My intention in writing these two articles is to give hope to the budding Andy Prestons and show that if you work from scratch it is possible to create some amazing sport kites which will be entirely your own without using a computer.

It is actually quite difficult to build a delta sport kite that won't fly as the delta shape is very forgiving. most designs can be made to fly but not always the way you thought they would (some better some worse some just different). The important thing is to be accurate in your building and take your time at the drawing stage.

All my drawing is done in scale of 1cm to 10cm (1/10th) this seems to fit well on a landscape A4 sheet and is easy to transfer. The whole design requires two drawings one for the frame shape and one for the sail shape.

For this first article I will concentrate on the frame Drawing. Carbon fibre frame material is available in all sorts of lengths and strengths these days. Strength will determine the wing and cross spar length for your kite design too long, light and flexible a spar will restrict you to flying only in light winds (unless this is what you want). Most moulded fittings require you to use the same exterior thickness of material for the whole kite frame. The internal diameter can be varied to provide stiffer spars were you wish. There is a convention that a slightly stiffer spine is a good thing. The length of material will mean a choice between certain frame shapes to prevent excessive wastage of the expensive carbon rod this factor is what has determined the common frame sizes in commercial sport kites. Early designs mostly used carbon arrows of 825mms in length and these sizes are still very common today.

For this exercise I will use a wing spar length of 1.5 metres as a guide. The rest of the spars of the frame can be divided in many ways depending on the end result you wish to achieve. The length of your carbon stock will determine the shape of the frame to a some extent. The frames on the right are all based on a material length of 3 metres of 6mm thick carbon tube. This frame drawing determines the position and length of the upper and lower spreaders and spine as well as the position of the crosspiece and leading edge connectors on the sail. Two 3 metre lengths of carbon are required for these frames, one for the 2 wing spars and one for the spine and the lower and upper spreader.

Starting at A. find the centreline on your A4 sheet measure down B.(10mm) then mark the length of the spine C. Now mark a line parallel to the centre line at distance D. You can now decide the lower spreader connection point. Too long and flimsy a wing may tend to twitter. I tend to start with a drawing at two thirds down the spar and work up or down depending on the carbons stiffness (and the wind strength I want it to fly in).

The top spreaders position is determined quite simply by it's length but it's importance to the quality of the kite's flight should not be underestimated. Some deltas can be made to change character completely just by changing the top spreader length by 5mm. Drawing 1 has 5cm of extra length to maintain support for the wingspar.

Part Two

The second part of this article deals with the complicated bit delta sport kite sail design. For this exercise I will use frame drawing 1's measurements for this exercise. Once again all drawings are 1mm to 1cm (1/10th) scale.

Your frame drawing from part 1 gives you the end shape of the total delta but because of the sail billow standoffs and wing curve, the sail drawing is much more complicated.

First question is how long and how many standoffs do you want and where do you want them. Depth of sail controls speed and stability. Increasing the depth of the sail will generally increase stability and reduce speed. Multiple standoffs produce a more complex tighter sail shape and are very common on modern commercial designs. Plotting the exact depth of each standoff at this stage is unwise. It is better to think of the total trailing edge depth required by drawing the sail as if the tail end of the spine is pointing straight at you as below.

These diagrams are a slice taken through the kite at the position of the lower cross spreader and only give the sail depth at this point. To project the depth further down the sail (to lower stand off position's) may require making a three dimensional paper model of the sail plan. Simply cutting out your sail plan shape and bending (folding it at the standoff positions) it will help you visualize the end shape of the kite (and may suggest a panel layout).

Adding together the measurements (90mm 92mm and 89mm for these drawings) gives you the sail width at the lower cross. Remember to check your measurements at every stage of the sail drawing and remember to write them on the drawing at every stage.

First draw your centre line (a). Measure 10mm down from the edge of the paper(b) Measure down the centre line 59.5mm (c)(nose to lower spreader on the frame drawing). Now taking the measurement (in this case 90mm from the first drawing,) and the distance from the nose to the lower spreader connector, (100mm) and plot the position of the lower spreader leading edge connector (d). A pair of good quality compasses can be a great help in achieving this.

Draw a line from the nose through the leading edge connector position to the edge of the page(n)and draw a line showing the lower spreader(m). When marking the actual wingtip position you have to allow 30mm for the nose webbing. You also have to allow for any curve you want to put in in the wing spar at the tip. To do this mark a point 160mm down the wing spar line(e) and a point 85mm (f) (the spine length) down the centre line. Using a drawing curve, a short piece of glass fibre or the ruler on its edge from the nose crossing the lower spreader connector point decide how much curve you require 13mm in this case and draw the line(g)(an extra pair of hands can help a lot). Mark the wing tip position (h) 53mm from the lower spreader connector. A gap between line (g) and line(s) at the upper spreader position will naturally appear. This can be refined to produce a certain amount of nose billow in the upper spreader area of the sail on your sail pattern. Mark the position of the upper spreader (34mm)from the nose on the leading edge(i).. Mark a point 40mm along the lower spreader from the central T and draw a line from the nose through this point (j). This is the line of the standoff. Decide how much above or below the spreader you want your standoff to go remembering the position will rise by 2-3mm(depending on sail depth) on the final kite. For this exercise the standoff will be 8mm below the spreader(k). Most modern kites use curved trailing edges to reduce noise and drag. Small differences in the trailing edge particularly the outer part can make very big differences in performance. A good quality pair of compasses is really useful at this point. Mark in the curves of the inner and outer part of the trailing edge(l & o)remembering to write down the radius of each curve on the plan.

To decide on your panel layout make a copy of your plan and cut it out. Draw round the copy on to several sheets of paper remember to mark the position of the spreaders and the central T. Both nylon and to a lesser degree polyester sail materials stretch diagonally across the weave (bias). Take this into account when designing your panel layout and remember that the seams between panels act as reinforcement tapes and tend to help to hold the sails shape along their length