 So, we did the validation for three airships which were available at that time or I should say the data for which was available at that time. One of them is this USLTA-138M and the other one is Sentinel 1000 which unfortunately did not really the program was cancelled midway. Sentinel 1000 was the airship which actually revived the airship technology after its downfall in the late 30s, in the mid 80s, early 90s. It was this Sentinel 1000 airship project which brought airship technology back into the focus. But because of budget cuts, this project was cancelled. So a smaller version of this airship called SkyShip 600 was made and then commercialized as 600B and sold. So data for these two airships and from one more airship from a company called ULTA and first of all the company has gone bust. So even if you start to search the website you will get no information. I could not get even a picture of the airship to show today but I do have the data about that airship from Jains All the World aircraft. So what I want you to do is tell me about the numbers, they do not matter. Look at the percentage difference, look at the last column. The last column showcases the percentage difference between what we estimated versus what is the actual data. But for the fin weight everything is within 10% and in most cases we are underestimating because it is negative that is not good. If you underestimate information it means there are certain factors which you are not being able to consider. However, theoreticians or academicians who do not have any practical experience on working on airships. We really cannot do better than this because we do not know what is the factor to be put for additional weight of the envelope because of patches. How do I do that? How do I know? Now I know it because I have made so many airships so I can say if you are making a remotely controlled blimp of this size you must put so much factor. Now people are referring to our papers on remotely controlled airship sizing because we have now data of our own but our work is focused on particular type of envelope, particular material. So within 10% error except for the fin, for the fin we are off by 21%. That means the actual fin for Sentinel 1000 was far heavier than what we predicted. That means our assumption, as I mentioned to you we had two formulae for fin assumption. One was Reimann's formulae for aircraft fin, the other one was area density method. But hopelessly both of them were giving us wrong value. So now we know that our fin estimation is wrong, needs to be corrected. So this opens up one more area for someone to look into in more detail. What went wrong in our fin calculation and maybe we can revisit this and go for better estimation. But everywhere else we are within 10% so which is not bad for initial conceptual design. This is the airship, small airship. Now one more thing I should tell you, smaller the airship better we were in the estimate. So remember this airship is a small one, you know. Here the errors were only half percent, 1.5%, 0.6% but again we are wrong in the fin by 16%. In this case we are overestimating. So our formulae are inappropriate for small airships because we overestimate by 16%. They are inappropriate for large airships because we underestimate by 20%. So we are grossly and hopelessly bad in our estimate of the fin weight. So this is a medium airship, US LTA relatively another medium airship. Then we are overestimating by around 13%. Empty weight we were wrong. Now empty weight under prediction is acceptable because actual airship may become heavier than what it needs to be because of certain structural modifications, some damages, repair work. So or they may say we want to make it statically heavy for some applications. So it is not a bad, still we are only over 13%. Now we looked at some bigger airships which were either on paper like PD300 and MD900 are Russian airships which were on paper at that time. And I think they are also on paper today, they have not been built. Similarly skyship 600 were theoretical airship it was built and A150 also was an airship. So again we are off by around 10 to 12% in most cases. So what we basically concluded is that our methodology is very simple. It can be easily put into a spreadsheet and you get errors within around 10%. So if you really want to be very particular you can say okay whatever number you get I will add 10% and that will be a realistic number. Let us look at some results that we got. So firstly to get the record straight you should know what are the input parameter that were given so that you get a mental idea about the requirements. So the demo airship trailer is not known. We are going to say how much can we get with 1000 meter cube envelope. Temperature will be IAC plus 15. The minimum multitudes, maximum multitudes and cruising multitudes are the same for both the airships. Engine speed was chosen based on the engines available that is why these odd numbers of 78 and 92 not 80 and 90 but 78 because we back calculated okay we have this engine available. With this engine what is the kind of speed I am getting that is the number. So nobody told us fly at this speed. We said we will use this engine it is available it is low cost we will get so much speed. Range 100 kilometers and 100 kilometers, envelope L by D ratio, length diameter ratio 3.05 in one case and 4 in the other case engine type was petrol and diesel and here we used normal and supercharging okay. So let us see the payload weight for 1000 meter cube envelope volume came to 33.2 kg. So this airship can barely take the pilot it cannot take anything extra but it is okay if you find not someone like me but a lightweight person who can manage within 73 kg. So you can have airship flown by a pilot demonstrated does not carry anything additional to as a payload but maximum speed was more than what we want anticipated in our initial calculation. Look at the fuel weight you are travelling 100 kilometers with only 10 kilograms of fuel that is a very big selling point okay and it is a it is a large structure it is a almost half a ton weight empty weight okay but it travels within 10 kg it goes 100 kilometers. For the bigger airship with 1.5 tons payload capacity it goes with around 120 kgs and it is 5 tons is the empty weight okay. Now let us look at some more details so here is the 3 view diagram of the demo airship that we got you will notice that the maximum height is 11 meters diameter of the envelope itself is around 9 meters 8.78 meters and the length is 26.78 meters what does it carry only one passenger and that is the pilot. So what has gone wrong why do we have to have 27 meter length and you know 11 meter height just to carry pilot itself and the pilot so which requirement do you think has been the most stringent that will flash to you the requirements altitude that is why altitude is the killer because airships are basically meant to fly at low altitudes as you meet them fly at higher altitudes they suffer a huge loss in the payload carrying capacity interestingly the same airship if I operate at sea level I can carry 4 passengers plus the pilot same airship the airship packs cargo which carries only 1.5 tons payload if I bring it to sea level it becomes a 30 seater aircraft okay. So that is the problem the problem is that the operating requirements are actually not suitable for airships because the altitude operation is very high.