A Look At Basic Kite Design & Model Characteristics

It is useful to understand some basics of kite design before choosing a kite to fly. The manufacturer will usually summarize the effect of each kite model’s characteristics so that you don’t have to know, for example, how high aspect ratio affects the kite’s flight, or the virtues of carbon versus fibreglass. However, the manufacturer will often oversimplify with limited comments such as ‘suitable for beginners’, so knowing a bit about the following variables will be invaluable when buying your own kite.

AR

Aspect ratio is the relationship between the length of the kite and its height, or, more specifically, it is the length of the wing span divided by the length of the ‘chord’ which is an imaginary line drawn from the leading edge to the trailing edge of the kite. The higher the AR lie. the wider the wing span in comparison with the chord), the quicker the kite can accelerate and the more manoeuvrable it will be.

Lift-to-drag ratio

Inextricably related to the AR is the lift-to-drag ratio. This is more relevant for power kites but is applicable to all kinds of kites. A kite with a higher AR will have a lower lift-to-drag ratio. ‘Lift’ is the force on a kite in an upward direction; ‘drag’ is the force on a kite in a horizontal direction. The lift-to-drag ratio is related to the camber of the kite; a kite with more camber (more curved and ‘C’-shaped) has a higher lift-to-drag ratio. What all this means, and ‘what you need to bear in mind when choosing which kite to buy, is that a more curved kite will create more lift, but will be slower in the air, whereas a kite with a narrower profile will not produce so much power for the flyer, but will fly faster through the air and will also respond more quickly to the flyer’s actions. A kite’s drag is related to the angle of attack (AOA).

AOA

The angle of attack is the angle between the kite’s chord and the direction of the wind, and it directly affects the amount of wind the kite can harness. Simply put, a kite with a lower built-in AOA (0-1 degrees) will be almost head-on to the wind when all lines are taut and of equal length. This means that it will be hard to fly delta and single-line kites, and for power kites it will produce less power than a kite with a higher AOA (4+ degrees).

Materials

In terms of the construction of a basic kite, the only rule is that the materials must be lightweight, so pretty much anything goes – from bamboo and silk to paper and plastic, in any structure that is wind-friendly. A basic kite which you would find in a toy shop is probably plastic and no doubt will fly very well. The more technical (power and stunt) kites have benefited from great advance in material design and production over the last three decades.

Sailcloth

The kite sailcloth is usually made from nylon as this is lightweight and durable. Although there are a few different names and hybrids on the market, nylon commonly used is ‘Ripstop’, which provides more durability due to the extra thread reinforcements, literally stopping the development of any rips. Other materials that can be used to create a kite sailcloth include Ripstop polyester (very lightweight), 3-ply polytheylene (very durable) and pre-coated ‘spinnaker’ nylons (in reference to the sailcloths used for the spinnaker sail of a boat). These materials perform perfectly for non-traction kites, but they are not as appropriate for coping with the conditions imposed upon power kites as Ripstop nylon.

As Ripstop nylon is so suited to the job of forming a windproof kite sail, little other material is needed. However, gauze is used on the leading edge of a land kite, and is needed to let air in to permeate the cells of the kite and inflate it. Dacron is a tough material used to reinforce the side panels of a kite, which improves its longevity.

Finally, one-way rubber valves are used on water-relaunchable kites, so that blowing up the bladders is easy and the chances of them coming undone and letting out air is slim.

Spars

Spars – also know ans batons, spreaders, sticks, rods, longerons – all refer to the skeleton-type bars used to fix a kite’s shape. Rods must be lightweight yet durable. For high-spec kites, fibreglass or graphite (carbon) are used. Graphite is both lightweight and durable, but is quite pricey, especially wrapped graphite (where individual strands of graphite are wrapped together to form the rod). Fibreglass is the slightly cheaper option: solid fibreglass is fairly tough; hollow fibreglass rods are lighter but they can break more easily.

Lines

Most kites have some kind of bridle, and all kites have lines to which they are attached. ‘Dyneema’ or the very similar ‘Spectra’ are the names of the polyethylene fibre most commonly used in kite lines. Dyneema is so strong that it is used for bullet-proof clothing. Dyneema and Spectra are expensive and are not as durable as other materials – they can break from friction if you cross lines with other kites. ‘Kevlar’ is strong but will cut like a knife once the kite is flying and tension is created. Dacron is a better option if flying in team events or near other people, as it is incredibly hard-wearing, although on the negative side, Dacron stretches and cannot support as heavy a load as Dyneema and Spectra.

The best option for beginners is blended Spectra/Dyneema and Dacron. If you choose a line which is more delicate and less durable – such as Spectra/Dyneema which has a low melting point – it will need to be ‘sleeved’ with Dacron at the ends to increase the knot strength where it is attached to the kite’s bridle.