 We know about LTA systems little bit by now and we have also looked at how they are different from the heavier than air. Now one area which is a serious limitation of the LTA systems is the need for ground handling. This imposes not only extremely high cost but also restricts the usability of these systems. You might say that airships and other stacks are simple and easy to fly but then you need to also do something to handle them. So this is a collage of pictures taken from various sources which shows the mooring masts used for various airships and aerostats. So you can notice that essentially we are holding this platform from the nose and in some cases such as in the bottom right where you see the Zeppelin NT airship, you can see that in this case the mast is also a movable system, it is a truck mounted mast. So it can be taken away. So apart from the massive size of the structure, you also need to have massive investment in terms of the ground handling. So why do we need ground handling in LTA systems as compared to HTA systems which need very little ground handling? Do you know for example what is the mechanism used to move a very heavy aircraft such as say 787 or Airbus A380? If I want to move it from place A to place B on the ground, how do I do it? What is the mechanism used? No, APU is not used for the APU is basically used only to provide power for air conditioning cooling, cooling of ionic systems, air conditioning, hydraulic system. There are simple tractors which have a link attached to them and you just attach this link to a hook in the nose landing gear and an aircraft as big as 380 can be simply pushed or simply pulled by a tractor. So very simple compared to what we will be seeing now. The reason is that even though 747 or 380 have a very large surface area like airships, the weight is 350 tons or more. So therefore it needs such a large amount of force to move it. For an LTA system even though it may be heavy, but it is a buoyant system. So its net weight or effective weight is very less. So in technical parlance, what would be the net weight of an LTA system when it is parked on the ground? How much will be the net weight? So you have heard of terms like static lift, net lift, buoyancy, weight, static lightness, static heaviness. So using these, please tell me what would be the apparent weight of a system which is standing on the ground? No, I do not want numbers. I want the term static heaviness, correct. So the weight that will be read by a scale on the floor if you put an LTA system on it will be equal to its static heaviness. This can be 500 kg, 600 kg for a typical large airship. But the forces which will act on such a large body especially when the winds are reasonably high they can easily exceed this 500 kg in the vertical direction and in the side direction of course there can be forces. So therefore we need something to hold it. So LTA systems are very sensitive to gusts and turbulence, they respond to it much more. You do not see aircraft shaking in gusts and turbulence when they are on the ground. They do shake and respond when they are in air because there is a lift force acting which overcomes the weight. So again they come to a situation of almost zero net weight. Now if there is a gust acting on it but they are very fast. So they cut through the air much faster than the LTA systems and their dimensions compared to their total weight are also much smaller. So a buoyant vehicle experiences loads from all directions. The most important and significant load is the side load which will come because of the large surface area. And therefore you need to have a pitch your role and your freedom that means freedom in nose up and down that is pitch, nose rotation that is role and yaw is nose left or right. This kind of you need to have some freedom in LTA system. If you constrain it it will simply tear off. So ground handling is really a problem and more than telling you what it is let us just have a look at a video from many years ago okay there is a website called critical past which talks about things which were in the past and looks at issues very critically. So the year is 1957 before even I was born forgot about you right and it just showcases what is meant by airship ground handling and you can see for yourself what the problems are. So observe very carefully then I am going to ask you questions based on purely what you have seen. For safe and efficient ground handling the ground crew must be alert to the ground handling officers orders. They must be thoroughly familiar with safety regulations and any pertinent weather conditions which may affect ground handling. In this film you will see how airships are handled during masting in the hangar, undocking, unmasting, and takeoff, landing, and masting, and docking. All wind directions relating to ground handling of airships are in reference to the hangar axis and the operating end of the hangar. There are three basic winds that we are concerned with. The down hangar wind which blows toward the operating end of the hangar, the up hangar wind which blows toward the non-operating end of the hangar, the cross hangar wind which blows toward either side of the hangar. In addition there are quartering winds, there are the quartering down hangar winds, and the quartering up hangar winds. Winds are important for two reasons, a moored airship always vanes into the wind from any direction causes piling up and turbulence and the wind becomes strong and gusty These effects increase. With a down hangar wind we have still another wind effect when the hangar doors are open. That is back draft in the hangar. Back draft can cause an airship here to kite and strike the hangar. Draft can be controlled by partially opening the after doors to establish a light flow of wind through the hangar. However with the after doors partially open to eliminate back draft, a quartering down hangar wind will cause bulkhead deflection in the hangar. A cross hangar wind causes turbulence at the side of the hangar. It offers no serious problem to airship ground handling, but up hangar and quartering up hangar winds cause spill and turbulence at the operating end of the hangar. Upmost care must be taken while passing through the turbulent area. The turbulence and winds coming around the corners of the hangar are likely to cause kiting. With aid docking and undocking operations, there are safety guidelines for each size and type of airship being handled. The radii of the arcs are equal to the length of the airship plus a margin for safety. Thus the guidelines assure clearance of the tail at the opposite corners of the hangar. The intersection of the lines here is the point nearest the hangar at which the tail of the airship will clear both corners. Okay, so what we have seen in this film, if you noticed as the airship was about to take off, there were two vehicles on the side which were moving and the people on the ground were actually running and attaching cables to these vehicles. The idea was that these vehicles being little bit heavy will resist the motion of the airship to some extent and also they can be used to pull it. So, there was a time in the past when ground handling of an airship involved 200 people, 250 people on the ground. I will show you one more video towards the end when we will see when an actual airship came into land, how many people on the ground were required to safely operate it. So, looking at now some specifics, ground handling means we have to look at hangar age. This can be a huge cost point in operating LTA systems. You need to create a hangar. So, whenever you are making or operating LTA systems, be them aerostats or airships, you have to invest a lot in the ground infrastructure and for airships, you need to have a reasonably sized hangar. Then we have ground movements, bringing the vehicle inside the hangar, outside the hangar, etc. Lift of recovery basically means takeoff or operating. Now, effect of size of ground handling is very evident. We know that larger the size of the airship, bigger will be the hangar required and therefore the cost will go up. Then we have an activity called as nearing, in which we basically attach the airship to a mast, called a mooring mast. There are various types of mooring mast, we will see when we go in more detail. The three main types are a simple type of mast. There can be an expert mast or there can be a mobile mast which moves on vehicle. And we will look at some design considerations for the mooring mast. We have to be very careful that when the airship is moving at low speeds in winds, we need to have sufficient control on it. And also to ensure that the mast does not impose additional forces. The mast should be a facilitator, not a rest trainer. It should not cause tearing of the envelope. Now, in ground handling, hangarage or providing of the hangar is very, very important. And a hangar as you all know is self-evident, it is basically a shed. This shed can be used first to make the airship because when you make a small airship, 5, 10, 15 meters, you can do it inside a laboratory and then take it out. But suppose the airship itself is 150 meters, then where do you have a place? So you have to first construct the hangar and then make the airship inside the hangar. So even to make an airship of a large size, first thing you need to do is to build a hangar. Let us say the airship is already built, we are now bringing it to operate it, you need for any refurbishment, for any installation, you need to do it. And obviously the size of the hangar will be connected already to the size of the airship.