Aeromodelling

When an aerofoil is moved through the air, as the velocity of the airflow increased at the upper surface, thereby the pressure above the aerofoil surface reduced. Simultaneously, the air pressure on the lower side surface of the aerofoil increased. Consequently, a pressure difference between the lower and upper surfaces exists in results of LIFT being produced.

The amount of lifts generated by an aerofoil depend upon:

a) The shape of the aerofoil.

b) The plane area of the aerofoil.

c) The square of the velocity.

d) The density of the air.

e) The aerofoil inclination to the airflow.

As the aircraft passes through the air it traverses a particular line of flight. The airflow passing by the surfaces of the aircraft in the opposite direction of travel is called the Relative Wind. The angle between chord line of the aerofoil and the direction of the Relative Wind is called Angle of Attack.

As increase the angle of attack of the aerofoil, the amount of lift and drag increases on the aerofoil. The angle of attack continuous increase towards 12 to 15 degrees. The air flowing over the top of the aerofoil surface begins to swirl and turbulent occur at the air stream. At this point, called the Critical Angle of Attack, where the airflow over the wing becomes so disturbed. The total lift drops suddenly, and the aerofoil enters into a stalled condition called Stalling Angle.

Below video have a good explanation how and why an airplane stalls.

Enjoy it!