# Bernoulli Principle

Topics: Lift, Aerodynamics, Wing Pages: 2 (593 words) Published: October 8, 1999
Airflow over an airfoil
Flight is one of the most important achievements of mankind. We owe this achievement to the invention of the airfoil and understanding the physics that allow it to lift enormous weights into the sky. All flight is the result of forces acting upon the wings of an airplane that allow it to counteract gravity. Contrary to popular belief, the Bernoulli principle is not responsible for most of the lift generated by an airplanes wings. Rather, the lift is created by air being deflected off the wings and transferring an upward force to those wings. The most important factor in determining the lift generated by an airplane is the angle of attack. The angle of attack is the degree measure from the horizontal that a wing is elevated or declined. When the angle of attack is between 1 and 20 degrees, the most lift is generated. To find the lift generated by a particular area of wing in a standard airfoil shape, a teardrop with the fat end facing forward, the equation L=Cl 1/2 (pV2)S. Cl is the lift coeficent, which is determined by the shape of the airfoil and the angle of attack. P stands for the air mass density, V for the velocity of the air passing over the wing, and S for the area of the wing when viewed from above or below. As the air flows over the wing producing lift, it grabs onto the wings surface and causes drag. Drag can be measured by the equation D=Cd 1/2 (pV2)S, much like the lift equation. The drag coeficent Cd is found, again, by determining the shape of the airfoil and then finding the angle of attack. Drag is less than lift up to a certain angle of attack. After that, the air encountering the surface of the wing is either pushed off or deflected in a way to cause turbulance. So, what does lift and drag have to do with airflow? As hinted in the above paragraph lift and drag are directly related to the shape of the airfoil. A special property of liquids is this, they will tend to follow a surface that is...