Hello, and welcome to Introduction to virtual aviation course. And in this lecture, we will answer a really common question. That is, how do airplanes fly? Let's dive right in. So I know this question is related to physics and aerodynamics, but I will keep it to the simplest form to explain it better. But to become a virtual aviator, you need to understand how this air How do airplanes fly?

And how do they interact with the air. So we have to go to a little bit of physics, but I promise I'll keep it easy to understand. So let's start with the basics. So there are four main forces as you can see, affecting an airplane during its flight. So, these forces are, start with the very basic one, the gravity or We can call it the weight of the airplane. So it pulls the airplane towards the center of the earth.

So towards the, to the bottom to the, to the ground, it pulls the airplane to the down. So gravity is always be always there and always affecting and more or less the same manner and in a in a manner consistent with the weight of the airplane. So for example, this is a small Cessna 172. But if we would have a really big jumbo jet, this gravity the same affecting the gravity is affecting the same way. But since its weight is much much higher than the low lower force the force that pulling it down would be much higher. So gravity is always there.

And then there is a contracting force which we call lift. So lift force is what makes the airplane stays in the air or aka flight. So this is the force that we will, we will look more into detail. But also, in order for the airplane to have its lift force to compete with the gravity, it needs to move forward because the wings are creating the lift. We will talk about how the wings are creating the lift. Let's just keep it like magic like on at this moment, but I will explain later.

But let's just say the wings somehow are creating lift. But in order for them to create lift, they need to go like they need they need to be in an airflow. And I don't know maybe you noticed it but there aren't always wind is blowing. So if the airplanes stand still, there is not much of airflow going over and under of the Wink. So In order for to have a you know, constant airflow to produce lifts, weighing and needs and airflow, so for this airplane needs to go forward or have a certain speed for this. And we have engines for most of the airplanes.

It could be a like a propeller engine, like we have talked in aviation history course, it could be an a propeller engine, or it could be a jet engine, or let's say rocket engine. But the main mechanism, the main rationale is the same to push or we can say like pull the airplane forward to the forward direction. So the trust force is produced by the propeller by the engine, and it pulls the aircraft to forward or pushes it to the forward, we can say, it depends on where you look, look at it. So the trust acts on to move the airplane forward. But also there's always a contracting for Like in the Star Wars like the forces, you know, like there's force, there's like Jedi and the Sith. So light and the dark side okay.

So always trust and the contracting force lift and the gravity, trust and the direct. So, drug comes after that. And direct is the air, the molecules of air air molecules resistance to the movement of the airplane or any object. So, and if you try to move an object through an in a dense air molecule, see that say it, it should resist you because the little molecules are hitting to the whole of the aircraft when it's moving. So that creates drag and drag tries to slow down the airplane so so to say pulls it's backfired in cotton On the contrary, force and contracting forces movement. Okay, so these four main forces are our basic understanding of how does an airplane fly.

But let's go a little bit into detail about them. So let's say first, if we take a look at the forces of lift and gravity, if the force of lift is greater than the force of gravity or the weight, then the aircraft or a plane should climb. And as long as this, this equation stands tails as valid, the airplane continues to climb, okay to infinity, but if it's the opposite, and then then the lift force is smaller than the gravity force. And that means gravity wins this argument or wins this fight. So it pulls down the aircraft so it descends. Okay.

And guess what if they are equal, then the aircraft flying in the level, we say level Flight so that means it's neither climbing nor descending, it's keeping it a certain height certain altitude while flying. So, whenever you see a cruising aircraft, which means like neither climb nor descending, it's like going in level flight, that means the lift of gravity and lift of sorry force of lift and the force of gravity and are equal, okay. So, if you look into the other forces that are in the picture, trust and drag, if the trust force is greater than the drag force, that means the aircraft is accelerating or any object is accelerating. So accelerating means its speed, it has a certain speed, and this speed is increasing in every in any buy time or every minute every second is speed is increasing. So accelerating means this. So as long as this this equation that Trust being greater than the drug stands valid, then the aircraft would gain speed until it reaches its maximum speed because all objects or all aircrafts has a maximum speed before they damage their whole because of the really strong air resistance.

So the air resistance is in correlation with an A positive correlation with with the speed and the higher goes to speed the faster you fly, the stronger the air resistance molecules because the faster you hit them through you, you go through them faster you hit them, so the resistance force would be much higher. But that doesn't mean that trust wouldn't be greater than direct. So as long as the trust is greater than drag, it means the airplane is accelerating. So also the opposite is could be true. So whenever there is decelerating or slowing down, the trust would be smaller than the drag. So drag wins this fight.

So that means it's slowing down it's losing its fight, but when they're equal so when the trust force and the drag force are equal, then it means it's not stopping it means it is flying in a certain speed and at constant speed. Okay, let's take this simulation to the very first moment. Let's say this a aircraft in the like standing in in the beginning of a runway before it takes takes off. Okay, so the engine is turning the engine is working the propeller is turning it creating some sort of trust of course since turning, but it's not enough for the for for aircraft to move. For this it should when the drakh force or it should when its own inertia see No like it's because of standing still is should first start a movement that's also requires a force. But when the pilot increase the throttle, they increase the throttle to increase the speed of turning speed of the propeller or the engine, the trust force is increasing it increases increases and a certain time at certain moment, it becomes a cool and becomes little bit greater than the drug or inertia force, then the aircraft starts moving starts moving forward, but really slowly, then, moment by moment, second bite second it gains speed then it accelerates accelerates then, as long as it has speed, it means the air molecules are flowing true, above and below the Wink.

So let's just keep in mind that the for the lift to be produced They should just remember there should be a airflow about and blowing okay. So, there is flow above and below the wing and then when when the speed of the aircraft increases, does the speed of airflow increases and how much speed is the speed increase and the lift increase? So, lift is produced, it is there always there but it's it's not so, great to be equal or greater than the force of gravity or the weight of the aircraft. So, whenever it is become equal, then at that point, we can say that aircraft is weightless is like in the like in space, okay, then, and in the very little bit of when the lift is becoming higher than the gravity, then the aircraft takes off, then the aircraft is airborne and starts to climb.

Okay, so this goes like this. Okay, so let's answer another question here. We understood the four main four And how they interact through like Junior flight. But there was one magical thing. That was how do wings create lift? How do how does the lift generated Okay, so as I told you before that we need an airflow so when the aircraft moves forward, then the opposite direction, because it's going through the air molecules, then there's the creating airflow created here, about and below the wing.

Okay, what we see here is that because of the specific shape of the airfoil, as you can see better in this animation, that air about the wing is faster, because it creates the shape of the Convert shape creates this effect, and the air about the wing is faster than the below one. That's the first reason and the second reason is that as you can see air above the wing are turned downwards when going on the trailing edge and that creates a downwash what we call the downwards. So that's an action and reaction in through dynamics burners principle states that an increase in speed of a flute let's say like water or air, air is a fluid here or q simultaneously with a decrease in the pressure or a decrease in fluids potential energy to simply put it the more the faster a flute moves and the less it is pressure.

So, the when when it when a flute travels or you know moves faster, it loses its energy potential energy, that means exerting less pressure on a surface. Okay, so this principle is named after Dan Daniel Bernal his name and who published it in his book hydrodynamic which is like this in 1738. Okay, now we have a small video to explain. Plain Bernards principle. Let's watch it together. The air thus flows faster and a partial vacuum is created, pulling the ball into the funnel.

If someone blows hard through a straw stuck through a beer mat, a second beer mat beneath it does not need to be held in place. It won't for the second mat is not blown away it's drawn closer. The reason is that air can only flow through the tiny gap between the beer mats, so it has to speed up. According to Bernoulli is law a partial vacuum is created between the mats and this draws them together. In industry, this effect is harnessed by so called Bernoulli suction pads. The outflow of air create suction enabling sensitive materials to be reliably picked up without contact and deposited again elsewhere.

When we take a shower, the flow pressure of the water drags the air along with it. This results in negative pressure inside the cubicle, which draws the shower curtain inwards. The same effect is seen in water. If a hose is used to create a current between two toy boats, they're gradually drawn together. Okay, so these effects are really interesting. And the Bernoulli principle, as you can see is used everywhere.

So it's really important so say a fluid like water or air if it's moves faster, then there is the like a decrease in pressure. When there's a decrease in pressure and the other. In other areas the pressure stays the same, then it creates an inequality then the nature works to equalize this system is to gain equilibrium again. So you can also try this and with an experiment of your own and you can Have a like a one like sheet of paper, but like you need to puff about it a paper but he only two above, not below, when you pass through to the above the paper and the air that's standing still there starts to move. So it's moving, it's starting to move faster. So this is the fluid moving faster.

So there should be a decrease in a disk pressure, as Bernoulli principle says, but down here, we don't we have a we have air molecules, but it's not moving so much. So it has an higher pressure. So here is higher pressure and here is lower pressure. So how do they you know, equalize themselves, then the air blowed paper, tries to you know, tries to travel about to equalize this display disequilibrium, and then it creates a force for the paper to go up. You can also try yourself, okay? You may be now asking yourself, okay, we know that error about the Wink must travel greater distance, okay?

And we know another thing. And and when an air airflow travels faster, it reduces its pressure. Okay? Let's keep these two together and now we will combine them. So how do we use the noise principle? Since since we know that the Nola principle says, if a flute let's say air here, moves faster, it loses its pressure.

So then it means air about the wing has lower pressure than below the wing. So there's a dis equilibrium here, about there's less pressure and below, relatively more pressure. So in order for a equilibrium to reach an equilibrium nature forces air molecules to go up, you know to equalize it because we know that all netta and has a tendency to move from move from when it's most dense to when it is less dense to create a homogeneous density okay. So, this is this is what happens to you, you can remember the paper experiment that we did in one slide ago So, this exactly like the same at that experiment you were puffing with the air to you know, make it move faster, but now we are using the shape of the air shape of the wing shape of the wing profile. Okay. So let's see within, within animation, so you can see the black dots, they are you know, this is the edge, the front edge, you know, when you see the, the air about the Wink travels faster so that it always Almost catches the one before it you know, they are becoming they are separated here.

Let's see they are separated here and it goes faster. So, that creates a speed difference in the air flows and this speed difference because of the Bernal this law creates a pressure difference and for this pressure difference to be equalized air has a tendency air blowing has a tendency to go upwards and by doing it It also takes the you know, wink to upward and this how the lift is generated okay. But also we have an another factor that affects how the you know how the lift is generated. This is one thing now I need I want to talk about another factor that affects how the lift is you know generated for four days. We need some more details about the design of the airfoil or A DD wing profile. Okay, so for this, let's see, we have an airfoil design here, the front edge called is leading edge because it's leading, and it's like no attacking to the, to the, to the air molecules, let's say we have, you know, air molecules here, excuse my drawing, it's not good I know.

So when they are when there's a you know, air molecules here, the leading edge leads it attack because when when the aircraft moves forward, it's attacking their molecules Okay, this is leading edge and the other side, the opposite side is trailing edge, this is when they when they the air trails here, this is the this is the tail side of okay. So, we have a lower cambered surface and upper cambered surface, as you have as you're seeing this, the upper Cambridge surface is more sort of a Cambridge more more like an arc shape than the below it because it has to be because we We, we explained it, how it helps to create a lift, okay. But also, when we look at the shape of the, you know, airfoil it's not too much geometrical, you know, I mean, it's not so linear, but we need to calculate an angle, which is called angle of attack.

So for days, we need at least two lines because angles could be, you know, could be measured between two, you know, crossing lines, okay, so, but in the airfoil, a foil design, we don't have any lines, they're old, you know, and cambered lines. So for this we have, we need to have a like linear line, which is called cord line. A cord line is a hypothetical line that connects the airfoil in a ring profiles leading and trailing edge, okay. So it's sort of it's, you know, like a basic form It's sort of central line to represent the air foils angle okay? It's like it's above average average line Okay, so cord line we call it so let's just keep in mind that we have core line that's connecting leading and trailing edge. So, when we see it, we have the airfoil design in the inner like real like animation but in like a similar to real airplane.

So we have this airfoil design here, but also inside this airfoil design we can draw a imaginary line which is called cord line that connects leading and trailing edge because I need another line to to have to calculate the angle between it Okay, so the other line is composed of the direction of the wind. So direction of the wind, let's say in this pictures like this, okay, and the aircraft goes to the front and to the to the left. side and the wind is you know blowing to the right side. So they are you know crossing each other ditch lines crossing each other and we have an angle, which is 18 degrees, okay. So this is called angle of attack. So we have the winds angle and the chord lines angle and when did they add the angle between these lines his angle of attack, we will talk in a minute why this is important for lift generation.

But for this we need to define another thing, which is relative wind. Why, you may ask because the picture that I showed you, you saw a wind but that wind wasn't a natural wind because it was there was a result of the aircraft's movement. You may remember in the first slide I talked about when the aircraft goes forward, it just attacks and goes through the air molecules and then air molecules in the consequence created a as a result of that resistance so that there's a there's an airflow created above and below the wing which is crucial for the lift to be produced. Okay? But in this wind although we call it when like we call it the wind, it's not a natural wind is the relative wind. So what does it relate to wind relative wind is a wind is created like generate because like you're feeling this wind because of the movement so it occurs on the opposite side and as a result of your movement, so in this picture, you may see like, it's like a Turkish flag here when the mother nature's wind blowing like this.

So this natural wind that makes the you know, flag to you know, go go the upper opposite side have like, kind of oscillation you know, have it's like movement, but when a man runs and it has has it scarf, you can see the scarf is you know, like having him Moment trailing the opposite side of Mother Nature's wind if there would be this this would be happening because of the mother nature's wind it shouldn't be this way but the other way but this is not the natural way and this is the relative wind it always occurs opposite direction exactly the opposite direction of your movement okay when you move right like with this picture we can say right to left when the man runs to the right the relative wind affects the the accused to the left Okay. And then we can see its effect with the with the men scarf, okay.

Let define it be a little bit in detail the relative wind is the direction of movement of the atmosphere, like the air lead relative to an aircraft or an airfoil. So, it is opposite to the direction of movement of the aircraft or airfoil relative to the atmosphere, okay. So, we can see like this in that picture, a When aircraft moves this side the blue shows motion and direction the relative wind happens the opposite when it goes like this, like this okay? And also when it goes like climbing decide and relate to it even if like it's like in freefall like rock falling like a rock than the movement the motion is down and then the relative wind should be up okay this is this is interesting, but if the, if the aircraft falls like this, they never fall like freefall like rock but when when it does, it would be the relative wind okay.

So let's just return to the angle of attack. Now, all the pieces come together. Now, we know why and how they relate to wind happens are created when the motion of the aircraft like this and the relative wind like this, but the the court line or the air foils angle is not always in parallel. With the motion of the aircraft, you know because the aircraft like moves parrot like level you know like not climbing but tip of the you know, tip of the the head of the aircraft or the wing looks like it's climbing but this is not in reality because it has no no enough not enough speed to climb, not enough lift to climb. So, climbing is a matter of lift not to the direction of the nose of the aircraft, it is not a rocket it is a craft okay it is different.

So when the motion goes like to the left, the relative wind like generated to the opposite side naturally, and the ring or the aircraft should feel this relate to wind, okay, and when, when there's a cord line, there's a line and there is another line because of the relative wind, there's an angle between them. So angle of attack basically, is the angle of relative wind. DD you know attacking angle or in which angle it hits to the hits to the wing under of the wing, okay? So at which angle that does relate to wind and hits below the wing, okay, that's the angle of attack. So, when you think of like this, that is important because angle of attack is also or the relative wind is also another source of lift other than the bandulus principle. Okay so let's see in this picture, we have five degrees of angle of attack a 10 degrees 30 degrees.

This 45 is a bit exaggeration, but but for you know, education purposes, I draw that 45 degrees so that means relative wind is like this. And guess what? Can you guess the motion direction of the aircraft In A, B, C, or D, they're always like the left side like this. Because relative wind only occurs on the opposite direction of your movement. Okay? So although this aircraft looks like it's, you know, like a rocket going upwards to the sky, it's not it is only moving like this, like hypothetically, I mean, it wouldn't happen it would, it would fall because knows, like this engine wouldn't, wouldn't support this kind of force.

But yeah, so that means the angle of attack, okay, let's think of this. This is related to wind. And in all of these pictures, for example, an A, the relative wind hits blow the wing in a five degrees of angle, and then there's 45 degrees of angle it attacks or it hits to the below the wing. That is Something because when there's action, there's also a reaction. Okay? So some airflow goes over and some air flows goes under, okay, when air flow goes over, it's moving faster and it is the it when it goes faster since the Bernoulli principle it loses pressure and then there's a pressure disequilibrium.

And in order for the system to reach its equilibrium, it creates a like force that lifts the wings to the to the to the upside, okay, this is one thing the other thing that some of the airflow goes on there if it hits in a certain angle, below the wing, it creates an action and this reaction is also the same for the wing to go upwards. Okay? Let's just see like this. Okay, so the black dots like the representing the air going blow, so when they are hitting here, they are changing their direction. Okay, so there's an action but then the reaction should be like this. Okay?

The End force. I know it's also creating drag, but it's also creating lift because when we, you know, break down this force, it is like this. One side lift, and the other side is drag, okay? Like this. It's really a brilliant example of hand. When you're you're inside a car or you know motorcycle when you're going really fast.

Then you open your window and pull your hand outside. If you you like it's like movement of the let's see like the movement of the car. And when you when you hold your hand like this in an angle, LED lights like 45 degrees or something in the air flows hits here. change its direction. So it's an effect here and the like the reaction is the like this, so it's like a lift, it's also putting your hand a little bit like pushing your hand limit backwards, but also upwards. So the force of this reaction depends on the angle here.

So if you would select an angle like this not so steep, then it would change this direction like this. And this end result effect. Let's select another color here, the end result effect would not be so much higher, okay? Because the steeper the steeper the angle that hits the mountain, the more force it exerts on the surface, the I mean airflow, okay. So, to summarize, lift from low pressure is about the wing about like, about the air about the wing Okay, at large angles of attack, the airflow is forced to curve below. The engineered shape of the wing, okay.

So, it's like this and impact lift we call So, we can say this impact lift because when the air is hits here the impact creating lift upwards on the bottom of the wing increases at a high angle of attack. So, when we increase the angle of attack, so, nose up, we can say pitch up or nose up, we increase our impact lift, but also risking our little you know, like bear no lift, you know, they are bear no lift, but we can say this and then if they are both working together and to make an aircraft fly okay to produce lift, so, we know how the lift is produced. And when you put this to our first slide, when the four forces how they are interacting, then you should understand how then how is an aircraft flies, okay, you can only So check some of the explaining videos in the resources section.

Okay, and if you have any questions, you can hit me in the q&a section of the course and I will do my best to answer it. Okay, let's see you in the next lecture.