 Hello everyone, today we will look at a special class of aircraft which are becoming very popular nowadays and you can see on the screen there are 6 of these modern versions of these aircraft. They belong to a family called as high altitude long endurance or hail aircraft. Most of these are unmanned aerial vehicles. Let us start by understanding what is meant by high altitude. How high is high? So here is the sketch of the atmosphere just above our earth and the hail aircraft or hail UAVs they normally operate in the stratosphere. Now let us look at long endurance. What is meant by long endurance? How long is long in aviation? So let us look at some flights from Mumbai. So here is Mumbai on the map of the world and I have just chosen a few flights based on the travel time from Mumbai. We are assuming that we are cruising at around 10 kilometers altitude and we are flying at approximately 0.8 mark number. So 2 hours from Mumbai is Delhi, 3 hours from Mumbai is Dubai in UAE, around 9 hours from Mumbai is Paris in France and the longest flight operated by Air India currently is from Mumbai to Newark which is a 16 hour non-stop flight. But do you know which is world's longest scheduled non-stop flight of a passenger aircraft? This record keeps changing. The current record is held by Singapore Airlines in a flight that is from Singapore to Newark as shown in the green sketch which lasts around 18 and a half hours. But depending on the wind conditions, it may also become as long as 22 hours in some cases. So that is really long. But then when we look at high altitude long endurance aircraft, the endurance records are really very, very challenging. For example, the Virgin Atlantic Global Flyer designed by Bert Rutan, it holds the record for non-stop unrefueled circumnavigation fastest. It is a 67 hours and 1 minute. Now this record was recently broken by a Gulfstream Challenger aircraft I think which went this distance in much lower time. But there it went for refueling. This one is unrefueled circumnavigation. So that is really a long 67 hours and 1 minute non-stop flight across the world. So let us look at the key mission features of hail UAVs and the best example of a hail UAV that we can think of is the global hawk that you see on your screen. Hail UAVs flies above problems. What do I mean by this? They fly above the weather. They fly above the interception altitudes. They fly above the commercial flight altitude of around 10 to 12 kilometers. So they have an unrestricted flying regime available to them. They carry payloads which can cover a large area of the earth at a time. They may use search and rescue radar or and they also use satellite communication for carrying out their tasks. Let us look at some applications of these aircraft. One of the most common application of a hail UAV is aerial surveillance. This surveillance could be for a military purpose or it could also be for non-military purposes. Then we use them for some experiments on earth sciences. For example, here we see a hail UAV, the same global hawk which is used by the defense services. It is used by the Aurora Atmospheric Sciences Research Institute to fly over hurricanes and to gather the data. Similarly, very novel configurations are being proposed these days to allow hail UAVs or hail aircraft to be pseudo satellites. These are low altitude satellites which maintain the station and hence are able to hover or stay at a place for a long time. Let us look at the legacy hail aircraft, the Lockheed U-2. In true sense, this was the first high altitude long endurance aircraft which was operated by US. But the big daddy and the most famous aircraft in this category is the Northrop German Global Hawk. This project was launched in 1998 and in 2000 the RQ-4A was launched followed by RQ-4B in 2007 followed by the Euro Hawk in the same year. If you want to fly a plane into a hostile environment, whether that's enemy territory or a raging hurricane, there aren't many better craft than an unmanned aerial vehicle like the Global Hawk. What's neat about these air planes is that you can get in a very high altitude. You can do that with manned airplanes too but uniquely you can get this over a weather system for a very long period of time. You observe a hurricane as it develops and then runs through its whole cycle for you know up to almost a day. To do missions like that, the Global Hawk climbs to 60,000 feet on its massive wings. Frank and I took a walk around one. Do you know off the top of your head how many feet this is? Yeah we've got about 116 feet from tip to tip and it's a high aspect ratio wing. You're trying to get a bunch of wing area out there. The airplane flies very high up around 60,000 feet. You've hit around the end of the wall back up to the front. Yeah so there's very little... So it needs this much wing for the lift. That's right, that's right. You're trying to support you know oh in the mid 20,000 pound range of weight up at altitude. And then again you have this one opened up for us which is fantastic because I've never seen the engine in these either so it's a full size jet engine at the back of it. Single jet engine big turbo fan made by Rolls Royce. So is this the type of thing we would see on you know a conventional airline or it looks like the sort of thing you'd see hung underneath a wing? This engine you might even see on a small corporate jet. NASA has been repurposing military global hawks since 2010. It uses them to study and to monitor extreme weather like hurricanes. So yeah this other airframe over here we're in the process of decommissioning. It did a long hard series of flights for us but it was fine getting kind of worn out. So that was a very early one? Very first global hawk ever produced. Very first one. Yeah and so we turned into a science bird when Department of Defense was done using it as a test bird. Global hawks can be programmed to fly completely autonomously but NASA of course keeps a close eye on the planes from a control room. The data they collect is critical to accurate weather forecasts. Yeah everybody looks at the weather every day they go to their websites. All those website information is based on modeling, forecasting what's going to be happening anywhere from the next few hours to the next few days. So the instruments on these type of aircraft collect data that's used to enhance those models and try to make them more correct over time. So the next time you check your favorite weather app the accuracy of that forecast might be because NASA has one of these flying robots aloft. Here are the specifications of RQ-4B Global Hawk aircraft. Notice that it has an endurance of 32 hours and this has also been further extended. Range of around 16,000 kilometers it can fly up to 60,000 feet which is far above the operating altitude of other aircraft and it flies at a leisurely speed of Mach 0.6. It is an unmanned aircraft so therefore it uses remote pilots. The duration of the flight is so large that you cannot expect one pilot to continuously monitor. So therefore you look at 3 pilots. It has a very large wingspan of 40 meters and the length of 15 meters. It is powered by Rolls Royce RR100 turbofan engine. The gross takeoff weight is around 15,000 kilograms of which around 9% is the payload. 45% is the fuel weight and 46% is the empty weight and the wing and the tail aerofoils are LRN1015. Here is the typical Global Hawk mission profile. So it takes off and then climbs slowly to a height of 50,000 feet and then travels around 1200 nautical miles which is approximately 2500 kilometers and then it can loiter for 24 hours at a particular location. Then it can travel back the same distance of around 2500 kilometers and then slowly come and descend. It can operate from a standard airfield which has 5000 feet of available runway length both for takeoff and landing and apart from the 12-24 hour endurance it has it can also while coming in loiter for about an hour reserve fuel and the aircraft can take off and land in a steady crosswind of up to 20 knots. Let us look at some key parameters of Global Hawk. As you can see here there is a picture that shows a typical human being and to show in the sill hot you can get an idea about how high it is, how large is the size of it. You can notice there are certain peculiar features very very slender and long wings and you have this very unique kind of a shape for the fuselage and the engine the single engine is mounted above and behind on the backside and you also see that the tail are having this V or butterfly tail configuration. So as I mentioned this aircraft has got very high aspect ratio unswept wings and the reason for that is very simple that if you have a high aspect ratio then your induced drag term reduces and induced drag is the largest component of drag in a cruising flight. So therefore in a low speed cruising flight it flies only at Mach 0.6. This term is going to be the larger of the two terms and by large aspect ratio we not only get better aerodynamic efficiency in terms of the Oswald efficiency E but also we get a lower value of induced drag. The second interesting feature is its unique nose shape. This particular nose shape is inspired by the beluga whale and this particular shape is actually covering for its radar dish which is inside and it gives a smooth aerodynamic shape and behind that is the intake of the engine. Here is a look inside. So as I mentioned to you there is this dish radar which rotates 360 degrees. So therefore we need to have a covering over it and that is why we had this beluga nose whale type shape. Notice how the engine is mounted just above the fuselage with specially designed intake. So the air is coming in from the top of the fuselage and getting inside the engine and then you have this V type butterfly tail and you can see the structure details inside. Although it may be an unmanned aircraft it needs a large amount of support on the ground to be operated. Here is the photograph of the Global Hawk Operations Center. Now what are so many people doing? Not all of them are flying the aircraft. In fact, I can tell you that most of them the ones especially which are having this image on their screen are the ones who are actually monitoring the payload. So as I mentioned there might be only one person or maybe two who are piloting the aircraft but there are a large number of people on the ground who are monitoring the sensors and the payloads and hence making it fly more efficiently. Let us take example of the benefits of unmanned aircraft over manned aircraft for surveillance purposes. Here is an example in Africa where there is a place called Darfur which is the conflict zone and let us say there is a requirement to do surveillance. So from Malta an aircraft can take off and travel 1900 nautical miles and come over this area and then do aerial surveillance. If we do it using an aircraft like U2 then 2% of the Darfur will be mapped in every mission because the time on station is around 3 hours. So you can imagine there has to be 50 flights required to map the whole country, the whole location. On the other hand if you operate using a global hawk then with one mission you can actually cover more than 58% of the area because you have a 20 hour time over the station. So therefore in couple of flights you can actually cover the entire surveillance area. So compared to 3 hours 20 hours compared to 2% 58% that is the advantage of unmanned aircraft over manned aircraft for aerial surveillance. To increase the range of the aircraft further it is possible to go for air to air refueling. So here is an interesting video that shows. Moving on let us look at a few modern hail aircraft designs. We have already seen Global Hawk it was launched in 1998. One year later NASA came up with a project called as Helios in 1999 and they contracted a company called Aeroberonmen to build this very unique aircraft which is nothing but distributed propulsion, distributed payload and a flying wing configuration with a very high slenderness ratio. Around 9 years later the Zafire project was launched by Kinetic in 2008 and in 2013 it was taken over by Airbus. So now it is called as Airbus Zafire. This is also a very slender unique wing with distributed payload. Then Aeroberonmen launched a project called Global Observer in the 2 years later in 2010. This is also a very unique aircraft and again you see distributed propulsion. In 2012 Boeing launched a program called as Phantom Eye which is also a high altitude long endurance UAV and recently Aurora with the help of Boeing has launched the project called Odessus in which the wing can actually bend at these locations so that the solar panels can be made to align with the in the optimal angle to get maximum power from the sun throughout the day. So let us have a quick look at each of these projects. So let us first compare these 5 UAVs. The NASA Helios as I said only one aircraft was built and this aircraft uses lithium battery and it has solar powered electrical engines which fly at 20 kilometers for about a day and the payload they can carry is around 329 or the payload they could carry is around 329 kg. This one aircraft which was built has been lost in an accident. The Airbus Zafire 4 of them have been built this one has a much smaller wingspan much smaller payload and also but the endurance is very high it is 14 days in fact it held a record at one time for the highest endurance of a UAV. It flies at around the same altitude with solar powered solar panels all over with synchronous motors and it has lithium sodium batteries. The Araburangan Global Observer was launched in 2010 the first flight was in 2010 two of them have been built it has a 53 meter wingspan and can carry 180 kgs for about 5 to 7 days and it operates in the stratospheric altitudes. The first flight was held with battery powered engines but now the propulsion system is converted to liquid hydrogen based IC engine and there is no battery on board. The Boeing Phantom i launched two years later in 2012 the first flight only one has been built and now it is in a museum it has a wingspan of 46 meters it can carry around 200 kg payload for 4 days again 20 kilometers again liquid helium IC engines without any battery. And finally the Aurora Odesis which was supposed to fly in April 2019 but there has been an indefinite delay in its flight and we are still awaiting its first flight two of them have been built with a wingspan of 74 meters and it can carry 25 kilograms of payload for about one full day at 20 kilometer altitude. This is powered by gallium arsenide solar cells and uses lithium polymer battery. Let us look at all of these UAVs one by one this is a NASA Helios let us watch a short video about this aircraft. There are some special features of NASA Helios it is a carbon fiber graphite epoxy based construction but it also has Kevlar and Styrofoam that is a very unique structure it is solar powered as you can see there are so many solar cells mounted on it. In August 2001 it had a world record for sustained horizontal flight but in 2003 because of gusts which it encountered during the flight which were beyond its design condition it is wing flexed a lot and there was a complete structural failure and it fell in the Pacific Ocean. There is a very interesting and detailed accident report available online for this particular aircraft which you can search and study. The Airbus Zafar as I mentioned started with a as a program from Kinetic in 2008 and then 2013 taken over by Airbus the main purpose of this particular aircraft is to act as a communications platform and also it can be used for maritime surveillance very slender very lightweight aircraft which is solar powered with carbon fiber construction and it holds the record for endurance. It flew for 14 days 22 hours and 8 seconds nonstop. For further information on this unique aircraft you can have a look at the website below. Let us have a look at the video of this very unique aircraft. Next we move on to the AeroVeronmen global observer. AeroVeronmen is a company which is very well known for bringing out very unique UAVs such as the Black Widow. This aircraft is essentially meant to be a high altitude communications relay it has a distributed payload system as you can see. There are these 8 engines mounted on the wing and also it can be used for disaster response maritime surveillance. Unfortunately it crashed in April 2011 and after that one year later the contract was cancelled. Let us have a look at this aircraft. The Boeing aircraft company also has come up with a product called Phantom Eye. This aircraft is also meant to be a communications relay with provision for continuous long range communications. It was launched in 2012 or first flew into 2012 but disassembled in 2016 and now it is deflated in the Air Force Flight Testing Museum. Let us have a look at a video of this unique aircraft. It was only Phantom Eye's second takeoff but it performed it as though it had done it a hundred times before. After reaching its takeoff speed of nearly 60 knots Phantom Eye lifted off from its ground cart and gracefully climbed to more than 8,000 feet to begin a 66 minute flight. Seeing that bird lift off the cart like that was a sight to see. Engineers and ground crew watched as Phantom Eye climbed to 5,000 feet and then as it banked and soared to its cruising altitude over Edwards Air Force Base. Powered by its two 150 horsepower liquid hydrogen engines, Phantom Eye's 150 foot wings glided the unmanned aircraft through California's high desert sky. That was one of the most amazing things and a great feeling seeing Phantom Eye return to flight. Phantom Eye's first flight was 28 minutes. It provided engineers with plenty of flight and performance information but this longer flight allowed for all systems to be analyzed. It has call signs. Scott, you'll be Phantom 2. Noelle Sokocio is Phantom Eye's flight test conductor. Got a lot of good high-speed taxi data which we didn't have previously above 40 knots and got some handling qualities, information and definitely some good landing data. The longer flight expanded the flight envelope bringing Phantom Eye a step closer to meeting its intended mission of up to four days of endurance to provide customers persistent ISR. So I think it was really nice to see the flight, the landing go so well and then to have customers there congratulating us on that and showing so much interest in what we're doing with this vehicle. Phantom Eye has been in the air for about an hour flying autonomously over Edwards Air Force Base. Engineers are in this ground control station monitoring Phantom Eye's every move and all eyes will be on Phantom Eye's landing because it'll be the first time new reinforced landing gear will be put to use. Phantom Eye will land, come to a stop, tilt to one side or the other and then rest on the wingtip. During Phantom Eye's first flight the landing gear dug into the dirt on the lake bed and broke but the second landing was picture perfect. Up next for Phantom Eye will be additional flights that take it higher and farther eventually reaching altitudes of 65,000 feet and staying airborne longer than any other unmanned aircraft. And finally let's look at the Aurora Odesis which has been built with the support of Boeing again. This aircraft is supposed to be a pseudo satellite, it's a low altitude satellite. You can see there are three fuselages with distributed propulsion and also for surveillance obviously anything that can fly at a high altitude for long endurance automatically becomes a candidate for surveillance and reconnaissance. There are a few special features it's a carbon fiber construction and the solar cells are gallium arsenide very thin film very lightweight solar cells. The unique thing about this aircraft is its ability to convert its configuration from a conventional aircraft to a z-wing configuration as shown here. Let's have a look at the video of this unique aircraft. Odesis is a dream aircraft that we've been working on for 30 years or so. It's a aircraft that is designed to fly almost indefinitely only on the power that it gets from the sun. The platform's innovative propulsion and power system combined with the lightweight structure make a very challenging and interesting engineering problem. The airplane has to be incredibly efficient that's why it's big it has to be incredibly light that's why it's so fragile and diaphanous the way it's built. The structure of the airplane is mostly trusses made of carbon fiber our coverings are made of UV resistant material very light film called tedlar and also solar cells on the top surfaces of the wings and fuselage. During daylight Odesis uses its solar ray to convert sunlight into electrical power. This electrical power is used to drive the propulsion motors and also stored in the batteries which provide energy for overnight flight. Odesis is able to stay aloft over long periods of time and station keep over specific locations because of that it is able to relay voice internet and other forms of communication. The key advantages for monitoring applications are both the high vantage point that gives you the ability to see and hear long distances and then also the persistence or the ability to stay in one location and monitor over long periods of time. The Odesis aircraft is exactly what's required to catalyze very rapid advances in climate research through the use of lasers for the determination of species that control ozone to the use of radar for ground penetrating determination of ice volume and ice flow to the determination of soil moisture all of these aspects turn out to be the most important measurements you can make. Odesis will go after these problems in a way that nobody ever imagined before. The idea of an airplane that can fly forever that makes no pollution that is completely green that's something that captures the imagination of people around the world. At Boeing our corporate motto is to connect, protect, explore and inspire and I don't know of another project that embodies all four of those elements as well as the Odesis solar powered airplane. In the recent past there have been emergence of I would say reemergence of lighter than air systems or airships for high altitude long endurance aerial platforms or HALAPS. One very interesting project was the Lockheed Martin Hale-D as you can see in the photograph here which flew in 2008 for the first time but there was an accident and so it was you know it just came down and after that it has not yet been taken up. In the recent past there are studies from Thales-Alenia space for an airship called as Statobus. So these platforms seem to have a promise for long endurance high altitude applications and there are several challenges the technological challenges are there and airships are making a very strong comeback. So watch this space for more information this is something that is definitely going to be the future of high altitude long endurance aircraft very promising but still not realized. Before I close I would like to acknowledge the contribution of Ms. Tanvi Prakash PhD scholar at IIT Bombay for her research on the span extension of high altitude long endurance UAVs and it is with her help I have got the information and the data regarding so many UAVs especially the Global Hawk which is her baseline UAV and my teaching assistant Namanuddin for help in creating this lecture. Thank you so much.