AIRCRAFT PERFORMANCE- A BRIEF INTRODUCTION

In our previous post we have discussed about what is aerodynamics and how its study with respect to air crafts is divided into two main categories; the subsonic and supersonic. In this post we will discuss about what is aerodynamic flight and how it affects the performance of an aircraft flying. But before going so deep into aerodynamics lets first understand how actually aerodynamic forces act on a body and how it affects an aircraft performance characters. There are two primary aerodynamic forces the lift and the drag, the lift is the component of the resultant aerodynamic force in the direction perpendicular to the air flow while the drag is the component of aerodynamic force parallel to the direction of flow. The lift is induced by the flow happening over an aerofoil inclined at an angle( angle of attack) to the flow direction. For flow to happen a forward pusher force is required which is the thrust provided by the engines of an aircraft. When an aircraft is flying steady level and straight then the aerodynamics forces hold the the following relations with the thrust and weight of the aircraft.
Thrust = Drag    

Weight = Lift
These would be the primary fundamental parameters that would help us analyse the performance of an aircraft. All our discussions on aircraft performance in future will deal with these conditions i.e. straight, steady and level flight. Now that we know the elemental conditions for analysing the performance characteristics of an aircraft let us start to understanding how various aerodynamic parameters such as lift, drag, velocity, thrust required, etc. vary under various conditions. Before doing that we need to know how the lift and drag coefficients are related. They are given by the drag polar which is
Cd = Cdo + K(CL)^2
where Cdo is the drag at zero lift,
          K is a constant given by 1/(3.141*Oswald efficiency*aspect ratio),
          CL is coefficient of lift and
          Cd is drag coefficient.

flaps

Now that we are done with some basics  let us now try to understand what happens to the lift and drag when HIGH LIFT DEVICES(HLD)are used. The HLD's include the flaps and slats which changes the camber of

slats

the wing aerofoil of an aircraft and hence generates a greater lift coefficient. but as we understand from the relation between the lift coefficient and drag coefficient, the drag coefficient increases with an increased lift coefficient. An increased drag would mean that the maximum distance the aircraft can fly under steady straight level conditions is now reduced because of greater fuel consumption to generate thrust which supports the increased drag. a natural question in any body's mind would be why do we need a device that will cause us  a disadvantage??? Well don't think too much the answer is quite simple, the devices as their name suggests are high lift devices which means they generate a greater lift at a given velocity when deployed compared to when not deployed. This in turn means that we can generate the lift required for the aircraft to be airborne at a lower speed, which on ground means the length of the runway required for the aircraft to attain that minimum velocity to be airborne is reduced, because velocity is proportional to distance. Now you must be having a clear idea as to when and why these HLD's are used. YES!!! They are used only when an aircraft wants to take off and also wants to land. Wait a second!!! Why did I mention the landing distance???? Well the answer is again simple, in fact you have already read the cause for the usage of HLD's in landing. Still guessing???? remember that the drag increases when lift is increased...???? Yes the relation between the lift and drag coefficients is what causes the drag to be increased and hence reduce the landing distance.

the flaps deployed for landing

Now that we have discussed about the performance of an aircraft when high lift devices are used we believe we have served our purpose of giving a small introduction to aircraft performance.Hope you enjoyed reading our blog for updates on our blogs please add us on +1 or follow the author on google plus. Do share it if you found the blog informative.

AERODYNAMICS: SUBSONIC Vs SUPERSONIC

Aerodynamics is the core of aeronautical engineering which deals with the study of air flow over a body and the behaviour of flow characteristics over the body. This has been a very interesting subject for many people from various fields proving to be one of the most important for their respective profession.

aerodynamics used in cars

The god of cricket Sachin Ramesh Tendulkar had attended crash courses on aerodynamics and flow over a ball just to understand how a cricket ball spins and learn to use it to his advantage. there have been similar other sportsmen who have learnt aerodynamics in sports such as golf, football and hockey and a wide variety of engineers who have been trying to make the most out of this wonderful subject. since our blogs are related to aeronautical engineering lets try understanding how well aerodynamics is applicable in the flying of of the huge beautiful metallic birds.

The aerodynamics or flow of air over an aircraft is generally divided into two main fields of study. Namely; subsonic aerodynamics and supersonic aerodynamics. The subsonic aerodynamics as the name suggests deals with the study of flow of air over an aircraft when the aircraft is flying at speeds lesser than mach 1 or less than the speed of sound. In this type of flow the air is considered to be inviscid, i.e. non viscous, and incompressible. Though air is practically a compressible fluid its compressibility effects do not show up much

in the subsonic regime only when the speed of flow reaches a value close to mach 1, i.e. around mach 0.8, the compressibility effects of air becomes significant and is taken into considerations for studies. On the other hand supersonic aircraft deals with flights involving speeds greater than mach 1 which also includes hypersonic flights (speed greater than mach 5).Supersonic aerodynamics aircraft takes into the consideration the compressibility effects as well as the viscous effects of the flow and the affects of these effects at such high velocities is what makes the base for supersonic aerodynamics. As soon as a flow gets changed into a supersonic from a subsonic flow it gives rise to what is known as shock waves

which generate a sudden and steep change in the drag induced. This is caused due to travelling of the aircraft at the speed of sound. Since the source of the sound generation travels at the speed of sound, sound waves ( which is nothing but a pressure disturbance itself) accumulate together with the aircraft giving rise to a very high and unnecessary drag. Due to this the aircraft's generally prefer travelling at speeds which are far from the speed of sound (either high supersonic or high subsonic). This region where the drag increases drastically is called as the transonic region in aerodynamics. We will deal with supersonic and subsonic flow phenomenons in our future posts.

Now that we know there are two flow type studies in aerodynamics we should also understand that both these types of flows can be generated in a laboratory by the help of experimental setup.

fig. a subsonic wind tunnel schematic

Such setups used to study the flow of air over a given body is called as a WIND TUNNEL. There are both subsonic as well as supersonic types of wind tunnels which are being used actively to study the slow of air over aerofoils and air crafts.

fig. a schematic of blow down supersonic wind tunnel

While subsonic wind tunnels are all continuous and run for a long duration of time, their supersonic counter parts run for a significantly lesser time lasting only up to a few seconds to a few minutes. But supersonic wind tunnels are used only in large research centres and universities where research is being carried out on supersonic flight. Do get back in future to read more on wind tunnels and their working in our future posts.

          

a subsonic wind tunnel

a supersonic wind tunnel

This was our post on aerodynamics-an introduction, hope you liked it. Add us on +1 and follow us to keep getting updated on our posts and blogs in future.

COURSE OF AERONAUTICAL ENGINEERING

after getting to know about what an aeronautical engineer is and how crucial he can be in designing and developing an aircraft let us now learn what the contents of any course of aeronautical engineering will contain in its scheme of syllabus. Aeronautical engineering is broadly divided into three different fields of study, and they are namely :

• Structures: deals with the basic structural design of an aircraft and the analysis of theses structures subjected to various tests
• Aircraft Instruments and Systems: this field deals with ll the mechanical and electrical & electronics instruments and systems used and their working and design aspects.
• Propulsion System: deals with the making and maintenance of the power plants of an aircraft.
• Aerodynamics: considered as the core of aeronautical engineering this field deals with the study of air and its flow properties.

So looking at the above broad classification of aeronautical engineering we can conclude that our branch aeronautics is a vast branch of engineering that consists of mechanical, electrical & electronics and power engineering along with its very own fluid engineering. let us now have a brief look at what these different branches of aeronautics deal with and learn their importance to an aeronautical engineer.

Structures:

talking about structures in aeronautical engineering we would deal with the construction and analysis of the structural frame and components as the name itself suggests. There are various software's and analysis tools that an aeronautical engineer can use to do all the structural assembly and analysis. There are also various software's that are used for performing the task of meshing or discretisation which helps in more better analysis of the structural member. 

Always remember my friends that just knowing a few software's and analysis tools doesn't make you a good structural aeronautical engineer, for being a quality structural engineer you need to be good with your basic subjects dealing with structural analysis which are: mechanics of materials 

                                                                           material science

                                                                           aircraft structural analysis

the above mentioned were a few subjects that help you in being a better structural engineer. Practising and performing tests based on your theoretical studies in the above mentioned subject you could expect yourself to become one good quality engineer in the field of aircraft structures and analysis.

Aircraft instruments and systems:

aircraft instruments and systems would be the field of aero engineering which would be dealing with design and development of more and more advanced instruments and systems which help the pilot make his journey more comfortable and easy. Being an instrument's and systems engineer one would have the pride of being the one who develops the most crucial devices which actually help the aircraft in flying. In fact in modern day aircraft's,be it a fighter or a passenger aircraft, a flight without such sophisticated instruments and systems will not be possible. So getting into this field of study would keep you satisfied and also equally responsible, if you fail to perform your duties well enough then a pilot would be flying blind in space without knowing where to go or what to do. so once you become an instruments and systems engineer be sure that you are not negligent with your work.

Aircraft Propulsion:

this is one field of study of aeronautics that is considered as the power house of aeronautics which in fact deals with the construction and the developments of better and more advanced engines which power the engine with more thrust and less fuel consumption for a longer time. So if you are that guy who wants to get your hands dirty and try out new things with power and engine stuff this is the field of study you should be focusing more on. But understand just like in the field of structures you need to be very clear with your basic subjects such as thermodynamics, heat and mass transfer, computational fluid dynamics and fluid mechanics. Being an engineer in anything related to engine design and maintenance is considered as one of the toughest jobs in the field of aeronautics. It takes a lot of courage and passion to be an engine designer or maintenance engineer.

Aerodynamics:

considered as the core of aeronautical engineering this is a branch of aeronautics which deals with the flow of air and the effects of the flow under various conditions. you get to decide what the shape of every single part exposed to air is and how each one them responds under different speeds. This is that field of studies which makes you stand apart from other engineers as a separate and unique engineer of highest calibre. You study the affects of a supersonic flight (any speeds greater than the speed of sound) the effects of compressibility of air at high speeds and so on. So always remember that when you become an aeronautical engineer you would be the only engineer dealing with such high speeds and such weirdest of phenomenons which are very hard to find anywhere else in engineering.

the above were the main fields of aeronautical engineering and any other subject in aeronautics could be classified and placed under any one of the above fields of study.

WHAT IT IS TO BE AN AERONAUTICAL ENGINEER

After making up your mind to take up aeronautical engineering as your field of higher studies you must now be wondering what would i do as an aeronautical engineer? What does it take to be a quality aeronautical engineer who is recognised as a quality engineer by the industry? If you have got questions like that then you are at the right place to find the answers to your questions and learn what it means to be a true aeronautical engineer.

aeronautical engineers are always given with four main objectives:

• higher: aeronautics always deals with designing aircrafts that fly higher and higher and conquer more of the sky range as it has always been an amusement for every single human being to fly hiher and higher in the air.
• faster: the second most important aspect for an aeronautical engineer would be to design metallic birds that fly faster and faster witouh cuasing any damage to itself or anything else in its vicinity. the only aim of flying faster is to save more and more time because time is the costliest thing a man can ever loose.
• longer: flying longer without touching the grounds would be the most important of factors for an aeronautical engineer to consider to build an aircraft simply because the longer you fly with great speeds the more distance you cover which is the core intention of aerial transportation
• safer: Along with higher, faster and longer flights its of at most importance for an aeronautical engineer to have a safe flight for all those people dependent on him.

Going into aeronautical engineering lets first understand what is the job of an aeronautical engineer, as most of you people would have guessed by now it would be your job to build a good quality flying mechanical

people watching as an aircraft burns

bird. And your freedom to make errors as an aeronautical engineer will be very narrow, in fact its close to zero percent. Any smallest of errors caused by you could cost hundreds of lives of passengers and crew members on an aircraft. So the first and most important thing you get to become as an aeronautical engineer is becoming a person who is almost error free with his decisions and calculations.

result of a small error by the maintanence engineer 

Do not all that excited and happy that you will be an error free person by becoming an aeronautical engineer, it takes a lot of hard work and months & years of practise to become one such quality engineer. So all of you who have decided to become an aeronautical engineer think again before choosing this branch of engineering. Do choose it if you are willing to work hard and put in more than the best of your efforts to be a quality engineer because unlike other branches of engineering you have no room for making error in this field. You make too many errors you loose your job go home and sit back for the rest of your life because the chances of you getting a job after making minor and silly errors in this field is very thin. There have been instances in past where engineers have been jailed for their entire lifetime for very infinitesimally small errors which cost lives of passengers and flight crew.

After discussing about the punishments you get for small errors you do in this field of engineering let us now also talk about the rewards that you can get as an aeronautical engineer. Well the first and most common reward anybody would look for is good salary packages and that's what you get. Yes as a good qualified aeronautical engineer you can expect attractive salary packages and expect it to grow big very quickly within very small time. But it comes with additional work load. just getting an aeronautical engineers degree from a university wont get you good pay packages you need to learn to apply your knowledge on real time simulation software's in which you can simulate the flow conditions over various components of an aircraft and prove it practically with experimental results as well. Moreover the salary that you get as a fresher in aeronautical engineer is nothing great when compared to other branches of engineering, but as you start gaining experience the hike in salary you start getting is significantly high when compared to your peers in other fields of engineering. with addition to the salary packages offered to you the other respect you get is that you are the one responsible for the safe flight of so many millions of people on any airline.
 People are able to travel longer faster and higher and safer just because of you. And the joy and proud feeling you get because of this fact is really nit comparable with the money that you can earn as an engineer. though they say the air warriors rule the skies the fact remains that its not the air warriors that rule the skies but its the magnificent metallic birds that you built that rule the skies and without you the sky warriors are never really the warriors of sky.