Why do airplanes fly?

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The million dollar question, Why do planes fly? an easy question, but with a more complex and interesting answer than you imagine.

post writer by: Juan Matheus

Commercial aviation has been present in the life of the human being for more than a century. For this reason, many people today see it as something normal and there is no longer the capacity for wonder at how we managed to conquer the skies.. This is why it is worth starting a series of posts that help #AvGeeks and people in general, to understand how a plane today manages to take us from A to B in such a short time and all that this entails.

This new series of deliveries that aim to inform, educate and teach about technical aspects to people who do not have a technical background, but the desire to learn and his passion for aviation will deal with interesting topics thanks to Juan, new blog contributor.

Why do airplanes fly?

without further ado, The first thing we must solve is the basic physical principles that govern the flight of an aircraft. The first thing we must recognize is the presence of certain physical forces that affect an object., in this case a plane in flight. We must recognize on a plane 4 very important physical forces that are related to each other by Newton's laws that everyone will have heard at some time. Two of them are exerted vertically (Axis y) and two of them horizontally (eje X). This is perhaps a simplification (we live in a 3d world) however it is sufficient for our purpose.

So that a plane can fly, must be able to overcome two key forces: Aerodynamic drag which is a force acting horizontally (let's think "drag") and the gravity that logically attracts an object to the ground, that is, it acts vertically (We will see why the weight of an aircraft is a key and limiting factor in aviation). Each of them, has its counterpart: push and lift. When the thrust and lift are greater than the weight of the aircraft and the effect of drag (which can be the friction of the track with the wheels on the ground or the resistance of the air) we can have a plane that flies. Later we will look at other components of modern aircraft design that help to overcome these forces..

When an airplane is flying at cruising speed and at a fixed altitude, push and pull are of the same magnitude and different direction and the same happens with weight and lift. Any imbalance in any of these forces results in an acceleration or deceleration (horizontal o vertical). This is just a proof of Newton's laws of motion in action..

One more time, simplifying things, we can see that the lift of an airplane (the force that pushes the aircraft up) it is due to the wings (and in particular its shape) and the thrust is given by the motors. This may seem obvious but it was not easy to understand the aerodynamics, a branch of physics that until recently seemed like “black magic” because the mathematics behind it is very complex and to this day we have not been able to find the solution to many equations that govern it and we have only been able to simulate its effects through a computer. Without understanding aerodynamic forces we could not have developed modern aviation and we owe this in part to the Swiss scientist Daniel Bernoulli.. In other words, not every object that has enough thrust (two jet turbines for example) will be able to fly.

El Airfoil

Earlier we talked about aerodynamic forces and how they contribute to an airplane being able to fly..

Now let's focus on how lift is generated., which is the aerodynamic force responsible for an aircraft being able to lift, and the most important, stay in the air.

air is a fluid. Not only liquids are. In the case of air, there are different pressures in our atmosphere that exert a force on it. (Later we will see other atmospheric factors such as temperature, which also play an important role.). And if we talk about movement, we can't help but think of speed as a way of knowing how fast an object is moving.

Now that we know what are some of the factors that influence the movement of a fluid, We can conclude that air pressure and speed are the variables that we would like to control so that an airplane can fly through the skies without setbacks.. Bernoulli's principle precisely describes the relationship between these two variables.. In a nutshell, Bernoulli's principle says that the velocity and pressure of a fluid are inversely proportional.. Namely, If the velocity of a fluid increases, pressure decreases and vice versa. If you are interested, you can search for videos about experiments in a Venturi tube so that you can observe it better.

But, What does all this have to do with an airplane?? Well, all. Above we mentioned that the shape of the wing of an airplane is what generates the lift so that it stays in the air. Well, it's exactly that way., known as airfoil or aerodynamic profile, which makes us control Bernoulli's principle in our favor. For a plane to move, we must move the air around it. And we already know that a fluid moves if there is a pressure differential. The purpose of an aircraft wing is, then, generate a pressure differential so that air can flow.

If we look at the image of the airfoil we can, By simple visual inspection, you can see that the “path” of an air particle over the upper edge will be different from the path if it does so below the wing.. away from the wing, air pressure is atmospheric. As the air gets closer, what we call relative wind we are going to see that a pressure gradient distribution is created around the airfoil.

There are many theories and ways to explain how it is that in the upper part of the wing we have high speed and low pressure and the opposite in its lower side, however it is too complex to develop here..

In conclusion, the wing profile gives us the pressure differential that we were looking for and that generates lift. Why the result is a force that goes up and not the other way around? The pressure differential is greater below than above. increased speed, lower pressure. Literally, the bottom “presses” the air up.

This topic is quite complex and requires reading and rereading it in order to better understand the logic behind the physics..

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