 So, these are the familiar expressions that we know already for any LTA vehicle for the net lift, gross lift and the weight of the lifting gas. What about whatever value net air? That is going to be 0 here, okay. So WBA will be equal to 0. What else will change if it is a rigid airship? What do you think will change? See we are not looking at the structure weight for anything so far. So why should it come for rigid airships? In all our discussions we are only looking at now the static lift produced by the system. So in static lift of the system we are not concerned about the weight because we are looking at, so now what about the super pressure, will you have any super pressure in rigid airships? No because you are not going to inflate the rigid airship at a pressure higher than atmospheric. We do that in a normal rigid, non-rigid airship because we need to maintain the shape. Here shape is maintained by the structure so therefore there is no super pressure. So PSP terms will go 0. Similarly, volume of the lifting gas will be equal to the net infraction, fraction I times VENV where this I is basically summation of IN VN upon VENV that is the volume of the lifting gas. So put this in the expression and you will get that the lifting gas instead of using VENV we will use directly V lifting gas because envelope is not containing the entire gas. The gas available is only VLG. Similarly, WLG we will knock off this delta PSP here and we will knock off this VENV as actually IN to VENV is already there. So catch up this IN VENV and replace it with VLG. So these are the changes that will happen if you have a rigid airships. Now let us look at another form of LTA vehicle which is the super pressure balloon. Now this is a very interesting system about which we should spend couple of minutes understanding. So a super pressure balloon is basically a balloon which is generally made of very thin fabric, very thin envelope material and we inflate it on this at the sea level or low altitude with less amount of LTA gas just enough to lift it up. Remember that as it goes up the envelope starts expanding because of the loss in the ambient pressure due to which there will be a pressure difference. Ultimately at the desired altitude or at the altitude where you want it to be deployed, it will occupy the maximum shape. If for some reason if the pressure has to, if the pressure falls, if the pressure becomes more than that pressure, there can be a pressure release valve also if needed but it will occupy the maximum shape when it is at the desired altitude. So the VENV is going to increase as it ascends. However the infractions will become now more than 1 because the volume occupied by the lifting gas at the altitude will be less and that volume will become larger and larger till it reaches equal to the total volume of the envelope. Secondly, we again have no balloonettes in this case so therefore the WBI is going to be 0. So you can change the expressions and get it. Now let us look at the hot air balloon which is what you are going to design. You have to ask the hot air balloon so you should pay more attention to this particular term. What happens in a hot air balloon? So please tell me, what happens in hot air balloon, do you have balloonettes? No. What about the infraction fraction? 0 or 100? 0. 0 means no gas, no lifting gas. That is possible if you put vacuum, if you fly with a vacuum. So I will be equal to 1 that is the infraction fraction and WBA will be equal to 0. So once you do that, WBA term will be cancelled and wherever you use I you have to put equal to 1. So these are the expressions you will get. I am just putting it here. If you also ignore humidity effects then E will be equal to 0 and then you got this classical formula which is used by balloonists. So what do balloonists do? They are interested in the net lift that is available because that is useful weight. If this net lift, now we come to the aircraft of the system weight, if this net lift is less than the weight then it will not go up. So net lift first thing you subtract is self weight, remaining will be payload that is how much you can take it up. So the net lift available will be the ambient pressure PS times temperature of the lifting gas which is inside the balloon minus temperature of the ambient air, this should be T subscript A, I will correct that, divided by TA into TLG times K into VENV where K is a constant. So when you design your balloon you can use this particular formula if you can convince yourself that in Mumbai you can ignore superheat. I do not know whether you can do that, probably you cannot do that. You must consider superheat when you fly your balloon in Mumbai at least because you know our atmosphere is actually having very high humidity and humidity is going to subtract from the lift. If you notice the terms which represent humidity basically this term 1 minus ID VW, WV into E, this term is a subtractive term which means the net lift is going to be, the net lift if you see the net lift is going to be less because of humidity. So if you ignore humidity it is up to you, you will make a mistake in your estimation.