BERNOULLI'S PRINCIPLE IN AVIATION

Bernoulli's Principle in Aviation

Bernoulli's Principle in Aviation

Introduction

Bernoulli's Principle is the form that the law of conservation of energy takes when applied to a fluid. The energy of a stationary mass of fluid consists, in general, of its gravitational potential energy and a potential energy that results from the downward "push" of any fluid above it. If the fluid is moving, it also possesses energy of motion, or kinetic energy. Bernoulli's principle states that for nonturbulent (streamline), nonviscous flow, the sum of these three energies does not change. The principle was first stated by the Swiss mathematician Daniel Bernoulli in the 1700s.

Bernoulli's Principle in Aviation & Major Factor in the Theory of Flight

In words of Bell (1997) Bernoulli's principle is useful in designing fluid conduit systems, aircraft, and boats. Its utility in aerodynamic and boat-design studies results particularly from the quantitative way in which it predicts that fluid pressure is reduced wherever the speed of flow is increased. An airplane wing is designed so that air travels faster over its upper surface than over its lower surface. This difference in speed of flow causes a lower pressure on the upper surface of the wing, according to Bernoulli's principle, and thus results in an upward force, or lift, on the wing.

The principle also explains how a pitcher can curve a baseball toward or away from a batter by spinning the baseball as he releases it. On the side of the ball that spins in the same direction as the ball's motion, friction between the ball's surface and the air slows the rate of airflow. On the opposite side to the ball's motion, friction speeds the rate of airflow. The difference in the relative motion between the air and the surface of the ball on the two sides results in a pressure difference that causes the ball to swerve in a curved path.

Daniel Bernoulli, an eighteenth-century Swiss scientist, discovered that as the velocity of a fluid increases, its pressure decreases. How and why does this work, and what does it have to do with aircraft in flight?

Bernoulli's principle can be seen most easily through the use of a venturi tube. The venturi will be discussed again in the unit on propulsion systems, since a venturi is an extremely important part of a carburetor. A venturi tube is simply a tube which is narrower in the middle than it is at the ends. When the fluid passing through the tube reaches the narrow part, it speeds up. According to Bernoulli's principle, it then should exert less pressure. Let's see how this works.

As the fluid passes over the central part of the tube, shown in Animation or the Figure to the right, more energy is used up as the molecules accelerate. This leaves less energy to exert pressure, and the pressure thus decreases. One way to describe this decrease in pressure is to call it a differential pressure. This simply means that the pressure at one point is different from the pressure ...