AERODYNAMICS

In the previous post, we looked at the types of engines available for making an airplane fly.

So, lets see how do aircrafts actually fly in the air.

There are four forces which act on an aircraft. These forces are like four hands, which balance each other to keep the aircraft afloat in air.

• Thrust - 

• It is the forward force that pulls the aircraft forward.
• Thrust is provided by the engines of the aircraft. It may be jet engines or propellers etc.

• Drag  - 

• Also known as air friction force.
• It is a backward force.
• It is the resisting force that is produced by the fluid medium, air, against any object moving in it.
• A simple example of drag is, while travelling in a car, if we stick out our hand of the window, we experience a resisting force trying to move our hand backwards. This is drag.
• Drag also depends on how we place our hand.
• If we place it vertically such that majority of the air hits the hand then drag is more. 
• If we place it horizontally, then we experience that the drag is less.

It is important to note that, for a  flight to take place - 

                       THRUST >= DRAG

If for any condition the thrust gets smaller than drag then the aircraft speed will reduce, which may result in stalling.

• Weight -

• It is the product of mass and gravity that acts on an object, acting down
• An aircraft too has a weight that keeps it attracted towards the ground.

• Lift - 

• This is the upward force which opposes the weight force acting downwards.
• Lift is achieved by the shape of the wings, which are aerofoil shaped (explained below).

Again it is important to note that -

                        LIFT = WEIGHT

Till now we have seen how the aircraft stays in air. Now lets see how the aircraft is navigated in air.

1. WINGS, FLAPS & SLATS.

• WINGS -

The wings are the most important parts of an aircraft. The design of the wings determine the navigation of the aircraft as well as the rising and decreasing the altitude of the aircraft.

The wings are normally aerofoil shaped and they follow Bernoulli's principle of fluid dynamics.

Bernoulli's principle gives relation between pressure and speed.Increase in speed of the fluid is simultaneously occuring when the pressure of the fluid reduces.

Taking a look at the aerofoil as shown above - 

• The air pressure on the upper part of the aerofoil is less, so the air speed is more
• The lower part is exposed to a high pressure of air, so the air moves slowly in the lower part of the aerofoil.
• This creates a lift force on the wings, thus lifting the aircraft upwards.

For creating a lift, the aerofoil has to be tilted by some angle, known as the Angle of Attack (AoA).

Angle of attack is defined as the angle made by the chord line of the aerofoil and the relative flow of air/wind.

The greater the AoA, more is the lift achieved by the aircraft. Generally to make the aircraft stable, ie cruising mode or for zero lift, the AoA should be negetive. So it is actually easy for an aircraft to climb because maintaining negetive AoA is rather difficult.

• FLAPS & SLATS -

These are the external parts connected to the wings that help in achieving lift or decreasing the lift. Flaps are on the backside of the wings, while slats are on the frontside of the wings. There are spoilers added which are above the flaps, controlling the braking of the aircraft. 

AIRBUS A380

When the flaps as well as slats are extended down during take-off and landing. Lowering of the flaps & slats increases the wing span. Thus creates more lift and more drag. This serves two purposes - 

[A] During take-off, more lift is needed. But as drag increases the thrust required is more. So during take-off more engine power is required.

[B ] During landing, low speed is required, and as drag increases the speed reduces further, thus facilitating the aircraft to land.

Flaps and slats not only helps in take-offs and landings but also during cruising and steering through the skies.

2. ELEVATORS, RUDDER & AILERONS.

• ELEVATORS - 

Elevators are the small wings on the tail of the aircraft. Elevators are also known as the horizontal stabilizers. They control the upward and downward movement of the aircraft.

  

As the elevator is moved upwards, the aircraft nose goes up, thus making the aircraft climb.

As elevator moves down, the aircraft nose falls down, thus making it descend.

• RUDDER -

Rudder is placed on the vertical tail of the aircraft. They are known as vertical stabilizers. They control the sideways movement of the aircraft, just as the rudder in boats work.

• AILERONS - 

These are the ones that are plced along with the flaps. They control the stability of the aircraft when it turns on the left or right side. 

There are two ailerons - one on the right side, another on the left side.

They work by balancing each other. 

When the aircraft rolls on right side, the right aileron goes up and simultaneously the left aileron goes down, and vice-versa. Thus balancing the aircraft when it rolls.

By varying the ailerons, elevators and rudders, a pilot can steer the aircraft as well as do various stunts like barell rolls, aileron rolls, flying upside down etc....

3. ROLL, PITCH, YAW.

A pilot uses all the above control methods to fly the aircraft in a 3d space. The three co-ordinate axis of this 3d space are -

• Roll
• Pitch
• Yaw

ROLL - The ailerons control the roll of the aircraft. The ailerons increase the lift on one wing, resulting in the wing going upwards, while the other goes down. Thus making the aircraft roll in one direction.

PITCH - The elevators control the pitch of the aircraft. As the elevators go up, the flow of wind is directed downwards, lifting the nose upwards. Thus the aircraft pitches upwards/downwards.

YAW - The rudder controls the yaw of the aircraft. As the rudder moves, the aircraft goes in left or right directions.

These are the main parts of the aircraft which help in controlling & navigating the aircraft.

Hope u guys liked it....
As always Comments & Suggesstions are welcome......

ARDUINO BASICS 03

Welcome back...

This tutorials is about creating a function and returning its variable.

• Function - 

• Mainly created if the same task needs to be done multiple times.
• Created to perform a definite task, then return the value of the function/calculations done to the main function which calls this one.
• It is used to make the code look clean and better. It is also easier to code. !!

• Return types -

• It is an important part of the writing the function.
• When the task to be performed is completed, the value is to be returned to the one calling it.
• Return types help to return the values.

Working of a function - 

As said earlier, the 'void loop' is the main function which runs the task continuously for infinite time. But sometimes, there may be one or more tasks that are needed to be performed many times in one run. So a function is created in which, the task to be performed is written. Now, on completion of the task the value has to be returned to the main function for continuing the looping operation. So there are return types used for the returning of the variables.

Eg -

Let, I want a function that adds two numbers and returns the result for further use.

int addition (int a, int b)

{

       int s;

       s = a +b;

       return (s);

}

1. int -- datatype of data to be returned - Can be int, long, double or void (if no return).

2. addition -- function name

3. (int a, int b) -- parameters used. The values of 'a' and 'b' were given previously by some other function. In this function only those values will be used.

4. return (s) - Return datatype should match the declaration datatype.  ('int' in this case)

Calling of the function - 

For execution of the function, it should be called. The below example shows how to call a function.

Eg - 

Extending the above example, let the calling function mention the values of the two variables. Then call the addition function which adds the values and returns the sum to the calling function.

void loop()

{

      int s = 10;

      int r = 20;

      int t = addition(s,r);

      Serial.println(t);

}

int addition (int a, int b)

{

       int c;

       c = a +b;

       return (c);

}

1. int t = addition(s,r)    ---  This statement -

• Creates a variable t of type int
• Calls the function addition, sending the two values of 's' & 'r'.
• The variables are added in addition and result is returned back to 't' . 

2. Serial.println(t)     ---- This statement prints the value of 't' ie  30

IMPORTANT POINTS - 

• For every function there has to be a 'return' statement, if the function is returning a value.
• The calling function must have a variable initialized to store the value returned when a function is called.
• The function sholud always be outside the main function. ('loop' in this case)
• If a function is to be stopped midway, a ' return(-1) ' statement can be used.
• If a return statement is used in a function, midway, then the codes after the return statement are not executed.
• Eg - 

int addition (int a, int b)

{

       int c;

       c = a +b;

       return (c);

       int d;                               //  This line of code will never be executed.

       d = a * b;                        //  This line of code will never be executed.  

       Serial.println(d);             //  This line of code will never be executed.

}         

Thank u ..... 

Comments and suggestions are welcome.... !!!

ARDUINO BASICS 02

In the previous post we learned about the two important functions that are a must in the arduino coding.

In this tutorial, let's see the types of conditional statements and loops.

CONDITIONAL STATEMENTS -

• if -

This statement is used when there are two conditions true/false. If condition is true then execute the function or come out of the condition. !!

SYNTAX - 

if (condition)

{                    

       // statements to be executed ;

}

EXAMPLE -

let a variable (a) if greater than a value then it is to be incremented by 1

if ( a > 10)

{

      a = a + 1;

}

• if ... else -

This statement is used for greater control than the basic if statement. Working of this code is as follows - if condition is true then do something , else do something different.

SYNTAX -

if (condition)

{

        // statement to be executed;

}

else

{

        // do something different;

}

EXAMPLE -

let variable (a) if greater than 10 , increment by 1, or, if less, then decrement by 1.

if ( a > 10)

{

         a = a + 1;

}

else

{

        a  = a - 1;

}

• switch case -

This statement is used when there are many things to do and any one has to be selected based on the condition applied.

SYNTAX -

switch (variable)

{

   case 1: //function one;

               break;                         // to break the switch case function, if case 1 is satisfied.

  

   case 2: // function two;

               break;                         // to break the switch case function, if case 2 is satisfied.

   

   case 3: // function three;

               break;                         // to break the switch case function, if case 3 is satisfied.

   

   default: // if nothing matches then execute this

}

EXAMPLE -

let a month number be given as input and the month is to be displayed if the month number correctly matches.

switch (month)

{

   case 1: serial.println("january");

               break;                                       // if month variable is 1 then display january.

  

   case 2: serial.println("february");

               break;                                      // if month variable is 2 then display february.

   

   case 3: serial.println("march");

               break;                                      // if month variable is 3 then display march..

   

   case 4: serial.println("april");

               break;                                       

  

   case 5: serial.println("may");

               break;                                      

   

   case 6: serial.println("june");

               break; 

   

   case 7: serial.println("july");

               break;                                       

  

   case 8: serial.println("august");

               break;                                      

   

   case 9: serial.println("september");

               break; 

   case 10: serial.println("october");

               break;                                       

  

   case 11: serial.println("november");

               break;                                      

   

   case 12: serial.println("december");

               break; 

   default: serial.println("Please enter correct month number.")

}

LOOPS -

• while - 

This loop is used when a function is to be executed till the time the condtion is satisfied.

SYNTAX -

while (condition)

{

         // function to be executed;

}

EXAMPLE -

let a variable (a) if greater than a value then it is to be incremented by 1

while (a > 10)

{

       a = a + 1;

}

• do ... while -

Same as the while loop exept that the condition is tested at the end of the loop.

SYNTAX - 

do

{

       // function to be executed.;

}while (condition);

EXAMPLE -

let a variable (a) if greater than a value then it is to be incremented by 1

do

{

       a = a + 1;

} while (a > 10);

• for -

This is the most mportant loop, which is widely used for writing many functions. The main reason is that it has a huge control over the functions in the loop.

SYNTAX - 

for ( initialize ; check condition ; increment)

{

        // function to be executed ;

}

EXAMPLE - 

Multiplication table of 2 from 2*1 to 2*10

int b = 0;

for(int a = 1; a <= 10; a++)

{

     b = 2 * a;

}

result generated by variable 'b' will be -  2,4,6,8,10,12,14,16,18,20

WORKING - 

• General working of the loop is - 
• First variable is initialized
• Then condition is checked. If true then statements inside loop is executed, else it comes out of the loop.
• After statement execution, variable value is incremented.
• After incrementation, value is checked.
• If true, statements executed. If false, come out of loop.
• In the example - 
• Variable 'a' is initialized to 1 ie value of a = 1.
• Value checked if it is less than 10 or not.
• Since 1 < 10 ,true - Statement ' b = 2*a ' is executed.
• Value of 'a' is then incremented by 1 ie value of a = 2.
• Since 2 < 10, true Statement executed.
• This continues till, value of a is 10. ie a = 10
• Since 10 <= 10, true - Statement executed - b = 2*10 = 20.
• Value of 'a' is incremented by 1 ie a = 11.
• Condition 11 <= 10, false.
• for loop is terminated.

Thank u ...

Keep tuned for next tutorial .... !!!

AERO ENGINES

Well this is the topic most of the aircraft lovers want to know or must know. I, myself being one, was greatly interested in this topic. Many think understanding this stuff is difficult, but in reality it's very simple.

Let's start :

First let's look at the types of engines -

• Reciprocating type - Also known as piston engines. These are mostly used in trainer aircrafts and in flying clubs.
• Air Breathing engines - Most commercial jets and Fighter jets use these engines.

Reciprocating (Piston) engines -

These engines use a normal assembly of cylinders fitted with pistons which compress the air and fuel mixtures. Most common are

• IC (Internal combustion) engines, used extensively in petrol cars.
• CI (Compression Ignition) engines used in diesel cars.

Internal combustion (IC) engines :-

The above image shows a general four stroke IC engine.

E = Exhaust camshaft

S = Spark plug

I = Inlet camshaft

W = Waterjacket for coolant flow

V = Valves

P = Piston

C = Crankshaft

R = Connecting Rod

Working :-

As we see from the above diagram, there are four strokes. Let's discuss the four strokes of this engine

• STROKE 1 : Intake stoke. In this the piston moves down. This action leads to the opening of the inlet valve, letting the air and fuel volume inside the cylinder.
• STROKE 2 : Compression stroke. The piston moves upwards compressing the air-fuel mixture. During the compression both the valves (I and E) remain closed. During compression the temperature and pressure increases to a great extent.
• STROKE 3 : Power stroke. The sparkplug creates a spark in the compressed mixture. This spark creates a combustion pushing the piston down with a great force.
• STROKE 4 : Exhaust stroke. The exhaust formed after combustion moves out of the exhaust line. The exhaust valve opens up letting the residual air out.

This is a general working of a 4-stroke engine.

Compression Ignition (CI) engine :-

The working Is similar to that of the IC engine, only difference is that it does not have a sparking mechanism.
In a diesel engine, only air is introduced into the combustion chamber. The air is then compressed with pressures reaching 40-bar. This high compression heats the air. Fuel is injected directly into the compressed air in the combustion chamber. The fuel injector ensures that the fuel is broken down into small droplets and is distributed evenly. The heat of the compressed air vaporizes fuel. The vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets continue to vaporise from their surfaces and burn, getting smaller, until all the fuel in the droplets has been burnt. As the vapour reaches ignition temperature it causes an abrupt increase in pressure above the piston. The rapid expansion of combustion gases then drives the piston downward, supplying power to the crankshaft.

AIR BREATHING ENGINES -

Most commercial aircrafts use this type of engine. There are many sub-categories in this type

Let's look at the two main types -

• Turbine powered - 
• Turbojet
• Turbofan
• Turboprop
• Ram powered -
• RAMJET
• SCRAMJET

Starting with Turbine engines -

Turbojet engines -

The above image shows the schematic of a turbojet engnie

As shown in the above diagram, there are two sections - Hot section
                                                                                        - Cold section

The cold section contains two types of axial compressors -

1. Low pressure axial compressor - This compressor rotates so that maximum air comes in through the intake opening. It also compresses the air but since the volume is more in the chamber, more air can be trapped, so the output pressure is low too.

2. High pressure axial compressor - This compressor again compresses the air coming through the low pressure axial compressor. But this time the volume is less than previous one. But the amount of air trapped in the chamber is same as previous. This leads to high pressure compression.

Due to both of the above compression actions, the temperature and pressure of the resulting air increases to a much large extent.

• eg - Let inlet temp and pressure be = 10°C, 40 bar resp
•        After the final cold section compression temp and pressure = 400°C, 350 bar resp

Now comes the Hot section consisting of - Combustion chamber
                                                                   - Exhaust turbine

1. Combustion chamber -

The above image shows the combustion chamber of a turbojet engine.

• The holes in the front side are given for fuel inlet.
• The holes on the sides of the entire tube structure is for the compressed gas coming through the compressors.

As discussed above, the temperature of the air entering the compression chamber is very high. As the fuel comes in drop by drop through the fuel nozzle gets heated up. This causes the air-fuel mixture to heat up and combustion occurs.

2. Exhaust turbine - The combusted heated air rotates another turbine on the rear end. This rotating action cools down the combusted exhaust gas. The exhaust turbines are internally connected to the front intake turbines.

Turbofan engine - 

FIG. A - LOW BYPASS TURBOFAN ENGINE

FIG. B - HIGH BYPASS TURBOFAN ENGINE

The above image shows the schematic of a turbofan engine.

The working of this engine is same as that of the turbojet engine.

• Only exception is that it has a fan attached to the front turbine.
• The fan creates a bypass.
• The air flowing towards the engine is divided into two sections -
• One which flows near the centre of the fan, passes through the compressor, combustor and finally comes out through the exhaust.
• Other part of the air which is flowing towards the upper part of the fan flows above the compressor-combustion assembly in the exhaust.
• This ratio of the air flowing out into the exhaust to the air into the gas combustion chamber is called the bypass ratio.
• eg - Bypass ratio of 10:1 denotes that for 10kg of air passing directly into the exhaust, 1kg of air passes into the gas combustion chamber.
• Depending on the bypass ratio, the turbofan engine is further divided into -
• High bypass turbofan - 
• Shown in fig. B
• These engines produce maximum thrust through the bypassed air.
• The thrust produced is low than low bypass engines.
• Mostly used in commercial aircrafts. 
• Low bypass turbofan - 
• Shown in fig. A
• These engines produce maximum thrust through the combustion.
• So the thrust produced is much much higher than high bypass engines.
• They are normally used in combat aircrafts due to the need of supersonic speeds.

The above video shows the working of the turbofan engine.

Turboprop engine -

The above image shows the schematic of a turboprop engine.

• Working is same as that of turbojet.
• A propeller rotates which is controlled by the gear box.

Exception -

• A part of the engine thrust is provided by the peopellers rather than completely relying on the jet thrusts.
• The performance of the turboprop is best than turbojets or turbofans at low altitudes.
• Mostly used in show aircrafts and trainer aircrafts.

Ram powered engine -

These engines are known as air breathing engines. They do not contain any mechanical moving parts. Entire functioning is dependent on the design of the engine and the amount of air the engine breathes, Ram powered engines can never start moving the aircraft at zero airspeed.
Ram engines are divided into two parts -

• Ramjet
• Scramjet

Ramjet engines - 

• As shown above, ramjet engine takes in the entire air coming into it.
• The design is such that the volume in the upper part of the engine is small ie the air gets compressed at high pressure.
• Fuel is then sprayed over the compressed air.
• The compressed air gains supersonic speed when it comes out of the exhaust.
• Speeds of upto Mach 3 can be gained.

Scramjet engine - 

Working of the Scramjet is similar to that of ramjet engines

Exceptions - 

• Scramjet engine forcefully compresses the incoming air before combustion. While ramjet engine decelerates the air to subsonic speed.
• Airflow in scramjet is supersonic through out the entire operation, which is not the case for ramjets.
• So projected (not tested) speeds of scramjets may reach upto Mach 12. !!!

WORKING OF A RAM POWERED ENGINE

Thank you !!!!

Any improvements or adding extra info is welcome.