 Let us look at first the steam engines. The first one we saw already with Henry Gifford. But steam engine basically can someone tell me what happened by steam engine? What is the steam engine? It uses steam as the fluid for doing mechanical work. So what is so special in steam so that it can be used to do mechanical work? Why is steam a preferred fluid for doing mechanical work in an automotive engine, locomotive engine sorry. That is right. That is right. The capacity to hold heat in a given amount of volume is very high for steam. That is the main reason. You must have heard or read about latent heat of steam. The amount of energy it can absorb for before undergoing a phase change or to undergo a phase change. So steam is a fluid that can retain a large amount of heat. Secondly, steam can be easily created by heating water which is easily available. So these are the two motivating factors which lead to the steam engine and if steam engine is available they also use it for the airship. So this is a small video of the working of a steam engine. So what you do is you basically pass steam from the inlet and that steam goes into a chamber. So now you can see there is a crankshaft and that crankshaft is being moved up and down by sequence of inlets and outlets containing steam. So there are three chambers here. In all three chambers what is happening is basically a reciprocating piston is being moved by steam. But the temperature of the steam is slowly reducing as it does work. So you may not be able to recover in a small space the entire energy that a steam engine can produce. So therefore we do it in stages. And then finally there is an outlet which throughout the steam. Such engines as you all know are very popular in locomotives and a very compact version of steam engines were used in the past to propel airships also. So the same engine, the same steam engine that goes into ships when made compacted may be less power but compacted is used in steam engines for airships. And inside steam engines also there are various subsystems. What we saw just now is the reciprocating engine. So steam is used for reciprocating piston. You could also have whirl motors where there are some cup like things which move rotate because of the flow of high speed steam. You can also put a turbine and make the turbine move by impinging steam into it. All of them have their pluses and minuses. But what I would like to share with you is a very interesting experiment done around 12 years ago, around 12 years ago, 2003 if I remember rightly. There were some people experimenting with bringing back steam for powering LTA systems. Now why on earth do you think people would like to look at steam as a LTA system in this today's generation? What do you think is the motivation? Now this particular experiment that I will show you, it is not the utmost to provide propulsive power for the engine. This is an attempt to use steam as a lifting gas. And what would be the motivation? The high cost of helium and more than high cost the continuous less availability. So recently we put a proposal to an agency for funding application of LTA systems for the farmers agricultural applications. So one question that was raised is how do you think farmers will be able to afford? helium is out of question. Availability is also a problem. Hydrogen, yes it is relatively cheaper but still operating cost can be very high. So someone said can we use steam as a lifting gas? So through that so I want to just showcase this thing to you. Looks like I will have to or I have this information offline so I will probably be able to but it was nice to see it there. So this website I would like you to study in detail when you go back home. It is called as the flying kettle and basically steam balloons and steam airships. It is called as flying kettle.com. So the idea is to use steam for balloons and airships. So let us see a testing of their what I will try to do is I will try to put the video audio also. I do not know which of these cables will work. So this is a very special purpose material called as hideous which is able to withstand steam at 100 degree centigrade. It is able to hold it, hold it without structural problems without leakage. So similarly these people are also and if you notice there is this steam engine here. This is a small steam engine which generates steam, steam generator I should say. So steam turbine engines very high power to weight ratio and that is their principal attraction. The power available versus the weight of the system is very high but they are not very straight forward to operate. They are complex expensive and require a lot of maintenance. Secondly you need very high RPMs. Therefore you need a very heavy gearbox because the engine will produce high RPM and to reduce it down to the propeller RPM you need to put a heavy gearbox. So another option would be to either use a reciprocating steam engine or a wind motor. Now this argument goes for steam turbines. So steam turbines are very commonly used and they are easily available but the argument being made here is that steam turbines are not going to be useful because they are going to be very very heavy and they are not going to be as effective. So this is the best suggestion reciprocating reciprocating steam engines or wind motors they should be used. Let us go to IC engines which are very common. So essentially an IC engine is one that uses an oxidizer which is mostly air and that is combusted inside a combustion chamber and that produces the required energy for the mechanical work. So you can see the functioning of the IC engine as shown here in this small video. So you can see that the piston gets compressed and then there is an explosion. In the explosion there is an expansion of the gas which pushes the piston down. As the piston is pushed down air is sucked in and then this cycle continues. The water is closed, air is compressed. Compressed air is exhausted, it causes an expansion. The gas is expelled here, the air is inhaled here. So is this a 2 stroke engine or a 4 stroke engine? So how many of you say it is a 2 stroke engine? Why do you say it is a 2 stroke engine? Yes but do not you have 4 separate steps? The triangle or cam. Now here is a picture of a piston engine which has been used for the R101 airship. Remember the airship which basically did not succeed which was supposed to come to India from London, from UK. So they had designed a very special, very narrowish piston prop engine for powering this particular airship. What you see here is the hub where the prop will be mounted and this is the IC engine of a modern airship. What you see is the framework of the airship. So this is the simulated airship with some framework inside and then we have mounted. So let us have a look at this particular concept. This particular airship is called as aeroscraft. So aeroscraft is one of the modern designs. In fact I would like to cover this in more detail when I look at modern airships. So let us move ahead. Now about IC engine we have to be very careful about the kind of fuel we use. So it is very important. In airships predominantly we use diesel engine IC and some other versions use gasoline. So now what is the basic limitation or a problem with a diesel engine as compared to a gasoline fired engine? What is it? Maintenance is more or less in diesel. Why is it more? Correct. The operating pressure is higher and therefore the vibration levels are also higher. So therefore even cars also, the diesel cars once they go beyond around 35,000 kilometers and then they go for maintenance. There is a sudden increase in the maintenance costs. Till that particular distance or till the engine is touched they might be efficient, they might be low in operation cost. So some other versions are using gasoline. Germans as you all know have also used this blue gas. Do you remember this blue gas? It was asked in the exam also and this particular gas was used in the zeppelins. So just to remind your refresh your memory, we know that one of our challenges is to maintain the buoyancy and this gets disturbed because of the loss of mass as the fuel is consumed. So the Germans came up with this secret weapon called blue gas which is similar to weight in the air as air. So its consumption during flight did not significantly change the balance of the airship. So it is a low density fuel, density matching with that of air. Chemically it is same as the coal gas and it is not blue in color. It is called blue gas because of this gentleman who discovered this particular gas, right. And the first airship to use blue gas was the graph zeppelin, LZ127. The volumes required were very large and therefore it is very handy. It is very handy to have a gas like this which does not upset the buoyancy of the airship.