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To better understand aerodynamic forces, early pilots

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and engineers pushed aircraft's tolerances to the limit.

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But by pushing the limits,

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some pilots experienced a very frightening aerodynamic

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phenomenon called a flat spin.

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In an effort to better understand this phenomenon,

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NASA's predecessor, NACA,

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developed a unique wind tunnel called the 20-foot

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vertical spin tunnel.

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This tunnel was designed to not only study the unique flight

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conditions of an aircraft in spin,

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but also teach pilots recovery techniques

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to avoid a fatal crash.

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The research performed at this tunnel would have a direct

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impact on virtually every American aircraft

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from World War II through today.

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Early in 1941, the National Advisory Committee

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for Aeronautics, or NACA,

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completed its new 20-foot vertical spin tunnel.

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This tunnel tested a very different type

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of flight situation than the tunnels researchers were

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accustomed to using.

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The traditional way to test aircraft

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in a wind tunnel is by mounting an aircraft in the wind stream

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to evaluate the aircraft's flight characteristics.

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This type of testing is very effective when testing an

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aircraft in normal flight situations.

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But data from a traditional wind tunnel could not adequately

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account for unusual flight conditions, like a flat spin.

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As a plane enters a flat spin, air is not moving

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over the control surfaces as it should,

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which renders the plane's controls virtually useless.

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To help find ways for aircraft to recover

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from these dangerous spins,

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researchers test small-scale models in the spin tunnel.

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The idea behind the spin tunnel is simple.

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A large fan pulls a column of air up through the middle

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of the tunnel.

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Then a researcher launches an airplane model directly

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into the airflow by hand.

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As the model spins downward,

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the operator increases wind speeds

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until the model's fall is just balanced by the uprushing air.

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Then the control surfaces

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of the model are systematically activated electromagnetically

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to find out which ones allow the model

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to recover from the spin.

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This same basic technique that was used

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in 1941 is still being used today,

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but researchers now use computers to track unique markers

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on the bottom of the plane

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to measure the aircraft's spin characteristics.

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With these measurements,

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researchers can determine design modifications

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and pilot training procedures, which can help pull a plane

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out of a spin, saving the plane and the pilot

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from a catastrophic accident.

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This simple system has worked especially well over the years.

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During World War II, every fighter, light bomber,

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attack plane, and trainer, over 300 designs

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in all were tested in the spin tunnel.

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Subsequently, over half of these aircraft were modified

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in some way to ensure that their controls would be able

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to pull them out of a spin.

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Today, the spin tunnel is still testing many different types

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of designs, from small general aviation planes

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to the Mars sample return capsules.

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Since it opened for business in 1941,

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nearly every American military fighter has been tested

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in this tunnel.

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However, with 10 percent

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of all military air accidents still occurring due

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to the flat spin, the NASA Langley 20-foot vertical spin

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tunnel will undoubtedly continue to save lives

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for many years to come.

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Did you know that Lieutenant Francis Evans became one

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of the first aviators

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to develop an effective spin recovery technique?

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In 1917, while attempting to get his pontoon plane

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into a loop, Lieutenant Evans inadvertently went into a spin.

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As he maneuvered out of the spin,

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he realized that he had unwittingly discovered an

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effective spin recovery maneuver.

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He was awarded the Distinguished Flying Cross nearly 20 years

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later for his life-saving discovery.