Dual Line Kites

Dual line kites change all that. If you pull the right line the right half of the sail is pulled towards you and the kite turns to the right, or clockwise, and if you pull the left line the kite goes left, or anticlockwise. Very simple and intuitive, but in fact the aerodynamic principles involved are less simple and have been the subject of lengthy discussions on rec.kites.

It is also possible to control the speed of the kite, by pulling both lines together - the harder you pull, the faster it goes, and if you allow the lines to go slack by throwing the hands forward, the kite stalls.

There are three widely available types of dual line kite: the Peter Powell diamond stunter, the delta sports kite, and the dual line parafoil.

Dual line flying was first popularised by Peter Powell with a dual line Eddy or Malay type of kite. Originally a dihedral design, modern versions, especially cheap polythene ones with sails printed with Disney characters or similar, are normally bowed by wind pressure. These are a familiar sight on the beach and for many people are their first experience of kite flying, or at least of steerable kite flying. Pelham gives plans for a Peter Powell stunter. The Trilby is a well known commercial version; here is a picture of a stack of 4 of them.

Diamond stunters can give a lot of fun and are easy to fly, though one-man launching is only possible by setting the kite on a ramp (easily made on a sandy beach) or a special launching stand, so that a sharp tug on the lines pulls it face-up into the wind. Long tails of polythene tubing are usual but these are for show rather than stability, tracing out turns and loops in the sky.

For a real head-turning spectacle, stack as many identical diamond stunters together as you can afford, attaching the second and each subsequent kite to its predecessor by three lengths of line, each half as long again as the height of the kite, connecting the two kites together by their bridle points.

The 90's saw an explosion in dual line flying with the invention of the delta sports kite. Usually spared with carbon fibre for strength and lightness, and having much greater aspect ratio than diamond stunters, the delta opens up a new world of possibilities. (The sketch was drawn from a photo of the MEFM.)

Several strands of development have already emerged, with their attendant jargon. In particular:

• Radical: many delta sports kites are described as "radical". This simply means they can turn very sharp corners, with the centre of the turning circle well inside the wing tip. The North Shore Radical (35k) is one example of many.
• Ultralight: these kites can fly in winds of 3mph or less. Since this is walking speed, you can fly these indoors. And a skilled flyer knows how to keep them aloft without simply walking backwards until he hits a wall. Tim Benson's Phantom will fly in a 2mph wind - this is the kite that nearly all other delta sports kites are derived from, and despite its age, could still outfly most middle ranking kites.
• Precision: such kites can be steered very precisely and are used in breathtaking displays in which several flyers fly together with a precision reminiscent of the Red Arrows aerobatics team. The Air Dynamics T2 (13k) kite is amongst the best precision kites.
• Trick: these kites sacrifice some precision for responsiveness, often having a degree of oversteer. Trick flying allows one person to go out and have a whale of a time on his own. One of the best trick kites is Tim Benson's Gemini(©Sam Eaton) (14k).
• Freestyle: combining precision with trickability gives a kite that can be used in very versatile displays, doing much more than simply tracing patterns in the sky. The Atelier Lithium (33k) is highly rated in this category.

Plans are available for a family of delta sports kites, the "Raaseri", which includes an ultra-light, a medium, and a heavy. Here is the family portrait (64k).

Many tricks have been developed with the delta sports kite, and whereas they are easier on a trick kite, an experienced flyer can perform most of them on any good delta. Some involve "groundwork"; in inexperienced hands, most landings are unplanned but experts can land on one or both wing tips in various ways and take off again. Others are built on the "axel": the kite is stalled by thowing both hands forward, and then is made to rotate through 360 degrees, still stalled and floating gently, with a yank on one line. Normally, pulling the right line causes the kite to turn clockwise; in an axel, a yank on the right sends it anticlockwise. A video clip (2.1M - big!) is online, showing Dodd Gross demonstrating the axel. (On a Windoze PC, view with mplayer.exe)

Dual line parafoils have also appeared in recent years. Being very efficient through their aerofoil shape and high aspect ratio, they can fly very fast, but they are not used in precision displays and are not suited to trick flying because, being almost entirely soft, loss of line tension can cause them to fold up in the air. Some are entirely soft, whilst others have a single flexible spar running the width of the leading edge. They are exemplified by the Flexifoil - a tradename that has become associated with the genre as Hoover has with vacuum cleaners. Here is a picture of one.

Flying such a kite is quite a different experience from a delta and has been described as being very relaxing. Arm movements are greater than with a delta, and the thrill comes from the pull it exerts, as well as the shear speed. The downside is that one-man launching is harder than with a delta, especially on long grass, but the Flexifoil comes with an instruction sheet which expains how it can be done quite easily with a couple of sticks to form a launching ramp.

A major use for dual line parafoils is for traction in the new sports of kite-buggying, kite-sailing, kite-surfing and kite-skiing. The Peter Lynn Peel is much favoured in these circles. Stacked parafoils, or single kites of large size can develop tremendous pull - the use of 300lb breaking strain line is quite usual.

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