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Flat Inflatable Kites, Flat LEIs, Bow Kites

It all started with a simple discussion on the Kitesurf group back in 2003 regarding "Fully Sheet Out Kite" which allows kiters to fully depower the kite.  The whole discussion was about being able to sheet out or depower a  classic LEI completely by adding a bridle system on the leading edge (based on Seasmik kites).  The thread can be found at http://sports.groups.yahoo.com/group/kitesurf/message/67005.


Classic LEI profile .vs. Flat LEI profile

The result of such discussion was the introduction of the WindWing kite with a bridle system on the leading edge allowing one to depower the kite much more than the classic LEI as discussed in the following post http://sports.groups.yahoo.com/group/kitesurf/message/68675.

Bow Kites

Bruno Legainoux, the inventor of the classic LEI, took the bridle on the leading edge concept further and filed a patent application in French on 2004/03/01, in Canada and in US on 2005/02/28 (Canadian Patent Application number CA 2498729, US patent application number 11/067,0842) for a kite design that incorporated a bridle on the leading edge with a flat, swept back profile and concave trailing edge.  The US version of the patent application can be found at http://www.freepatentsonline.com/20050230556.pdf.  The French version can be found at http://inflatablekite.com/siteinf/gb/docs/FR2866859%20bow.pdf

Coincidentally, there was a design posted on the net since 2001 which also had a flat, swept back profile and concave trailing edge at http://www.template-toolkit.org/tpc5/kitesurfing/index.html.

The result of Bruno's design were the new bow kites as introduced by Takoon and Cabrinha as the Nova and Crossbow in 2005.

The early bow kites, while allowing the kites to be depowered fully, have a number of disadvantages compared to the classic LEI:

  1. The kite can get in to an invert position and can't fly properly
  2. The kite is a bit twitchy (like foil) and not as stable as classic inflatable
  3. Pretty heavy bar pressure
  4. Pretty difficult to relaunch
  5. Lack of "Sled Boosting" effect when jumping

Flat Inflatable Kites

Since then, both Bruno and other kite designers has improved the original generation of bow kites and introduce a new generation of flat Inflatable kites (Flat LEIs) that may or may not use Bruno's design.  Those Flat LEIs are apparently so excel in safety, performance and ease of use that will create a major stir in the kitesurfing market.  The main differences between the ones that use Bruno's design and the ones that don't are:

  • The bow Flat LEIs (bow kites) have concave trailing edge, the non-bow Flat LEIs (Supported Leading Edge, SLE kites) don't have concave trailing edge (most are straight, some even convex)
  • The bow Flat LEIs tend to be flatter,  the non-bow Flat LEIs tend to have more depth and therefore has more "Sled Boosting" effect


This flat kite has a flat or convex trailing edge (different from the original bow kite)
 


The same kite in flight.  The front bridle is more forward and completely separated from the back lines, the kite is not as flat as the original Bow and therefore has more "Sled Boosting" effect

The new generation of flat LEIs shares the following characteristics:

  1. Don't invert easily as the original bow kites (the less flat the kite, the less invert tendency)
  2. Not as twitchy as the original bow kite
  3. Can fully depower (very safe for beginners and all kiters)
  4. Light bar pressure, similar to classic LEI (no complex pulley system is needed)
  5. Very easy to relaunch (sometime even easier than classic LEI with 5th line)
  6. Very easy, safe self-launch and self-land (easier than classic LEI)
  7. Has similar "Sled Boosting" effect as classic LEI (the flatter the kite the less "Sled Boosting" effect it has)
  8. Better L/D ratio than classic LEI therefore faster

Furthermore, a newer generation of Flat LEI called "Hybrid" started appearing on the market.  These newer Flat LEIs are more or less the hybrid of the traditional LEI and the Flat LEI.

Flat LEI Bar

Flat LEIs require the use of bars with a longer trim strap and longer chicken loop to be able to fully depower the kite.  Even with the ability to fully depower the kite, the kiter should also have a safety leash connecting to one of the front line or back line as in traditional bars.  Following is a diagram of a typical Flat LEI bar:

Flat LEI bar

Safety

Compared to the standard LEI, flat LEI kites are much safer.  One can fully depower the kite while it is sweeping cross the power zone.  If you have a chance to test drive a new flat LEI kite, try to fly the kite across the power zone and then depower the kite (fully extend your arms or drop the bar).  If a flat LEI kite does not drag you at all, it is a fully depowerable kite.

While safety leash is still recommended and necessary, some experienced kiters don't rig a safety leash on a fully depowerable flat kite and use a safety handle (attached to a front or back line) when things go wrong.  There are enough incidents happened locally to convince us that a safety leash is still mandatory for Flat LEI (at least a safety leash that simply attaches to the chicken loop).

Impacts

Which such characteristics, the flat LEIs will have major impact to the kiting world.  We anticipate the following impacts:

  1. Kitesurfing will be safer as the kiter can just let go of the bar
  2. Kitesurfing will be safer as launching and landing are safer
  3. Kitesurfing will be safer as the kite can handle gusty wind better
  4. Learning will be easier (very easy to relaunch) and safer
  5. No need to body drag upwind, just depower completely and swim back to the board
  6. Bar design becomes much simpler and all are spinnable (the safety leash can simply attach to the chicken loop)
  7. Even unhooked bar are simpler and spinnable
  8. Very wide wind range per kite, need less kites per kiter
  9. Higher performance kites, kiters can probably break out-right speed record
  10. Easy boat launching and better power handling for kiteboating

So far the annual of Flat LEIs have surpassed the sales of traditional inflatables.

 


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