 Let us look at some key issues in the design of airliners. First of all the wing of a transport aircraft or an airliner is subject to a large amount of optimization and why is it so many people wonder that all airliners whether they are from Boeing or Airbus they look very much alike because both of them have been subjected to the same amount of optimization similar requirements and similar objectives. So independently they have come up the solution which have arrived from various companies are very similar. There are certain variants of course and it will be interesting for students to actually be given an exercise to identify totally different approaches and totally different solutions to meet the same requirements. But in transport aircraft of this particular type you will find most of them have certain common features what are these features. The wings are swept in most of these cases but the range in which the quarter chord sweep that you will observe will be between 35 and 38 degrees mostly. Now some of them might use supercritical aerofoils which allow you to obtain the benefits at a lower sweep angle and also when you sweep less you can get more efficient flaps and lower wing weight. So this is one thing. So most of the aircraft in this category airliners which fly near transonic speed mark numbers of around 0.8 they are going to have swept wings with a sweep in a very small band or supercritical aerofoils allowing it a little bit lesser sweep. The sizing of the fuselage is actually not a very difficult task. So fuselage is basically going to be almost like a cylindrical body with some nose and some tail. The nose is required to put the cockpit and to put some instrumentation and some features in the front and the tail is required essentially to accommodate things like the APU some amount of baggage maybe and adequate length and taper to conical taper to allow the distancing of the tails to provide sufficient moment arms. So the fuselage design is subjected to volume and for passenger and cargo whatever is the volume required and what we want to do is we want to make it as small as possible to reduce the cruise drive. When you come to the power plant all of them have generally a high bypass ratio turbo fan aircraft because these give you lower SFCs and lower noise levels and also lower emissions especially the NOx emissions and easy maintenance. One example I would like to show you this has been taken again from the book by Professor John Fielding about how some advanced features have been provided in a transport aircraft to address particular requirements. So this aircraft for example is one of the aircraft which has come with two member crew this is now standard but when this aircraft appeared in the market it was one of the first aircraft that came up before this we had aircraft like Boeing 747 older versions which had a pilot a co-pilot and a flight test engineer or navigator. So the cost of the crew has come up because the workload is low so we have a low workload cockpit so you can manage with two people and this was possible by extensive aeronics integration. This is an example of how technological developments drive the requirements earlier people were happy to customers were happy to have the requirement of 3 or 4 people in the cockpit but now it is only 2. This aircraft has got a center of gravity management system which allows it to fly optimally at various conditions and there is a flight envelope protection and load alleviation by automatic deflection of the control surfaces to handle the gust loading and this is possible because of the extended flight through computer system. On the structure side the designers have gone for use of new materials and processes composites and super plastic volume and diffusion bonding and also aluminum lithium alloys. On the power plant side they have been installed with the CFM-36 engine which gives you the so it is an old it is an old engine which was on Airbus A320 it has been enhanced to power the A340. We will come again to this aircraft in the future because there are certain other additional features that I will discuss. Now let us look at some trends in the design of airliners especially let us look at families and commonalities. Now just like we have families in our own personal life we also have families in aircraft design. Now what you do in families is basically you design a baseline aircraft and then you meet the changing market requirements or provide a competition to an other existing aircraft by stretching or shrinking the aircraft okay. So what do you mean by stretching and shrinking basically by inserting and removing the fuselage plugs you could also do it by changing the engine or by increasing the thrust of the same engine to meet a requirement and there are many many examples of this in the Airbus and the Boeing stable which we will see very shortly. The aim of this exercise is to ensure that every aircraft with the competition makes available there is a equivalent or similar aircraft in your stable so you give the airline a choice that if you want to beat that aircraft in the competition here is our solution to that particular problem. You can see for example if you look at the large twin market okay twin engine aircraft you can see you have for example you have 767-200 which was for this particular range and this particular you know this particular capacity and it has been stretched and again you know and again similarly you know you have this family similarly you have another family of the Boeing 767 family where you are just reducing the range by or I would say the other way you are increasing the capacity by putting you know sorry you are you are changing the market requirements let us look at this in more detail as you go ahead let us look at the Airbus A320 family this is a very popular family worldwide it started with Airbus A320 the base aircraft which came in 1984 okay right it had approximately it had 575 5700 km range and it has a capacity of around 150 passengers then in 1988 4 years later the A321 was made available with a larger capacity but a 100 nautical miles smaller range after that we had the A319 which was a stretched version as far as the range is concerned but a shrunk version as far as the capacity is concerned 6800 nautical kilometers and 124 passengers this is one way of fighting the long-range regional aircraft and then here is another example of A318 which came in 1995 here the range was reduced to 6000 kilometers and the capacity was brought down to 107 kilometers so the same basic aircraft is serving 4 different markets by using the family concept similarly you have the 777 family chart where you go from you know one aircraft to the other and then this one to the other and then there is a kind of a fallout and there is also a fallout aircraft so you can see 4 different markets I would say 5 different markets are being addressed so one aircraft is actually able to handle such a large range of capacity and range by stretching and shrinking there are also some commonalities in the design and this is very interesting interestingly you will notice that in the Boeing stable the Boeing 787 fuselage cross section continues to be used for further aircraft with minimal change in the case of Airbus you use the same wing for 2 aircraft the twin engine Airbus E330 and 4 engine Airbus 340 they both have almost the same identical wing this leads to lower manufacturing cost and commonality in service okay and in operation there are commonalities possible using what is called as the cross queue qualification in the Airbus aircraft you can see for example here that you know there is a aircraft called a A340 all varieties within a day the pilot can convert to flying a 330 and from 330 to A340 it takes just 3 days these are large aircraft now if you have a pilot qualified for 340 and 330 and you want that pilot to operate smaller aircraft so matter of just 11 or 15 days you can convert them okay and then 380s they are saying will also have a similar operational advantage Boeing also allows okay now commonality is available only between Boeing 757 and 767 so from 777 to 787 you can go in 5 days but notice here from a non Boeing aircraft basically it means an Airbus aircraft to 787 you require 21 days of training so commonality is also there in both the company here is a cockpit or the flight deck of Boeing 787 okay a very modern cockpit and a similar configuration you will see now in the future Boeing aircraft and here is an example of commonality inside if I draw a line here on the left hand side you have A330 on the right hand side you have A340 one of the versions both of them are having a common wing platform okay on one side you see a single engine because there is twin engine on here you see 2 engines because there is 4 engine but they have a common cockpit they have a common cockpit common fuselage common landing air common empanage or tail common systems and common wings the only difference is in the fuel piping you know the piping that will go to the fuel it will be the engine here to the engine here but for that it is all common and from Airbus A340 300 to Airbus A340 200 you just have 8 frames shorter and you get a new aircraft to meet the market okay this commonality does not come without a cost it is good to have commonality but here is one assessment by Professor Scott Eberhardt about the drawbacks of commonality the result is non optimal design for example if you look at the deliveries of Airbus A330 and A340 as compared to 767 and 777 you notice that 330 sold quite well any aircraft that sells around 400 you know 400 units typically just is able to recover its market this is for a new aircraft of course A330, A340 are not new aircraft but you notice that 767 and 777 have around as on 2012 they had around 1000 aircraft being sold compared to only around 850 and 400 for A330 so common wing is good but too heavy and it result in the interior airplane okay look at the loss in sales what we saw earlier was loss in numbers this is the loss in sales so compared to 767 and 777 340s have around 10 hundred billion dollars loss in the sales and consequently we notice that there is no new order so commonality is good but commonality can lead to serious financial considerations also thanks a lot