Solving Problems

In just one day of experiments, the wind tunnel showed the Wright brothers why their gliders were not performing well. The data they had been using to design their wings was not correct. When the Wrights corrected the errors they had discovered, the performance of their new wings and gliders improved.

The first wind tunnel was such a suc­cess that the Wrights built a bigger one, 6 feet (about 2 meters) long. A fan blew air through it at about 30 miles per hour (48 kilometers per hour). One problem they had was ensuring that the air
flowed smoothly through the tunnel. Wilbur said, “Our greatest trouble was obtaining a perfectly straight current of air.” It took nearly a month to solve this problem. They did it by blowing air into the tunnel through a honeycomb. Modern wind tunnels have a similar part, called the settling chamber.

Seeing the Air

The supports that hold a model in today’s wind tunnel are fitted with instruments that measure the forces experienced by the model. Researchers who use wind tunnels have to find addi­tional ways to measure the airflow so that they can see how it is behaving. One of the oldest methods is to stick short tufts of wool-like material all over

the test object. The way the tufts lay flat, or stick up, or flutter shows the airflow. Another testing method is to release fine streams of smoke into a wind tunnel. The smoke follows the airflow and shows whether it is smooth or turbulent. In a third method, the model being stud­ied in the wind tunnel is painted with a pressure-sensitive liquid that changes when air blows against it. Another type of tunnel has small holes, called pressure taps, drilled at important points. The air pressure in the holes is measured.

Most of these methods for studying airflow disturb or change it in some way. Lasers are now used to study airflow in wind tunnels without disturbing it. A laser produces an intense beam of light of only one wavelength. When light

О The world’s largest wind tunnel at NASA’s Ames Research Center was used to test a parafoil designed to deliver a new type of manned spacecraft back to Earth.

bounces off something, its wavelength changes if the object is moving. When a laser beam is fired into a wind tun­nel, it is reflected by specks of dust in the air and is changed by their motion. A fine mist of oil or air is sometimes added to the air to make its move­ments easier to detect.