A Science Project on Wind Tunnels: How a Wing Affects the Aerodynamic Drag

Wing Aerodynamics

• There are four main forces acting on an airplane wing during flight; weight, lift, thrust and drag. Weight and lift are the forces responsible for the vertical component of the plane's motion, while thrust and drag determine to the horizontal motion. Aviation engineers design airplane wings to minimize drag, which is caused by the interaction of the solid wing structure with free, gas molecules in the atmosphere.

Drag

• When a solid object moves through a fluid, the force that opposes the object's motion is known as drag. In the case of an airplane wing, drag is analogous to friction and is generated at every point that the air comes in contact with the wing. As a vector quantity, drag forces are composed of two components: direction and magnitude. While the direction of drag always opposes the direction of the aircraft, the magnitude of this force on an airplane wing is determined on two independent variables: air viscosity and the texture of the wing. For example, a smooth wing with a waxy coating will experience less drag than a rough, textured wing surface would.

Form Drag

• There are several subtypes of drag, which can be equated to the aerodynamic resistance of an object's motion through a fluid. The movement of air molecules across the surface of the wing creates a difference in air pressure distribution, thus creating a force of drag that opposes the motion of the object. "Form drag", which is a component of the overall drag force, acts through the wing's "center of pressure", which is determined by the angle of attack, or the degree a wing deviates from running parallel with the horizon.

Induced Drag

• As the wing generates the lift force responsible for getting a plane to fly, an additional drag component is created. Known as the "induced drag", this force is the result of the pressure difference between the top and bottom of the wing. In order for the plane to get off the ground, the pressure must be greater beneath the wing than above it. As a result, air vortices are formed at the wing's tips, inducing a flow of swirling, turbulent air when the two pressures collide. The magnitude of this form of drag is determined by the wing geometry, as well as the amount of lift produced by the craft. For example, long and thin wings produce a smaller amount of induced drag compared to short, thick wings. Reduction of induced drag can also be accomplished by disrupting the swirling flow of air at the wing tips using winglets or wing tips.

Science Projects

• Using a miniature wind tunnel and several different types of model airplane wings, the principles of flight can be explored in a classroom setting as an engaging science project for kids. By varying the length, width, texture and angle of attack of the model's wing, the amount of thrust required to produce flight will vary according to the aforementioned principles. For example, the smoothest, longest, thinnest wings will create the least amount of drag; this trend will be evident as you compare the velocity of air in the wind tunnel required to get the plane off the ground.