You've probably heard of Newton's three laws. If you have an understanding of these three laws, it will be easier to understand how a plane can stay in the air and how the different forces affect the plane. I will try explaining it as simple as possible!

Newton's laws
Newton's 1st law (law of inertia)

An object remains at rest or moves with constant velocity in a straight line, if no force acts on the object or if the sum of the forces equals zero

Explanation: A body that is not affected by any net force will not be able to change its motion (Zero Acceleration). If the body is at rest, it will remain at rest. If the body has a speed, it will continue with this speed in a straight line.







Newton's 2nd Law
The sum of the forces acting on a body is equal to the product of the body's mass and its acceleration, and that acceleration has the same direction as the sum of the forces.





Explanation
A body subjected to a net force will experience an acceleration in the same direction.
Newton's 2nd law gives a mathematical expression for the connection between an acting net force and the acceleration that occurs. The law states that the net force is proportional to the acceleration.

If we use SI-Units, the proportionality factor is equal to the mass:

F = ma (Net force = Mass Acceleration)

The force (F) is measured in Newtons
Earth's gravity is approximately 9.81 m/s. If we multiply it by the mass (kg) of an object we find the weight (Measured in Newton).
When you describe Newton's 2nd law, you also describe inertia. The greater the mass an object has the bigger inertia has it. The greater the inertia, the more the object will resist change in speed or direction.

Newtons 3rd Law

When an object exerts a force on another object, the other object exerts an equal and opposite force on the first one (Action - Reaction).




Explanation
If an object is placed on a table, the object exerts a force on the table, but the table also exerts a force on the object. These two forces act in opposite directions and are equal in magnitude. When you shoot a gun, you experience Newton's 3rd Law. When the bullet accelerates, you feel this as a force on your shoulder. The reason you don't get shot backward is that you have a much larger mass than the bullet. If you had the same mass as the bullet, you would move backward with the same speed that the bullet moves forward.

Before we explain Bernoulli's law, we need to explain these definitions:

• Static pressure
  
• Dynamic pressure
  
• Total pressure

Static Pressure (p)
This is the atmospheric pressure. When you are completely still and the air around you is not moving, you are measuring the static pressure.
Measuring this pressure around an aircraft moving rapidly through the air poses challenges. This is resolved by measuring the static pressure on the side of the aircraft body (at a 90-degree angle to the airflow) where the airflow is completely smooth. The point where the static pressure is measured is called the static inntake



Dynamic Pressure (q)
The formula for dynamic pressure is as follows: (p) is the density of the air, and (V) is the relative velocity of the air.
q = 1/2 ρ v 2

From the formula, you can see that the dynamic pressure increases with the square of the velocity. This means that if the velocity is doubled, the dynamic pressure (q) becomes four times larger. This pressure is the result of air in motion or moving through the air. When you feel the wind blowing on your face, it is the dynamic air pressure you are experiencing. This pressure is also dependent on the density of the air (the amount of air molecules).

Total pressure
It is the sum of static pressure and dynamic pressure:
Total pressure = Dynamic Pressure + Static Pressure

When measuring the pressure directly against the airflow, we obtain the dynamic pressure, but we also capture the static pressure. This means that we are reading the total pressure. The total pressure can also be referred to as the pitot pressure. It is a device used to measure the total pressure: the pitot tube.


Daniel Bernoulli discovered that the static pressure in a fluid decreases as the velocity increases. In an ideal fluid, the total energy remains constant. This means that if the dynamic pressure changes, it will affect the static pressure (or vice versa).

If you take a tube that has a smaller diameter in the middle than at one of the ends and blow air through it, the static pressure in the middle will be lower because velocity and pressure influence each other. Increasing the velocity (dynamic pressure) will result in a decrease in static pressure, and vice versa. This phenomenon is also known as the Venturi effect.



This principle is also utilized in a carburetor to draw in fuel.

Aerodynamic forces refer to

• Lift
  
• Drag

Lift acts perpendicular to the relative airflow. It is the force that opposes gravity and allows an object, such as an aircraft wing, to stay airborne.
Drag acts parallel to the relative wind (direction of motion). It is the resistance encountered by an object moving through a fluid (such as air) and acts to slow down the object's motion.




The aerodynamic forces are generated due to the pressure distribution around the wing. Multiple factors affect these aerodynamic forces.

• The area on the upper side of the wing
  
• The dynamic pressure (energy in the airflow)
  
• The relative pressure distribution around the wing
  
• Angle of attack.

Wing Profile

If we look at a Wing profile, there are several terms you need to familiarize yourself with. Many of these terms are later used to explain other phenomena.

• 1 - Chord line: This is a straight line connecting the leading edge and trailing edge of the airfoil.
  Chord: The length of the chord line.
  
  
• 2 - Mean camber line: It is a line that runs halfway between the upper and lower surfaces of the airfoil
  
  
• 3 - Maximum camber of the airfoil: This is found where there is the greatest distance between the chord line and the mean camber line.
  
  
• 4 - Maximum thickness of the airfoil: This is where the airfoil is thickest. The location of maximum thickness and the actual thickness of the airfoil are expressed as a percentage of the chord length.
  
  
• 5 - Leading edge radius: The larger this imaginary circle is, the rounder the leading edge of the airfoil is.

Geometric angle of attack:
The angle between the relative airflow and the chord line. Normally, this is simply referred to as the angle of attack. In the figure below, it is the green angle marked as "A".

Aerodynamic angle of attack:
The angle between the relative airflow and the zero-lift line. The zero-lift line represents the angle of the airfoil when it does not generate any lift.

Streamlines.
These are used to visualize how air moves around an object. In wind tunnels, smoke strips are used to visualize the movement of air.



In illustrations, lines are used to visualize how air moves around an object. These lines will not cross each other except where the velocity is zero. When these lines come closer together, it indicates a reduction in static pressure, which means increased dynamic pressure (as per Bernoulli's Law). Smaller spacing between the streamlines = Increased velocity.

Stagnation point:
The point where the airflow separates in front of an airfoil. Theoretically, the velocity of the local airflow is zero at this point. If there were no friction between the air and the wing, a stagnation point would also form on the backside of the wing where the airflow rejoins. This is called the rear stagnation point.



If you measure the air pressure around an airfoil, you will find that it is at its highest at the leading stagnation point. As the angle of attack increases, this point will move downward and backward along the leading edge of the wing.




The pressure at the leading stagnation point will be an absolute static pressure and equal to the total pressure of the airflow. This means that the static pressure at this point will be higher than the atmospheric pressure.
If we place a ball in an ideal airflow that has no viscosity or air resistance, it would appear as follows. The fields are marked with + and - signs, representing the pressure relative to the atmospheric pressure. The result in such a hypothetical experiment is that the sum of the forces is equal, and the ball will not move.




If we consider the factors present in reality, such as viscosity and air resistance, the picture becomes quite different. Turbulence forms on the backside of the ball. This leads to lower pressure on the back of the ball, and in this case, it will move towards the left.



Pressure distribution around the wing
The figure below shows a symmetrical airfoil with an angle of attack of 0 degrees in a flow without viscosity and without air resistance. As the airflow moves from the leading stagnation point, it must either go over or under the wing. This causes an increase in the velocity of the air, resulting in reduced static pressure.



If we consider the real factors:

• Air viscosity
  
• Air resistance

The pressure distribution looks like this:



Pressure Center
If we consider a small thin slice of the wing, this is called an airfoil. We can also say that this is a two-dimensional part of the wing. If we gather all the forces around an airfoil and concentrate them at a point, it is called the pressure center.

Explanation: Pressure Center
The point where the sum of all the forces on an airfoil is concentrated.



The pressure center is typically located approximately 25% of the chord length behind the leading edge of the airfoil. The location of the pressure center is not fixed; it moves depending on several factors. We will look at two of them now.

Change in angle of attack
Use of Flaps

Change in angle of attack
When the angle of attack increases, the pressure center will move forward until the wing stalls. At that point, the pressure center moves backward. We will discuss stalling a bit later.


Use of flaps
When flaps are extended, the curvature of the wing's trailing edge increases, causing the pressure center to move backward. We will describe flaps in more detail later as well.

If we look at the force acting at the pressure center, it is the total lift on the airfoil. This force can be divided into two components: Drag (parallel to the relative airflow) and Lift (perpendicular to the relative airflow).

Center of Lift
So far, we have only looked at an airfoil, which is just a part of the entire wing. If we now consider how pressure acts on a complete wing, we find the center of lift.

Center of Lift
The point where the sum of the lift on the entire wing acts.

The center of lift moves in the same way as the pressure center. The only thing we need to remember is that a wing is usually not symmetric, and the flaps do not extend along the entire wing. Typically, you will find the center of lift in the middle of the wingspan.

Pressure Difference between the Upper and Lower Surfaces of the Wing

When the air accelerates over the wing, the static pressure decreases. This creates a pressure difference between the lower and upper surfaces of the wing. This pressure difference seeks to equalize at the wingtips, resulting in an airflow from the lower surface to the upper surface of the wing.



This movement of air from the lower surface to the upper surface of the wing affects the airflow over the entire wing. If this movement of air were not present, the air would move parallel to the fuselage, but that is not the case. The air on the lower surface of the wing moves almost parallel to the fuselage but slightly outward. The air on the upper surface of the wing moves almost parallel to the fuselage but slightly inward.


Direction of Lift: When lift is generated by a wing, it acts perpendicular to the relative airflow. This means that when the angle of attack increases, the lift will point slightly backward. If we break down the lift into vectors, we can see that there is a component of the lift that points backward.

Air Movement

When we are sufficiently far away from the wing, the airflow remains unaffected. As we approach the wing, we enter the boundary layer:
Boundary Layer
This is the region around an object where the velocity of the air decreases towards zero.

First, we need to explain what viscosity is. Imagine how water and syrup flow. It is evident that syrup is more viscous than water. The more viscous a liquid is, the higher its viscosity.

The reason there is friction between an object and the air is due to the viscosity of the air. The initial part of the boundary layer along a wing is laminar, meaning there is no turbulence. However, it doesn't take much for turbulence to form.



Transition Point: When turbulence forms, the laminar boundary layer transitions into a turbulent boundary layer. The point where this transition occurs is called the transition point.




The turbulent boundary layer is triggered by disturbances from the surface. An increase in pressure that alters the boundary layer's velocity can also trigger the turbulent boundary layer. The turbulent boundary layer is thicker than the laminar boundary layer. The laminar boundary layer is usually quite small, while the turbulent boundary layer extends over a larger area. In fact, there is an advantage to the turbulent boundary layer because turbulent air contains more energy. This makes it more resistant to separation from the wing.

We have previously seen how the static pressure changes on the upper surface of the wing. At the point of maximum curvature, the static pressure is lowest. As the air moves backward from this point, the static pressure increases again. This is known as a negative pressure gradient. A negative pressure gradient causes the boundary layer to transition into turbulence. This means that the transition point moves forward when there is a negative pressure gradient. Therefore, you will find the transition point at the point of maximum curvature or further forward.

Separation Point
Where the turbulent boundary layer starts to move forward.

The turbulent boundary layer will slow down due to the negative pressure gradient behind the wing. Eventually, the air in the turbulent boundary layer comes to a halt, and some of it actually starts moving forward again. Where this occurs is called the separation point. The turbulent boundary layer cannot follow the wing, resulting in significant turbulence and air resistance, as well as the cessation of lift production behind this point. As the angle of attack increases, the separation point moves forward.



Some of the turbulent air formed after the separation point will hit the aircraft behind the wing. This air is experienced as shaking or vibrations in the fuselage, and if it hits the elevator, the control stick will also start shaking, a phenomenon known as buffeting. This can serve as a clear indication that the aircraft is approaching a stall.


How the elevator is positioned will determine the amount of buffeting or shaking you experience in the control stick. If it is directly placed in the turbulent airflow, this will be noticeable. If the circumstances allow, this turbulent airflow can reduce the effectiveness of the elevator. As you can see from the figure, the effect of buffeting on the elevator can vary greatly between different aircraft types.

How Lift is Generated

What creates lift is introducing a wing into an airflow, which changes the direction of the air and generates lift. There is lower pressure on the upper surface of the wing and higher pressure on the lower surface. If we look at the airflow around a wing, we will see that the air moves upwards in front of the wing and downwards behind it. This is called upwash and downwash. The fact that the air is moving in this manner creates an upward force, which can be explained by Newton's laws:




The fact that air has mass and viscosity allows for the generation of lift. Newton's 2nd law states the following: the net force is proportional to the acceleration. When using SI units, the proportionality factor is equal to the mass. When a wing deflects the air, there must be a force causing this: F = m*a.

Newton's 3rd law states the following: When one object exerts a force on another object, the second object exerts an equal and opposite force on the first object (action and reaction). If one body exerts a force on another body, the second body will exert a force on the first body that is equal in magnitude but opposite in direction. When the air is deflected, there will therefore be a force acting in the opposite direction.

Not only the aspect ratio contributes to the characteristics of a wing, but also its shape has a significant impact. I won't go into detail about this in this guide, but if you're interested, Google can be a helpful resource to explore further.

The effect of using flaps:
Change in the center of pressure. When the curvature of the wing increases, it affects the airflow. The air is deflected more downward behind the wing. This also increases the pressure difference between the upper and lower surfaces. The induced drag also increases with increased flaps.

Types of Flaps

• Plain: This type of flap only increases the curvature of the airfoil. It contributes to generating a significant amount of air resistance.
  
• Split: This type of flap also increases the curvature of the airfoil. It contributes to generating even more air resistance than plain flaps.
  
• Slotted: This type of flap increases the curvature of the airfoil. A slot delays the formation of the separation point.
  
• Fowler: This type of flap increases both the curvature and the area of the airfoil. It is the most efficient type of flap.

There are many more types of flaps than those described here. There can also be various combinations of these flap types. For example, slotted Fowler flaps, and so on.

Thank you so much for reading especially if you got this far. I put alot of time and effort in this guide so i hope if you liked it that you can consider leaving me a like. Also if there is something you feel is missing in my guide please give me a shout!

If there is anything else you guys want me to talk about like VFR Communication, AFIS Comms, Instruments etc please dont be shy! Aviation is an amazing hobby i love talking about and sharing knowledge. And i have learned from my Flight Instructor that a good pilot is always learning and that a pilot license is merely a License To Learn!