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12,000 meters of Ultra High Molecular Weight Polyethylene (UHMWPE) braided fibre or Dyneema® braid which is, weight for weight, the World's Strongest Fibre. Here is a big reel with a solid core and wooden sides reinforced with 5 mm aluminium reel ends. The line at that time (2009) consisted of 2 strengths joined by splicing. The inner line is 6,000 meters of white, 131 kg breaking strain (289 lb) and 0.9 mm diameter braided Dyneema. The outer pink line is 6,000 meters, 86 kg breaking strain (192 lb) and 0.8 mm diameter braided Dyneema. I retired the pink line for high altitude flying because it may be just too close the self imposed safety marging of 40% maximum line pull verses breaking strength. The standard is 4 x the maximum anticipated load verses the breaking strength where human safety is involved. I need to go as close to the limit of breaking strength as I dare to minimise line weight and the wind drag on the line. This strategy enabled me to use a smaller kite and a lower powered winch and it worked as we broke the record with a flight to 16,009 ft in 2014.
meters 1mm diam
100 kg test
||Wind resistance per 1000 meters
per 1m/sec 100kg test
|Steel music wire
|Dyneema SK 75
Early on it became clear that line drag and line weight were the top 2 factors limiting the ultimate altitude reached. Selecting and building a kite of the right design and size has proved relatively easy and building a good winch is a matter of simple mechanics and improvements incorporated with trial and error. Initially it was a process of eliminating faults, thinking about improvements and steadily evolving the design with practical solutions and affordable materials that can be constructed in a home workshop. Line selection was uncompromising, for without the best, thinnest and strongest lines, the kite altitude record, with these relatively small kites, would not be possible. Despite the need for the best lines, I am still only a kite hobbyist, with a modest budget. It has taken me 8 years to build up a stock of Dyneema and Spectra lines but each year I need to replace lines. Fortunately I have assistance from Dutch company DSM Dyneema and Cousin-Trestec of France but even then I need to purchase replacement lines from Taiwan and China. All the lines need to be tested to at least 140 lbs pull, especially the Chinese lines as they are of unknown quality. Fortunately Dyneema and Spectra are very durable but still need to be handle carefully to minimise wear, tear and abrasions. In 2006 I pull tested the entire length of Amika Dyneema (Taiwan) at a sheep station near Dubbo in Central Western NSW. This operation was repeated at Lake George near Canberra, NSW. A new test method will be commenced in early 2013. This will done by winding the line against brake friction between 2 capstans and tension measured dynamically with the La Rock Tensiometer. I anticipate testing all lines to 140 lbs.
Steel music wire (piano wire) was ruled out because of the danger of contacting power transmission lines and handling difficulties. It is also relatively difficult to obtain compared to other line types
Natural fibres such as jute, linen and hemp are simply too heavy for their strength and too thick. I have flown medium deltas on these lines and it is very clear that they significantly restrict altitude because of their weight and wind drag. Linen thread on small kites has some merit but only to relatively low altitudes. All of these natural fibres are subject to UV degradation and rot from mould so need to be handled with care and stored in a clean, dark and dry place
Nylon fishing line is not strong enough weight for lb test and diameter for lb test. It is generally shunned by kite enthusiasts as a kite line because it is difficult to see, difficult to handle and is not strong enough for bigger kites. It is often used by casual kite fliers who want more length than the twisted nylon lines that come with shop bought kites. It is, however, smooth and has low drag for it's diameter. Some monofilament line types, such as fluorocarbon, have better abrasion resistance that ordinary nylon lines. There is often inconsistent labelling of line strengths and it is difficult to trust stated specifications.
Twisted nylon is too thick and too heavy.
Dacron is too thick and relatively heavy compared to Ultra High Molecular Weight Polyethylene (UHMWPE) such as Spectra and Dyneema.
Kevlar (Aramid) is very strong for its diameter but is not as strong as UHMWPE and is 40% heavier. It is also degrades relatively quickly under exposure to UV radiation and would need to be replaced after several uses, especially under the harsh conditions of outback NSW. It also weakens after relatively few bending cycles as the fibres fracture and the bonds between fibres are stressed. It loses up to 15% of its strength when saturated with water. It cuts into pullies and line guides. It is spurned by serious kite fliers as it is deemed antisocial because of its ability to sever just about any other line.
Spectra is the Honeywell version of the DSM patented fibre. It's made in the USA and several companies such as Innotex manufacture braided lines and ropes. As the manufacturing methods have evolved, higher strength and thinner fibres have been produced. This results in thinner braided lines that are also lighter. Spectra comes in 2 main types, Spectra 900 and Spectra 1,000. The latter has higher strength and less stretch.
Dyneema is virtually the same as Spectra except it is generally cheaper and more Chinese manufacturers are calling their fibre Dyneema than Spectra. The Chinese braided Dyneema lines have been more variable in quality as DSM Dyneema in Holland has not had control of production quality or the rights to use their name. This situation is improving as DSM Dyneema takes steps to protect it's patents and brand. Our line have been sourced from Innotex (Spectra), Amika, Taiwan (Dyneema) and Cousin-Trestec, France (Dyneema). Both these UHMWPE lines have a melting point of only 150 deg C and so it is very important to reduce friction heating of line guides and if possible use pullies instead of fixed guides. These lines are also very slippery with a friction coefficient in contact with steel of only 0.2. At least 16 wraps around the capstan are needed to properly grip the line and so reduce the reel storage compression
The wind drag on line is directly proportional to line diameter. However wind drag quadruples as wind speed doubles. Wind drag decreases as a proportion of line strength because as a line doubles in diameter, it's strength quadruples. Due to this fixed mathematical relationship, the ratio between a kite's lifting area and line drag improves as the kite size increases. A 100 sq ft kite may need a 150 lb line and a 200 sq ft kite a 300 lb line but the 300 lb line is only 41% thicker and hence has only 41% more drag. Wind drag decreases with altitude for the same ground wind speed. Wind drag on the line increases as the line angle increases from parallel to the ground to vertical. In other words it is at minimum when parallel to the wind and maximum when at 90 degrees to the wind.
Kite line for High Altitude
LEFT The first version of the winch was completed in 2004. Here it is being tested with 1,000 metres of 300 lb braided Dacron on a plastic spool. It was clear early on that direct winding of the line under tension to the storage reel produced tremendous crushing forces on the spool and this spool became badly deformed after 900 metres of line and would have been crushed by 2,000 metres. If the line is under 10 kg tension then 10 wraps will produce a net force of 100 kg on the reel. 100 wraps, 1000 kg of Force and so on. It can be seen how 10,000 wraps under 50 kg would crush even the strongest reels.
Dyneema® derives its enormous strength from a proprietary gel-spinning process that results in extremely long, straight polymer chains.
Van der Waals forces are mostly responsible for the strength of UHMWPE polymer chains. Van der Waals forces include attractions between atoms, molecules, and surfaces, as well as other intermolecular forces.
Dyneema® is produced in a patented gel spinning process in which the fibers are drawn, heated, elongated, and cooled. Stretching and spinning leads to molecular alignment, high crystallization, and low density. Dyneema® has extremely long molecular chains that transfer load more effectively to the polymer backbone. So it's stronger at the same weight or lighter at the same strength than alternatives.
Up to 15 times stronger than steel (weight for weight basis)
Up to 40% stronger than aramids (Kevlar, Twaron on a weight for weight basis) and 10 % thinner.
Dyneema floats on water and resistant to moisture, UV & chemicals.
Dyneema has a friction coeficient of 0.2 on steel.
An 8 weave braided Dyneema SK 78 134 Kg breaking strength line enlarged showing that each strand (weave) consists of tiny Dyneema micro fibres. These 8 bundles of micro fibres are woven by a braiding machine in the continuous lengths of line, cord and rope. The actual diameter of the line is shown on the right. Lines cords and ropes are defined by their diameter, braiding structure and use. The thinnest braided lines are about 0.15 mm thick up to 3 mm. then they become cord and finally ropes which can be up to 150 mm diameter to moor large ships. The lines I used have been:
Dacron 20, 30, 50, 80, 100, 160, 200 and 300 lb braided lines. For their strength, Dacron is about twice as thick as Dyneema 78
The actual diameter of the 300 lb (134 kg) breaking strength line not under tension (left of large image). Under a tension of over 50 kg (110 lb) the line is 0.70 - 0.75 mm thick. It has a specific gravity of 0.97 so will float on water. It is 15 times stronger than steel weight for weight. Its light weight, thinness and high strength have been very important factors in setting the world record altitude with a relatively small kite of 12.34 sq. metres. Richard Synergies record of the year 2000 used a 42 sq. metre kite to lift 2.34 mm, 3 times thicker and 3.5 times heavier Kevlar line to a 16% lower altitude. That’s a 3.5 times bigger kite flying 16% lower than our kite. Line tension on the Synergy kite did not exceed 100 lbs because he had a tension limiting mechanism. His strategy seems very flawed.
Raw Dyneema and Spectra (UHMWPE) fibres, up to 2016, have always been white when the fibres have finished the production process. Later, during the braiding process the lines can be dyed and coated with polyurethane to improve dust and UV resistance which is good even in it's uncoated form. The dye and urethane coating are usually combined before coating the line and can produce a wide range of colours for finished lines. The colours do fade with exposure to UV but the line strength is not affected much A new Dyneema fibre was created recently (2018?) by DSM Dyneema which is black and this colour is very stable according to DSM.
The black braid to the right is 12 weave I think but I have not confirmed that with DSM. You can see the 12 weave compared to the 8 weave is smoother and more even (less "ropey"). It is in fact, strength for strength, slightly smaller than the 8 weave line on the left I believe.
For instance a 200 kg, 8 weave line may be 1.1 mm but a 200 kg 12 weave line may be 1.05 mm or about 5% thinner.
There was 11,000 metres of Amika Dyneema SK78 134 kg breaking strength (300 lb) line on this reel This reel used a solid pine core of 250 mm diameter and composite timber and epoxy reinforced reel sides. The ends were capped with 5 mm aluminium. despite the apparent stength of these reels, the line must be stored under low tension. This requires a detensioning system of capstan and line laying. The line wrapped 16 times around the capstan and as the reel pulled the line off the capstan under about 1 kg tension. This was accomplished with a spring loaded adjustable slipper clutch driven from the caapstan via belts and pulleys. The line laying was provided with a guide carriage on a 15 mm threaded shaft that ran full length across the width of the reel. The line guide carriage was driven by the rotation of the shaft connected with a 12 volt wind screen wiper motor. Reversing the carriage was orinally automatic but the system failed and reversing had to be done with a manual switch. https://www.youtube.com/watch?v=IG_Y9ESbS4c 2:04
you can see the video of the record flight and clear shots of the reel and layering system.
This is how I join a hollow braid line. It retains 100% of line strength whereas knots will always weaken a line, some more than others.
DaHo splicing needles are high quality tools for joining lines. There is a limit to the differences between the diameters of the line to be joined. In my experience 30 % difference in diameter and about 50% diffeence in strength between two lines to be joined is the limit.
This is the best diagram for splicing courtesy of the DaHo site. Click on the DaHo link for more details of their products. It does take practice but once mastered it is fairly easy and very satisfying to know the joins are stronger than the lines themselves.
DaHo needles for joining hollow braids
NOT TO SCALE X 10 approx.
Kite Altitude World Record
Dyneema, Specrtra, Vectran, Kevlar, Dacron, Twaron, Monoflilament, Steel wire?