 So these are the inputs to the methodology. So 3 kinds of parameters were used by us as inputs. The first are the operational parameters. Now none of you mentioned pressure altitude which you should have mentioned. You mentioned operating altitude but you did not say what should be the pressure altitude. So it is important and also I expected somebody to say that from a height of so much I want to go so much Delta H because you know that the balloon will be size based on the Delta H. We have spent so much time in the inflation fraction calculation. I thought some of you will think and say oh this airship has to fly from this altitude let us say sea level to the operating altitude that can change from place to place. So pressure altitude is an important parameter that is equivalent to the operational ceiling. Then minimum operating altitude, then atmospheric properties and then the priority level of the gas because this is something which is based on the availability of the gas. Helium gas as you know is not a very commonly available gas and if you insist on very high purity it becomes further difficult and also more expensive. So you may have to make do with helium available at 95% purity or at 99.9% purity or 99.99% purity. This is not in your hands the cost and the availability are going to dictate. So helium purity level is the important parameter which we have incorporated. In our 11 parameters we also looked at helium purity or gas purity gamma as one of our parameters. Then an airship is going to have some accessories is going to have some other systems which are going to be mounted on it. They will consume power and who will give the power to them the same engine which is used for the airship. So how much power is consumed by accessories? So of the engine power which I generate what percentage is consumed by other things like fuel pressurization system like air conditioning system and the remaining will be available to me as a user. Then performance requirements this specialty is common and minimum is also common but cruising speed and range are important. Now in our problem here we were not looking at keeping in the air for long time as a requirement. This was not meant for surveillance. This was meant for transporting goods and passengers. So therefore endurance is not there as a given requirement. Range is the given requirement. So cruising altitude, cruising speed range, minimum altitude from cruising which gives you the ballooning sizing, sorry minimum altitude to pressure altitude gives you the ballooning sizing. And then there are some configuration parameters. Now this is not, these parameters cannot be given by the user. User does not care about them but the designer has to assume otherwise there will be so many things to calculate that you will never be able to make any progress. So certain parameters we have assumed as constants or fixed and we have to change. If you change them you have to do the whole analysis again. So one is fin layout. Now what kinds of fins are available for airships? For large passenger getting airships do we have any options about fins? What have you seen? So what type of fins have you seen in the videos I showed you of airships flying with passengers? What is it? Yes? Delta. No I am not talking about the shape of the fins, I am talking about configuration. So there are basically if you look at the airships available, there are two basic types of fins available in literature for conventional airships. Yes? So one is called as the conventional, this is the rear view of the airship. The other one are mounted this way. So either you have a plus configuration, so this is called as a plus configuration and this is called as a cross configuration. Now tell me what are the basic differences between these two types of configurations? First of all which one will you prefer, a plus configuration or a cross configuration? So most of you will prefer a plus configuration, why would that be? Because the pitch and the yaw motions are uncoupled, right because we have two distinct vertical surfaces, two distinct horizontal surfaces. But then if that is everybody's preference, then why do we have something with cross fins? How will a cross fin get you better maneuverability? So that is pure guess work, that is not correct, that is not correct. What would be the advantage of a cross fin? See the wake of the bluff body is almost symmetric all around. So whether you put fin on the top or bottom, wake wise I do not think there will be lesser or more disturbances. Cross will be more stable than yaw. No, but if I have a dedicated vertical on top and bottom, I think the stability of that will be the best compared to a mixed configuration. So I have nothing horizontal, I have nothing vertical in the cross, yes Chetan what do you think? Why no, in fact no, the size of the fins may not be small because all the four fins are supposed to be used for both yawing as well as pitching. So did you think, what you are saying is that you will use all four, therefore you can have smaller area of each of them, but you know only a component, only a component of each is going to do the desired thing, okay. Anybody else? Yes, I mean yes, what do you think? That is the main thing, remember we are looking at big and bluff bodies, large bodies. So if I have a plus fin configuration, everything is fine except that the ground clearance becomes a problem, bottom fin is going to, so the maximum height of the airship is going to be more. So the size that goes inside the hanger, so that is the reason. So now when you have a cross fin configuration, the only advantage you have is a smaller height. Listen, making a wide hanger is not a big problem, making a high hanger is a bigger problem, okay, making a wide one is not a problem, you just need more area on the land, that is okay, but when you want to, the difficulty is when you want to make a very high hanger, so that is why reduction in the vertical dimension because of cross fins is one advantage, many big airships, large airships have gone for cross configuration only for this particular feature, but then there is a complication that now the control system becomes complicated, it has to be mixed, so you require a mixing unit, the pilot will deflect the control stick in the desired fashion, but this control system must take over and do mixing, so this leads to complexity. However, in a big airship, you anyway are going to have a flyer wire control system to make the system light, so when you have that system or when you have a computer control system, this mixing is not a really big additional complexity, it can be easily incorporated, so now the moral question for you is identify actual man carrying airships or large airships which have gone for a cross fin configuration and I want to know that their names and maybe a picture and some data and if you can get some literature which says yes a study was done and it was found that cross configuration was better than plus for this particular case, it will be helpful for us to learn more about it, so you can choose plus or you can choose cross.