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
Flying techniques and other issues
Flying a kite really high is easy providing wind is there. Getting it back is a problem!
Flying a kite is easy, is it not? Well, one would think so, however, it is surprising how many people find it difficult to launch a kite let alone have it fly for any longer that 5 or 10 seconds. Yet there is a lot of people who have no problems what-so-ever. The problem may be confined to those people who have a poor understanding of physics, a lower Visio-spatial IQ or lack hand-eye coordination. Often people ask me:
"How do you get your kites so high"? "I can barely get my kite off the ground". Whether it's some intrinsic characteristic of the person's brain wiring, some innate inherited talent for the way things work and an understanding of how our world is put together, I am not sure. Perhaps it's just learning. Perhaps it's the same reason some people are mechanics or rocket scientists and others are musicians. Anyhow even a few of those people who do build and fly kites for a hobby don't necessarily know how to fly big kites high but most understand immediately when I relate big kite, high flying techniques to smaller kites at normal altitudes. There are a few things that aren't normally issues flying recreational kites from hand on 300 ft of line. They are, line weight, line sag from line drag, accumulated line tension from line drag, delayed kite response, kite out of sight and need for a winch to control the line.
I could teach most kite enthusiasts the mechanics of flying kites to record altitudes but would they have the will? Could they be bothered? Do they want to? Does it "float their boat"? I don't think it's hard from a technical point of view. It just takes, dogged determination, a moderate amount of mechanical aptitude, a big kite, some wind and a bit of luck. There are enthusiasts on the kite builder's forum that show the same dogged determination as me such as Doug who built a massive Delta with small geometric applique patterns. This determination is is just applied in a different direction. His kite must have over 1km of sewing and hundreds of man hours invested. There are other people who are passionate about their hobbies. They show a similar unwavering determination. Perhaps I have an obsessive streak, I don't think I'm obsessive. I can think of lots of people who show that characteristic and far more determined and chose much more physically and mentally challenging targets. Marathon runners, mountain climbers, vintage car enthusiasts, artists. We all get the same sense of achievement, the same buzz from reaching a target, the same buzz from getting close. I don't know how I will feel after breaking the record. Is the journey more important? Is it the personal challenge? I can think of lots of people at the opposite end of the spectrum such as those who seek instant gratification and reward for little effort. There are some people like that who look at me with puzzlement and say "why on earth would you want to do that"? "What’s the point"? "what money do you get at the end"? "Is there a prize"? "Is it a competition?"
I don't bother trying to explain in much detail or rationalise and justify my activities. I just say because it pleases me and because I want to. I guess sometimes I may bore people stupid with my stories of the kite record attempts. I think if I were a hermit I would still do it and get the same pleasure from reaching the target.
The answer my friend is blowing in the wind.
A kite is a tethered flying device and, it relies on moving air for the energy to fly aloft. We take into account the position of trees and the likely direction of the line as the kite rises. it is no good assuming the line is going to remain heading in the same direction throughout the flight, it rarely does. If we don't plan the positioning of the trailer before launch we may have to move it mid-flight. That includes all the ancillary equipment, shelter, table and generator. We do have to rotate the trailer from time to time so the line exits directly between the line guides. Early last century, some weather stations used a rotating winch house which automatically faced in the direction the tether moved. I contemplated mounting the winch on a trailer mounted turret which I may do in the future for attempts at the kite train record. With more massive kites or kite trains the trailer would need to be anchored with guy ropes and large pegs but choking the wheels is enough to stop the trailer being dragged.
A general rule is you should have the wind at your back when holding the string. The only differences between flying my kite and your kite is the size of the kite and my string is attached to a winch. If that seems to be stating the obvious, you would be surprised that there are some people who don't get it and try to do odd things like flying cross wind, into the wind, kite upside down and the line tied to the tail.
If the wind is steady and well over the minimum speed required then 100 meters of line is walked out with the winch running in reverse at slow walking pace. Before that is done the line is attached to the bridle attachment point. The line has no knots as they weaken the line significantly so the line end is sleeved and loop spliced to make an enclosed loop. The bridle is a three-legged heavy set of lines that distribute the kite's pull evenly over the length of the front fibreglass tube spar. The length of the bridle legs is set with special locking slip knots at the attachment point. The bridle line is about 3 times stronger than the kite line so prussic knots attaching the kite line to the bridle doesn’t cause line breaks The length of each bridle leg determines the kites angle of attack or how much the kite's top tilts into the wind before it leaves the ground. Too little angle of attack and the kite will not rise and if it does it tends to overfly beyond vertical. Too much angle of attack and the kite becomes skittish then does not develop enough lift at higher flying angles. It's ultimate flying angle is also lower. The angle of attack is established by trial and error. The knot is marked with permanent marker and alternate positions for different winds may also be marked.
So far, the spreader for the 120 sq ft DT Delta has remained a fixed size with 15 mm FG tube and 1.3 mm wall thickness. There are heavy Dacron loops attached to the 2 rear spars at the spreader cross over point. The spreader is inserted inside these loops when assembling the kite. These loops restrict the bowing of the spreader and so increase the stiffness and power the wings develop. We seem to have discovered a very good combination of spar weight, stiffness and spreader position. The bridle dimensions also contribute to the kite's flying qualities. After the kite is positioned on the ground, upright and facing into the wind, it is ready for launch. It requires good judgement and clear signalling from the kite handlers to the winch operator. When the handlers feel sufficient wind they signal to the winch operator then thrust the kite into the air. If the wind is above the lift-off threshold then it will rise, slowly at first then faster and faster as it climbs. In marginal wind we put out longer line lengths which can be over 500 meters. We use walkie-talkies to coordinate the launch in these circumstances. It is more likely the kite will fail to stay aloft if long line launches are required, however, at least the line is being reeled in so it's not as tiring as it could be. If we encounter those conditions then we now will not try for 5 or 6 hours to "flog a dead horse" like we did in 2005. The optimum flying angle is about 60 degrees but maybe more or less depending on the air temperature (density), thermals and wind speed. I try to keep the kites as light as possible consistent with strength, stiffness and instrument load. The kite weighs 3kg bare and 3.5 kg with instruments, batteries and light. The GPS telemetry unit, batteries and Garmin GPS is in a high density foam box inserted into a poach on the lower rear of the kite. The radio and GPS aerial are oriented so the kite flying at 60 degrees will orient the aerials for the strongest GPS reception and radio telemetry signal transmission. The strobe light is a 3 LED high intensity tubular cycle light with a relatively narrow beam attached to and pointing down the flying line. The strobe is a 3 LED, super bright white light with a 10 Hz clustered strobe pattern of about 1 Hz. It is visible from 5,000 ft in 1/2 light near dusk. It is not visible in daylight from more than a few hundred meters.
Rather than functioning like an aircraft strobe, that is, to make an aircraft more visible to other airspace users 24 hour a day, the kite strobe is to help the winch operator know the position of the kite when it drops within 2000 ft of the winch and then it is critical to drive the winch when the kite is nearing the ground.
For the first few thousand feet of the flight the kite is usually clearly visible flying at a angle of between 50 and 60 degrees from horizontal. that's providing the wind is 10 knots and above and so the line can be released at 2 or 3 knots. Any lower than that then the line release needs to be slowed to between 1 & 2 knots. The alternative is to release almost as fast as the wind then stop, pause for a few minutes, regain some altitude then reverse the winch for maximum speed for 10 seconds or so. That way the kite gains more altitude than it loses and the kite climbs in zig-zag steps. In a wind of 20 knots, the line can be released at the full speed of 5 knots without loss of flying angle. However, 20 knots at ground level on an inland location usually is accompanied by gusty conditions and much greater wind speeds up high. When the kite is beyond visible range, we rely on the telemetry to provide position, altitude, climb rate and horizontal speed. We have learned to use this information like our eyes. Without it we would be pretty much lost. We don't just use the telemetry but we observe the line angle and feel the line tension. In 2012 we will have a line tensiometer which will add greatly to our record attempts.
Some interesting facts
1. During the record flight of 2014, 12,620 metres of line was indicated on the line payout meter yet 12,400 metres of line was on the reel. This indicates that the line stretched 220 metres or 1.77%.
2. The Dyneema line is made from micro fibres, braided into high strength line. Dyneema is weight for weight, 8 times stronger than steel. There is little difference between Spectra and Dyneema as these fibres are formed from very similar base chemicals and pultrusion processes. Honeywell, the owner of Spectra, was licenced by DSM Dyneema to use these manufacturing processes.
3. The line is hollow which enables it to be joined with splices using special splicing needles and wires. It can take several months of regular practice to perfect splicing of very small diameter braided lines.
4. There are no knots in the kite lines apart from a Prusic hitch attaching the flying line to the kite bridle. It is a special case and does not provide a weak point.
5. There are no knots that will give 100% of line strength despite claims to the contrary by some fishing "experts".
6. Dyneema, in its SK78 form, can support its own weight of 378 km of line of uniform diameter. Nylon fishing line can support a little over 17 km of it's own weight of uniform diameter line.
7. Dyneema has a specific gravity of 0.97 and so floats on water.
8. Dyneema has a friction coefficient of 0.17 on steel. This property required the line to be wrapped 20 tomes around the winch capstan before it would grip and enable low tension tthe storage reel to be less than 1kg or 2.2 lbs.
9. The line on the storage reel is layered in an orderly manner courtesy of a 12 volt electric windscreen motor from a 1985 XF Ford Falcon.
10. The trailer mounted winch was built from structural steel beams and hardware purchased from Bunnings.
11, In 2012, a line break occured when the kite was at 12,500 ft. The kite was recovered by Endeavour Mine workers. GPS recorded the kite speed as 57 knots or nearly 100 kph after the break. This is an exact reflection of the wind speed and is a testament to the kites strength and resilience although the kite was retired after this event due to fabric stretch.
12. Our big kites weigh 3,000 grams and 3,500 with instruments and lights. Line weighs 500g/1,000 metres or 12,200 grams for the full length at record altitude. The line drag is the biggest force restricting kite altitude. Thinnest line is crutial although line and kite weight are important factors.
13, Originally anticipated that kites would be naked eye visible to 10,000 ft bit usually are difficult to see over 6,000 ft. Telescopically it is also very hard to track a moving kite unless it is constantly viewed for the entire flight. There have been far more clouds that first thought. Avoiding flying through clouds is next to impossible.
12, Theodolite tracking for altitude measurement was abandoned after 2007 when it was realised it required more expert theodolite operators and that cloudless skies could not be ensured.
13. Small strobe lights were not visible when the kite was above 5,000 ft but were helpful in guiding the kite to landing in fading light. More recent Cree strobe lights may be visble at much higher altitudes. "Strobe" lights are a condition of CASA.
14. The Dyneema 134 kg (300 lb) breaking strength line purchased in 2005 was 0.8 mm in diameter. It is now 0.75 mm in diameter after being used on 30 high altitude flights and is equivalent to factory stretched and bedded line which is a property of the most expensive, high quality lines. The difference in line quality between genuine Dyneema/Spectra lines and cheap Chinese copies is like comparing a Mercedes AMG sports car to a Great Wall SUV.
15. Dyneema braided line is 40% lighter then Kevlar and size for size is 10% stronger. Dyneema line is far more UV resistant and after 10 years of intermittent use has retained 95% of it's strength. Kevlar line would be virtually unuseable after 3 series of attempts due to UV degradation.
16. If Kevlar 300 lb line were used on the record flight, it probably would have resulted in a 14,000 ft flight rather than a record 16,000 ft flight. This is becuae it is 40% heavier than Dyneema and slightly thicker.
2005: October the Sydney Morning Herald photographer snaps us in action. The kite is out 1,500 ft and up 400 ft. We are saw-toothing the kite up in marginal winds. We let the kite out until the kite drops almost to the trees then reel the kite in rapidy for a few seconds. The kite gains more altitude than it loses as we get as much line out as possible. Later that day we lost the kite with a line break but recovered it the next morning.
Kite flying is not an exact science however that hasn'r stopped me from trying to generate computer simulations of high altitude flying. Here is an excel spreadsheet that generates fairly good results which match actual flights. More data is needed to make the calculations more accurate.
These diagrams represent simulations of the 2 classes of altitude records, the single line, single kite record and the multiple kite or absolute record. Both require varying line strengths to reduce line drag and weight. The line lengths and strengths are only educated guesses. We reached 16,009 ft. in 2014with 12,400 ft. of line consistin of 6,000 metres of 300 lb Dyneema and 6,400 metres of 350 lb Dyneema.
Diagram of theoretical kite track. The path would be much more jagged than the illustration but the approximate path is shown and illustrates how the kites path usually describes a saw-tooth pattern in marginal winds. If the line were just released at a steady speed in these winds, than it would go to ground. The alternate release and retrieval gives energy to the system. Some kite enthusiasts ask me "why don't you just release line until the kite nears the ground then winch up?" This may work on a beach or other area without obstacles such as trees but at Cable Downs, getting line out of trees is not easy and the line can touch the ground well before the kite is below 6,000 ft. The line is released as far as possible without snagging the line. It can be a delicate operation requiring balancing the risk of kite loss, line damage and maximising altitude gain.