Kite lines are usually the last thing people think about, and one of the first things they complain about. Lines can make or break your flying experience, and they can turn a good kite into a poor flying one. There are many factors that go into line making and line selection, and knowing the differences between the various options can help you get the most out of your kite.
There are two characteristics you see when you look up a line, one is the weight or tensile strength, and this is literally how much weight the line could hold before it snaps. There is a little bit of overage built in by most manufacturers, but it is safe to assume that if I have a line that says it is 50 pound line, if I were to hang a 50lb weight off of it, it would be at it’s breaking point. 51 and it would snap. The other thing you see on sport kite lines is length, but this is pretty self explanatory. It is literally how long the kite line is. In a future episode we will get into what playing with the length of line can do to your flying. What are ideal lengths etc…
But.. let’s get back to actual line make up.
The main factor affecting lines in flight, regardless of their makeup, is wind drag. As the wind blows across the lines, it creates a drag on the line, and this in turn creates weight pulling on the kite. Too heavy of a line for a kite creates a sluggish feeling as it is literally pulling the kite out of the sky. Too light and you run the risk of the strength of the line not being able to sustain the dynamic and static loads of flying. This is the same for any kind of kite you fly, be it a sport kite, a single line, a big display kite, etc….
The second most important factor in lines is their stretch. It is worth noting that most higher end, purpose built sport kite line sets come pre-stretched, meaning that this should not be too much of an issue. Stretch has its benefits and difficulties. Stretch is only noticeable when the lines are taut, not when they are slack. There are two kinds of stretch, there is elastic stretch and creep stretch. Elastic stretch comes from the braid of the line where the fibers are pulled taught, and the braid is pulled, when the tension relaxes the fibers can also relax and it causes some elastic rebounded in the fibers.
Creep stretch is a permanent deforming under tensile load, and the fibers are effectively locking into place.
Most higher end sport kite fliers would actually prefer to fly on pre-stretched lines, and eliminate that extra bit of squishiness you feel. It is really annoying when you are flying and flying and trying to do something and keep noticing that all though your hands are perfectly equal, the kite keeps spinning off one way or the other without input. This is usually a result of uneven stretch in the lines. The easiest way to see if your lines have stretched unevenly is to stake out one end, then walk them out till they are taut. If one is longer than the other, than voila, you have your culprit. There are ways you can fix and equalize this, and perhaps we will have to leave that to another episode. It involves untying the sleeving, adjusting, and retying to equilibrium. Stretch is really one of those things that sport kite fliers don’t tend to see as a benefit. Ideally you would want to pick the lower stretch line for your flying.
Now, lets get into construction of lines. Good kite lines are either twisted or braided, not extruded. Forget about those monofilament lines which are extruded plastic fiber. A few folks have asked in the various kite groups about replacing their flying line with fishing line, and generally I would recommend against this, with a few exceptions. Most fishing line is monofilament extruded plastic, and it has a high stretch ratio. Some of these lines will stretch an additional 50% over the length of the line. You simply can not have this when it comes to sport kite flying, your inputs would need to change and adapt every second of your flying to compensate for feets worth of difference in line length (vice a low or pre-stretched line might shift an inch with hours of flying)
Cotton and linen lines are used primarily for fighter kites, they have a relatively low stretch. For some fighter kite fliers the weight of the line that comes with cotton and linen lines, or even manja which is ground up glass coated cotton line specifically for kite fighting, is a benefit. The added weight allows the flyer to fly his kite at a low angle of attack and use the length to maneuver the kite higher in light winds.
Nylon line was the first widely used synthetic fiber. While it has advantages over cotton, like being thinner, cheaper, and not prone to mildew damage, it has one major drawback. It stretches roughly 20% making it completely useless for sport kite flying. This stretch percentage drops to about 14% if you switch to polyester. Polyester kite line suffers from having different grades, and other characteristics that make it better suited for single line kite flying.
Then there is kevlar, everyone has heard of kevlar, whether it is bullet proofing or kite line. This is a very strong line, and with an average stretch of 3.5% and a line diameter that is rather small compared to other lines of the same tensile strength, meaning less drag and less stretch. The downside however, other than cutting everyone elses lines out of the sky, comes down to their molecular makeup. The aramid molecules are oriented to bond linearly, which prohibits stretch from end to end…. However, this also makes it very fragile in a bend. Any knots or clips, or even winding the lines around a standard winder can decrease the strength of the material by most estimates around 60%. This means your 100 pound line you are flying on, because of the one knot you have tying the line to the handle has an effective tensile strength of only 40 pounds.
To avoid this massive decrease, or at least to minimize it a bit, most folks use ‘sleeving of the lines. Sleeving is where you run the thinner kevlar flying line through the hollow core of another thicker line, and use the thicker line as the end point to tie your knots, thus making any bends bigger and less fragile.
Last but not least we come to the standard for sport kites, and that is UHMWP. Or.
Ultra high molecular weight polyethylene also known as high modulus polyethylene.
Dyneema and Spectra are common brands of lightweight high-strength oriented-strand gels spun through a spinneret. There are other brands as well such as Shanti Lines and also the Matrix line through Level One Kite USA.
UHMWP lines also have a stretch rate of about 3.5%. Overall they are the best choice for sport kite flying. They do have a few downsides however, but these are not major detractors when compared to other lines. They do have a low melting point, however this is only an issue if you are repeatedly wrapping your lines with lines of another material with a higher melting point. The friction between the lines can be enough that it will snap your spectra line set. There is also creep in spectra lines, but it is typically a very small amount, and it only is a real issue if you are replacing one line from a set at a time. Typically most people fly equally enough that the creep that might happen, will happen equally across both lines. If not it is easily adjustable. Where this tends to be the most notable is in quad line fliers. There may be more creep in the top lines versus the bottom lines if they tend to fly heavily in a drive position versus a braked or balanced position.
Now, what lines come with your kite? Well most entry level sport kites come with a mid grade polyester line set depending on manufacturer. This is not inherently bad, given how often most entry level sport kites are flown. Those that are looking to take a step up in their flying usually will also upgrade to a UHMWP line, and over time begin to tailor what line set they like the best. One thing I haven’t really touched on in this whole thing is coatings or interweaving of other materials. This does happen, and coatings especially can effect things like how slippery the line is, if it gums up, or other stuff like that. I would love to be able to give a comprehensive discussion on it, but ultimately after talking with so many folks about it, it really comes down to how it feels for you.
One of the other reasons that you might not see a UHMWP line set with entry level kites is the cost. Where as a polyester pre made line set purchased independently may cost you about 5-10$ a UHMWP set will set you back 35$ and up. Of course this can be cheaper if you buy your own materials and cut your own linesets, tie your own sleeving, and your own handles. But it gives you an idea. Polyester is great for someone that is flying maybe 5 times a year when they go to the beach with their kids and the kite comes out of the closet. UHMWP is better suited to hold up to the wear and tear of someone that is wanting to be a weekend warrior up to a professional flier.
So yah, there ya go.