Bernoulli's Principle

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Bernoulli's Principle

Bernoulli's Principle (top) says that increased air velocity produces decreased pressure.

Lift (bottom) is produced by an airfoil through a combination of decreased pressure above the airfoil and increased pressure beneath it.

Credits - AVStop Magazine Online, Helicopter Handbook

Bernoulli's Principle is a physical phenomenon that was named after the Swiss scientist Daniel Bernoulli who lived during the eighteenth century. Bernoulli studied the relationship of the speed of a fluid and pressure.

The principle states that "the pressure of a fluid [liquid or gas] decreases as the speed of the fluid increases." Within the same fluid (air in the example of aircraft moving through air), high-speed flow is associated with low pressure, and low-speed flow is associated with high pressure.

Daniel Bernoulli (1700-1782)

Daniel Bernoulli (1700-1782)

Credits -SCETI, The Walter H. & Lenore Annanberg Rare
Book and manuscript Library, University of Pennsylvania

This phenomenon applies to the lift produced by the wing of an airplane, i.e., an airfoil. The airfoil is designed so that the air moves more rapidly over its upper surface than its lower surface, thereby decreasing pressure
above the airfoil. At the same time, the impact of the air on the lower surface of the airfoil increases the pressure below the airfoil.
This difference between the decreased pressure above and the increased pressure below produces lift. Thus, a wing with more curvature on the top surface (greater camber) has greater lift than a wing with flat surfaces.