 Okay, so let us see some fastest flying birds, so one on the left is the one that has a record for the fastest flight, so I found this very interesting video, this talks about the spine tailed swift okay, so I have just put the video with no editing, now only you can see it, there you go, can you see it, were you able to see, let us see it once again now, okay, look carefully and try to spot the bird, only at 25% or 10% speed you can actually see that something is moving, so that is the speed of this bird, 10% with zoom, so that is the speed, now let us look at dive. Pilots could choose their reincarnations, they come back as falcons, peregrines seem to love pulling Gs as much as any pilot, they experience maximum Gs in one of the greatest demonstrations of flight control in any bird, their signature attack, the stew, it is in the hunt that peregrine falcons show off an adjustability of flight surfaces far beyond that of any aircraft, to spot prey peregrines often fly high up to 3000 feet, where prey have a hard time seeing them, when a peregrine locks onto a target it rolls, pulls its wings in and plunges, coming out of a stoop the peregrine feels the highest forces known for large animals up to 25 Gs, so as I mentioned they encounter 25 G force, let us see how do birds glide, now we have done a complete lecture on gravity, on gliding, so we do not have to really spend too much time, it is the same thing like you have studied on the gliders, they also have to maintain a particular glide angle, they also have to maintain L by D maximum, so as the L by D increases the glide angle reduces and hand force the glide range also increases, so when you increase in size you have a higher Reynolds number, higher Reynolds number normally gives you higher L by D, so very large bird let us say let us say albatross which is 3 meters wingspan L by D can be around 19, this is comparable to Boeing 747, 747 has L by D max of around 17 and a half to 18 okay and the bird has L by D of 19, but if you take a very small bird called as a fruit fly which is only 6 millimeters wingspan, it is actually an insect not a bird, but if you look at it carefully it is a bird, so 6 millimeter wingspan L by D is only 1.8 but still more than 1 nearing to 2 okay and can you believe that even snakes are able to glide, so this is a very interesting video about gliding snakes, those of you who are scared of snakes you can close your eyes, five species of snakes in the Malaysian jungles that are able to transform their skeletons to glide through the air, this is a gliding snake how these gliding snakes can torque their bodies to cover a great deal of ground, when it leaps off a high tree branch it rotates its ribs forwards and upwards making its body double in width, this transforms it into a much flatter aerodynamic shape similar to an airplane wing, it moves its head back and forth which passes waves down its body like it's swimming in air, Professor Jake Socia carried out the study by creating a plastic copy of the snake's cross section and placed it in a tank of flowing water and gathered data on the way the water moves around it using lasers and high speed cameras okay so this is a faculty member from Virginia Tech who has taken up a project these snakes can go up to 50 meters in a glide so they go up a tree they launch themselves they flatten their body so that they give an aerodynamic shape and then they launch their head and keep moving it so that the body goes in waves okay let's see it once again let's see this once again there are five species of snakes in the Malaysian jungles that are able to transform their skeletons to glide through the air the study has revealed exactly how these gliding snakes contort their bodies to cover a great deal of ground when it leaps off a high tree branch it rotates its ribs forwards and upwards making its body double in width this transforms it into a much flatter aerodynamic shape similar to an airplane wing it moves its head back and forth which passes waves down its body like it's swimming in air Professor Jake Socia carried out the study by creating a plastic copy of the snake's cross section and placed it in a tank of flowing water and gathered data on the way the water moves around it using lasers and high speed cameras so there is also a very interesting video when there are five students who work with these professors so the snakes are launched and then they run after the snake to catch it and bring it back now I would not work on such a project okay right now the thing is how do you actually improve your shape you do it by changing your wing or by wing morphing okay so we can see there that if you take a very very shallow glide and ignore theta then the velocity at which you launch yourself is just proportional to the square root of 2w by rho scl okay so if you assume some cl value and assume some rho value you can see that depending on the wing loading values you would have a glide velocity so it is very interesting with a very simple formula we can estimate the coated or calculated glide velocity and you can see that the percentage error is well within 2% plus minus through a simple formula so you just get the wing loading and you can estimate the velocity in glide okay so in birds as their glide velocity reduces or I should say like this as they increase the wing area the glide velocity reduces and hence the time in the air also increases okay also the distance traveled by them will also be a function so larger birds which have larger wing area they glide slowly at the same time if they want to change their glide velocity just like we saw in the video about the swan about this vulture if you want to change if you want to change the glide velocity you can change the area so the same bird when traveling at 31 kilometers per hour has the wings coming out and it goes for very very closely placed wings this is just like the variable sweep that we see in the aircraft so we can always say that the variable sweep concept of the aircraft is inspired by the birds okay so there are two examples there about the falcon and the pigeon who undergo a shape change so this shape change is called as morphing so heavier birds glide at higher speed if you look at rotary wing aircraft or helicopters versus natural flyers you see a lot of similarities first of all in a helicopter what do you do is you create a relative flow around the rotors by rotating continuously and here also they are flapping it along the arc if you actually take the locus of the tips of the bird wing you will be surprised it goes in a circular path or elliptical path I will show you some videos of that also similarly when you want to tilt when you want to go forward you tilt the thrust rotational plane same thing is done by the birds and by the insects also they tilt the flapping stroke plane and that is how they get the forward motion and during forward flight you change the angle of the rotors similarly you change the angle of flapping so I would say that the helicopters are actually doing many things just like what the birds are doing so here is a here is an example of some birds and insects now these figures are not in the same scale for example we have a bird here okay and we have a fly here they are not the same size only in movies you can have same size but if you see the pattern in which the wings are being flapped generally becomes more complex when you have going to a smaller animal larger insects or larger flying objects they have a very simpler flapping motion look at albatross for example one of the largest birds it just has a simple helical fashion but look at the bow fly look at the low cast for example it goes forward and backwards so smaller flyers normally clap in a larger so we will have a look at some animation so this is the flapping motion of the bird called canada goose so the locus of the inboard tip and the outboard tip shows you the flapping plane on the other hand if I look at a moth you can see now it is more complicated so now not only is there are two distinct top and bottom there are two distincts the bottom is actually figure of it the top is not figure of it and also notice that the body also keeps flipping along with the one that is meant for center of gravity control if they do not do that then they will also start moving and they will not be able to hover at a particular place if we look at dragonfly now there are two sets of wings dragonfly has two wings and as you can see here they are not moving in the same manner there is a lag between them okay so you can say that these are two independent set of wings which are flapping in a conical in a in a frustum of a cone manner but that is inclined and one behind the other with a lag in between okay let us look at the hummingbird a hummingbird is one of the most amazing birds the amount of control it demonstrates in keeping its position flying backwards flying upwards flying sideways so looking at the flapping pattern you can realize more more you are near the frustum of a cone more you are able to maintain hover hovering condition depends on the motion so for the hummingbird I have actually many many more amazing images so let us look at flapping in slow motion we have already seen a video which was an animation okay so look at it in ultra slow motion it will give you an idea about how the wings flap so the pigeon is now perched at a particular location so now starts taking the wings out so the first requirement is to leave the ground so you can see the downs and also the tail is morphing out but the tail has also given an angle because they want to turn so they would like the air to give you a turning flight now it wants to go forward after it has bounced and turned it wants to go forward so when it is going forward notice the tail also deflects there is an angle change in the tail there is an area change in the tail there is a camber change in the tail and that is happening naturally with the wings now it is going to turn so there you go one more look so wants to launch so therefore it bends down and the wings are going up basically to flap down so you throw yourself up and now you flap the air down so basically down and forward so it's down and forward I can't do I'm not so efficient like a pigeon look at the landing gear being retracted inside everything that you see in aircraft has actually been inspired by birds it's amazing how much aerodynamics you can look by just looking at these animals this is a fruit bat which is in again captured in slow motion now look at this particular pattern carefully because I will very soon show you a study about the aerodynamics of this particular animal done by one of your students one of your seniors so notice now how the outboard tips so it's like a human hand only it's like a human hand if you see but the motion is very complex now let's look at hovering flight so you see how she is able to maintain position at just one place and the tail is also twisting slightly the rear is also going on and now a slight change in the inclination and you can go turn this is in slow motion I have some very beautiful pictures of these birds in full speed I'll show them also to you towards the end when I have some time so the material for this presentation has been taken from these two very interesting textbooks which are available freely online okay the one is called as a simple science of flight from insect to jumbo jets by Tenekes okay this is available with me also if you are interested and there is also a very nice AIAA textbook by she et al on introduction to the flapping wing aerodynamics this one is more formal it contains a lot of mathematical expressions derivations for the flight okay