YOU are plunging towards Earth at 200 kilometres per hour 鈥� your terminal velocity. With your back arched and your limbs outstretched, the forces on your body are balanced, your orientation stable. You are about to link up with another skydiver who is falling next to you, but she misjudges her approach and flies beneath you. The near miss spells disaster. You begin to tumble. Unless you can regain control and deploy your parachute, you have only seconds to live. You鈥檝e encountered a burble.
A burble is the name skydivers give the wake they generate as they fall. For a metre or so behind the diver, the burble consists of a vortex of air currents. Further behind, the airflow becomes pure turbulence. Silent and invisible, burbles can be life-threatening when they interfere with jumpers or their equipment.
鈥淪ilent and invisible, burbles can be life-threatening鈥�
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What happens if you get caught in a burble? Under normal free fall conditions, divers can change their orientation and rate of descent by moving their arms and legs to adjust the force of air on their bodies. Fly into a burble, however, and the forces change suddenly, sending you into a tumble. The risks are highest during formation dives with large numbers of divers. When two or more divers join together their burbles combine to create an even bigger problem for the divers above them. Turbulence also makes altimeters unreliable, leaving you unsure of when to open your parachute.
When divers release their parachutes, they must be sure to keep them clear of burbles. One common method of deployment is to release a small pilot chute that catches the air, dragging the main canopy out of its bag, but if the pilot chute gets trapped in the recirculating air of a burble, the main chute will not deploy. Rolling your body 30 degrees in either direction, though, can pull the pilot chute out of the burble and into free-flowing air.
Even when you鈥檝e deployed your main chute, you are not necessarily out of the woods, especially during a formation dive, where the canopies of your fellow divers create powerful burbles. Earlier this year, Russian skydiver Kirill Samotsvetov died during an attempt to create a 200-person formation in free fall. After the formation broke up and Samotsvetov had deployed his chute, he flew into the burble of another canopy, and his parachute collapsed.
Burbles aren鈥檛 always a bad thing. Geese have learned to use burbles to their advantage. Each bird creates one at its wing tips. A fellow bird flying directly behind would get caught up and tossed about by the turbulent air, but by flying at just the right position it can use the updraught from the burble as a helpful boost. The V-formation allows geese 鈥� except for the leader of the pack 鈥� to fly long distances without working too hard.
Skydivers, however, haven鈥檛 evolved to fully appreciate burbles. You can at ; just type 鈥渟kydiving鈥� and 鈥渂urble鈥� into the search box.
