Science Behind The Photo #53

Defying Gravity!

Freestyle kiteboarder, Ruben Lenten struts his stuff at sunset in Perth, Western Australia

Sponsored by Red Bull, Ruben Lenten – the “King of Extreme Kiteboarding” – certainly fits the brand’s daredevil image. Constantly pushing the sport’s boundaries, Lenten is all about going faster, jumping higher and pushing harder. But just how does he pull off the type of “Big Air” stunt that makes the kiting community drool?

In order to defy gravity, kites – like planes – require movement to generate aerodynamic lift. The more movement, the more lift. On a windy day, the lift produced by the movement of air relative to a kite is enough to keep it in the sky. So, unlike their considerably heavier winged cousins, kites can fly in a stationary position. The upward force results from the kite’s asymmetric profile: wind passing over the top moves faster than wind passing underneath, generating a pressure difference that lifts the kite upwards.

But Lenten doesn’t wow his fans by standing stationary on a beach. Kite flight is one thing; kiteboarder flight is another. So how does he generate enough lift to send himself 25 meters skywards? The key is velocity. The faster the wind, the greater the lift, so it’s no surprise that one of Lenten’s favourite hobbies is “storm-chasing”. He increases the effective wind speed further by travelling in a slightly upwind direction prior to take-off.

To make sure he’s pulled upwards, rather than forwards, he steers his kite from a low position at the side of the wind window, to a high position at the top of the window, sending it through the central “power zone” on the way, to maximise the pulling force. At the crucial moment, he “powers up” the kite and takes off by pulling the control bar towards him. This shortens the two back lines of the kite relative to the front lines, tilting its wing-like form so that a broader surface area faces the wind. The difference in air speed above and below the kite becomes much greater, as does the lift. Time all this nicely with a large wave – nature’s ready-made ramp – and you have yourself the perfect Big Air recipe!

IMAGE: Alex Parker

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *