Kite surfing – leading edge inflatables versus foilMay 6, 2008
I have decided to restrict this morning’s entry on kite surfing to talk about the type of kites that are available today. Being a relatively young sport the design of the kite is changing with some regularity . You are therefore advised to use equipment provided by your kite surfing instructor/school before rushing out and spending a considerable amount of money on purchasing a kite. You need to get familiar with all the jargon of kite surfing world so you can talk from a position of knowledge when it comes to making a purchase and this is a topic I will be addressing over the next couple of days. The power kite is available in two major forms: leading edge inflatables and foil kites.
Leading edge inflatables
Leading edge inflatable kites, known also as inflatables, LEI kites or C-shaped kites, are typically made from ripstop nylon with inflatable plastic bladders. The inflated bladders give the kite its shape and also keep the kite floating once dropped in the water. LEIs are the most popular choice among most kitesurfers thanks to their quicker and more direct response to the rider’s inputs, easy relaunchability once crashed into the water, and resillient nature. If a LEI kite hits the water/ground too hard or is subjected on water to substantial wave activity, bladders can burst or it can be torn apart.
In 2005 Bow kites (also known as flat LEI kites) were developed with features including a concave trailing edge, a shallower arc in planform, and frequently a bridle along the leading edge. These features allow the kite’s angle of attack to be altered more and thus adjust the amount and range of power being generated to a much greater degree than previous LEIs. These kites can be fully depowered, which is a significant safety feature. They can also cover a wider wind range than a comparable C-shaped kite. The ability to adjust the angle of attack also makes them easier to re-launch when lying front first on the water. Bow kites are popular with riders from beginner to advanced levels. Most LEI kite manufacturers developed a variation of the bow kite by 2006.
However, early bow kites had the following disadvantages compared to classic LEI kites:
* They can get inverted and not fly properly
* They are a bit twitchy and not as stable
* Heavier bar pressure makes them more tiring to fly
* More difficult to relaunch
* Lack of “sled boosting” effect when jumping
In 2006 second generation flat LEI kites were developed which combine 100% depower and easy, safe relaunch with higher performance, no performance penalties and reduced bar pressure. These kites are suitable for both beginners and experts.
Foil kites are also mostly fabric (ripstop nylon) with air pockets (air cells) to provide it with lift and a fixed bridle to maintain the kite’s arc-shape, similar to a paraglider. Foil kites are designed with either an open or closed cell configuration; open cell foils rely on a constant airflow against the inlet valves to stay inflated, but are generally impossible to relaunch if they hit the water, since they have no means of avoiding deflation, and quickly become soaked.
Closed cell foils are almost identical to open cell foils except they are equipped with inlet valves to hold air in the chambers, thus keeping the kite inflated (or, at least, making the deflation extremely slow) even once in the water. Water relaunches with closed cell foil kites are simpler; a steady tug on the power lines typically allows them to take off again.
Foil kites are more popular for land or snow, where getting the kite wet is not a factor. A depowerable foil kite can cover about the same wind range as two traditional C-shape LEI kite sizes, so the rider can use a smaller kite, giving a wider depower range, although the new LEI “bow” kites have a comparable wide range. Foil kites have the advantage of not needing to have bladders manually inflated, a process which, with a LEI, can take up to ten minutes.
Kites come in various sizes ranging from 7 square meters to 21 square meters, or even larger. In general, the larger the surface area, the more power the kite has, although kite power is also directly linked to speed, and smaller kites can be flown faster; a tapering curve results, where going to a larger kite to reach lower wind ranges becomes futile at a wind speed of around eight knots. Kites come in a variety of designs. Some kites are more rectangular in shape; others have more tapered ends; each design determines the kites flying characteristics. ‘Aspect ratio’ is the ratio of span to length. Wider shorter (ribbon-like) kites have less drag because the wing-tip vortices are smaller. High aspect ratios (ribbon-like kites) develop more power in lower wind speeds.
Seasoned kiteboarders will likely have 3 or more kite sizes which are needed to accommodate various wind levels, although bow kites may change this, as they present an enormous wind range; some advanced kiters use only one bow kite. Smaller kites are used by light riders, or in strong wind conditions; larger kites are used by heavier riders or in light wind conditions. Larger and smaller kiteboards have the same effect: with more available power a given rider can ride a smaller board. In general, however, most kiteboarders only need one board and one to three kites.
So there you have it – leading edge inflatables certainly seem to have it over on the foil kites, particularly when it comes to kite surfing on the water but as I said earlier do not rush into making a decision before you have some proficiency and understanding of what your requirements are – I would hate to hear that you had been ripped off by some overly aggressive salesman and ended up with the wrong kite. My thanks go out again to Adventure Escapades of South Africa for their useful input to this article.