THE WING AND ITS FUNCTIONS

An aeroplane flies because it has a wing that is capable of generating an aerodynamic force that enables the aeroplane to sustain itself in the air. This force is due to the pressure difference created on two opposite surfaces hit by the moving air.
The aerodynamic force can be broken down into a component, called 'lift', which is always perpendicular to the direction of air speed and another component, called 'drag', which is always in the same direction as air speed, but opposite to that of motion. Furthermore, it is usual to attribute a positive value to lift when this component of the aerodynamic force is oriented towards the upper part of the aircraft. In most cases, it is this component of aerodynamic force that makes it possible for an aeroplane to fly. In contrast, one speaks of 'downforce' if this component is oriented towards the lower part of the aircraft.
In level flight, characterised by the horizontal motion of an aircraft, lift is in fact directed upwards and balances the weight force, which, on the other hand, is always directed downwards. The force generated by the propeller also continuously counteracts the action of aerodynamic drag. Sometimes the propulsive force can also be generated by a vector component of the weight force. This occurs, for example, during a glide, a mode of flight that occurs when the propeller is not used and is typical of gliders.
A wing can also be imagined as a pair of 'wingtips', called the 'right wing' and the 'left wing'. The distance between the two 'wingtips' is called the 'wingspan'. By dissecting a wing with planes parallel to the plane of symmetry of the aircraft, profiles are obtained, called 'airfoils'. Usually, the airfoils thus identified have a shape similar to the outline of a drop arranged horizontally and slightly arched upwards. The front part, the convex one, is called the leading edge or 'leading edge'. The back, the pointed part, is called the 'trailing edge' or 'trailing edge'. The upper part is called the 'back' or 'extrados'. The lower part is called the 'belly' or 'intrados'. It is these parts of the wing that are lapped by air currents.
In general, when the wing passes through the air, a zone of depression is generated in the upper part of the wing and a zone of pressure in the lower part, which contribute to creating the aerodynamic force that makes flight possible. In fact, as demonstrated by Bernoulli's theorem, the air current that laps the back, before rejoining the current that laps the belly, travels a longer distance than that travelled by the current in the belly area, creating a depression that is much more intense than the pressure generated in the belly area.
The lift developed by the entire wing can be considered as the sum of the lift contributions that are generated by each of the profiles that meet along the wingspan. The lift depends, in fact, on numerical constants and parameters related to the shape of the wing, the density of the air and its relative speed with respect to the aircraft. Therefore, it is possible to vary the lift value by changing the altitude, attitude and speed of the aircraft with respect to the air, and the shape of the wing profile, as happens when using "hypersosters", of which flaps and slats are a part. Flaps modify the wing profile in the trailing edge area, while slats modify it in the leading edge area.