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What is a wind tunnel? How is a wind tunnel used as a measuring tool? Why is the SR-71

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an ideal research test point?

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Hi Jennifer. Hi. Hi Ben. Hi. Can you tell me what you might be having in our dynamics

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problem with your vehicle? We do. Well, let me welcome you to my department, the Advanced

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Measurements and Dynostics Branch. Here we make tools to measure the performance of an

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aircraft in a wind tunnel. Now, a wind tunnel, isn't that just like a big fan? Well, let

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me explain what a wind tunnel is and how we use it to measure aerodynamic forces like

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draft. A wind tunnel is a device consisting of an enclosed passage to which air is driven

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by a fan. The heart of a wind tunnel is the test section, in which a scale model is supported

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in a controlled air stream that flows about the model, duplicating the air of the stream

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of a full scale aircraft. We use different techniques to measure aerodynamic forces.

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Things like flow visualization, use smoke, and a laser light sheet. Sometimes we use

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oil or water instead of air and streams of dye to watch the vortices and other unusual

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phenomena. Surface deformations, such as wind flexing, can affect drag. Here at NASA Langley,

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one instrument that we designed projects a pattern laser light onto a surface of a model

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being studied. Later we compare photographs and measure the differences in the pattern

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light. These differences show changes in the shape of the wind surface that might be

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disrupting the airflow. We call this turbulence. Data are collected during the testing and

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checked for accuracy. Speaking of accuracy, it is not until an aircraft is flight tested

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in the real world that design efficiency can be fully verified. NASA does most of its flight

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testing at NASA Dryden and California Mojave Desert. As an aeronautical engineer at NASA

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Dryden Flight Research Center, I'm interested in all the measurements that are made during

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test and flight research missions. Blackbirds are the world's fastest and highest flying jets.

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They cruise along at speeds over 2,000 miles per hour at heights over 24 kilometers or

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above 80,000 feet. That's so high that when I look out the airplane's window, the sky seems

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to be darker, even during the daylight. The SR-71's unique capabilities make it an ideal

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platform for aeronautical research and experiments that are beyond the reach of any other jet.

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All of these data, plus reports from the pilots, are compared with computer, wind tunnel, and

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flight simulator information so that engineers will understand exactly what is happening with

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the design.