 Hello friends, today we will take a peek into the world of solar powered airships. The first autonomous flying solar powered airship was developed at University of Stuttgart under the leadership of Professor Dr. Bayant Helmut. This unique airship was called as Lotte. The Lotte airship was used or designed with keeping in mind multiple applications ranging from traffic monitoring aerial photography, urban planning tasks, monitoring the environment, pollutants, early warning for marine propulsion etc. So actually anything that requires a long endurance operation of an aerial platform with lower level of noise and vibration, a solar powered airship could be considered as a good candidate. Some technical data about this airship is listed here. As you can see it is about 109 cubic meters of volume with 20% occupied by the two balloone. It had on top a solar array of around 4.8 square meters, it could go up to a kilometer altitude and fly at a maximum speed of 45 kilometers per hour. The length upon diameter ratio was 4 with the maximum length is 16 meters. I had the great pleasure of seeing this airship in person when I visited University of Stuttgart in the year 2003. I remember there were two young engineers who started a company and that company used to operate this airship commercially. They used to transport it in a small van and I had the chance of spending a weekend with them. Recently a new solar powered airship by the name Dirisvallar was launched by a French company. This airship has separate very interesting features. It has a very unusual shell shape. You can see the bottom is flat-ish and the top is more curved and its thrust is based on solar energy. So this is a solar powered airship. There are many advantages claimed for Dirisvallar. First of all the environmental footprint of this airship is very small because it does not use any fuel for generating the lift or propulsion and hence there are no carbon emissions plus it has also got low noise. This is a helium powered airship which is certified by IASA for commercial use and it actually lands very benignly. Let us have a look at a small video explaining the working of this particular airship. Imagine yourself flying over the most beautiful places in the world with the sun as your only energy and the caress of the air as your only noise. This dream can become a reality thanks to you. Since I was a kid I have been passionate about airships. The stories of my grandfather, the captain of the Fleurus airship in 1910 have rocked my childhood. I have surrendered myself with a team of engineers and created Dirisvallar in 2009. Thanks to the new digital technologies such as virtual prototyping, Dirisvallar has studied the limits of conventional airships. We identified a shape with a flat bottom. This greatly improves the aerodynamics of this device. A breakthrough innovation that changes the game. A dream to discover the most beautiful landscapes in the world in the most innovative and echo-responsible way. Imagine yourself above Mount Saint-Michel or the Grand Canyon. An immersive and silent discovery of the most beautiful places in the world. A border cabin offering a 180-degree panoramic view, you will enjoy an environmentally friendly and silent mode of travel. This dream will become a reality thanks to Dirisvallar and its new generation airship. A jewel of engineering and technique that greatly improved the capabilities of airships. Practical and safe airships are now possible thanks to advanced technologies and new materials, such as helium as a lifting gas and solar panels powering up silent electric motors. Furthermore, in an ecological context more important than ever, this mean of transport offers zero consumption of fossil fuels. The Dirisvallar is meant to fly over the most beautiful natural places in the world with an impact on the environment as neutral as possible. We have already completed a long journey since the start of the Dirisvallar adventure. This engineering and technical promise is in your hands today. Dirisvallar needs your help and solicits you to create together the transport of the future. Dirisvallar is born from a child dream, a dream to fly in an airship in all freedom. Today, we are making it a reality, join us. In China, a solar-powered spy airship called Yuan Meng has been developed. Details are not available in open literature but some photographs have been obtained. It is claimed that this is an helium-filled airship for surveillance essentially for hunting the US aircraft carriers in the high seas. Yuan Meng is claimed to be able to stay a lot for about 48 hours nonstop although we have no idea about it. It flies in near space region between the height of 65,000 to 328,000 feet, about 100,000 meters to, you know, 20 kilometers to 100 kilometers. It has a volume of 18,000 cubic meters and it is fitted with various kinds of communications and surveillance gear such as for wideband communications, digital data links, good quality HD cameras and spatial imaging technologies. So as I mentioned, nothing much is officially declared or known about this airship. So in recent times, solar-powered flying wings have also been proposed, as you can see in this particular video. Solar ship is a cross between an airship with lifting gas in the wing and a bush plane and what we do is we design and build and fly these and we target disaster relief and peacekeeping. So everything is really focused on that mission. In summer of 2014, we did something that stunned everybody in the disaster relief community. We took off and landed from a soccer field with only solar-electric power. So we thought the solar-electric power was the big thing but all the disaster relief people were stunned and we were able to take 1.8 tons, lift it off a soccer field and land it back on a soccer field. That was the stunning thing. We used the soccer field as the infrastructure for accessing virtually anywhere. Being able to bring medicine supplies critical cargo to places that just would previously be supplied by bicycle or donkey or anything at all, you know, that's big. The more we fly, the more we come up with ideas and when we come up with ideas, we put them in the solid work. And when we use solid work, we turn it around into a better aircraft. We use solid works for everything. I use it every day and really I can't imagine what other tools I would use if I had to replace it. One of the issues that we had in a fast-paced environment is that we had to be able to arrive to answers quickly. And so solid simulation allows us to go from a 4-fit function model to the actual strength analysis of that model and make any changes and go back to the simulation with great ease. It feels like we're cheating. A big thing that we're concerned with is propeller placement. We need to carefully tailor the airflow, we need to make sure that we don't run the ground strike issues, and we also need to make sure that the structural placement is accommodated by the fuselage. Solid works helps us solve the propeller placement issue by rapidly and easily allowing us to visualize the placement and work through all the issues associated with the aerodynamics, the ground strike issues, and mechanical structures associated with that. Our current mission is, with the Royal Canadian Air Force, to deliver critical supplies from Nairobi and Kampala into the war zones of eastern Congo, South Sudan, and solid works allows us to build the vehicles that allow lifesavers to save more lives. Working at SolarChip is really exciting for me because it's working towards something that is going to make such a big difference in the world and change people's lives for the better. It's a great feeling. There is also a company which has provided a solar powered remotely controlled airship. This is the eblimp.com. You can see a black patch on top of the airship which is the solar panel mounted on it. As you can notice, the airship is quite maneuverable. It has twin swivelable motors mounted on the bottom. The testing here is being done in an open ground. Notice the ability of almost a spot turn. That is because in the tail on the bottom they have mounted a yaw motor which gives a direct side force and that can give such a high maneuverability to the airship. On top you can see a series of solar panels mounted which provide the solar power to the airship. The solar power is augmented with batteries. So there are some batteries also on the airship and whenever there is an excessive requirement of power which may not come from just the solar power, then those batteries help in augmenting it. You can see it almost climbs vertically, very good performance. So let us have a very quick look at the classification of later than air or LTA systems. There are basically two types powered and unpowered. When you have unpowered systems they are called generally as aerostats. They could be tethered or untethered balloons. When you have powered airships you can look at them in two categories depending on the shape of their envelope. It could be a body of revolution or a non-body of revolution. If it is a body of revolution then there are three possible structural configurations normally proposed the rigid, semi-rigid and non-rigid about which I will talk in the next slide. The non-rigid has a special subcategory called as a hot air airship which is basically a hot air balloon masquerading as an airship. In the category of non-body of revolution generally you have high altitude airships and hybrid airships. And hybrid airships are ones which have a combination of buoyancy and some other force. It could be rotor type systems such as in rotor stats or it could be the shape of the envelope or a wing in which case it is called as a dinostat. These are the three structural configurations as I mentioned rigid, semi-rigid and non-rigid. There are several factors involved in the sizing of any solar powered airship. So the important variables are the geographic location because the wind speed, the air density and the solar intensity vary from geographical location. Then so that means an airship designed for a particular location may not be suitable for some other location. The other parameters are payload, airship size and the size of the array but generally the airship size and the array size are tuned to meet the requirement of the payload. The power available is a function of these output of the solar array which depends upon the size of the array and the system efficiency or the efficiency of this array also. The power consumed depends upon what kind of propulsion you have on board, how much power it needs depending on the speed that you have to overcome or speed at which you have to fly and also how much power is consumed by the on board mounted payload and the avionics systems. So you need to have a match between the power available and the power required. On the other hand, the every airship has mass which is a function of the payload, the structure, the weight of the propulsion unit and the avionics envelope also comes a part of structure and then based on the volume of the airship there is a lifting capacity. So two types of parameters have to be matched when you do the sizing of the airship. You need to match the power available against power required and lift available against the airship mass or the lift required. So when you match both these parameters only then the airship can get properly sized for the given requirements. What are the requirements of the platform? Generally a solar powered airship have to meet the following requirements. There is a specific amount of payload it is supposed to carry, there is a particular altitude up to which it has to fly called as a ceiling altitude. Then you have to look at what kind of energy system is there, is it rechargeable batteries, is it fuel cells, is it a combination, is it a hybrid. Also we need to be sensitive about how much power is to be carried for onboard avionics and payload. We need to look at what kind of cruise speed is expected in still air or how much is the ambient wind speed which has to be fought and maintained the station. Then what is the duration of the night at the location you fly because at some places you may have longer nights and smaller days and also you might have very low intensity of solar available and then you have to look at also the mission duration. How long is the mission going to be? All these requirements decide the sizing of the platform. This is one approach to the sizing of a solar powered airship. You start with some initial size which is an assumption. You carry out the design of the airship using some standard procedures and then you compute the lift, the weight, the power required and the power available which is supplied through the onboard propulsion system. First question you ask is power supplied more than or equal to the power required? If the answer is yes, then you can go ahead, if the answer is no then the only option you have is to increase the size of the solar array which was initially assumed. Once you have convergence, you proceed further and check whether the lift available is equal to the weight or more than the weight. Lift is a function of the volume of the envelope. If you find that the answer is no then you change the size again and repeat these calculations and when you change the size you might actually encounter a requirement for larger power and hence you may have to do the power match once again inside. Finally, if you find that your power requirements are met and also the lift requirements are met then you can say that your design is complete and you can exit the method logic sizing. There are several disciplines involved when we carry out the sizing of a solar powered airship. You have the geometry which is basically dependent upon the shape of the envelope and the solar array layout and orientation. You have to look at aerodynamics mainly looking at the CL and CD evaluation for a given shape. Then you look at the structures where you have to look at what fabric material to choose, how to do the stress analysis, how to estimate the load coming on the various components. The next important discipline is the dynamics where you have to look at the added mass computation and the stability analysis. After that you need to expose the, you need to study the thermal characteristics and different components and then finally go into the energy and propulsion system where you select the storage device and the energy producing device, you select the propulsion device and the associated propeller. So you cannot do any of these in isolation, they have to be all done together in a unique multidisciplinary approach. Solar irradiance basically is the amount of solar energy that is available and this number is not same everywhere, it also varies from time to time, from season to season from place to place. This particular graph shows the difference in the solar irradiance available during the time of the day at two cities Mumbai in India and Beijing in China and we have drawn lines for summer as well as winter. So we notice that during summer the number is almost the same, the peak irradiance is almost around 1200 or 1250 both for Mumbai and China and that happens when the sky is completely, when the sun is completely overhead around 12 noon but the solar irradiance in Mumbai during winter peak is available at around 1000 which is 60% less at 600 for Beijing. And also notice that the time at which solar irradiance starts being available is around 5 a.m. and 6.30 a.m. but it changes from 4 and a half to maybe around 8 depending on the location. Let us look at the variation during the month of the year. So you can see over Mumbai during the duration the amount of the number of hours for which we have the sunlight or the day it can be as high as 13 hours in the months of June and July but the irradiance may not be maximum, the irradiance may be maximum in April and August. This is the trend of power trade off between the usage of power and the saving of power. So the requirement of energy is shown in the red colored line. So you have a particular requirement during the day time you have excess power and therefore the yellow line, the yellow portion shows you the excess available. So that can be used for saving into the battery or in the RFC. So that is what is normally done. Now these particular high altitude long endurance configurations they fly at near space conditions around 20 kilometers but the band in which they normally fly all over the world is between 15 and 25 kilometers. The reason for this is that all over the world in this particular band there is a inversion in the direction of the wind. So therefore the wind actually undergoes a zero value at some particular location. It could be any altitude between 15 and 25 kilometers. Sometimes it is 17 kilometers, sometimes it is 18 kilometers. So that is why all high altitude airships are generally deployed at those altitudes. They can be used for earth observation, for monitoring and surveillance, for telecommunications, for spying and many many other applications. The advantage of flying in stratosphere is that the weather remains calm and the temperature remains constant. So the variability of the atmosphere is much lower. The wind intensity also is quite lower and because you are in clear sky there is no cloud effect you are far above the clouds. Therefore the solar radiation intensity is very high. But the density of the ambient air is quite small it is 115th of the sea level value. So therefore buoyancy becomes less. As you can see the high altitude airships can be used for applications requiring persistence and proximity. So you can use it as a pseudo-satellite, you can use it for disaster management, you can use it for border surveillance and any other application. Then you also have high altitude pseudo-satellites or HABS, high altitude platforms. There could be many types, there could be a zero pressure balloon which can easily be launched and this is actually very common. It can only fly vertically upwards because of buoyancy but it is completely at the mercy of the winds. You can have a high altitude UAV, in this case we have shown it to be full of solar cells all over the place. But studies have shown that such things are having very small payload capacity and because the wings are very long and flexible to increase their L by D and hence get larger endurance they suffer from aeroelastic problems and hence takeoff and landing is very difficult. On the airship side there are many advantages but the size tends to be very large and it is not easy. It is a complex structure to build especially in those large sizes. So if you compare a high altitude long endurance airship a conventional versus the body of revolution there can be various advantages and disadvantages. The main advantage you can see is that you have a flatter upper surface. So therefore the solar panels are going to be far more effective as compared to those on a curved surface for a single load envelope. When we fly in stratosphere we need to encounter, we encounter very serious temperature conditions, temperatures are very low and you can also see that the density also gets reduced. And this is the plot for the ambient wind between you know the altitudes of interest. So you can notice that the winds can actually be much lower. So in Mumbai for example the winds are very low at around 21 to 23 kilometers altitude both during spring and winter whereas in the case of Beijing the lower values occur at a slightly higher altitude. And if you look at the maximum and the average value of the ambient wind this is for Mumbai you notice that there is a particular day called Somal Stolstice. If you take January 1st as 1 and 31st December of that year as 365 you can number the days. On day number 172 you have summer solstice when you have the maximum duration of the sun. At that time the average wind speeds are higher whereas there is a critical day of operation which is day number 209 and at this particular day the magnitude of the winds are quite high and therefore this will be the most critical day from the sizing point of view. There are many advantages of hail configurations. First of all they are low cost alternate solution to satellites. And one of the best parts is that the payload that you mount on them could be maintained and upgraded as and when needed because they are relaunchable whereas once you launch a satellite you have effectively launched the technology available during that year and after that you really cannot easily go and refurbish it. They are also able to maintain station at a particular predefined area and although the altitude is significantly lower than that of the geosynchronous satellite lower than the geosynchronous satellites but they allow observation of a less extended area only about 100 kilometers ground footprint compared to satellites but the resolution is much larger. So, let us look at the electric propulsion and energy storage system that is typically used on such airships. You could go for a rechargeable battery system where the battery is connected to the power controller and then there is a motor controller that controls the RPM of the motor attached to a propeller and you can use solar arrays to charge one of the direction goes to the payload the other goes to the airship onboard system and the third of them goes to the propulsive motor. This battery is recharged with a solar array or you could go for a regenerative fuel cell system in which we use electrolyzer to create H2 and O2 and give it to the fuel cell. Once the fuel cell generates the energy the hydrogen and oxygen are recovered to create water which is then electrolyzed so there is no loss of fuel and it is a system that can work for a fairly long time. This is where we are currently as far as the rechargeable battery technology is concerned. We see that when you look at the energy density which is measured in watt hours per kg, lithium polymer and lithium phosphate are the winners in that category. However, when you look at the watt hour you know W watt hour consideration you will find that nickel metal hydride and lithium ions so the old technology of lead acid battery is the least capable both energy density wise and also the watt hour related. So thanks for your attention and I hope you have enjoyed this particular session. Thank you.