 So finally we look at some work that we have done in our lab on characterizing these fabrics and for that some machines have been procured and installed in the LTS systems lab. So I will just showcase to you these machines one by one. This is a machine that we have for dedicated machine, special purpose machine for testing the strengths of ropes or fabrics. So in the current configuration that you see the jaw that has been put this is the jaw of the machine. So in between these two jaws you will attach the sample. This jaw is currently meant for cables. So you will see there are some turnings in the particular that is if you take a close look at this you will find that it is meant for winding a rope. So we use this machine for testing the strength, breaking strength of the tethers and the breaking strength of the holding lines that we use in our airships. If you want to test the strength of these ropes or these cables in a standard testing machine you will not be able to do it because there are no jaws available to hold the material. Plus the range of this particular machine is in such a value where you know it can calculate the property. So I think it has got the breaking strength of 200 kilograms and the lease count is also very low. So this is used for tensile and compressive strength and you can test various types of forms. You can test round forms that means round graph section cable. You can test flat cables. You can test threads. We use a lot of threads in our airships. You can test wires. You can test fabric. You can test belts. You can test strips. You can test ropes. So all these can be tested in this particular machine. So if you have any requirement you can always visit it now. As part of this course I am going to recommend that all of you should visit the lab one day and we will try to arrange a demonstration session for you in which the students will showcase to you the work that has been done. This is one special equipment. Around 3.5 to 4 lakhs is the cost of this machine. Then the next equipment which I want to showcase is a very special equipment is the helium leak detector. So as you know helium is one of our preferred LTA gases and leakage of helium can be disastrous from the point of view of cost and operational efficiency. So let us say one of you makes a small airship or envelope for aerostat. And now you have fabricated it but how do you test it for leakages? So one way of testing for leakages is go to the swimming pool and dip it in the water just like the tire punctures are checked by the cycle mechanics. So you fill it with air and the air will bubble out from the leakages. Now do you think we can use this technique for our LTA fabrics? Why not? What is the problem? I am using air that is very right. You will require huge amount of manpower to push a large envelope full of air because remember the buoyancy force will not come from the weight of the air it will come from the weight of the water displaced and the weight of the water will be quite high. What is the weight of 1 meter cube of water? 1 ton. Imagine. Okay. This is one reason. Any other reason? Why a cycle mechanic can use but we cannot use. Suppose I make a small balloon which you can push inside let us say. I still cannot use it very efficiently for LTA systems leak detection. Bye. I mean what do you say? Yeah. So I am saying that now the airship is only 1 meter in length and swimming pool is available. So still there is a problem that is one problem the fabric normally not LTA fabrics normally are not supposed to soak water they are supposed to repel or resist water. So if I use for example PVC there will be no problem raincoats are made up of PVC. So nothing will happen water will repel. The problem is that a typical LTA fabric LTA system is under low pressure. A cycle tube is under very high pressure. So the air is gushing out when you put it okay. In the LTA system if you put it on a very high pressure it will tear. It is not designed for very high pressure right. The pressure inside you know is only little bit more than outside. So what will happen is if you push the airship in the swimming pool because of the hydrostatic pressure of the water it will just cave inside it will cave inside and that will resist the air to come out. So resistance of air to water so you will see some bubble somewhere but it will be difficult to locate. So you cannot use. So can you think of some other method of using? Can you think of some other method by which you can determine leakages in an inflated envelope. Now those from the LTA lab who know let us not do not tell what it is think about it. You have made an airship envelope of let us say 5 meter 5 meter length. You have filled it with air okay the shape looks okay but there could be micro leaks at some places how do you find out? Think about it it is difficult we tried it out. We tried we put Agarbati and Dhup flames inside okay. So first of all it is not easy. You can generate. See Dhup is something that creates a lot of smoke and it is easily available in the market. So you can put a pump which will suck the products of burning the Dhup stick and you can push it inside the envelope out of sometime the whole thing smells of Dhup. So orderly very difficult. Now in which place you have a larger concentration of Dhup you need a very very nice nose for it. It is very difficult okay. So we tried we failed anything else? Colour dye we mean liquid colour gas okay. So we are saying that we take a gas which is coloured and we fill the envelope with coloured gas and then we look for places from where it comes out okay. You will notice that the rate at which the gas comes out is very very small. So therefore colour dyes also may not work very well except when there is a big leak. If there is a big leak you can see it. Then you need a special kind of a gas where there is a accumulation. You are assuming that the colour will accumulate at the hole. It does not happen. It just comes out okay. So we have tried all these things that is why I am very confident anything else. And just look at the tactical situation. Now you are stuck somewhere in some college you are going doing a demonstration. Now where do you get the coloured gas? Are you going to carry with you okay? You might say okay I know some chemicals if you burn them it gives yellow coloured gas then you pump that gas inside it is not very straight forward. Think of something else which is much cheaper and much practicable. Think about it. You have to use some innovation. Let me give you a couple of minutes to think. In the meantime I am going to locate a picture of our testing and show it to you. So think about it. Take a time. Take some time. Okay so there is a method called as a soap bubble method in which what you do is you now first thing is you are assuming that the liquid will be only at the joints. That is not necessary. It is quite possible that the fabric itself has got a small hairline or a small spot where it leaks. So do not assume that the leakage will happen only at that point. And the method which you suggested is possible. I am not saying it is not possible but it is not really very cumbersome. Very exotic solution. So you fill it with hot air and then you wait. Look you are in the middle, you are somewhere else, you are not in your lab. Think of a simple method which can be implemented in a laboratory. The beauty of solutions which work are that they are simple. Think of simpler solutions. So think of very simple solutions which can be implemented. So anything that detects the leakage by looking at or sensing the gas or air which comes out is not going to work practically because the rate at which it comes out is very, very small if the leakage is small. The pressure inside is less. If you precise it too much you are stressing the fabric, I will not permit it. Because you may create a tear. If there is a very small pinhole you may pressurize and you may blow it more. So in the process you will give me 10 more holes, I do not want that. So no brute force method. Something else that can be sensed, we can drop a film of water, it is not easy to drop it. But let us say if I drop, if I have a rope with bucket and that bucket is moved and the water is slowly falling, the rate at which the gas is coming out is very less. So you will not have so much pressure that the bubble will be formed. That is why as I said any sensor that detects leakage by capturing or sensing the air coming out may not practically work in a normal situation. Of course what we do look, I will show you what we do. So in our helium lead detector or in the system that I showed you, what we do is there are two methods that is something called as a vacuum mode, in a vacuum mode basically. So you can detect the presence of helium, so this is a sniffer. You can see the probe here, this is a probe. You connect this to the machine and then you take the probe and now you can move it at the locations where you expect leakage. If helium is coming out, this fellow will sniff it and it will tell you that there is a leakage coming and this is a sniffer mode. But for this I must fill it with helium and let us say there is a leak at three places. So helium is slowly coming out of that place. The second thing is it is a humanly difficult task to go all over the envelope with the probe. Very difficult. Try to do it 15 feet length envelope, 1.5 meters dia, just go all over the envelope. You will be bored to death, it will take you 3-4 hours by the time the gas will leak. So it needs, so using this method for detection means you should be prepared to be patient and then suppose you missed it, so leakage is there but you missed it. So it can be done, but not recommended. But our ingenious came up with a very ingenious method which can be used anywhere. It does not require anything other than what is available in a typical hostel, I will give you a hint now. In a typical hostel room, you have some things, you have a desk, you have a table lamp, you have a computer, you have calculator, laptop bag, scale, pens, that is it. This is what they use and they can detect the leak. Any hints? So let me show it to you. We use what is called as visual leak detection method. And what we do is on one side of the envelope, we illuminate with a table lamp. You can see Vishal is holding a handheld table lamp, they do not dark, on one side put a table lamp or a big illuminating bulb, on the other side the whole team starts looking. Now lighting is something that can come outside the hole. If there is a pinhole, you will see star like illumination points. So on the bottom left is a zoom, 10 times zoom of one of the holes. So by visually inspecting the envelope, you can find pinholes. This works beautifully and we have used it. And this was suggested by some students who work in the lab when I gave them this problem. We tried all the methods you mentioned, we tried soap fill method, nothing is happening. The lab became dirty, okay, slippery. Then someone said, swimming pool chaltain, okay, we went to swimming pool. Then they all became completely wet and the balloon would keep bopping up and they said sir, there is no leak, we are only leaking. Then we tried all sorts of things, agarapakti, dhoop, everything. Ultimately one bychap said, sir, why not use light and then we tried it, it works. So to give a technical name, it is called as a reverse illumination method. Actually it is nothing but putting a light source on one side, making the room dark and observing using human eye as a sensor, observing on it. It works very beautifully for small pinhole leaks even when you are in the field, okay. So I can show you one, I can show you one image of, this is in the laboratory, this picture is in the laboratory, but I can show you one more picture where we know we will be in this, yeah. So when we went to Manali, okay, at that time, there is one picture here I think, yeah. You can see this is in the lab, this is the leak, zoomed. And then this is Manali, we go there, we do our testing. There you go, in Manali we did the illumination using the lamp that they gave us. So this was a small hangar and like typical IITNs, we work in the night because we have to fly early morning, the best time to fly typically is 6 a.m. to 7 a.m. and the winds are less, that is the best time to fly. So we worked whole night and around 2 o'clock or so, you can see on the left side there are 2 students looking for leaks, on the right side there is a lamp. So but this time we are doing it with gas. So whether you have gas inside or air inside, does not matter, light will still pass through, okay. Yes, we cannot use this method. No, polythene material will show up, the leak will show up, problem is you must have seen in our videos, I showed you some videos of a black coloured airship, it could not work in that. So that was one drawback of this black, that was a very good fabric by the way, it was 100, it was 95, I think 9, 121 GSM. It was given to us by a company for testing that is this fabric good for your airship and there was a dual degree project by a student, he made the airship from that. Very good, small airship of 4 meter length gave us around 1 kg of net lift. So it was very good, lightweight, but the problem is that that fabric, it could also be sealed by RS sealing, so we could use our machine, but the problem is that we could not use our elimination method to calculate to find the leaks. So therefore that envelope is available in the lab, it has many leaks and no one is able to find the leaks, okay, the only thing available is our helium thing, but that is very expensive, okay. So this is coming back now to the other equipment. So this particular, by the way this helium detector is 17.5 lakh rupees, just this one small equipment and the trolley of that, the trolley is another half a lakh, 30,000 rupees. The sniffers are coming for around 5,000, 8,000 rupees, it is a very expensive item and I cannot take it with me to some place. So it can only be used for those situations where we are desperate, we have some location and now we want to pinpoint exactly, so there we can search very minutely. What we normally do is, in locations where we get a leak, we put a red colored circle so that we know that this is the prone area, we touch it up, but there could be. However if it comes somewhere else, this method is very cumbersome, hence it is not used.