How Wind Tunnels Work

A wind tunnel is a machine used to fly aircraft’s, missiles, engines, and rockets on the ground under pre-set conditions. With a wind tunnel you can chose the air speed, pressure, altitude and temperature to name a few things. A wind tunnel is usually has a tube like appearance with which wind is produced by a large fan to flow over what they are testing (plane, missiles, rockets, etc.)or a model of it. The object in the wind tunnel is fixed and placed in the test section of the tunnel and instruments are placed on the model to record the aerodynamic forces acting on the model.

Types of Wind Tunnels

There are four basic types of wind tunnels. Which are low subsonic, transonic, supersonic, and hypersonic. The wind tunnels are classified by the amount of speed they can produce. The subsonic has a speed lower than the speed of sound. The transonic has a speed which is about equal to the speed of sound (Mach 1 760 miles per hour at sea level). . The supersonic (Mach 2.75 to 4.96) has a speed of about five times the speed of sound And the fasts of them all the hypersonic (Mach39.5) which has a speed of more than 30,000 miles per hour. Wind Tunnel Test There are basically two types of wind tunnel test which are static stability and the pressure test. With these two tests you can determine the aerodynamic characteristics of the aircraft. The static stability test the measures the forces moments due to the external characteristic. These forces include axial, side and normal force, rolling, pitching and yawing moment. These forces are found by using a strain gauge which is located on the external portion of the plane. It measures the external flow fields. Then the shadowgraph is used to show the shock waves and flow fields at a certain speed or angle of attack. There is also the oil flow which shows you the surface flow pattern.  The pressure test is used to provide the pressures acting on the test object. This is done by placing taps over the surface. The taps are then connected to transducers that read the local pressures. With this information they can balance out the plane. Then the static stability and the pressure test data are combined to find the distributed loads.

Wind Tunnels Used Today

Wind tunnel vary in size from a few inches to 12m by 24m (40ft by 80ft) located at the Ames Research Center of the National Aeronautics and Space Administration or NASA, at moffet Field, California. This wind tunnel at Ames can accommodate a Full-size aircraft with a wingspan of 22m (72ft). They also have a hypervelocity tunnel at Ames that can create air velocities of up to 30,000 mph (48,000 km/h) for one second. This high speed is able to be done by placing a small model of the spacecraft in a device that produces an explosive charge into the tunnel in one direction, while this is going on there is another explosive charge that simultaneously pushes gas into the tunnel from the other direction. There is also a wind tunnel at the Lewis Flight Propulsion Laboratory also own by NASA in Cleveland, Ohio, can test full-size jet engines at air velocities of up to 2,400mph (3860km/h) and at altitudes of up to 100,000ft (30,500m). Benefits of the Wind Tunnel There are many benefits that one can gain in using a wind tunnel. Since designing an airplane is a long and complicated process and an expensive one as well. With the wind tunnel you can build models and test them at a fraction of the price compared to making the real thing. When designing an airplane one has to take into account the public safety and still be able to keep the design in mind to do what it is designed to do. With a wind tunnel you can design and test what you make before you make it. With a wind tunnel you can also solve problems that already exist. One example of this is when the first jet engine propelled aircraft’s where produced in the 40’s. The problem occurred when the jet planes released there missiles that where on the external part of the plane, the missiles had a tendency to move up when released causing a collision with the plane resulting in death of the pilot .With the wind tunnel they were able to solve this problem without the lost of any more lives. On February 1, 1956 wind tunnels were so important that the Army formed the ABMA at Redstone Arsenal in Huntsville, Alabama from army missile program assets. This program was made to support for ongoing research and development projects for the army ballistic missile program in this program they made a 14inc wind tunnel to test the missiles. Early test were done to determine the aerodynamics of the Jupiter IRBM (Intermediate Range Ballistic Missile) and its nose cone. The Jupiter C missile was one of the first Launch Vehicles tested in the wind tunnel. The Jupiter C was a modified Redstone rocket made of nose cone re-entry testing. A modified Jupiter C the Juno 1, launched America’s first satellite, the explorer 1 into orbit. Soon after this the ABMA wind tunnel went to NASA. The wind tunnel played a vital role in the exploration of space. The wind tunnel played a major role in the Saturn V, the first rocket that put the first man on the moon(Apollo mission) to the current Space Shuttle Launch Vehicle. The tunnel mission changed from testing medium to long range missiles to supporting America’s “Race Into Space”. NASA increased the payload of the original 10lb satellite(explorer 1 ) to a man in a capsule(project Mercury). To the Apollo Project. The Saturn family of launch vehicles spent hundreds of hours in the wind tunnel. There were various configurations that were tried to find the best result. At first they were going to make a fully reusable shuttle but that idea cost too much and was ruled out due to their budget. With the budget in mind the current space shuttle started to be formed. But it still took many years in a wind tunnel before the final design of the Orbiter, External Tank and Solid Rocket Boosters final took their shape as the one we know of today. Even after the space shuttle took flight they were still being tested to increase performance. Tests were done to determine the cause of tile damage. As the shuttle program continued to progress at a rapid pace it came to a standstill when the Challenger Accident occurred. After the accident the 14in wind tunnel was immediately put into use. To analyze what had occurred. These test verified what happen to the SRB leak and the rupture of the aft external tank STA 2058 ring frame. The data was used to determine the trajectory and control reconstruction. With all of this information they got from this they are trying to develop a way to abort scenarios involving orbiter separation during transonic flight. All of these configurations were done to the scale model that is .004 of the real shuttle. This is just a few applications of the wind tunnel. There are many more things that they can do. With the invention of the wind tunnel the cost of designing an aircraft and testing an aircraft has been reduced, and most important lives have been saved. Without the wind tunnel there would be no way for us to know what will happen before it happens.

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