 Hello and welcome to this lecture series on jet aircraft propulsion. So, this is a new course that is being offered under the NPTEL phase two initiative and this is primarily a course meant for the aerospace engineering students. And there are two of us who are offering this course, my name is Pradeep and along with me my colleague Professor Bhaskar Roy both of us from the aerospace engineering department IIT Bombay would be offering this course. So, over the next few lectures our aim or intention is to educate you with some of the basic aspects of jet aircraft propulsion. We would be primarily focusing on the aircraft propulsion mode that is the air breathing mode of propulsion, we shall not be covering rocket propulsion in this course. And so, this particular course that we are offering is primarily intended for aerospace engineering students with some background and prerequisites that we shall which I shall explain in a few minutes. And so, before we go into some of those details let us take a very quick look at what is what are the contents of this particular course. So, basically this course consists of these broad areas of topics and we shall begin this course with a brief introduction to this whole course on aircraft jet propulsion which will be primarily covered by Professor Bhaskar Roy. Following this I shall be covering the thermodynamic analysis of real cycles I shall of course also give some quick review of an ideal cycle of the jet engines followed by the real cycle and it is thermodynamic analysis. Subsequently we shall be discussing about compressors and turbines basically we will be discussing the various components in which constitute an aircraft engine. And the two main components of the aircraft engine are compressors and turbines and we also have combustion systems which we shall cover subsequently. And then we shall be taking up intakes and propelling nozzles. And then Professor Roy will also be covering aircraft engine install performance it is sizing and matching in detail. And then towards the end of the course we will also be discussing in brief about ramjets scramjets and pulse jets. And more details of the syllabus and the contents are to be put up on the NPTEL website. So, we are requested to take a look at the details of the course and the various topics that will be covered in this course through the NPTEL website. So, the basic aim as I was mentioning earlier of this course is to give you an overview and also some in depth analysis of the different components that constitute an aircraft jet engine. And what are the different types of jet engines that are prevalent? And what makes these jet engines different? And what is the need for these different types of jet engines? What are the components that are different in each of these engines? So, these are some of the topics that we shall be covering. And which as I mentioned we will also be taking up the aircraft installed performance and how it is matched the various components of the aircraft engine are matched. So, that all these individual components operate as a single unit because though these components are designed separately ultimately all these components have to fit into one single engine and operate as more or less a single unit. So, it is important that there is a matching between these different components. Now, this course as I mentioned is meant for aerospace engineers and as an aerospace engineering students. And so, there are certain prerequisites that are expected from you regarding some basic courses that you need to have undergone to be able to understand and appreciate various contents of this course. So, there are couple of courses that we feel are prerequisites for this course. One is one of our own course that is in on introduction to aerospace propulsion which we had offered under NPTEL phase 2. And so that is one of the courses that we strongly recommend that you undergo before taking up this course. Or if you have undergone a course in engineering thermodynamics as well as a course in basic fluid mechanics as both these courses will be helpful in your understanding of the various topics which are to be discussed in this course. So, we strongly recommend that you have undergone these courses before you start taking up this course. So, that you are able to appreciate and understand the various aspects of jet aircraft propulsion. And so, during the next several lectures we will be having about 42 lectures in total. And so, during all these lectures we shall be discussing various topics and what I shall do next is to take you through the contents which shall be discussed in the subsequent lectures. So, before that let me also mention about the various textbooks that we recommend for this course. One of the textbooks that we recommend for this course is by Michael and Thomas on aircraft power plants which was published the seventh edition of this book published by Tata McGraw Hill in 2010. And the second textbook which has been there for quite some time and is popularly followed many colleges is by Hill and Peterson which is Mechanics and Thermodynamics of Propulsion. There is an earlier version of this available that is published way back in 1992 by Addis and Wesley. And the third book that we would recommend is by Mattingly. So, this textbook discusses primarily about the cycle analysis in very much detail. So, Mattingly's textbook discusses cycle analysis in good detail and this is published by the AIAA Education Series and published in 2006. Another textbook that you could also refer to is by Ahmed Syed on aircraft propulsion and gas turbine engines published by Taylor and Francis CRC Press in 2008. And one of the classical textbooks on gas turbine theory is by Sarvanamutu Rogers and Kohen. And this is gas turbine theory 2001 Pearson Education Series. And this book is primarily meant for land based gas turbine engines, but they do have chapters for aircraft propulsion. There is also a textbook which one of the instructors of this course Professor Roy has written on aircraft propulsion published by Elsevier India in 2008. So, this is also a textbook that I would strongly recommend that you can take up for this particular course. So, these are some of the textbooks and reference material that you should be referring to while undergoing this course. And in addition if we come across some other interesting textbooks or reading material, we shall also discuss those during the schedule of this course. And so, we shall now look at what are the different contents of the course in little more detail lecture by lecture starting from today's lecture. And so, today's lecture is basically an introductory lecture which both the instructors are going to handle. So, part of this course, part of this particular lecture will also be taken up by Professor Roy. It is primarily to do with introduction and development of aircraft jet propulsion with a little bit of historical perspective. The second lecture is to be taken by Professor Roy on how the jet aircraft engines make thrust or how is thrust produced by the jet engines. So, this is a very fundamental concept that you need to understand very well. And so, that will be discussed in detail during the second lecture. The third lecture is on the basic performance parameters of jet engines. This again will be covered by Professor Roy. And subsequently we shall look at the different types of engines in detail starting with the turbojet engine, the different forms of turbojet, the turbojet with reheat, the multi spool engines etcetera. And in lecture 5, we will continue the discussion on turbo fans, turboprops and turbo shaft engines. In lecture 6, we shall take up the ideal and real Brayton cycle, Joule Brayton cycle which I shall be taking up. And then, we will also discuss the differences between the ideal and real cycle. And how is it that we can carry out a cycle analysis of these cycles. And then, we shall take up the jet engine cycles for aircraft propulsion. The ideal Joule Brayton cycle is basically a closed cycle. And so, an aircraft engine as you know does not really operate in a closed cycle mode. And there are certain differences between the ideal Brayton cycle as applied to jet aircraft propulsion. So, we will discuss that in the seventh lecture. And then, we will also take up the different components of the jet cycle thermodynamically. And how do you analyze the performance of these cycle components like the intake, the compressors, combustion chamber, turbine, nozzle etcetera. That will be discussed in lecture 8. In lecture 9, we will have a tutorial session. We will take up cycle analysis. And we will solve some problems from cycle analysis, the real cycle analysis of some of the engines. And that would give us some idea of how we could carry out a cycle analysis given some of the performance parameters. Lecture 10 will be detailed analysis of the real cycles followed by a tutorial during lecture 11. And in lecture 12 onwards, we will discuss about the components in much more detail. We will start with the thermodynamics of compressors which Professor Roy will take up. In lecture 13, we will take up the thermodynamics of turbines. Lecture 14 will be the axial compressors. We will discuss about two-dimensional analytical model for axial compressors followed by in lecture 15, we will take up the cascade analysis and how to estimate the loss and blade performance of cascades. Lecture 16, we shall devote to what is known as the free vortex theory and also about the single and multi stage characteristics of an axial compressor. So, this will be followed by a tutorial on axial compressors in lecture 17. Lecture 18, we shall devote for a centrifugal compressor, what are the elements of centrifugal compressor. And then in lecture 19, we will take up centrifugal analysis, its characteristics like surging, choking etcetera in detail. In lecture 20, we will take up the next component that is axial flow turbine and its 2-D analysis cascade analysis. Lecture 21 is multi-staging of axial turbines, turbine cooling etcetera, which again will be handled by Professor Roy. Lecture 22 is radial turbine aerodynamics and thermodynamics estimation of losses and efficiency followed by tutorial in lecture 23. Lecture 24, we will start with the combustion chambers, the mechanism of combustion and what are the parameters involved in combustion chamber performance. In lecture 25, we will discuss about pressure loss, combustion efficiency, and intensity. And then in lecture 26, we will discuss the practical combustion system which is applied, which is what it is in aircraft engines, the stability of combustion and fuel injection. In lecture 27, we will take up another component of the aircraft engine that is the intake and we will discuss the transport and military aircraft intake separately. We will also be discussing about different types of aircraft intakes, the subsonic intake, the transonic and the supersonic intake designs that will be in lecture 28. Lecture 29, we will discuss about the nozzle, the different types of nozzle, the fixed and variable geometry nozzles. And then in lecture 30, we will discuss about the convergent divergent nozzle and their applications. Lecture 31 will be basically a tutorial session on intakes and nozzles. And in lecture 32, we have engine off design parameters and operation which will be discussed by Professor Roy. Lecture 33, we will discuss about engine component matching and dimensional analysis. And in lecture 34, this will be continued and we will discuss that in more detail of component matching and sizing. Lecture 35 will be installed performance of engines and there will be a tutorial session which will be during lecture 36 on off design performance and matching. In lecture 37, we will discuss about use of ramjets, pulsejets in aircraft propulsion and you might have already heard about ramjets and pulsejets. So, we will discuss that in little detail during that lecture and take up some analysis, thermodynamic analysis of ramjets in lecture 38. And in lecture 39, we will discuss about flow in diffusers, combustors and nozzles as applied for a ramjet engine. Lecture 40 will be about design performance of ramjets, ramjet engines and followed by a tutorial during lecture 41. And the last lecture that is lecture 42, we shall be discussing about future of aircraft propulsion. We will discuss the conventional propulsion as well as the propulsion concepts that are being used currently. We will then discuss about where is that the aircraft propulsion is going in the future and what are the different concepts that will probably be used in future aircraft propulsion systems. So, these were the lecture wise schedule and contents that we shall be discussing over this lecture series. And so, in today's lecture as we as I mentioned, we will discuss about fundamental aspects of jet aircraft propulsion, introduction to jet aircraft propulsion and some amount of historical perspective of that. So, I guess if you have already undergone the basic course of introduction to aerospace propulsion that we have already taken up in NPTEL, you would have already had some idea about what are the different types of aircraft engines that are jet engines that are currently in use. So, let me give you some overview of what are the different types of jet engines that are existing and also what are the different basically the differences between different types of these jet engines. So, aircraft jet engines can be classified into many of these groups which I am sure you would have already heard about. One of the basic forms of the aircraft jet engines is the turbo jet and a turbo jet engine can operate in two modes it could operate with an afterburner or without an afterburner. And afterburning is basically used to generate additional thrust when the aircraft has to cruise to super has to accelerate to supersonic Mach numbers and also cruise at the same Mach number. So, it could operate either in the afterburning mode or the non afterburning mode. The other form of the aircraft jet engine is the turboprop and turboprop is consists of a jet engine one of the turbines of the jet engine drives a propeller and propeller generates a substantial thrust in addition to the nozzle thrust itself. So, turboprops are still used in transport aviation you might have seen some of the smaller jet engines which use turboprops and so turboprops can again be driven either by propeller it could the turboprops or the turbo shaft. In fact, they are also similar because turbo shaft is the engine used in helicopters. And in helicopters as we know there is no jet thrust it is basically the thrust generated by the main rotor blade. And in both these cases the propeller in the case of turboprop or the rotor blade in the case of turbo shaft is driven by the free turbine. And it is in some cases bounded on the compressor shaft itself with a gearbox. Now, the other popular type of aircraft engine is the turbofan. We will discuss the classification of turbofan in the next slide because there are many types of turbofans which are prevalent. And then some of the advanced concepts like the unducted propfan and deducted fan engines. And the these both of these could either have a single propeller system or a counter rotating propfan system. So, some of these will again be discussed in little more detail in later lectures or it has already been discussed in the earlier course on introduction to aerospace propulsion. Now, turbofan as you know is the engine that is used in most of the transport aircraft the larger sized transport aircraft. And turbofan engines can as you can see constitute of different types or different classes. It could either be broadly classified as forward fan system and aft fan system or the other classification is the high bypass ratio system and the low bypass ratio system. Now, let us take up the forward fan system which is how most of the engines are in if the turbofan is a forward fan system the turbofan could either be operating in the mixed flow mode or in the unmixed flow mode. In the unmixed flow mode the bypass air does not mix with the core flow within the engine itself. In the mixed flow mode the bypass and the core flow mix within the engine before they exit the nozzle. And therefore, they can operate in both the modes that is non after burning mode or with an after burner mode. And the other type or classification of the forward fan turbofan could be based on different spools. These engines could either be a single spool system two spool or three spool system. And they could be operate operating with either a geared fan or an ungeared fan that is with a gear box which will reduce the speed of the fan or not. And depending upon bypass ratio the engines could be classified as high bypass or a low bypass ratio engine. In a low bypass ratio engine which is similar to that of a mixed flow engine the engine could operate in non after burning or an after burning mode. And with low bypass ratio the turbofan approaches that of a turbojet engine because of bypass ratios tend to be very low and they are sometimes used in military engines. So, turbofan could also be operating let us say with a prop fan operating in the where the propeller is or the prop fan is in the rear of the engine. So, it is operating in the aft fan mode that is the fan is located not in the initial part of the engine, but the later part of the engine that is the aft fan mode of the engine. So, these are different types of engines and their classification and what are how these different types of engines operate etcetera will be discussed in more detail as we proceed. And so, what we shall now do is to discuss about the development of aircraft jet engines. So, Professor Roy will now take up the development of aircraft jet engines and with some historical perspective in much more detail. My name is Bhaskar Roy, I am in Aerospace Engineering Department of IIT Bombay. Along with Professor Pradeep, I will be participating in the lecture series on jet aircraft propulsion talking about various aspects of jet propulsion. In today's lecture, Professor Pradeep has already introduced to you the various topics that we will be covering the various aspects of jet propulsion that we will be covering in the course of this entire lecture series over approximately 42 lectures. He has also introduced to you the various books and the various prerequisites that are required for this propulsion course. In today's lecture, in the remainder of the today's lecture, I will try to introduce to you the various aspects of development of jet engine with a certain touch of the historical perspective. Jet propulsion has been around for nearly 60 years now, a little more than that. Over the period of this 60 or odd years, the jet propulsion has improved and it has become one of the most glamorous field of engineering and technology the world over. It makes the human being fly higher and faster, takes them all over the world in a very short space of time, meeting both personnel as well as business requirements of various kinds of people. However, the development of this jet aircraft propulsion has been going on long before the jet propulsion actually came into being and started flying. Jet propulsion as a concept has been around for quite some time before they actually got materialized and various aspects of jet propulsion conceptually and technology have been in development for quite some time at least for a period of 50 years before they actually flew. Today, we will try to take a look at how this jet propulsion development took place and where we are today and the various aspects of jet propulsion that make an aircraft engine such a fascinating technological marvel. We will see that jet propulsion as a concept has been around for more than 100 years. If we start with how it all started, Sir Isaac Newton, he theorized for the first time based on his own laws of motion that if you have a acceleration of flow rearward, this could actually propel a machine forward at a sufficient speed to make a body move. Now, this is a theory that based on his own laws of motion that started the whole thinking that one could possibly have a jet propulsion and if you the working medium that he conceived and people later on have theorized and materialized is the use of air. Now, this is an important aspect that you use air that is abundantly available in atmosphere and you simply recycle the air to create jet propulsion. Now, this is an important aspect in the sense that if you have to continuously depend on other kind of material for creating propulsive force then your dependence of the other kind of material could limit your propulsive activity. Now, that is exactly what is done in rocket propulsion that the material that is used for propulsion is completely generated by human beings and stored inside the rocket body. But in a aircraft propulsion, the material that is fundamentally used for propulsive purposes is the air itself. It is taken from the atmosphere and it is given back to the atmosphere. It comes into the engine and goes out of the engine back into the atmosphere and this is what professor Pradeep mentioned as an open cycle that it occurs in a cycle. It is taken inside the engine. It goes through what we call thermodynamically a cycle and we will discuss that through the course of this lecture series in some detail and at the end of this operation of creation of propulsion force, the air is ejected out of the cycle into the atmosphere back into the atmosphere. Now, this is an important concept and because of the success of this concept, the jet aircraft propulsion has become such a all prevading technological use in our life. Now, let us look at various aspects of how the propulsive devices are developed. Surprisingly, in the 1920s, immediately after the World War I, in U.S., under the high-powered committee working under NACA, which was the National Administrative Council for aspects, various aspects of aeronautical developments and they actually concluded that a jet engine was not a feasible proposition at that point of time after going through various aspects of science and technology that is required to make a jet engine work and because of this high-powered committee's recommendation, very little work was done in U.S. on jet engine development. Now, we all of course know that most of the jet engine development have been going on for last 50 years, a big chunk of it is actually in U.S. But, quite surprisingly, prior to that, prior to World War II, very little work was going on in U.S. because this particular committee had decided that jet engine was not a feasible proposition. However, Frank Whittle and later on Sir Frank Whittle, he went ahead quietly and patented his concept of jet engine and we will have a look at his jet engine in few minutes from now and he did that in England in 1930 and this patent is what is normally considered the first patent of a jet engine or first patent granted to a jet engine in the whole world. Later on, after the World War II, Sir Frank Whittle actually migrated to U.S. and he spent most of his developments, developing years in U.S., developing various forms of jet engine, starting of course from his own concept of jet engine. Dr. Hans von Wein, working independently in Germany around the same time as Sir Frank Whittle, also went ahead and patented in Germany his concept of jet engine in 1936. Now, these two are independent development. They had no connection with each other and those days remember the communication channels were not very easily established. So, they did their work independently, developed the concept independently and went ahead and patented them independently in their own countries and this engine developed by Dr. Hans von Wein actually flew with the Henkel aircraft in 1939 and this was indeed the first jet engine to fly. So, the jet engine developed in Germany by Dr. von Wein was indeed the first jet engine to fly before Sir Frank Whittle's engine. Now, after the World War II, we know that the world was in turmoil and after the World War II, Dr. von Wein also migrated to U.S. and he also developed many of his later developments in U.S.A. So, both the further figures of the jet engine development, the modern jet engine development later on did most of their work in U.S. And that also explains why after the World War II, many of the jet engine were indeed developed in U.S. Of course, we have seen lot of development also going on in England and Germany and many other countries in Europe. Let us take a quick look at the fundamental concept of how a jet propulsion device indeed creates a propulsive force. Now, as I mentioned, the typical aircraft actually uses air. Now, what we see in this simple hand sketch is that air comes into the propulsive device from the front and this air comes in with a certain velocity, let us say V A and this is the scenario you would have when the aircraft is indeed flying. So, when the aircraft is flying, it is coming in with a certain velocity which is matching with the flight speed of the aircraft. So, the flight speed of the aircraft makes a certain amount of air come inside the jet propulsion device and then the propulsive device does its propulsive work on this air and then lets it out through the rear with another velocity which is V E and the Newton's laws quite clearly tell us that if you are to get a positive amount of force created out of this device, it is necessary that V E should be substantially higher than V A and then the amount of mass that is activated. So, the product of the mass that is activated and the acceleration or the change of velocity that takes place over this propulsive device indeed creates the propulsive force. Now, this is the simple concept based on which the propulsive devices have been created. So, all jet aircraft engines that we will be talking about over the period of this lecture series will indeed be operative based on this fundamental concept. Now, let us see how the whole concept have indeed developed. You see the key to a practical jet engine was the gas turbine from which it indeed derives its name. The basic jet engine is technically also referred to as a gas turbine engine and the key to this is actually the operation of a turbine or a gas turbine which is used to extract energy from the engine itself and you need this gas turbine to drive a compressor. So, you have a coupling of a turbine and a compressor which is an absolute necessity for working of this kind of an engine and you need a combination of turbine and compressor which then creates a loop energy loop inside the engine and this energy loop is the key to the development of practical jet engine. Now, gas turbine is an old concept. It has been around for a very long time. The development actually practical development started in 1930s. Compressor development started actually a little later, but the patent for a stationary turbine was granted to one John Barber in England way back in 1791. That is a little more than 200 years back. So, turbine as a concept or a gas turbine as a concept has been around for little more than actually 200 years. Now, turbines have been around. Turbines have been around as wind turbines. They have been around as water turbines literally for hundreds of years. People have been using the concept of using either water or air to rotate a turbine like rotor to develop energy, to develop shaft power and to develop work and this is how the wind turbines have been developed. They have been around for centuries now. The water turbines have been around for also centuries. So, the concept of using flowing fluid whether it is water or air to run a turbine in a rotating mode and to create shaft power and to get work out of it as a concept has been around for literally centuries. Gas turbine as a concept has been around for now little more than 200 years. The first gas turbine was successfully run technologically proven was built in 1903 according to the documents that are available by a Norwegian engineer A. G. Deers Elling. Now, this is little more than 100 years back. The point is making a gas turbine work, you need gas, you need turbine material that can withstand the gas temperature and pressure and hence there are certain technological requirements for making a gas turbine work. So, in design and practical engineering and certain aspects of material requirement of metallurgy quite often prevented actual manufacturing of these engines on large scale. So, large scale use of gas turbine came off a little later even though it was proven way back in 1903. Mark the date 1903 is also the year in which Wright brothers flew their first aircraft. Now, this is the engine which was created by Sir Frank Whittle and this particular engine you are looking at is indeed the engine that flew. So, the first patent he created was way back in 1930. This jet engine flew about 7, 8 years after that, a little after Dr. Bonn-Ohine's engine flew in Enkel aircraft. Now, this engine is conceptually and in detail somewhat different from Dr. Bonn-Ohine's engine. Now, this concepts of for example, a centrifugal compressor, a number of these cylinders that you see around that look like gas cylinders. They are indeed the combustion chambers and on this side you can see centrifugal compressor. We will have a look at what centrifugal compressor is later on in this course in some detail and on this one what you can see here is the back of the engine the jet nozzle. The nozzle through which the jet comes out a hot jet which has been gone through which is gone through a process of compression in the centrifugal compressor, a process of combustion in these combustion chambers which are wrapped around the engine. They supply the hot gas which has been compressed. So, it goes into a turbine which one is not able to see here very clearly and then it comes out through this jet for creation of jet thrust. So, this is what Sir Frank Whittle's jet engine was that flew for the first time around 1938. If on the other hand, if you look at the Enkel engine that was created by Dr. Bonn-Ohine that looks a little more like various kinds of jet engines that we see today. Now, this is the engine, this is of course a picture taken in a museum and you can see the various modern components of the jet engine. You can see the compressors over here and then you have the combustion chamber and then you have the turbine and it looks more like a modern jet engine and the jet nozzle through which the hot jet finally comes out. Now, this is Bonn-Ohine's concept of jet engine and this is the kind of engine that indeed flew as Enkel engine. Enkel is the businessman who supported the work of Dr. Bonn-Ohine who was indeed a proper academician and a researcher and this engine was as we know the first jet engine that flew. Now, this is the kind of concept that he would see. You see what happens is if you look at Sir Bonn-Ohine's engine, it is a sleek long engine that takes in air from the front and lets out air from the rear creating jet propulsion force. If for example, if you put such an engine inside the body of the aircraft, this is the scenario you would probably have with you. The engine is good and proper buried inside the body of an aircraft and air has to be ingested into this engine. So, you would need a rather long air intake system. We will be talking about the intake system later on in this course and this intake system delivers the air into, it takes from the atmosphere, delivers it inside the engine. The engine does its various kinds of technological work on the air and then the hot air or gas is finally let out through a long tailpipe creating a propelling jet. Now, this is how the jet thrust would indeed be created if you have an engine that is buried inside an aircraft and this is how the whole business indeed started that you have one engine buried inside an aircraft. In those days, in the early days the aircraft were indeed small and one engine was considered quite often sufficient to make the aircraft fly. The typical components of the jet engine are for example, shown here and we will be looking at them more and more as we go along in this lecture series. You would indeed have a rotary compressor which we shall see is quite different from the piston compressor which you would normally do in other courses and we have done a little bit of that in the introduction to propulsion course. This rotary compressor then actually moves in a rotary shaft which is indeed run by the turbine. So, what just now I was saying is that you need a turbine to run the compressor. So, a turbine compressor is a kind of a combination which is buried inside this jet engine device and this is essential or key to the development of the jet engine. In the sense, the turbine compressor combination creates the high pressure air or working medium which is then ingested with fuel and raised to high temperature. So, that one finally creates high temperature and pressure gas which is used to create the propelling jet. So, key to the development of jet engine was indeed development of turbine and immediately thereafter development of rotary compressor and we shall see various kinds of compressors as we go along in this lecture series. Here we look at a very simple schematic of a modern gas turbine based jet engine. Typically, you would have the air coming in from the front ingested into this jet engine through this opening that is available and these are to be properly geometrically designed and the air as it comes in goes through a rotary compressor as we just saw. The rotary compressor or the process of compression may be done in stages. The typical compression process we would be studying in this course effectively refers to what is also known as aerodynamic compression as opposed to positive displacement compressor which we do in piston engines. Now, this kind of compression which is a rotary compressor uses rotary compressor uses various laws of aerodynamics to create the compression of air. This compressed air is then delivered into this combustion chamber in which fuel is indeed burned a very small amount of fuel is burned and that is sufficient to raise the temperature of the air to very high temperatures. So, what we have is air infused with a small amount of fuel and one may call it then gas fundamentally it is air and then this hot highly compressed and high temperature gas is then released onto the turbine which is indeed also a rotary turbine and this rotary turbine extracts work out of it as is required of a turbine all kinds of turbine and this turbine then through this shaft runs the compressor. So, this is what I was saying that you need a mechanical coupling of the turbine compressor and this turbine compressor coupling creates the high pressure gas inside of which is the stomach of the engine and that is where the fuel is burned and the combination of turbine compressor combustion chamber often referred to as the core engine creates the high pressure high temperature gas and this is then let out through the nozzle which creates the jet propulsion thrust. So, this is the development that has taken place. So, all the aircraft engine that we will be talking about over the course of this lecture series will have some form of rotary compressor it will have some form of combustion chamber and some form of rotary turbine and we will be also talking about various aspects of the intakes shapes and their geometries and various kinds of nozzles that create the that help create the final thrust and their geometries. These are the various things that we will be talking about over the course of this lecture series. We will take a look at a very modern aircraft jet engine you see if you just go back very quickly to the earlier one this schematic actually shows the line drawing or just a cut out let us say a 2 D cut out of the rotary compressor combustion chamber turbine it looks at this moment reasonably a simple device. The moment you look at a three dimensional picture of a modern aircraft jet engine and this particular picture is indeed a picture of a actual modern jet engine you can actually see inside of this literally hundreds probably thousands of parts. This is the mechanical engineering that goes into creation of a modern jet engine. The front parts are the parts that we refer to as the rotary compressor and then you have the combustion chamber here and then you have the rotary turbines over here all these and then you have the shaft system along shaft system which as you can see in this engine and most of the engine that we will see later on are actually hollow shafts and of course they need to be hollow these parts need to be devised very carefully because they are going on an aircraft. One of the most important parameters that we will see a little later on in this course is the thrust to weight ratio. So, weight of this engine is a crucial point in the development and design of this kind of jet engine every part will have to be literally weighed in and should qualify to be on an aircraft engine. So, these hundreds of parts that go into it are very carefully designed and weighed in and their utility have to be completely justified to be inside an aircraft engine. Hence you can see here that an aircraft engine indeed consists of literally hundreds and thousands of parts which actually finally make an aircraft engine that is worthy of putting on an aircraft and flying on an aircraft various kinds of aircraft whether it is large aircraft or small aircraft some of the basic requirements of aircraft are very similar. We shall have a look at various kinds of engines that go into various kinds of aircraft and over the course of this lecture series we will have a look at all these parts that you are looking at and how these parts have been put in place to make up a whole aircraft jet propulsion system.