GRADES 9-12
AERODYNAMICS OF CYCLING

BACKGROUND INFORMATION: What Is A Wind Tunnel A wind tunnel is generally sort of a duct or pipe shape and air is either blown or pulled out of the tunnel by a fan or other drive system (a machine which creates force). One of the most important sections of the tunnel is what is called the "test section". This is the area where the model to be tested is placed. The controlled stream of air flows over the model. Test instruments and/or a balance record the data to be collected from the test. Wind Tunnel With Permission and Courtesy Of Cislunar Aerospace, Inc. The tunnel pictured above is a low speed tunnel. Air flow starts at the inlet of the tunnel. You can see that the opening between the inlet and the test section gets smaller. The air is compressed (squeezed) in this region. When the air is compressed it moves faster. The air flows over the model in the test section. The balance contains or is attached to measuring instruments to calculate forces like lift and drag. The instruments attached to the balance register the measurements. For example, to measure drag, the instrument attached to the balance could be a strain gauge. A strain gauge can record small changes in deflection (bending). As air pushes against the model, the strain gauge registers this deflection. The air then flows into a large section called a diffuser. The air expands and is slower as it exits through the exhaust. In the wind tunnel pictured here the fan or drive assembly is located in the rear of the tunnel. If you were designing and building a new airplane how would you test it? How would you know if it would have enough lift to fly? You would want a less expensive and safer way to understand the forces on your new design. It would be very expensive to build a full scale airplane model every time you had an idea for an airplane. An engineer named Osborne Reynolds discovered the relationship between the forces on a full scale object and a model (like a commercial Boeing 777 airplane and a model of a Boeing 777 airplane). This is one reason why wind tunnels are used. Wind tunnel testing is one step of the aircraft design process. Generally, a model of the object is placed in the wind tunnel and the aerodynamic forces (lift and drag), pressure and velocity can be measured. Paula Newby-Fraser, the 8 time Ironman Hawaii champion, in the Allied Aerospace low speed wind tunnel. She has also won a total of 23 Ironman races, #1 alltime. With Permission and Courtesy Of Allied Aerospace Today, wind tunnels come in all shapes and sizes - some fit on a table, while others are several city blocks long. Regardless of the size, shape and type, all wind tunnels have the same basic components (parts).