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Is a Kite’s Weight Important?

While writing a paper for his master’s thesis, Reinhart Paelinck did some scientific research to determine how a kite’s weight affects it handling in the air.

In 2008, Flysurfer introduced a ‘Deluxe’ version of their soft kites; kites that are identical to the ‘standard’ versions, with one exception: the weight. The ‘Deluxe’ version promises :”The lighter cloth radically increases canopy stability, turning speed and light wind performance of every kite in our line!”

Reinhart, a master student in product development, wanted to know if that is entirely true, and called Flysurfer for some test kites. These would be compared in a head-to-head field test.

Four kites (Speed3 19 Standard/Deluxe & Outlaw 8 Standard/Deluxe ) have been subjected to a series of tests, to determine the differences in four criteria:

  • Turning speed/radius
  • Flying speed
  • Pull
  • Stability

It immediately became clear that this would not be an easy test. A day with a constant wind speed (in which a 19m² AND an 8m² can be flown), clear skies (for the camera) and an open space (without turbulence), was needed to accurately measure the results.

January 17 was D-Day, after nearly a month with either storm, rain/snow, or offshore winds. An anchor point (aka bag filled with sand) was installed on the beach, the camera was rolling, and in a first test the depower-ratio (pull) of the kites were registered in a steady wind speed of 5m/s.

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A strength measurement container was attached to the anchor point, and the chicken loop of the kites was attached to the container. The kites remained in the zenith position during this investigation.

This test resulted in 4 values (averages of a 20 second time-period) per kite: fully depowered (strap pulled in & bar sheeted out), depowered (bar sheeted out) and powered (bar  pulled in). Also a ‘peak’ value was registered when the bar was pulled in to the maximum; This value lasted for about 5 seconds before it lowered to the ‘powered’ value.

When comparing the results of the Deluxe vs. Standard kite, it becomes clear that the differences between the 8m² Outlaws are negligible. At the other hand, the peak value and powered-up results of the Speed3 19m² are very different, about 11 kgs !

This can be explained because of the influence of the weight on the drag of the kite. A heavier kite has a higher induced drag (drag that’s a result of creating lift), because it needs more lift to stay in the air.

Secondly, the stability was derived from these results. As said before, the kite’s pull was averaged over a time frame of 20 seconds.

In these 20 seconds, the pull of the kite changes because of minor differences in the wind speed. This deflection in the pull of the kite is an indicator for the stability. Both ‘Deluxe’-kites showed much lower deflections, probably related to a higher canopy stability.

For the third and fourth test, the kites were disconnected from the anchor point, and were flown by hand.

To measure the flying and turning speed, a video camera registered the flying maneuvers of each kite, while they performed a kite loop (with the bar in the depowered position).

Afterwords, this footage was analyzed to determine the differences between the kites.

First the Speed3 19′s were compared (some scary moments, looping a kite this large on the beach). On this image the differences become clear instantly. The ‘Standard’ 19m² has a larger inertia then the Deluxe version, resulting in a much larger turning radius and a slower reaction time (0.3 seconds slower).

When analyzing the flying speed, the difference becoms even bigger:
At the lowest point of the kite loop the standard kite is already lagging 1.3 seconds behind (also because of the larger turning radius), but when the kite reaches the zenith point again, the difference has grown to 3.4 seconds!

After the 19, the 8m²’s were compared. The Standard version also reacts slower to steering input (0.2 seconds slower). The turning radius is about the same, but still a bit larger for the Standard kite.
The Outlaw Deluxe reaches the end of the loop in 5.6 seconds, the Standard version in 6.3. This difference is due to the slower acceleration of the heavier kite, that also loses ground in the upwards stroke of the kiteloop.

To conclude this investigation:

The promise Flysurfer made (The lighter cloth radically increases canopy stability, turning speed and light wind performance of every kite in our line!) is true, but even more true for bigger kites then for the smaller ones.

Reinhart Paelinck
April 2010

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