Power kites have but one aim to create power for the flyer. Just as for stunt kites, the result of this focus is that most power kites loosely fit the same design mould. The design idiosyncrasies that do exist have an appreciable effect on the flying of the kite, so it’s useful to understand a bit more about the diversity in power kites in order to choose which kite is right for you.
Power kites have a rectangular-type shape, a broad wingspan with a short chord, and are typified by a strong, rounded leading edge with a pointed trailing edge. lt is this aerofoil shape which creates lift for the kite in exactly the same way as does the wing of a plane. Simply explained, the shape diverts air downwards, meaning that the kite is pushed upwards. The curved, convex shape of a traction kite is important for harnessing the wind’s power, and, although this is standard across all power kites, how this shape is created differs for land and water kites.
Traction kites can be distinguished by whether they are for use on water or land. Those used for land-based flying use the wind to become inflated by letting air into the cells of the kite (‘ram-air’ kites). Kites which are water-relaunchable use a pre-inflated leading edge and inflated batons to create their shape (‘leading edge inflatables’ or ‘LEIs’). Inflatable kites were invented because a ram air kite crashing on water will let in water through its open gauze area rendering the kite useless after sitting on water for any length of time (anything over about 10 seconds!).
The second distinction in power kiting is how many lines a kite has. Dual-line kites generally fly faster and are more responsive than quad-line kites, and are also easy to set up and fly for beginners. On the design side, generally two-line kites are not suitable for kite sports as they do not have the two extra ‘brake’ lines and therefore cannot spill any wind if it gets too strong (i.e. they cannot de-power easily). However, some enthusiasts still swear by two-line kites as they are generally quicker to react than four lines.
Four-line kites offer more control to the flyer than two-lines, and are slower in the air. This means they are more stable, which is great for traction sports where you do not want a ‘twitchy’ kite to which you have to pay loads of attention whilst you are trying to perfect your manoeuvres down at ground level. You are able to hold your kite in a steady position in the power zone with four lines which is pretty tricky to achieve with two-lined kites. Also, you can adjust the angle of attack by making your brake lines either shorter or longer, to counter the effects of varying wind strength. This becomes more important when you are attached to the kite with a harness. Quad-lined kites make life easier at the time of re-launching, especially on water, as the four lines enable the kite to be flown in reverse.
For traction sports it is generally advisable to use a four-line kite as you have more control; however, for recreational use, two-line kites are perfect and you can stack these kites for extra power and to create an awe-inspiring sky decoration for spectators! if you can’t decide, there are kites which you can change from four to two lines by essentially losing the ‘brake’ lines’. But be warned, using a large kite without its brake lines is not a good idea.
Dual-line ram-air kite (for use on land)
Power kites for use on land are ‘ram-air’ kites. Ram-air kites use the wind to fill their cells and give them form, rather than having a fixed structure like stunt kites. They are constructed with two pieces of material between which there are cells that become inflated in flight by air filtered through the (gauze) leading edge. They do not historically have any batons to assist with holding their form but there are some ram-air kites that do use a baton, neatly avoiding a complex bridle system. Ram-air power kites are also referred to as soft kites, parafoils or foils. Foils have a lower AR and thinner profile than inflatable power kites, meaning that they are generally faster in the air but do not create as much power as a similar-sized inflatable. The bridle on some ram-air kites can be pretty complex as it alone is relied upon to create form for the kite. In the case of foils with a leading-edge spar, the lines are attached directly on to the kite, which is considerably easier and less daunting for a beginner.
Size does matter. For power kites, size is hugely important as, roughly speaking, the bigger the kite the more wind power is capable of being harnessed. Whereas for sports kites the overall size is less important than the size relationship between the various parts of the kite as discussed previously, for power kites both these issues are important.
As two-line kites do not have any brake lines and therefore no de-powering capabilities, it is very important to get the size right. The size of power kite you choose is dependent on three variables -your weight, your ability and the wind strength.
A kite of 1m (3ft) projected size (the size it is when laid out on the floor) should be fine for a 50kg (110lb) beginner adult flying in average (force 3 or 4) wind, providing the AR is not too low (about 3 would be good). However, as kites differ so much, it is crucial to consult the manufacturer‘s guidelines as to the conditions for which the kite is suitable.
The same rules apply for the lines of two-line foils as for the lighter sports kites: the bigger the kite, the stronger the wind, the shorter and/or stronger the lines need to be. A pretty standard length for a power kite line is 25m (80ft), but longer lines may also be used in recreational flying if the wind is weak, or where objects close by interfere with the wind, allowing the kite to reach the ‘clean’ wind above the objects.
Two-line kites generally fly faster through the air than four-line kites, so it is possible to use longer lines and still fly a fast kite (although four lines can turn faster). As a general guide to line strength, a 1m (3ft) kite in average winds (force 3 or 4) would be fine flying on around 100kg (225lb) lines and could even work on lines of 75kg (170lb) at lengths of 20-25m (65-80ft).
Just as for stunt kites, padded straps or handles are normally used to fly two-line power kites recreationally. For kite sports, like buggying or landboarding, it is possible to use a bar for stability and to free up one hand. In this case the bar length needs to fit the kite; a smaller kite needs a smaller bar. You can ‘tune’ the kite by using a different length bar; if the kite is too twitchy, use a shorter bar, but if it is too slow to react, use a longer bar.
Harnesses can be used with a two-line kite, but make certain you have a quick-release system and that you know how to use it as a situation can become an emergency in the time it takes for you to shout ‘woohoo, I’m flying!‘
Four-line water relaunchable kite
Inflatable kites are made from one piece of sailcloth, with an inflatable bladder along the entire length of the leading edge. When this is blown up, the kite forms a ‘C’-shape, and to hold the structure more rigidly in place a number of inflatable bladders are sewn in across the chord of the kite to act as rigid rods. This airtight and watertight design means that the kite can land on water without becoming waterlogged and, of course, it will not sink. The disadvantage is that, if the kite is flown on land and it comes down hard, the leading edge may split on impact.
Just as for all power kites, inflatables have a high AR (they are much longer than they are wide), for example an advanced kitesurfer would be comfortable with a kite of around AR 6. An inflatable will usually have a higher AR than a foil as more power is needed to create friction on water than on land. The joy of inflatables is that they do not need bridle lines all over the place, as the inflatable batons hold the kite’s shape.
Generally speaking all traction kites used on water need to be around 40% bigger, or one or two sizes bigger (around 6.5ft (2m)) than their land equivalent. Always check the manufacturer’s recommendations for the appropriate conditions in which to fly your kite.
As for all power kites, size is related to the ability and weight of the flyer, the wind strength and the sport that the kite is being used for.
As a conservative guide, a 50kg (110lb) adult in medium wind (force 4) should be comfortable using a 5m (15ft) kite. Be aware that kites behave very differently depending on their design: one kite may generate twice the power of a similar-sized kite because of variants in design.
The two front lines are often called the ‘main’ or ‘steering’ lines, the two back lines are sometimes called the ‘power’ or ‘brake’ lines. The front lines need to be pretty strong, so a breaking strain of around 250kg (600lb) is common, at a length of at least 20m (65ft). The back lines are usually the same length as the control lines (unless you adjust them to change the AOA), but they do not need to be quite as strong as they do not play such a dominant role in harnessing the wind’s power.
For water use, a bar is usually used to control the kite. Although bars do not offer quite as much control of the kite as handles, they do offer stability when you are busy attending to your sea or ground-level activity. They also allow the kite to fly at the top of the wind window happily on its own without any hands on the bar whatsoever – if it is attached to you via a harness! – which is a welcome benefit of the control bar for those tricky situation where you can’t deal with everything at once. Make sure you know how to use your kite’s quick-release system if you do attach yourself to the kite.