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Kite Altitude World Record
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Kites - which ones, why and how we build them
This DT Delta in the front garden at Baulkham Hills, is derived from the kite on the right. This 165 sq ft kite  was built by Bob Moore from material grade ripstop Nylon and 15 mm fibreglass tube. It was designed for light winds but has proved inferior to the 120 sq ft version. This kite has flown to 6,500 ft in October 2005 on thermals. I may modify it as I think it is too "floppy". Kites often don't scale up as the material doesn't stretch to scale nor are the spars proportionally stiffer. In any case the 120 sq ft model has nearly reached record height, there is no need to use this kite.
Above: DT delta "fast climber" is the basis for my record attempt kites
The Rokkaku or Rok is a Japanese traditional design that many western kite enthusiasts have embraced to build with ripstop and fibreglass. Is a nice flyer in many respects but several flight characteristics eliminate from selection.
The Conyne Delta is a modern version of the Conyne or French Military Kite. Closing the central cell converts it to a DT delta but without the scalloped wings. The central triangular cell gives it extra rigidity compared to a delta design. The Box Delta (below right) has no extra lift compared to the DT Delta but has added weight and drag from the extra longeron and the diagonal cell braces. It may be more stable in theory but this has not been shown in practice to be a significant enough advantage to justify changing from a DT Delta to a Box Delta.
This excel delta kite dimension calculator was developed by Bob Moore to keep the dimensional relationships to scale irrespective of the kite size. Only one value needs entry, that is, the top left at 'A'. then 7 dimensions are automatically filled.
The size of our DT Deltas are somewhat arbitrary and for no technical  reason. It's a 4 x scaled up version of red/yellow 30 sq ft DT Delta kite shown in the Rooty Hill image. This kite's dimension were determine by the ripstop width on roll. The biggest influence on the 120 sq ft DT Delta's flying characteristics is the spar lengths and stiffness. The 90 degree angle  formed between the leading edge of the wings is derived from an isosceles triangle where the height is equal to half the base width.
This is an original Hargrave Box Kite weighing about 12 lb. Very stable but flys at a lower angle compared to our DT deltas due to higher drag. Note the curved top spars and Hargrave was one of the first to recognise the extra lift of aerofoil profiles.
This is my version of a Hargrave Box. The skin is 1.5 wt ripstop nylon and the frome is 15 mm fibreglass tube. It weighs 3 kg or about half the original kite. Difficult to construct with sufficient stiffness in the joints to be a viable record kite although with further development may prove to be a good alternative. It would be good to have such a famous Australian design capture the world record.
The parafoil. With a steady wind probably the best kite of all. Very light and tremendous lift from the aerofoil profile. Its Archilles Heel is the tendency to collapse and not recover in gusty and turbulent winds.
Our kites are made from 1.5 wt Ripstop Nylon cloth.
The rolls of cloth are 1.5 metres wide. First a scale drawing is either manually done or composed on the computer. I use the Paint program in MS Windows. It is simple and I can experiment with different color combinations to see which may give the highest visibility against a variety of skies. Light blue would be hopeless against a blue sky. We chose white with a black centre cell so the kite would be visible against a blue sky and against cloud as well. The original kite was black and was reasonably visible against various skies excet dark grey cloud. We currently have 4 DT Deltas, 2 of these are active kites and the other 2 backups. We have a carbon fibre framed version but we reserve that for light conditions. The 169 sq metre DT delta is not in active use as I have "borrowed" the spars.
The next step is to make a 3 ply template of the panels. The cloth is then hot cut with an electric knife to seal the cloth and prevent fraying.
We are careful to align the weft and weave of the cloth to maximise lift. The seams and spar pockets are sewn and reinforced in stress points. Spar ends have caps to preven the sharp ends from punching through the spar pockets. Mike Richard's construction has proved very robust. We occasionally need to make repairs and insignia, sticky backed repair cloth is invaluable. One of the kites survived 59 knot winds without much damage.
Richard Synergy, the current record holder, used a low aspect ratio Dan Leigh Delta, 270 sq ft. We use kites 1/3 the size but have reached or exceeded the claimed altitude.
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