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Demystifying Kite Design

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Demystifying Design: Kites
By Paul Lang

It never fails. Whenever we bring new gear to the beach to test out, it feels like we’re immediately surrounded by people who like to comment on how it will or won’t work based entirely on how it looks. Everybody seems to have a different opinion on how the kite will perform based on the size of the leading edge, the length of the bridles, how rigid the kite feels, the number of struts, and anything else they can point out.

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Now be honest: Do you really know what any of the visual clues on a new kite actually tell you about how it rides? I’ll admit that I don’t have a clue when it comes to the subtle visual clues that you can find on a kite, so we decided to ask the designers to let us know what we can expect to learn by looking at a piece of gear.

Remember, there is no substitute for actually riding a kite to find out if it’s the one for you, but hopefully the information here will help you know what you can expect from a new piece of gear.

Tony Logosz and Amery Bernard stand among two years worth of Slingshot R&D. Photo Courtesy Slingshot

What are the most obvious visual clues on a kite that might tell you a bit about how it will perform?

“You can look at the aspect ratio (AR). High AR means a punchy kite that flies to the edge of wind window. Low AR leads to constant power and a kite that sits deeper in the window,” Peter Stiewe, Best Kiteboarding.

“The bigger the kite, the more aerodynamically efficient it needs to be in order to perform well. Therefore, larger kites should have a really good match between leading edge arc and trailing edge arc. In smaller kites, too much aerodynamic efficiency makes them hard to handle and gives them a harsh feel. In those sizes we intentionally cause a bit of a mismatch between leading edge arc and trailing edge arc specifically to take the edge off the kite’s handling,” Ken Winner, North Kiteboarding.

“I would say look at its overall outline. For example a kite with a more compact look (lower Aspect Ratio) should tend to turn faster, be more forgiving, and should be easy to jump. A higher aspect ratio kite should make longer jumps and be more efficient,” Damien Girardin, Naish Kiteboarding.

“The most obvious clue is the general shape of the kite, meaning how “C’d” up the hoop shape is, the amount the LE is swept back (the amount of rake), and also the wingtip shape. Generally, the more C-shape a kite is, the less depower it has, and the kite will have a tendency to carve through turns. The more open a kite is, the more depower potential it has and the kite will pivot in turns more. Lots of rake in the LE tends to mean that the kite will depower more than a kite with little rake. A fuller, squarer wingtip will usually mean that the kite will carve through turns versus a pointier, narrower wingtip which would tend to pivot more through turns,” Amery Bernard, Slingshot Kiteboarding.

“Look at the arc shape of the kite and how swept back the wingtips are. This would give you hints on how the kite basically flies and turns,” Julien Fillion, Liquid Force Kiteboarding.

How does the size of the leading edge affect the kite’s characteristics?

“Generally, a big LE diameter means more stability and a slower turning kite that flies deeper in the window. A small LE diameter means a less stable but faster turning kite,” Peter Stiewe.

“Several companies increase the size of the LE at the end of the design process when the bridle geometry is not adequate to hold the arc of the LE in place. This will definitely slow down the speed at which the kite flies across the wind window, but most importantly this will add lots of weight on the front top axis section of the kite and make it less stable, increasing the tendency for it to fall light wind. On the other hand, some of the high performance kites out there are equipped with a very solid bridle structure, and for this reason have a much smaller LE, which creates good speed and a lightweight feel, but it could make the kite overfly and difficult to relaunch. My goal is usually to find the middle ground between LE size, weight, and bridle arc structure,” Julien Fillion.

“The diameter of the LE affects a few different characteristics of the kite: Rigidity: A larger LE tends to make a kite more solid (less jellyfishing, although a big LE will not correct jellyfishing that is due to the wrong balance of the kite). A more rigid kite will behave better when dropped in the water as it will be less likely to lose its shape when dropped, but a more rigid kite will also turn slower. Turning Speed: A smaller LE will allow for more twist of the overall wing when turning, which will result in a fast turning kite. Upwind Ability and Depower: A kite with a smaller LE will create less drag and will fly further forward in the wind window which will allow for a better upwind ability, better pop when unhooked, and more depower overall since your kite will fly with less drag. Overall there is a fine balance to find for the LE diameter. You want it as small as possible but must also keep enough rigidity in the kite,” Damien Girardin.

“In general, a larger LE will provide the kite with more structure, slow down the turning, and increase lift in the kite. A smaller LE will tend to have less structure, faster turning, and less lift,” Amery Bernard.

“Back when we had C-kites that didn’t depower very well, I thought a small leading edge was a good thing because it allowed the kite to fly farther to the edge of the window, which allowed it to depower better. But now that most kites have such great depower through angle-of-attack control (sheeting out), the small leading edge is less of an asset to most riders. When fully inflated, the kite with a small leading edge tends to fold in half during relaunch. In the air it is likely to have less stability and a less positive feel. Nowadays, I see a small leading edge as something racers should be interested in, but not so much cruisers, jumpers, tricksters, and surfers,” Ken Winner.

Is there anything on a kite visually that will give clues to the kite’s turning and depowering characteristics? What about jumping?

“Regarding turning, the most obvious way to see if a kite will turn fast is to see how big its wing tips are. Larger means the rider will have more leverage to create torque in order to twist the kite in to turn. On kites with swept wing tips, look at the distance between the lowest point of the front bridle and the back line — this is basically a virtual wing tip. For depower, it’s harder to see because it all depends on how the bridles are set up on the kite. If the kite has no bridles (like a Torch), it’s depower will depend on how far forward the front lines are and how small the foil and LE are in order to let the kite go far in the wind window,” Damien Girardin.

“Another thing that can give a clue for turning characteristics is the bridle. Namely, the position where the front lines lie. The further towards the center of the kite, the more the kite will tend to pivot in turns. The further towards the outside of the kite, the more the kite tends to carve through turns,” Amery Bernard.

“If the wingtips are more swept towards the back of the kite, it will most likely be a kite that pivots on itself during turns. If the front of the wingtips are closer to the center axis of the LE, the kite will turn around a wider axis and generate more speed during the turns. Jumping performance is very hard to tell just by looking at a kite on the beach; it’s all about the profile setup and the ability to quickly depower and power the kite up again,” Julien Fillion.

“A C-shaped LE means more power during turns, while a Bow/Delta shaped LE equals less power during turns,” Peter Stiewe.

What does a strut-less middle canopy do for the kite’s performance?

“It increases both low end performance and drift stability,” Peter Stiewe.

“Lots of Things: First it removes weight. This year we realized that weight is the key of kite design, and true performance (stability, reliability, ease of use, relaunch) starts with the weight of the kite. The kite also responds quicker to the turning signal since the LE and canopy are freer to twist in the center. It also cleans up the center canopy, giving room for deeper profiles where it’s really needed (in the center of the kite). Let’s not forget that the kites are also quicker to inflate and cheaper to produce. It was a big challenge to take an existing kite such as the Havoc and change it from a 5-strut to a 4-strut kite as we had to find the perfect balance of outline, arc, AR, and bridles to not lose any of the performance of this kite,” Julien Fillion.

What does the Sigma outline and geo-tech shaping do for the kite’s performance?

“Sigma outline provides superior stability to a kite. Basically, it allows the kite to achieve really low angles of attack without falling out of the sky as the weight on the front of the kite is moved back, behind the center of effort of the kite. Geo-tech provides a very stable canopy when the kite is flying since it keeps the canopy under tension at all times preventing the foil from losing its shape, especially when ridden overpowered. For the rider, this translates into a kite that has superior handling in the high end of the range and allows the kite to steer even when sheeted out,” Damien Girardin.

What do more or less struts on a kite do for the kite’s performance?

“More struts add more rigidity to the kite and also more weight. In general, a kite with less struts can be lighter feeling and more responsive. A nice thing about fewer struts is the convenience of having to inflate/deflate less, and the kite also packs smaller,” Amery Bernard.

“You can get an inexpensive, light, and quick-turning kite by reducing the number of struts, but you give up some aerodynamic efficiency and load-carrying capacity. A three-strut kite, for example, distorts and flutters badly in big sizes in moderate to high winds and under the load of an average or heavyweight rider. After experimenting a lot with different strut counts, we find we can get adequate performance with three struts (particularly for light riders), but we get the best all-around performance with five. We’re willing to go to six or seven in a race kite,” Ken Winner.

Remember that while this is all great information, there is no true way to find out how a kite will fly without flying it yourself. Amery Bernard said it best. “Overall, these visual clues are just that: Clues. I wouldn’t suggest that anyone base a buying decision on visual clues because what one clue says, another clue could trump it and the performance of the kite could be a lot different than what you expect. The best thing to do is demo a kite.” Hopefully the info here will help you know what you are looking at a little better when checking out a new kite, but to really know how a kite will perform you’ll have to get out there and fly it yourself.

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