project patterns extremely fast as well. So we put the fly in the middle of this large sphere, project around the outside of it, and then it feels to the fly as though it really is flying through a visual environment.

Chris - And then how are you monitoring what the fly is doing exactly to work out how it's flying?

Graham - The fly itself is mounted on a little balance that's a bit like a complicated weighing scale, but it measures the forces and turning moments or torques, a bit like you'd apply to a tap to turn that on. So it measures all of those, which tells you how the insect would have been flying if it hadn't been superglued on top of this balance in the first place.

Chris - And do you then try and work out how its brain is responding or are you literally taking a step back and working out how the whole fly responds to visual stimuli? Because obviously understanding the nervous system correlates of how it controls flight must be quite important, because I know people are interested in working out if insects can do this, can we therefore make a better computer programme to control our planes and our artificial flying machines better.

Graham - That's the thing that we're most interested in getting at, so we look at both levels really; the overall black box level where you treat the insect as a black box that you don't know what's in. On top of that and at the same time as recording the forces the insect produces, we're also able to monitor what the nerves are doing. So by making recordings from its nerves, we're able to tell what signals are being sent to its brain and how it's using those to control itself. So yes, we're trying to get into that black box.

Chris - Well that's insects, but what about the bigger animals? Do they apply the same principles that an insect does? Does an eagle soaring around using exactly the same mechanisms as a gnat over a pond?

Graham - Well it's almost certainly not using the same mechanisms, but interestingly we actually know rather less about how birds fly than insects. It's not quite clear why this should be. They're bigger, which makes them a little bit easier to study but of course it does mean that you can't put them into a virtual reality flight simulator. So with the birds we do something quite different. What we've done is to make a backpack which we put on an eagle. He's called Cossack because he's a Steppe Eagle and comes from that part of the world. He flies around over the cliffs in Denmark and is actually coming over to Wales shortly. As he's soaring over the hill tops, what we're able to do with this backpack is to put a couple of miniature video cameras on and monitor where he's looking, what his wings are doing and what his tail is doing. These are radio signalled back to the little base station where we record this, so we get in-flight video at the same time as having the sort of instrumentation you'd get on an aircraft. So we know how fast he's accelerating, how quickly he's turning.

Chris - And when you actually do this, does it give you clues about how birds achieve something that's actually quite an enigma I think; how do they manage to fly without having a tail fin? All of the aeroplanes we've ever built have to have one or else they don't fly properly, but birds don't have one.

Graham - That's right and that for me is the sort of holy grail of this line of research: to understand how birds are able to make do without having a vertical tail fin. Now there are some aircraft which manage to do this.

Chris - Harriers and things?

Graham - They still have a vertical tail fin, a harrier, but there are one or two that manage it. And there what you have to do is have a very complicated control system where the computer controls the plane. So with something like the stealth fighter, the pilot's almost fooled into thinking that he's flying that aircraft, because really it's the computer that's controlling all of the detail.

Chris - So what are the birds doing?

Graham - Well we're trying to find out whether they're doing something similar; whether they're also making use of active controls as an alternative to having this vertical tail fin. Another thing that might be going on is that there might be something clever in the way the tail is shaped, so the twisted triangular tail has some unusual properties. Now if we could mimic those in an aircraft then you'd really be onto something quite interesting.

Chris - I can't believe that people haven't already. If you wanted to build a flying machine, surely the logical place to start is to borrow from biology and steal what nature has evolved over millions of years.

Graham - Well in many ways that is the logical place to start and it was the logical place. So early on in the history of flight people did look to birds and try to copy some of those mechanisms. If you look at the Wright flyer for example, unlike modern aircraft which have flaps on its wings and uses those to control itself, the Wright flyer had its wings twist and deform in a way that mimicked the way the Wrights saw buzzards over their house doing. So yes, that's where people started but in more recent years, for very good reasons actually, people have moved away from copying in a sort of slave-ish fashion how birds fly.

Chris - So the bottom line summary is that at the moment we still don't really know, but we're getting some quite good insights into the tricks they use.

Graham - That's right.

Chris - Are we any closer to actually building an artificial bird?

Graham - There are quite a few orni-thopters, which are flapping aircraft, little remote controlled ones that you can buy. You can get these things on the internet quite cheaply. So there one or two of these things around but as of yet they're not very operational in the way that people who want to use them would want them to be. 

PETE bottles

Why do water bottles shrink when they freeze?

I would say that it's the air inside the bottle also contracting.

Air gets bigger as it gets warmer and smaller as it gets colder.

So, although you're right that water expands when it freezes, the air will also shrink down. And if you have a good seal on your bottle so that no more air can creep in, I think that it might crumple when it got colder.

The material of the bottle itself might even contract when it gets cold, which would crumple the bottle into a distorted shape.

Hot air balloon

Make your own hot air balloon
with Dave Ansell, The Naked Scientists

Here is the answer to how to make your own bin-bag hot air balloon. 

Part 1, in which we set up the experiment, is here...

Can ramjets get enough oxygen to burn their fuel?

You're flying pretty fast so you'd be able to scoop up quite a lot of air as you're going along. So yeah, it's fine getting air at that height.

Do swallows roll 360 degrees?

The quick answer is that it might be the case. Most birds don't do that because they actually keep their head horizontal in flight, so if you turn 360 degrees you end up turning your head around. The only bird I know that definitely does it is the raven, but swallows are very manoeuvrable so I guess it's perfectly possible that they do too.


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