{"id":30096,"date":"2020-12-09T11:23:26","date_gmt":"2020-12-09T11:23:26","guid":{"rendered":"https:\/\/www.skydivemag.com\/new\/?p=30096"},"modified":"2023-08-17T08:41:13","modified_gmt":"2023-08-17T08:41:13","slug":"what-you-dont-see-can-kill-you","status":"publish","type":"post","link":"https:\/\/www.skydivemag.com\/new\/what-you-dont-see-can-kill-you\/","title":{"rendered":"What You Don’t See Can Kill You"},"content":{"rendered":"\n

Water fascinates us. How else do you explain the price premium on beachfront, lakefront, and riverfront properties? <\/strong><\/h2>\n\n\n\n
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Running water provides a visible parallel to the behavior of turbulent air 
Photo by Nadezhda Bolotina<\/figcaption><\/figure>\n\n\n\n
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As skydivers, water should fascinate us for another reason \u2013 it moves and responds to physics much like air, only we can see and thereby learn from it. <\/strong><\/h3>\n\n\n\n

As such, water has a whole lot to teach us about airflow and \u2013 more importantly \u2013 turbulence.<\/strong><\/h4>\n\n\n\n
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There have been an alarming number of cases of skydivers getting injured, or worse, due to collapsed canopies. Air turbulence<\/strong> is something most of us understand conceptually, but not so much in practice. Why? We can\u2019t see it. And if we\u2019re on the ground, it usually doesn\u2019t even affect us that much unless winds are extreme, so we don\u2019t think about it that much. But when you\u2019re flying a parachute, turbulence can radically affect your parachute\u2019s flight and change your life very quickly. A little turbulence might feel like driving over a bumpy road, but severe turbulence can partially or completely collapse your canopy. Canopy collapses can cause radical, diving turns and even put you back in freefall at an altitude where you absolutely never want to be in freefall.<\/p>\n\n\n\n

The good news is that turbulent airflow does follow the laws of physics, just like a river flowing around rocks (watch that closely next time you get a chance).  Thus, we usually have a pretty good idea of where it will appear when winds pick up. Turbulent airflow exists downwind of obstacles, extending horizontally to 10-20 times the height of the obstacle!<\/strong> It also exists behind moving objects, and very much so behind airplanes with props turning, even if they are parked. Winds can also affect the location of turbulence generated by aircraft.<\/p>\n\n\n\n

Turbulent airflow exists downwind of obstacles, extending horizontally to 10-20 times the height of the obstacle<\/strong>“<\/p><\/blockquote><\/figure>\n\n\n\n

American skydivers might remember learning this concept in their skydiver training programs with the following graphic from USPA’s Skydiver’s Information Manual.<\/p>\n\n\n\n

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Turbulence diagram from SIM by USPA<\/figcaption><\/figure>\n\n\n\n
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Let\u2019s put this into practice. For example, with the 34-foot-tall hangar at Skydive Spaceland Houston, turbulence in a north wind could be expected at distances of up to 340-680 feet to the south. The runway is 450 feet away, so the entire area between the hangar and the runway is considered a hazardous landing zone in a north wind. This is why we generally see even highly experienced jumpers landing east of the hangar in north winds; it\u2019s just safer. The laws of physics do not bend for skydivers, no matter how many jumps they have!<\/p>\n\n\n\n

Notice also the turbulence behind the airplane on the graphic.<\/p>\n\n\n\n

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Infograph of Skydive Spaceland DZ, Houston 
Courtesy of Skydive Spaceland<\/figcaption><\/figure>\n\n\n\n
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Turbulence is a potential factor on any skydive. Before you make a skydive, consider the likely areas of turbulence in today\u2019s conditions and plan to avoid those areas. A good rule of thumb is to never land anywhere behind a running airplane or close to and facing an obstacle. Downwind of an obstacle, any significant wind will create turbulence right where you can least afford to deal with it \u2013 close to the ground where you have very little time and altitude to recover from a canopy collapse. Besides, if you overshoot while facing said obstacle, you might end up pulling a Wile E Coyote faceplant on the obstacle.<\/p>\n\n\n\n

Now to the really cool stuff: Here\u2019s a video to help you visualize air turbulence, using smoke. As you watch this video, note the extreme change in direction and speed of the wind when the smoke canister is placed downwind of obstacles. Now imagine what your canopy will do when flying through the same highly variable wind conditions. Thanks to Skydive Spaceland instructors\/videographers Ken Stone, Rosy Booker, Nicholas Lott, and Ben Nelson for the idea and their hard work on this video.<\/p>\n\n\n\n

Video: Turbulence shown by smoke<\/em><\/h4>\n\n\n\n
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