We aim to fly a kite to the highest altitude in the world
Designed by Robert Moore
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Kite Altitude World Record
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 3 mm aluminium reel ends. The line consists of 2 strengths joined by splicing. The inner line is 6,000 meters 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. The clutch and drive pulley is not attached to the aluminium disk on the right in this image. The wood blocks were temporary to align the reel during fabrication of permanent bearing mounts.
meters 1mm diam
100 kg test
||wind resistance per 1000 meters
per 1m/sec 100kg test
|Steel music wire
|Dyneema SK 75
Dyneema®, the world’s strongest fiber™
Structure of UHMWPE, with n greater than 100,000
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. (information courtesy of DSM Dyneema, Holland)
Dyneema® is an UHMWPE (Ultra High Molecular Weight PolyEthylene fiber. DSM invented the gelspinning manufacturing process over 25 years ago and it's been in production since 1990 with various versions improving the qualities and strength over time.. The fiber is versatile with virtually numerous applications such as ropes, cords electrical wire sheaths, reinforced composites, helmets and body armour. The fiber is manufactured by means of a gel-spinning process through water and results in a micro fibre that comines extreme strength with incredible softness. The fiber has been improved through several evolutions and refinements of processes. Temperature control is very important and quality control of processes are very critical in ensuring the finished fibre has unifirm physical dimensions and properties So what are the properties that make this fiber so special?
High strength/low weight - Dyneema® is 15 times stronger than steel, and 40% stronger than aramids on a weight-for-weight basis.
Low specific gravity (0.97) - Dyneema® floats on water and is ideal for lightweight solutions.
Excellent chemical resistance - Dyneema® is chemically inert, and independent studies have confirmed that Dyneema® performs well in dry, wet, salty and humid conditions, as well as other situations where chemicals are present.
UV resistant - Products made with Dyneema® fiber show strong resistance to photo degradation when exposed to UV light. The high UV resistance of the fiber ensures continuing high performance.
Moisture resistant - Dyneema® fiber is hydrophobic. It resists water absorption, providing an extra level of protection and durability.
High durability - Dyneema® fiber can withstand the harshest environments for a longer time. This is due to its inherent strength, and its resistance to many damaging chemical agents..
DSM Dyneema created the gelspinning process for manufacturing fibres from UHMWPE. The company continue to research new products and processes as well as improvement current products. There has been an evolution of improvements to Dyneema fibre including Dyneema® 65, Dyneema® 75 and most recently, Dyneema® SB71. Quality control at it's plants is a very high priority and DSM Dyneema protects the integrity of the Dyneema name closely to prevent illicit manufacture from eroding it's reputation and rights and to protect it's intellectual property.
DSM Dyneema has licenced several companies including Honeywell in the USA and Toyobo in Japan. Honeywell produces Spectra which has comparable properties to Dyneema.
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.
The wooden sided reels have been replaced with solid core and aluminium sides. Shafts are welded and keyed running on self aligning bearings. The original sytem was direct wind to a storage reel. The reel sides collapsed under the accumulated pressure of 4,000 meters of line. The current reels store at a 1.5 - 2lb line tension. The line guide can be seen mounted on a carrier (left) and this is carried back and forth across the face of the strorage reel by a threaded shaft. The shaft is driven by a 12 volt DC motor with reverse controlled manually the winch operator
The properties of these materials have been calculated from the following sources.
Early in my record program it became clear to me that line drag and line weight were among the top factors, if not the most important, to consider when trying to break kite altitude records. An unnecessarily heavy and thick line will drag the power out of the kite, lowering the flying angle and limit the ultimate altitude reached. The main symptoms are line sag and a low flying angle.
So, how did I select an appropriate line weight? Testing of small kites, larger kites, spring balance, digital balance and wind speed meter were essential tools to find the facts. Note taking and recording my tests were crucial as it becomes far more scientific and less an exercise in guesswork. it is difficult to separate variations in wind speed from other factors that influence kite performance.
I came to a general conclusion that, while it was essential to use the thinnest line, it would be far worse to lose big kites due to line breaks. In testing I lost 4 small kites 3 medium kites and 1 large kite. It is necessary to fail to establish the limits. Better to lose kites at lower altitudes on short line lengths were recovery is possible. The first line I used was monofilament fishing line. These lines were useful in developing kite designs, training in kite flying and testing of GPS devices. The limitation of readily available fishing line was 60 lbs. I hadn't come across Dyneema®®, Spectra® or Kevlar® and when I did, I realised that monofilament would not meet requirements as it was just too thick for it's strength compared to these super high strength lines. I rejected natural fibres such as hemp, linen and sisal at the start because even a quick glance at the specs for these lines eliminated them from consideration. I even purchased 4,000 meters of plastic bailing twine.
For each kite there is a maximum altitude attainable in a given wind strength with a particular line. This is when kite lift equals the combined drag of kite and line. It is a dynamic condition with wind strength playing a vital role in the equation. With 2 identical kites flying side by side but one having 100 meters of 200 lb Dacron® and the other having 100 meters of 50 lb Dacron®. The difference may be 50 feet in altitude with the kite on the lighter, thinner line noticeably higher. This is not rocket science, it's a logic that most people can understand. So, the rule is, for high altitude flight, use the lightest, thinnest line available consistent with not breaking the line under the kite's maximum pull generated in the winds of the day. Selecting and building a kite of the right design and size has proved relatively easy because I had spent hundreds of hours thinking, researching and testing kites. 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 have needed to replace line sets or replace worn sections. Fortunately, I have assistance from Dutch company DSM Dyneema® and Cousin-Trestec of France but even then, I needed to purchase replacement lines from Taiwan and China. All the lines have 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 handled 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 was 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. The Amika Dyneema® and Cousin-Trestec line combination was excellent with the Amika line looking almost brand new after 9 years of intermittent use and storage. This is the first-time use for the Cousin-Trestec 350 lb line but it is 4 years old.
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. It is 8 times heavier than synthetic lines which was a major factor limiting single kite altitudes in the period 1890 - 1930.
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 in relation to diameter and weight although it is smooth with slightly lower drag than braided lines of the same diameter but much larger diameters are required compared to UHMWPE or Aramid lines. This more than outweighs any advantage in wind drag. 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 cheap. 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. Fishing line manufacturers have a reputation for overstating line breaking strength irrespective of line type and many fishing forums are devoted to the subject of line breaking strength. It is for this reason I avoid sourcing lines from fishing wholesalers and especially ebay where cheap imitations from South East Asia (mainly China) proliferate.
Twisted nylon or Dacron is too thick and too heavy although it is the main small diameter line supplied with small recreational kites.
Dacron is too thick and relatively heavy for high altitude flight compared to Ultra High Molecular Weight Polyethylene (UHMWPE) such as Spectra and Dyneema®. However, it is the line of choice for kite enthusiast flying all but the largest recreational single line kites
Kevlar® (Aramid) is very strong for its diameter but is not as strong as UHMWPE for the same diameter and is 40% heavier. It is also degrades relatively quickly under exposure to UV radiation and would need to be replaced after several uses in of high altitude flying, 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. there are coated versions available but they suffer a small weight and diameter penalty, enough to rule the lines out for serious high altitude flying IMO.
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. More Chinese manufacturers are calling their fibre Dyneema® than Spectra and this brings the average price of Dyneema down. This doesn't factor in that generally Chinese braided lines are of variable quality and dubious specifications IMO. The Chinese braided Dyneema® lines have been more variable in quality because 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 its patents and brand. Our lines 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 tension to less than 3% of the high-tension line. These line properties, while creating particular handling problems, are a blessing when the kite goes down in thick scrub. The line can be winched back easily despite being dragged through 1,000's of branches over km of tree tops. Dyneema® and Spectra are not generally used for single line recreational flying but are the lines of choice for dual and quad control line kites. They are used for big display kites as sheathed cords and ropes where tensions exceed several hundred pounds and up to 1,000 lbs and more.
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.
There is a physical limit to all things structural and mechanical. The guidelines and observations I have made are subject to the rules of material science and their application to rules of scale. A steel bridge cannot be made to atomic dimensions nor can it be made to span the Pacific Ocean with a centrally unsupported arch. A fibreglass kite spar cannot be made that will construct a 1,000-square metre delta kite and retain the stiffness required. However, it is possible to make a 1,000 sq. metre parafoil but it will need 100's of bridle lines. There is a physical and practical limit to the size of sparred high-altitude kites.
Line which is as slippery and thin as Dyneema, is almost impossible to handle with bare hands and even with a gloved hand, tensions more than a few kilograms are difficult to manage. Throw in very long line lengths and high tensions and and some mechanical means of controlling line release and retrieval are essential. The winch with a capstan and storage reel is the machine for the job. In it's simplest form the winch or windlass is just a reel with a shaft and winding knob on its side. This is represented by the side cast fishing reel and the garden hose reel. Long line lengths, if wound in directly to a storage reel, accumulate tremendous compression on the reel centre. This may result in implosion of the reel and breakage of the reel sides. I discovered that after I building my first big reel (see below left). I also used many large electrician's reels in my first 18 months of exploratory flights over 1,000 ft. I soon tired of hand winding
Designing and building a winch is not difficult for a person with a modicum of mechanical knowledge, the ability to draw simple designs and use basic tools such as a hammer, drill, screw drivers and a set of spanners. I was fortunate in that I studied mechanical engineering and engineering drafting although I never completed my degree. The design brief was to build a robust machine that could stand up to the rigors of outdoor use, be transport on a trailer and was affordable with a small budget. Fortunately, I could see many good commercial fishing, industrial and mining winches on the Internet so I just need to transfer the principles of these designs and scale them down to a version that could control 15 km of line at tensions of up to 200 lbs. Subsequent record attempts with the line tension gauge have shown the maximum tension to be 130 lbs with the 12 sq metre DT deltas we have used for record attempts over the last 10 years. The motor and pulley design needed to provide enough startup torque to counter maximum line pull and enough line speed to just keep a kite aloft in calm conditions but the kite would drop in hot calm conditions despite running the winch motor at maximum