 Let us look at the typical components of hybrid airship. You have these multiple lobed envelope. The multiple lobing is going to give you a larger width lower height for a given envelope volume that you need and this shape also gives you higher L over D lift over drag. So the L over D which gives you the aerodynamic performance is also improved. Applications are many. You can just imagine wherever you need heavy lift or wherever you need to cruise for long distance. You could also use it for things like disaster relief by dousing the forest fires or for providing medical facilities at disturbed areas. So these are the four basic limitations of the cargo airships. First of all they will not be as maneuverable as aircraft because they are bulky in shape and because they are buoyant body and secondly their large size will require totally new infrastructure. It is very difficult to expect that you make these airships and you can operate them from existing hangars because existing hangars are not so large in size. So you require very large hangars and secondly you cannot actually climb to very high altitudes. So while transporting cargo if in the way there are very high altitudes you have to skirt it rather than going over it because with heavy cargo if you want to go over an obstacle or a mountain or some such high structure then the volume and size will become very large. Now last thing I will do today very very briefly is I will try to show you a comparison between how the performance of an aircraft is estimated along with the performance of airship. There are a series of four very interesting papers on performance estimation of hybrid airships. So the first such paper appeared in 0.9 for what is called as the airship which is basically a winged airship either you have a wing and a tail mounted below or you have just the wing with engines mounted below. So a hybrid flight platform was proposed by these researchers and then they carried out performance estimation for that. So what they have done is they basically done a first order analysis of aerodynamic interaction between airship wing and production system I mean the interaction is in electric so it is a first order analysis and therefore and also the drag on the lift is decoupled. So you have a CL and a CD and you are not going to use it for coupling. Now for an airship you will get the buoyant lift as L ship which will be density into volume into difference of density difference into volume correct the G is only meant for the units. For airship there will be a airship lift coefficient which will be L by G rho V because for an airship volume of the V ship is the volume of the airship envelope. So lift available per unit so you just divide this and therefore that will be simply 1 minus density ratio rho H by rho A which is sigma or not sigma it is like it is a relative density R D rho H mean density of helium and rho A means density of air you could have helium or hydrogen. Similarly you have an airship drag coefficient which is the drag obtained divided by half rho V square S. So U basically is velocity. So now you can see on the aircraft and the airship there are 2 sides on the aircraft side we have only the aerodynamic lift so we have just CL which is L by half rho V square we have drag which is CD D by half rho V square but what is the V area? So what do we take as the S wing in the analysis so can someone tell me this what is the answer to this question on the aircraft side what is the S wing in this formula plan from area of the wing. So how do you define the plan from area of the wing? Correct. So this is basically so it is called as the wing reference area not plan from area but wing reference area which includes the area inside the fuselage projected from the wing route to the centre line. Is this one clear to everybody? Yes or no? In the airship you have buoyancy which is and also you have which is basically the density difference into volume and as I already showed you there are there is an efficient of lift coefficient but now what will be used as the area for the airship for the drag estimation of the airship what will you do as the area? What are the justification for that? It does not make sense exactly it does not give you a proper scaling parameter it does not make sense what makes sense is to use volume of the scaling parameter and therefore to get the units of area from volume you just do volume power 2 by 3. So the reference area in the case of airships will be volume power 2 by 3 and therefore the drag coefficient will be also called as CDV volumetric drag coefficient. So this is what we have already seen in the last couple of minutes for aircraft we have this cross sectional area including the not across an area reference area including the area inside the fuselage and for the airship we have volume power 2 by 3. Now no need to really get psyched I do not have animation in this unfortunately but my suggestion to you will be that this is essentially taken from 3 or 4 papers which I am going to upload. So it is nothing but bringing in an aircraft like coefficient into the airship formulae. So you basically say that there is something called as CD total which is CDO wing plus CDO airship. Similarly for lift you have the dynamic lift plus the lift acting because of the airship size okay and then there are force this is of not much relevance. So LROD will be CL wing CL airship upon CD wing CD airship very really 2 components and then you can get expression for LDMAT. Now finally just to conclude you will get an expression like this which will say L by D max is equal to 1 by K times some function F of P and X which is this this is P this is X and P is CD0 by K and X is CL of airship. Now my question to you is how do you find the optimum value of X which maximizes L by D for a fixed P. So now this is a simple optimization problem you have F is equal to FX is equal to 1 by K root of P plus X square upon P plus root P minus X square minus X square P is a constant. So you can use any optimization method to obtain the optimum X or I used a simple graphical method. So what I have done is for various values of P as I have plotted this curve. So we notice that as P increases the peak is coming down it is flattening as if somebody is pulling this on this side. So for various values one can get the values of the peak and then one can easily create a correlation between X and P which is just almost like a line of course it is a power series curve and then you can do a L by D comparison for both aircraft and airship. I am going to skip this in detail because I think you will be able to appreciate this only and only if you go through these papers. Now what you see are basically two general papers and two conference papers. The conference papers have been updated as general papers. So once you read these two papers the first one is 11 and 9 where this concept is introduced airship or a typical wind aerostat and in the second paper the flight performance formulae have been given. So that is all I think with this we will end today.