Dyneema®, the world’s strongest fiber™
WORLD ALTITUDE RECORD

 

Kite line

We use UHMWPE or Ultra High Molecular Weight Polyethylene fibre based kite line. The raw fibre is made by DSM in Holland and some other factories around the world are licenced to produce it. The fibre is called Dyneema and it is the strongest commercially made fibre in the world. Thin line, cords and ropes are manufactured from the fibre mostly by braiding which is a type of interlocking twisting process where very fine Dyneema filaments are spun into a compact hollow braid. The lines ropes and cords can be made in very long lengths without joins.  Dyneema and it’s related fibre, Spectra are made from UHMWPE. Both are used in line for steerable sports kites, parasailing, kite surfing and related wind sports. Generally Dyneema line is not used for large hand held single line kites as it is too slippery and in festivals is subject to being severed by friction melting from thin Dacron and other line types. 

Above is the reel with 12,270 meters of Dyneema® line. the line is two strengths. The pink line is 6,020 meters of 186 lb 0.7 mm diameter line and underlying and joined by splice is 6250 meters of 292 lb, 0.9mm diameter white line. The pink is a semi permanent plastic “wax” which is infused between the line fibers at relatively low temperature. The white line is unwaxed and in its natural state. Dyneema® is very smooth and slippery. It is UV and abrasive resistant. It doesn’t absorb water so it’s strength is not reduced in wet conditions. It’s only practical limitations are it’s relatively low melting point of about 150 degrees C and it can’t be handled easily by hand unless flying small kites nder light loads but for my application this isn’t an issue. Dyneema® is a great product that has made routine flights over 10,000 ft possible. As a comparison, ordinary braided synthetic lines such as Dacron would limit the same kites to 5,000 ft in my opinion. I have never flown a kite beyond 4,000 ft on Dacron or any other similar synthetic line. Natural plant fibres such as jute or hemp are well and truly outclassed when compared to Dyneema. Mono Filament fishing line is is well below the performance required for big kite flying. It’s much too thick for it’s strength, too heavy and has way too much stretch. It’s only positives are it’s smoothness, which minimises wind drag and price. A monofilament, Nylon fishing line would need to be about 3 times the diameter of Dyneema for the same strength. A 300 lb Dyneema 75 line is 0.9 mm diameter. A 300 lb monofilament line would be over 2.6 mm diameter. This results in 3 times the aerodynamic line drag  and also the monofilament nylon line is 20% heavier for the same diameter and 350% heavier for the same strength. 

The current record holder used Kevlar® line however he required a 300% bigger kite to carry what is a 40% heavier and thicker line. I am able to have a greater margin of safety by using a smaller kite, thinner yet stronger line and I’m able to use the Dyneema over and over again without a significant reduction in strength.

 

Above are 2 spools of Dyneema being load onto the winch reel. The line pink line is 186 lb test and 0.65 mm diam under load. The white line is 292 lb test and 0.85 mm diam under load.

10,000 meters of UHMWPE line from Amika in Taiwan. Good quality line at a reasonable price.

Above - Some braided fishing lines made from HMWPE (5 x scale) to show the structure of braided line. Each braid is a bundle of micro fibers or filaments. Lines are measured as grams per 9,000 meters and expressed as DTEX (decitex). The white Dyneema (left) is 570 TEX or 570 grams per 900 meters or 5,700 g/9,000 meters. Fibres are classified microfilaments if they are less than 1 gram/900 meters. There are 12 bundles of fibres in the white Dyneema and then at least 48 micro fibres/bundle. Each microfibre is thinner and stronger than the strongest spider silk. The sheer number of fibres results in a line that is difficult to induce sudden failure by abrasion. This is not the case with mono filament lines.

Left - A bunch of lines that I tested early in 2004. These include monofilament fishing lines, twisted nylon, braided Dacron, Spectra, Kevlar, Dyneema, Jute, Hemp, linen and composite lines. I already had a reasonable idea about what line was good for high altitude flight. Cost was also a factor but this has been solved to some extent by sponsorship from DSM (Dyneema) in Holland

 This graph was based on testing and formulas derived from drag data and on field testing. It assisted with line and kite selection. Our most recent high altitude flights resulted in an altitude of 10,681 ft above ground level. During this flight, 6,555 meters of line was out but the line sagged until it was at 8 degrees at the winch because of winds were below 8 knots at 10,000 ft and above. Line tension was below 5 kg (11 lb). The kite reached it’s maximum altitude after 300 meters of line was wound in at 2 meters/sec (7kph). The line was then 20 Degrees to horizontal and the kite 32 degrees 

Here you can see the trailer mounted winch which consists of a reel (with yellow line) capstan (silver wheel) and electric motor. The motor drives the capstan and reel through belts and pulleys and the line is wound around the capstan about 15 times so it grips the capstan without slipping. The line is very slippery and the coefficient of friction between Dyneema line and the steel capstan drum is 0.2. A minimum of 15 turns is needed so that the line tension on the reel is not excessive. The line exits the capstan via pullies and a guide horn at the rear. In this image 2.5 km of line was being recovered from bush after the kite went down. The line tolerates being dragged through scrub remarkable well with very little evidence of abrasion however, this type of wear on the line is avoided and the line is checked visually and passed through the hands to check for rough sections or damage. It is not practical to perform a strength pull test for the entire length of line each time this occurs. The first few hundred meters of line is subject to contacting the ground during launch so after a few flights this section is removed. The current Dyneema line is 12,000 meters, 2,000 meters longer than required to break the record. This provides plenty of spare line to compensate for removal of worn or damaged sections.