The video recording shows an attempted launch of the TU Delft V3 kite from an upside-down hanging position on 2 August 2012 at the former airfield Valkenburg, Leiden, Netherlands. The GoPro camera is taped to the rear side of the leading edge tube of the wing, between the two center struts, looking at the kite control unit. During the upswing of the kite, the kite control unit remains in the line of sight between video camera and mast head. At 11 s into the video, the ground station appears at the top of the field of view. Also clearly visible is the tether running from the mast head to the ground station. At 15 s into the video, the tether suddenly disengages from the mast head, which leads to a strong dynamic perturbation of the tensile system. Playing the video in slow motion reveals that the disengaged tether moves within 1 s towards a new equilibrium shape, which is the straight line connecting ground station and kite. This rapid straigthening of the tether yanks the kite control unit upwards, into the line of sight between video camera and ground station. The tensile system stays in this new equilibrium state for only 0.1-0.2 s, after which the weak link, just below the kite control unit, breaks due to overload. The shock force of this event yanks the video camera by about 90 degrees in its mount, now looking in the direction of the heading, along the leading edge tube. Between 20-22 s into the video, a loose bridle line connected to the leading edge tube can be seen flying by. Around 23 s into the video, fabric debris from the progressive-tearing energy absorber, that is integrated into the safety line, passes the field of view. The wing impacts the ground at 27 s into the video. This launch attempt was also covered by data recording, by a regular photo camera and by a second GoPro video camera that was positioned on the ground, next to the launch mast. The remaining course of events can be reconstructed from the photo footage: with the break of the weak link, the pulling force of the detached kite immediately shifts to the safety line, which at this point in time remains the only physical connection between the kite and the tether. The sudden force increase in this line activates the integrated progressive-tearing energy absorber. The kite control unit, on the other hand, is catapulted in radial direction towards the wing and eventually caught by the bridle line system. This ballistic event leads to an irreversible collapse of the wing. Secured by the safety line, the parachute-like assembly of curled-up wing and kite control unit slowly descends and hits the ground at about 27 s into the video. Because the time setting of the GoPro video camera was incorrect, the time information in the metadata was synchronized with the absolute time available from the data recording. The creation date of the video was set to the launch time 18:27:18 such that the weak link ruptures about 16 s later, at 18:27:34. |