Interactive Lecture Demonstration: Bernoulli’s principle and airfoil

by Reese Macabebe and Ivan Culaba

Objective

Demonstrate one application of Bernoulli’s Principle: the lift on an airplane’s wing.

Description of the Set-Up

The set-up is a small wind tunnel. A high-speed fan, controlled by a VARIAC provides the air stream on the air foil, a miniature section of an airplane’s wing. The airfoil is tilted at an angle (the angle of attack) with respect to the direction of the air stream. A counterweight, which is not present in real wings, is attached to the airfoil so that the airfoil will lift at lower air speeds.

Demonstration

The airfoil is first set at its lowest position. The VARIAC is slowly adjusted to increase the voltage in the motor of the fan. What will happen to the airfoil when the speed of the air stream is increased? Why?

Precaution

1. Do not apply a voltage on the fan motor beyond 110 V otherwise it will be damaged.
2. Do not hold the fan nor put anything on the wind tunnel while it is in operation.

Interactive Lecture Demonstration: Bernoulli’s principle and objects suspended in air stream

by Erees Queen Macabebe and Ivan Culaba

Variac, styrofoam ball, and air blower

Objective

Demonstrate object suspension in an air stream.

Description of the Set-Up

The set-up consists of a blower, styrofoam ball, VARIAC, and extension wire for the blower.

Demonstration

Connect the blower to the VARIAC. The VARIAC controls the input voltage to the blower and thus, controls the rate of airflow from the blower.

Place the ball on the mouth of the blower. Switch on the blower and slowly adjust the VARIAC until the air stream lifts the ball above the blower.

What will happen if the ball is slightly pushed off the line of the air flow?

Tilt the blower to one side. What will happen to the ball? Why?

Balance the ball in the air stream and then move the blower toward a wall (try the corner of a room). What will happen to the ball?