 Let us move on to the next system. This system is not as exciting or as dramatic as airships because it is just a balloon which is tethered to the ground. But even though it is tethered to the ground, it can be made use for very interesting and far reaching applications. So this is a photograph of a small portable airship which is launched from the back of a pickup truck. So what is it? Basically an aerodynamically shaped tethered LTA platform. So it is not a vehicle, it is not an aircraft, it is a platform because it is expected and desired to remain stationary. So one huge degree of freedom we have removed. The payload that can be mounted on this is again limited by our imagination. Most people use it for either communication equipment or for surveillance equipment. Now what are the desired features of a good aerostat? For a given size, we should be able to carry the largest amount of payload, look like just like any other aeronautical system, we should have high payload fraction. It should be able to maintain a specified altitude on its own without any great intervention. And once it maintains its position, it should remain stable. That means as the wind direction changes or disturbances occur, it should on its own align itself and not demonstrate a continuous motion which will basically distract it from its application. Now all of these are affected by the envelope shape and hence the sizing of the envelope, the shaping of the envelope and very accurate calculation of the size, location and type and shape of the fins that you see on the back is an important exercise. And we have to learn all these things as part of this course. So this particular aerostat as an example can carry around 10 to 15 pounds of payload at a height of 700 to 2000 feet and it is not very long, it will probably easily fit into this room but it can remain up for around 48 hours. Now my question to you is should it not remain endlessly, why should there be 48 hour limit or so for this particular system? So what do you think is the reason due to which 48, yes, I would also encourage people to speak their names because we are still new to each other. Swami, from which department are you? Manu Technology. So might be because of the leakage of the gas contained inside over a period of time, that is precisely the reason. If we are able to make an envelope which has got little or no leakage, then actually there is no limit to endurance but typically fabrics have a particular leak rate and that introduces the limit to how many hours you can keep it without popping up. In this case it is around 48 hours which is good enough if you want to do, if you want to have a system for around two days to do surveillance, just one deployment and it is there. Interestingly it can withstand winds of around 45 knots which becomes almost 90 kilometers per hour approximately and it just needs one crew member who is standing below you can see. So it is a single man operation or a single woman operation and it can be easily deployed and the same person can even drive the vehicle and take it around. Alright, let us look at what are the key parts of the aerostat. So the first and the most important part obviously is the envelope. Here we say the helium chamber because we are assuming that helium is being used but it could also contain hydrogen or any other lifting gas. So it is basically the one that contains the lifting gas so it is nothing but a container with nothing but an envelope to carry a given volume of gas to control the pressure inside the envelope and to ensure that the envelope does not reach breaking point due to stretching because of the change in temperature or because of any other reason which causes stress in the envelope. We have a relieving system called as the air balloon ne. Please note the T in this word is silent. So it is called as air balloon ne. It is actually a small air bag inside the gas bag and by controlling intentionally the volume of this air bag that means by taking out the air or taking in the air in this gas bag you can control the volume available for the helium or hydrogen or LTA gas inside to expand or contract. So we use it essentially for buoyancy control and stress relieving the envelope. Then we have a payload platform now in this sketch we have shown the payload directly attached to the envelope and we have shown it below the balloon ne but it could be actually anywhere on the body of the aerostat. And in many cases such as the picture which I showed you ahead the payload is mounted not on the envelope but at a particular place called as a confluence point below the aerostat. So the payload or the equipment that you want to carry could be directly on the balloon if the local loads can be handled by the envelope material or else you can delink that by mounting it on a point called as a confluence point. And then the connection between the envelope and the ground is this tether. In this case we have shown some kind of a catenary profile because we are expecting it to be under high wind conditions but there is one serious mistake in this figure. I do not know whether you can make out what do you think is not correct at least conceptually in this particular figure. At the ground yes the tether will be connected to something on the ground in this case they have shown a winching. Yeah so this is the winching and mooring system not necessary I mean you one can have various kinds of systems the sketch shows a system which has a small you know cup like thing to hold the nose etc but one can mount it anywhere so it is a conceptual sketch what is it just a minute I mean you are saying something that can happen if the wind is very high when you fly a kite for example in high wind conditions this is the kind of profile you see for even the kite. So the tether can remain in high winds in this particular shape yes you had you had a point yes your name name Ashish yes why should it face opposite yeah so it is actually facing opposite the wing that is right the wind if the wind is from left to right then that is the right direction in which it is facing why should it face opposite to the wind it should not it is remaining stationary so the best way to do remain stationary is to face the wind and use the fins on the back because as the wind direction changes the fin will bring you back this is called as weather caulking so the direction is right yes Jagdish that is just a conceptual sketch as I said that tether is connected to the envelope it may not be there may be some other I know this is a conceptual sketch I agree there is something more fundamental which is wrong yes Sunira yes can be the payload can be on the balloon as I said it can be on the balloon or it can be below anything else okay fine so basically what we wanted to show was a three tail configuration with the third one hidden because it is behind and this one is actually the top fin it may it may seem to you as something inclined towards you but actually it is meant to be vertical okay I tell you the problem is with the angle that the aerostat envelope is shown actually if there is wind it will trim to some angle of attack it will not remain horizontal the balloon will actually acquire some equilibrium angle okay so I will correct this figure I have the correct figure I do not know how this wrong figure has come here this was made by one of our M. Tech students and I had told him that this has to be corrected but it is my mistake I put the wrong figure in the presentation okay yes it could be but in that case the tether will not be so much catenary when there is a catenary position we normally expected to trim at some angle but you are right I could alter the center of gravity and create a situation where the trimmed angle is kind of 0 but normally that is not the case okay so let us go ahead the tail fins that are mounted behind are essentially for static and dynamic stability okay so now there are two words here static stability and dynamic stability so the aerospace engineers among you I am sure you will appreciate the difference between the meaning of static and dynamic stability but for the benefit of others who may not know or for those who have forgotten let us have a brief idea about what is meant by static stability what is meant by dynamic stability and what is the difference between them so any volunteers to explain the difference between these two terms then worry about aerostats talk about aircraft in general we have the same things apply here what is meant by static stability of an aircraft or a system so Nina we want to try yes so what you said is if a force is applied on the system it returns back to the original position no this is not static stability this is of course if this happens if this happens the system is statically stable but something less also is acceptable okay so this is not the requirement this is more than the requirement what do you think is the minimum requirement for a system to be statically stable okay so we do not have to really use the many new terms to explain it basically we should say if a system is in equilibrium and if some unbalanced force acts on it or an external force acts on it what is the tendency of the system under the action of this external force if the response of the system natural response without any intervention is to tend towards the original position rather than going away then it is statically stable okay it may not lead to stability so what may happen is if I disturb a system if I take it let us say away it should tend to come back it may exceed and go on the other side it is still statically stable okay but then as Pratik mentioned over a period of time normally we expect the oscillations to slowly reduce and it should actually come back to the position that is dynamic stability so dynamic stability is what happens in the end does it actually come back static stability is does it tend to come back or not so we should have both in aerostats we should have static stability that means we should have a tendency of it to automatically react in such a way that it tends to come back and not only that over a period of time or a reasonable period of time we want it to actually also come back not keep on oscillating for whole life so the pair since help in both and their size from both the considerations the tether is basically a cable which attaches the envelope to the ground and the payload is what you as a user mount onto the system either on the envelope or at a point below it and the ground station is something that helps in two things in winching and in mooring so what is the meaning of winching what is the meaning of mooring and how are they different can someone try to explain what comes to your mind winching and mooring yes your name Kiran the winching is a process of holding in the place and what is mooring okay so it is not correct actually mooring is the holding in a particular place and winching is basically in raising or lowering it to the desired location so a winch is a system which pulls or pushes to intentionally change the location and a mooring system is the one where you attach it when you do not want it to move so you have to have a winching system for up lowering and raising and lowering and a mooring system to hold it when you do not want for example if you want to leave the aerostat on the ground for some reason for a couple of hours you do not want it to keep moving around you want it to be moored on the ground okay this is a moored aerostat developed in India by a DRDO laboratory called as aerial delivery R&D establishment in Agra so pioneering institute or lab in the country which has done work in the area of LTA systems mostly they have worked in aerostats but now I believe they are also starting to work on airships so this is one of their first aerostats so you can see that there is this hull or envelope now hull and envelope are interchangeable words they come from the aerospace lineage and which comes from the ship lineage or naval lineage hull is basically the body so hull is as same as anonymous with the envelope you have fins on the back and notice the fins are quite large in size in aerostats and then you have this mooring mast and here you have a system for winching it up and down and then you also see something called as confluence lines which are basically lines which are then attached together I am sure when you fly kites you will remember when you when you flew kites that we attach a single tether to the kite with two ropes towards the end which are properly sized okay the angle between the two ropes is actually done how much is the angle between the two ropes as children when you flew kites did someone teach you how to do kani so we hold the knot it should be it should hit the top portion at the top attachment point and bottom attachment point so the two of them should be the same length which means what if I degree angle that gives the best characteristics but those of you who are kite enthusiasts if I want to have a highly maneuverable kite what should I do I was taught by my seniors that there should be one inch or one finger width more on the top that gives you a more maneuverable kite if the wind conditions are very poor and you are going to basically fly by giving it a constant jerk then the bottom should be longer than the top so these are the things you learn similarly there are confluence lines which are used to attach the envelope to the tether which and the length of these lines and their orientations helps in deciding the stability characteristics we will study this when we come to the stability of aerostats this is one of the recent aerostats developed by the same laboratory and this photograph was taken at the Aero India show so you can see that there is a very neat winching and mooring system developed incidentally by LNT in Poway and then you have this envelope and here you can see the payload is mounted in this case directly on to the envelope okay okay so let's see and okay now this particular aerostat 17 crore rupees that they mentioned please note the bulk of the money has gone in the radar development or the cost of the radar is much more than the aerostat okay my guess would be that the aerostat system everything together will be not more than 4 to 5 crores and the remaining money will be for the radar okay but the whole system is what is important not just the balloon okay so now we have NDTV's confirmation that aerostats are available and made in India