Centro Aerodinamico

Aerodynamic Center

What is the aerodynamic center?

The aerodynamic center or pressure center is a point of the airfoil where the force of lift, drag and cross wind force are represented. This point is situated between of the 20% and 50% of the chord it depends of the type the airfoil. If it is a subsonic airfoil the pressure center is between of 23% and 27%. For a supersonic airfoil the pressure center is exactly at the 50% of the chordline.

The principal factors that create the lift force is principally the pressure difference, but the surface, velocity, density, viscosity, and attack angle have the same importance. Why the surface? The surface implies the time of the fluid that is crossing at long of airfoil, whit more time, and more pressure difference. When the velocity increases we have the same effect because the velocity energy is converted to pressure energy and then we have more pressure difference. Now we have a directly proportional ratio, the lift is proportional at the density because we have more mass flux and more transition of energy. The viscosity provides grip at wind to the airfoil and do that the air flow remain for all the surface of the airfoil.

All of those elements are indispensable to have a lift force, but if we increase the surface we will have more drag force. We will not air whit a good viscosity and we have lots of problems because we will can have the detachment of the boundary layer but nowadays the designers creates some irregular shapes to create a little turbulence for then continue with the normally flow and boundary layer. The airfoils must to have the shape for the future use of the airfoil, because each airfoil have a propose.

When the attack angle increases the pressure center change the position a long of the chord. In this point the pitching moments are zero because there are the neutral axis, this is perpendicular at the lift force. Generally the gravity center and the pressure center are the same for simplify the flight of the airplane and it will exploited the most efficiency.

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