It was the next year before things started to progress. I met some fliers in Windsor Great Park, who told me about a kite store (With Flying Colours in Frimley Green), so that I knew where to spend my money. There was also an announcement on the front page of the local paper about the formation of a kite group in Basingstoke, so I phone up and asked if I could join without actualy having a kite yet - they were most welcoming. Soon this fool and his money were parted and I was the proud owner of a yellow and blue 10' Flexifoil, complete with a set of 300lb lines (a little heavier than I needed, but I was already thinking about stacking them).
Having spent such a huge sum of money on my new toy, I went out to Windsor to try it out. It was a low-wind day and the grass was long and damp. I spent a frustrating afternoon trying to launch the thing, only to find that when it did get airbourne, it flew straight to the edge of the window and promptly fell out of the sky.
Soon I had the hang of it, and I went back to buy more power. I stacked two 10's, then three, and before long, I had a stack of six of the kites.
As the stack grew, I started running into problems with line. The stack-lines were prone to wear - the tension in the line would cause the metal o-rings to cut through the stack line. I was also scared of breaking my flying lines, so on the basis that 300lb was OK for 2 10's, I bought some very expensive 800lb lines for the big stack. All these heavy lines slowed the kite down and took away the performance that I was after.
Eventualy it dawned on me that *I* simply wasn't pulling hard enough to break the 800lb lines and I swapped back for lighter lines. I also learned that I could make the stack lines much lighter by taking the strain on one pair of main stack lines, and attatching little loops for each individual kite, so that I didn't have the strain of then entire stack trying to cut the lines on the metal O-rings.
It was at about this time that I joined rec.kites on Usenet news. My very first posting was something along the lines of "I'm flying a stack of 6 10' flexifoils, does anyone have any advice or hints for me?". There was no reply. Suspecting a problem with my newsreader, I tried again. This elicited a response from Jeff Burka: "Sure, we heard you the first time, we just didn't think you were *serious*". I sat down and wrote an article about what I had learned so far and thus began my involvement with the community behind the newsgroup.
It has always been a little tricky to launch Flexifoils, so I worked on ways to improve it. Two schemes proved most effective:
During the summer of 1993, I went to the first Portsmouth kite festival and met Peter Lynn. On the first day, I didn't say much to him, but I listened intently. I went home with my head buzzing from his ideas, and worked late into the night writing notes. What happened if you try this? Have you considered that? I talked to him the next day and found him very approachable. He had considered everything I had thought of and would happily detail the incorrect assumptions in my thinking.
The following year, I bought a 5m Peel. It was Nylon and had a Polyester bridle, but it was a good flier. One of the things that they noticed was that they could take 20 Peels straight out of the factory and give them to a bunch of racers and find that as they swapped kites around, it was always the same kite that won. In this way, Peter selected the kites that *he* would race with. My kite was such a kite, but on the first day that he went to use it himself, he was at a festival at an airport in Germany. He jumped into the buggy and found the kite in a power dive. Unable to pull out, he was in difficulty because of the crowd - if he were to let go, his handles would likely hit someone. The kite powered onto the wet tarmac and exploded. Afterwards, he patched it up and sold it to me.
The Peel quickly became my favorite kite. I grew impatient with the stack of Flexies, because it took so much time to assemble and tape the spars and to set up the stack lines. The Peel could just be pulled from the stuff-bag and thrown in the air.
Shortly, I got myself a wire-spoked Lynn buggy and began to find out what traction kiteing was really all about. I quickly learned that the Peel was much more *useful* on the buggy than the flexifoils, because it had much more power at the edge and was less likely to send you on a ballistic trajectory if you put it through the middle of the window.
I took the 15m kite down to the AYRS speed week in Weymouth and did some body-surfing there. With just short lines, I was able to speed across the harbour, using only my lower legs as a plaining hull. I felt sure that I would be able to progress upwind if only I had some kind of fins on my feet.
In January 1994, Corey Jensen and Scott Dyer organised (?) the first Buggy Boogie Thang, to be held at lake Ivanpah, just after the KTA. It looked like it would be a massive event, and I wanted to do this too.
New Zealand airlines held the answer. They did a flight to NZ, that stopped in Los Angeles. I could fit both Peter Lynn and the Buggy Boogie Thang into one trip, so I booked a months holiday and went off.
The Buggy Boogie Thang was a massive success. It was, without question, the kite buggying equivalent of Woodstock.
The three weeks I spent in Ashburton were an apprenticeship. Peter told me that my fin idea wouldn't work (I'm still not entirely convinced), but I learned a lot more than I was expecting. I had the use of a sewing machine in the factory, together with their knives, templates and jigs, so I built myself an Icarex 10m Peel. I was astounded to see it fly perfectly first time (althought there were a few bridle bugs I had to fix before I even took it outside), so I built another one - this time a 7m, and this again flew fine.
There was a lot that I picked up just by being with the crew in Ashburton. I learned how hard they work and I learned how self-reliant they are. It actualy feels a kind of unfriendly and unhelpful place, because everyone expects you to be capable of doing things on your own. In Ashburton, I began to learn just how much I *can* do, just by myself.
On evening, Peter showed me a boat he was sketching. It was rather odd. It had 4 plaining hulls. 2 main ones, fore and aft, and two outriggrers. The outriggers made the boat wider than it was long. The next day, we started building it. The outriggers were hulls from the standard Lynn kitesailer. The main hulls were similar, but larger - all stuff that was lying around in the grass. To join the two hulls, we took some aluminium tubes and joined them in a shallow, up-turned 'V'. The tubes wern't man enough for the job, so we laid them up with fibreglass to make them stronger. To reach the outriggers, we scratch-built a spaceframe from reject windsurf masts and assorted fibreglass tube found in the yard. Peter had a mast that could be put to use, but it had been bent in a previous adventure, so we had to start by cutting out the kink joining the good bits together. For the sail, Peter had a second-hand one from a Tornado going spare, but he wasn't happy with it. He wanted it shorter and fatter. He simply cut 4' off the bottom, then added a slice 2' wide at the bottom, tapering off to nothing at the top, as he glued, sewed and re-battoned the sail. We built the rigging from scratch, laced up a trampolene and built joints so that the thing could be disassembled and transported by road. Whilst I learned a little about building boats, what I really learned about was Peter's design and build process. It was mostly through his hard work, determination, design, use of available materials and inginuity that this boat took only 5 days from initial design sketch to maiden voyage.
This wasn't the only boat that we built. Later, during my stay, he took a buggy and lashed together some fibreglass skis. I was witness to the very first Lynn surf-boat. This boat was built and sailed on the same day. He learned from from it, and had another prototype built with different construction techniques and ski shapes in time for sailing the very next day.
Also during my stay, I saw Peter design and build the modern Lynn down-tube clamp, replacing the fiddly 2 studs and 4 nuts of the old system, with a single, simpler, more adjustable, stronger single nut and bolted clamp.
Whilst I learned a good deal in Ashburton about specific issues to do with kite design and boat design, the real lesson was in how to design, that it is possible to just look at a problem, pick up the tools and materials that you have available, and build something to fit the problem, all the time looking criticaly at your results and modifying your work in the light of the experience.
When I left New Zealand, I took home 2 Icarex Peels that I had built in the workshop, a 7m in Orange and a 10m in pink. I also took home a new fat-wheel buggy to replace the the thin-wheel one that I had lost in Ivanpah (Peter had sold my buggy and owed me a replacement!). I also took home a buggy-boat conversion kit and 9(!) tentacles from a midi-octopus which I had started but not completed.
One incident was when winding round the paths, quite gently, with a 10m Peel. I was following the path slightly down-wind and downhill, going carefuly, with the kite stalled in the sky above me. Rather than cut the corner, I decided to stick to the path before turning to the up-wind up-hill leg. The moment I turned, the large kite immediately powered up and I accellerated off the path. Until this point, I had not noticed the block of concrete about 4' square and 1' high, partialy hidden by long grass that sat just off the corner. I was so surprised that I hadn't noticed it that I failed to take any evasive action and I just powered straight into it. The buggy stopped dead and I sailed rather painlesley over the top to land on the other side. Whilst I was unhurt, the buggy was badly damaged. The down-tube was bent like it was pasta, with the wheel folded under. Surprisingly the forks were undamaged.
The lesson from this incident was that I never want to consider using foot-straps of any description. If my feet had been strapped to the pegs, I would have left my feet behind.
Another incident was during a buggy demo. Peter's Icarex Peels usualy have a 3-colour wave design. Rather than stick with this, I had chosen the same flo-orange for both the leading and trailing panels, with a black wave in the middle. This gave the kite rotational symetry. It was this symetry which was to prove to be my undoing. I am not a competent trick buggier - I do very little of the 2-wheel, backwards and 360-spin stuff, but during the Berkeley demo, I tried a little backwards buggying. As I did a 180 spin to come out of reverse, I also turned the kite from pointing up to pointing down. When I glanced quickly up at the kite at the end of the spin, the symetry led me to simply not notice that the kite was not facing safely up, but was rather just starting a power dive. By the time that I had realised what was going on, I had left the buggy behind, and looking forwards to eating some Berkeley grass. At the banquet, they presented me with a plaque for puting my "body and soul" into my demonstration, but quietly I was promising myself that I would never again build a power kite whre I could easily mistake it's orientation. Peel
I sold off my stack of Flexifoils on rec.kites and used the money to buy Icarex P31 from Tom Marvin. I bought a roll of Flo-orange and some Black.
I read "Stunt Kites 2" the book, but built the design using "Stunt Kites 1.0", the accompanying disk. One of the basic design problems is that the kite has a chord which is considerably wider than the regulation 40" of Icarex fabric. Nop incorporates a diagonal stripe into his design, which serves to make the fabric wider. Unfortunately, this gives the kite rotational symetry, so with the slipup at Berkeley still in my mind, I modified the idea, treating the two halves individualy, to form not a diagonal stripe, but rather a "Chevron" graphic.
The canopy of the first kite was about 8m^2, based strictly on Nop's Sputnik 4, with 36 cells, but with a cross-bridle rather than the original Catenary-arch design. Because I knew that I would want to sell the kite I asked both Nop and Peter Lynn how they felt about me selling a kite based on their ideas. Both were encouraging, so I set about building.
There is an important subject which should be broached here. Is it OK to copy someone else's design? The answer to this question is so obvious that most people seem to miss it. ASK them! Most designers and builders are unconcerned by private individuals copying kites, provided that permission is obtained. The real threat to the designer is when a commercial company with financial backing starts flooding the market with rip-off kites. If the rip-off guys can point to lots of other individal rip-offs that the designer hasn't pursued, the the designer's case will start to crumble. If the individual copies are authorised (even at no charge), then no damage has been done.
The canopy and primary bridle on this, the very first Chevron was taken straight from the design disk. For the cross-bridle, I tried to take the dimensions from my 5m Peel and scale them up.
The plan for the 8m was that I would be able to fly it at Fano '95, but it took me rather a while to build, and it was on this first Chevron that I also started the tradition of bridling in unlikley places. I rigged the cross-bridle at home, then took a piece of wood, banged some nails in to take the loops, and wrapped the lines round, neatly. The cross-bridle was attatched to the primary bridle in the back of a minibus somewhere between England and Denmark.
When I flew the kite on the island, it was clear that the bridle was not really large enough. It made the canopy too curved, and the tips were inclined to curl under. I was busy investigating the kite when *bang* the entire kite came departed from the end of the line and floated down the beach. I learned that when tying bridle-knots in Spectra, it is important to use a stopper-knot. The strain on one knot joining the cross-bridle to the primary bridle had caused the knot to slip. As soon as this knot had slipped, the strain was transferred to the adjacent knots and they also slipped. Rapidly, the entire bridle unzipped across the primary bridle/cross bridle interface. The effect was so rapid that the entire bridle had undone in less than half a second.
I did consider untangling the cross-bridle and rebuilding it, but I wanted to fly, not fiddle, so I built a larger jig by banging a row of nails along the top of a fence and into parts of the wooden patio furnature and built a larger cross-bridle. In error, I used 80lb Spectra rather than the 150lb line that I had intended, but by the time I had noticed, I was attatching the primaries, so I just let it pass, figuring that it would last for a while, and that it would be worth it to learn when it would breeak.
This second cross bridle was better, but it still wasn't right. However, despite a determined effort, I was unable to break it, so I had to take it apart by hand in order to try again with a third even larger configuration.
By the third cross-bridle, I was beginning to get somwhere, and I used the kite in this format for the rest of my stay in Denmark. Having sold both of my Peels in order to buy fabric (by the roll), this 8m kite was the only thing that I had to buggy with, so regardless of how windy it was, I'd use it. One morning we got out to find so much wind that most of the fliers had stayed indoors. Nonetheless, I wanted to buggy with my 8m.
I had, by this time equipped myself with a buggy which was designed for coping with extra-strong winds. The buggy is a tandem, consisting of a front buggy which I bought from Chris Lamb, and the Buggy which I brought back from New Zealand, but which I mangled at Berkley. I had replacd the broken down-tube with a Steve Shapson tandem attatchment, which is a simple bar and foot-rest that attatches in place of the down-tube - a strong arrangement which neatly replacd my broken tube. On the front buggy, I have two sets positions for the foot-pegs - one pair of fittings is right at the top of the fork, so that I can take considerably more power before being forced out of the buggy, because so much more of my weight is below the pegs that I'm pushing against. My buggy is also fitted with "buggy-hooks". These are not unlike windsurf hooks fitted to both the siderails on the seat. I hook the strap of my dead-man handle under them, so that I can transfer the power of the kite directly to the buggy, without any danger of it pulling me out.
It was using this setup that I set off on that windy beach. I took Andy Hawkens in the back of the buggy as "ballast". Very gingerly, we would trundle up and down the beach, endevering to go as *slowly* as possible, soas to retain control. The guys in the shelter of the van were dissapointed and egged us to go faster. I dipped the kite just slightly in from the edge of the window, and the buggy responded and took us at a more respectable pace down the beach towards the sea. At the shorline, I tried to turn gently, but alas, we gave the kite a bit of a pump, and suddenly the canopy powered up. The next thing I knew was that I was looking down towards the ground thinking "It's further down there than the length of the tandem". We had managed to get the entire shebang completely clear of the ground. Instinctively, I held on until we hit the sand again, but when I released the grip on the dead-man only to find that there had been so much tension in the line that I hit my face with my own hand hard enough to cut my nose with my thumb.
The kite was undamaged, so from this adventure, we concluded that an 80lb cross-bridle was sufficiently strong for any reasonable use.
John Gabby was brave enough to be my first customer and to buy this kite, sight unseen.
I took advanage of the fact that I had a large, temporarily uncarpeted floorspace at home and built a monster - 7m span, 2m chord, giving an area of around 13m^2 (when you take off the corners of the typical Sputnik 4 planform).
To get the better low-end performance (which was particularly important because this a kite this size was unlikely to see too much of the higher windspeeds), I made the ribs fatter. I also used 24 cells rather than 24 of Nop's original design for increased profile thickness and reduced weight. I increased the depth of the gauze to help with inflation problems.
The aim for this kite was to fly it at the Buggy Boogie Thang II at El Mirage dry lake. True to form, It wasn't quite ready in time, so I took a handful of nails with me, banged them into the lakebed, and built the crossbridle in the middle of the camp.
The maiden flight, in front of the assembled rabble was rather dissapointing - it launched, folded up and collapsed in a heap. It took rather a while to work out the problem, but it turned out that I had managed to fit the shorter, tip bridles all to the same side of the kite, rather than half to on side and half to the other(!)
I think it was the next day before I had sorted out the mess, but eventualy, it flew properly. It's first successful flight was ideal. I launched it early in the morning, when the air was too still for anyone to fly anything, and found it a willing partner. Soon, I had a buggy and the lakebed to myself. By the time I had crossed the lake and back again, the wind had come up from "zilch" to "sod all" and I was ready to try a tandem. I grabbed young XXX name ??? XXX and sped out across the lakebed. When I returned, the wind had picked up to the point where some others were beginning to launch kites and dig out buggies, so I had all the power I could ask for. Determined to make the most of it, I dumped the canopy into the middle of the power and screamed past the camp at high speed, without a hope of stopping before the shore, so I dumped the kite while I still had a chance and found that the buggy easily had the momentum for us to coast down to where the kite landed and still have to put our feet out as brakes.
Also making a debut at El Mirage was the 7.1m Chevron. In a fit of optimism, I made three of these, only one of which was finished at El Mirage (mostly in Dan Rubesh's motel room and in the back of John Gabby's truck). The 7 also had the fatter profile and the deeper gauze, but although they flew first time, they didn't fly particularly well. They didn't really pull as hard as they should and they tended to banana a little. The first kite went to Steve Bateman at El Mirage, then one to XXX name ??? XXX in Australia, and the third to Matthew Hurrell. Steve worked on the bridle himself, and for some reason that escapes me, he replaced the crossbridle with a Catenary bridle, but is happy with it. Six months later, at Washington Tyne & Wear, I met up with Matthew and spent some time applying some of the lessons that I had learned over the intervening months and completely transformed the kite, making it faster, more powerful and more manoevrable too. Both he and I was astonished at the difference. I'd dearly like to to the same work on Steve's kite, the one in Australia and the John Gabby's 8m.
I wanted the highest aspect ratio, but I wanted a kite that was less prone to banana-ing, so I switched from a plan that was mostly rectangular to one which is more diamond-shaped, giving a structuraly strong centre-section, to resist the banana forces, yet small tips to reduce the tip-drag problem.
I looked at the way that I had learned to tune the Sputnik profile - to take the nose down, and the rear down, but leaving the centre much the same - effectively, I was flatening the curve of the bottom, and I adjusted the shape of the profile so as to give a shape closer to this in the first place. I simply got the Plot program to make me different thicknesses of profile and I mixed and matched them till I got a shape that looked about right.
Looking again at the profiles, I decided that I wanted different profiles across the span of the kite. Not only different sizes, to suit the changing chord, but different shapes too. In the middle, I wanted a fatter profile to give more grunt at the bottom end of the wind range, in particular to help smooth in the power as the kite started flying. I wanted to work more on reducing the tip drag by using a narrow profile which was not only small, but was also thin, producing less lift and was thus less likely to contribute less to the tip vortexes.
Again I used a wider gauze, to ensure rapid inflation, but having learned a lesson from the 13, I placed the attatchhment points further down, so that they did not emerge through the easily damaged gauze.
Because the tips tapred nearly to the middle, I changed the graphic design making the chevron run along the leading edge, with the field colour towards the rear. Aside from fitting the graphic to the new shape, this had some extra side effects. Firstly, it reduced the skin from a 6 panel construction to 4 panels, a small saving in labour. It also made effective use of fabric - the rear section was triangles, which fitted neatly into the width of the fabric, and the stripe on the 5m was designed to use exactly half of the width of the roll. The way that the fabric was cut meant that the grain followed the angle of the leading edge, rather than the angle of the rib. This is an important structural consideration. The place on the kite which is most likely to burst is the hem-line along the top of the rib. The very place where you punch a line of perforations with the sewing machine... If the grain is aligned with the rib, then it is the same threads in the fabric which are repeatedly broken. With a small angle, the strain is distributed through many threads, and the fabric is much less inclined to "tear down the dotted line".
So, everything changed. The plan, the profile, the rib spaceing, the fabric orientation, the rib thicknesses. I built a 5m kite, with a black Chevron on a white field.
It took a little tuning to get it right. To start with, it didn't have enough power and is was inclined to overfly. The overflying turned out to be an important lesson. This kite was capable of overflying in the *middle* of the window. Sound odd? let me explain...
If you take a simple aerofoil, such as one with a rib like a slice off a circle, it will produce lift fine, but the pressure of the air on the front slope of the nose tends to push the nose under. On an aeroplane, this is counteracted by using a tailplane, stuck out the back on a big stick, which counteracts this turning moment. The Wright brothers had the even better idea of puting the surface out the front, so that everything is lifting, rather than have surfaces pushing down. Unfortunatly, we don't have the facility to hang sticks out the front or the back of soft kites. It was, however at this point that I properly understood why Peter Lynn put a kick-tail on the trailing edge of his Peels - *this* is precisely what he was struggling with.
The problem of the nose folding under is much to do with the angle of attack of the kite. If the angle is too shallow, the nose folds under and you are lost. As the kite builds up apparent windspeed through the window, then the *apparent* angle of attack becomes less. From this (particularly if aided by other things such as angle-of attack changes due to steering input or the pilot being jerked about the field), you could reach the point at which the kite would nose-under, anywhere in the window.
This problem didn't always effect the entire wing. If you did a down-turn, you could stall the outer-half of the wing. This was particularly embarassing, because the kite would continue to fly - you just couldn't steer it, and it would simply pile nose-on into the ground.
Initially, it seemed like the kite might be a dog, but I perserveered and tried different tuning setups on it. Slowly, it began to come together and I became happy with it.
I had a chat with Mike Smith, our local vendor of buggy safety equipment and complete buggy-loonie, and borrowed a 5m Icarex Peel from him, so that I could do some side-by-side comparison, to judge how far short of the master I was trailing. I was delighted with the result. L/D seemed to be the same, if not better, steering response seemed to be better, luff resistance seemed to be significantly better. The only thing where I may have been a little below the Peel was in overall pull, but that's easy to solve - you just make a bigger kite! A small price to pay for such gains.
A few weeks later, I had the chance to meet Peter at Berk sur mere, just south of Calais. It was a perfect day for buggying - a decent, smooth on-shore breeze, and the kite was flying the best that that it had ever done. I gave the kite to Peter and he went off for a buzz on it, testing it to the full. I maintain that the first thing he said on returning was "Bloody hell, that's good", but he denies this and I may have miss-heard in the wind. He reported that he had done all sorts of silly things with it, but it had completely failed to put a foot wrong. You can luff it as hard as you like, and it just hangs around, waiting for the wind to come back.
I was delighted - all the gambles had paid off at once. The thin, small tips had helped the L/D, The fat middle had given it the grunt I wanted, together with the structural integrity to hold everything together solidly, and somehow, I had managed to tune the thing so that it would just float through a luff asif it didn't care.
This last point has become a bit of a party trick. You must be careful with a Peel not to let it overfly. With the 5m Chevron, in any half-decent breeze, you could fly it right up to the top of the window with your hands above your head, then heave the line right down to the ground. The kite would be forced right out of the window, where it would simply stall and hang around till it floated back into the window. No collapse. No fuss.
Having calculated the coordinates, the program could output them in whatever manner I chose. Andy Hawken gave me a little program that was loosely based on the PLOT.EXE that comes in "Stunt Kites 1.0", except that it understood that I had a continuous feed printer - rather than plotting A4 sheets, it could plot strips of indefinate length. This means that you only need to stick sheets together to plot the fattest of rib profiles, and means that plotting the entire skin becomes reasonable.
I did this - I plotted *everything*. To cut the fabric, I would lay the plan on a board and smooth it down. The Icarex lies flat and the static cling from smoothing it is enough to hold it firm enough for tracing the outline with a hot knife. The hot knife in turn lightly welds the fabric to the plan, holding it firm enough for marking.
The action of tracing the plan means that the technique simply doesn't work on black. Looking at the fabrics I have here at the moment, the darkest is purple, yet if you lay it on a newspaper, you can read through it easily. It would appear that all the colours are manufactured by taking white cloth and dying it. The black on the other hand would appear to be constructed from black thread, dyed black, and is completely opaque. You can't see through it to cut. You can't see through it when sewing. I vowed never to use the stuff again.
I put a posting on rec.kites saying that I wanted to swap it for something else. I got a reply from Martin Thomas, who was working with Tim Benson on kites like the aclaimed Box of Tricks. Each of their kites has a black and white graphic, and he said that he was having difficulty in sourcing both black and white. I sent him 50m of black and 50m of white in exchange for 100m of any of their other colors. It never arrived. I'd like to give Martin Thomas a swift kick in the bollocks, but he appears to have vanished from the face of the planet, and there is quite a queue of others in front of me...
I didn't only use the computer for plotting the skin and ribs. I also used it to plot a jig for the primary bridle. The primary bridle consists of 52 lines with an average length of around 1m, each set of 4 lines being slightly different in length from the previous set. The jig is basically a zig-zag line, where every line is the length of a bridle line. Fortunately, the geometry of the bridle is such that the plan doesn't "wander" - in fact, the maximum length of the jig is the same as the length of the longest bridle line.
I actually use slightly more than just the line length - at each corner, there is a mark for end of the measured length, then an additional 5cm, to allow for later adjustment, and to ensure that I don't have to tie a knot on the *end* of the line. The computer plots out the bridle jig on continuous listing paper, then I simply bang nails in at each point on the zig-zag and wind the Spectra round each nail in turn. I use plaited pins rather than regular nails, because they are smoother and less likely to snag the Spectra.
When the Spectra has been woven round all the pins, it needs to be marked. I do this with a magic marker. Although the mark is more than 5mm wide, it is still fairly well defined and the marks can be aligned within 1mm or so. I mark the position to be cut, the position of the knots and the position where end of the loop will be.
The primary bridles are built in pairs like this:
__________ / ------------_______ ( RIB ---------\ \______________________________________/ \ | / / A B C D \ | / / \ | / / \ | // & &Where A & B is made from a single line and C & D is another single line.
The A-B line would be marked thus:
It is important that the lines are marked with a magic marker. Spectra is very soft, so much so that the ink from the marker makes the line noteably stiffer when it dries. When tying the fig-8 knots, the mark is placed in the middle of the knot. As the knot is tightened, the stiffness makes it easy to keep the mark exactly in the middle. It takes a little practice to get the hand of this, but with approaching 100 fig-8 knots to tie on a regular bridle (and double the figure on a reefing bridle), you will soon be tieing knots quickly and within very tight tollerances.
One of the problems with building kites at home is that it tends to get in the way of other things that have to happen. Building cross-bridles is particularly antisocial. The jig looks something like this:
a b c d e f g h i j k l m 1 2Where a-m is of the order of 3 meters and b-1 is about 1.5 meters and a cats-cradle is woven a-1-b-2-c-1-d-2-e-1-f-2-g-1-h-2-i-1-j-2-k-1-l-2-m Each point is occupied by a nail banged into a piece of wood, and the danger of a bare foot finding one is consideable.
After much headscratching, I modified my program to plot a compressed cross-bridle, by allowing points 1 and 2 to migrate as required. This was a leap in the dark - I had no idea whether it would work or not, but I was delighted to eventually plot a cross-bridle which looks like this:
XXXX thin cross bridle!
The width is the same as my printer - 13 inches, and the length is the same as the longest bridle line, around 3m.
We agreed on a delivery date - the Scheveningen festival 1996. True to form, I wasn't quite ready in time. We built the cross-bridle the night before, and wrapped it round some wood as had been done for Fano. I had designed the kite with a three-stage bridle - a set off connecter lines ran between the primary and cross bridle to increase the effective length of the primary bridle. This portion of the bridle was actualy cut and marked while passing through the channel tunnel. When we got to Scheveningen beach the next morning (anyone that tells you that it's not for from Callais to Scheveningen is lying!), we found some shelter behind a beach hut and connected the two parts of the bridle together.
The kite flew first time, but was severely underpowered. This was fortunate, because there was severely too much wind. We had fun buggying up and down the beach with 10m^2 when ordinarily 5m^2 would be too much. In a moment of weakness, I was persuaded to switch the 10m^2 for a 3.5m Sputnik and within a matter of seconds I was airbourne and looking forward to a bumpy landing some distance away...
I took Matthew's 10 back with me to do some tuning work on it in some sensible wind, but there was an important lesson here - I now knew that I could de-power kites much more than I had expected.
Looking back, Matthew's kite has been a bit of a pain. I've re-tuned that kite more often than I can remember, but I'm still not happy with it. *sigh*
I wanted to tackle this issue nonetheless. The idea came fom Dave Culp. If you fit a zip down the trailing edge, you can fill the kite with bladders - one per cell - and pre-inflate the kite. The bladders only need enough pressure to lightly inflate the cell - the kite still has a vent at the stagnation point, so it can still inflate here to push the bladder back, inclreasing the pressure in the bladder to the maximum pressure at the vent as usual.
Bladders would also open up the possibility of Helium (or Hydrogen!?) inflation. I don't conside the use of low density gasses as "cheating". The 13m^2 Chevron weighs about 1.5kg, but is inflated with around 6kg of air. I simply wish to remove some of the mass from my heaviest structural component. The mass issue is not so much about whether or not the kite can fly (with a wing loading of 1.2Kg/m^2, they'll fly in nothing), but rather about momentum and inertia issues - 7.5 kg of kite is not inclined to get going or to stop in a hurry.
Fist step towards this was to look at the issue of the zip. I wanted a zip to stretch right acoss the trailing edge. This is over 5m on a 5m^2 kite to over 7m on a 10m^2 or 13m^2. My local dress shop wasn't much help - they could only stretch to 5m, you I called up YKK. They wouldn't deal with me direct, but they pointed me to a distributor who sold me a 200m long dress zip and a box of sliders.
Attatching the zip is a matter of careful alignment and blind faith. You mark both sides of the zip at a suitable starting point, and fix one side of the zip to the kite. Then you align the other half and attatch that. Then you fiddle with the slider to ease it onto the zip (a difficult job without the correct tool). You can't see whether you alignment is good until the entire zip is finished and closed. I don't have the tools to properly terminate the zip, but this doesn't matter - I don't need to take the zip completely apart, so I just run the flat of the blade of the hot-knife over a few teeth at the ends, and thus weld the zip together to stop the slider from falling off. Both ends of the zip tuck right inside the kite, so there is nothing nasty to catch on things.
One unexpected thing about the zip is that it makes the trailing edge just a fraction heavier. No-one else has noticed this, but I can tell the way that it alters the balance of the kite. The fraction of extra weight in the tail made the kite even less likely to luff than usual.
The kite that I built to prove that the zip worked was an all-red 5m Chevron, which I sold to Robin Green.
The next kites to be built were 10m^2. I chose the same 7m span which had been successful on the 13m kite, but the chord went from 2m in the centre to 1m at the tips. I built two at the same time. One was built specifically fo Dave Culp. Dave is a keen kitesailer. He has put a lot of time (and money!) into working with flexifoils for kitesailing, but he's now looking at completely soft kites. Because of the extra forces that the boat is expected to put on the kite, is kite was constructed with an extra strong bridle - the 80lb primaries were switched for 150lb and I sacificed a 200lb set of flying lines in order to build the cross-bridle. The bridling of is kite was completed in the marquee at Berrow '96. Dave's kite also had the zip fitted down the trailing edge, for fitting bladders, but his was the first kite for which bladders were actualy built.
It was Dave Culp himself who sourced the film for building the bladders. The film is a 2-layer afair, which is completely transparent and weighs about 32g/m^2 (much the same as Icarex P31). The film is a laminate, and only one side is suitable for heat-sealing joints. This side is easily identified, because the film has a severe curl - a 1m^2 sheet will curl into a 1cm diameter tube if left to it's own devices. The side that can be heat-sealed is the side that it curls towards.
I bought a modeling iron, about 2"x1" and teflon coated, which would join the film quickly, when you got the hang of finding the right temperature. Dave also supplied me with valves - manufactured from much the same stuff, you could simply weld them into the seam to provide a place that you could stick a narrow tube for inflation/deflation.
The construction of the bladders took much longer than anticipated. For each one, you roll out the film, then stick it down with tape to hold it firm and stretch it out on a board. Place the valve in an appropriate place, then roll the film back over (ensuring that the right sides are facing, then tape it down again. Then you trace round an appropriate shape with the iron, lifting and laying it repeatedly (rubbing the iron just doesn't work), then tracing again with a hot knife. The size of the cells on Dave's 10m is just wrong so that the wastage is about 30% of the film. It doesn't sound like a difficult job to build them, but it just seemed to take ages...
To start with, I inflated with an air-bed foot pump, but I soon tired of that game and invested in a small compressor. Inflation is fiddly because the bladders don't want to sit right in the cell first time. They have no strength to fill the shape when they are empty and as soon as they inflate against the skin, they like to stick fast. It takes several minutes to inflate each cell, and with 30 cells, that means a matter of a couple of hours to prepare the entire kite.
Investigation into Helium reveals that in reasonable qualities, enough He to inflate the kite will cost something of the order of 25 pounds. This is rather a lot for a day's flying, but if you've gone to the trouble of going to an event for a week, and can store the kite inflated overnight, to only top-up in the morning, then it may well be reasonable.
After all this effort came the test flight. My nearest test-field is just at the end of the road, which is fortunate, because if you can't carry the kite from the pump to the field, you've got to stand in the field, pumping. Even with someone to help you, it was a struggle to manoever the thing down the road. There was little wind, but this didn't put me off - I'm happy to fly a chevron to find out which way the wind is blowing...
I gave the kite a heave to launch it, and it lept off the ground, but rather than carry on, it stopped dead and fell back to the ground. It was simply too heavy. I tried hard, and ran round the field till I was exhausted, but whilst I could maintain it for maybe a few 10's of seconds, there was no way that I could get it to stay airborne with just human effort. I retired, feeling dissapointed and with a strained back.
The problem is that the bladder more than doubles the weight of the kite. As a rule of thumb, a soft kite has three times as much fabric as the area of the wing. One for the top, one for the bottom and one for the ribs. With the bladders, there is a bladder-skin on each side of each rib, so with film weighing as much as fabric, you end up with a 7 times the area as a bare minimum and in practice even more still, because the bladder must be larger than the cell that it fills. Whilst a normal Chevron is amongst the lightest kites available at around 120g/m^2 (compare with photocopier paper at 80g/m^2), doubling the wing-loading completely destroys it.
Even with Helium, it is clear that I wouldn't be able to make the thing lighter than air, and whether or not I would find any net benefit at all is highly dependant on just how well sized the bladders are.
The answer to the first question wasn't good. Things that were obvious to me needed careful explaining and re-explaining to someone not familiar with my ways. When I build, I am forever checking in my mind that I'm putting the right parts together, this spacial understanding of how the kite assembles, and being able to keep track of it when it's inside out and upside down on the sewing machine is particularly difficult to pass on by mere explanation. All the parts of the skin are duplicated and are nearly, but not quite symetrical - without proper understanding, it's very easy to attatch something upside down.
The kite took much longer to complete than was anticipated and indeed, it's maiden flight wasn't until after Berrow. When it flew, it was apparant that there were quite a few bridles connected to entirely the wrong places, and number of bridles fell out due to poor tying. The use of 2nd quality Carrington Nylon hampered the construction because the lack of dimentional stability meant that alignment was sloppy. I would like to comment on how much the Nylon affected the flying performance, but unfortunatley, I've yet to see it flying properly.
The single skin foils have several advantages:
I built a single skin Chevron based on the 5m plan. I wanted to follow the NASA model, so I designed for no ribs. I sewed a reinforcing line into the line where the rib would normaly fit and attatched the bridle to there. I increased the number of bridle lines from 4 to 7 and bridled every rib point rather than every second rib. Nearly 200 primary bridle lines. I bought some "20lb Dyneema" (which turned out to break at around 35lb) and used over 1000' of it. I calculated the bridle-lengths to give me the same shape on the top skin as on the regular 5m Chevron.
The test proved to be dissapointing. By using 7 bridle-points per rib, I had been expecting the skin to billow in the normal manner, from leading edge to trailing edge. Instead, the kite billowed the other way - 6 hollows running from tip to tip. Sure enough, it inflated nice and quickly, but as soon as it had any forward speed at all, and the apparent wind started to shift from it's belly to it's nose, the billow on the leading edge would catch the wind and fold under.
I must revisit this kite and cut off the bridle from every second rib, to see if I can get it to billow the other way...
20m^2+ = Huge Too large to useful in regular applcations 13m^2+ = Extra Large Specialist kite for extreemly low wind 10m^2 = Large Light wind kite 7m^2 = Medium All rounder. Useful in most applications on most days. 5m^2 = Small For when the wind really starts to pick up 3m^2 = Extra small Specialist kite for extreemly high wind
I wanted to make a Medium kite... This kite was sewn in time for Berrow '96, but, true to form but the bridle wasn't finished. All the primary bridles were attatched by one end to the skin. As usual, when everyone else was drinking beer, I sat with a bridle-tool in my hand. When the bridle was built and I went down to the beach to try it out, it was a complete failure. It didn't launch. It looked like a quad with the brakes jammed on. A quick inspection of the bridle showed something to be clearly wrong - all the rear bridles were too short.
After some head-scratching, I went back to the program that drew the bridle-rig - it has supplied incorrect figures. I looked at the code for ages before stumbling on the error. The bridle lengths are calculated by trig - I calculate the co-ordinates of the position of the tow-point for the primary bridle (where the 4 primary bridles co-incide), then the coordinates of the position of the attatchment point on the skin, then calculate the distance between the two points. Unfortunately, I was setting the x-coordinate of the skin-point to zero, mapping all the bridles to a point on the nose. The y-coordinate was correct, so the bridles were all different lengths in a pattern similar to the regular pattern, so I didn't recognise the problem while building the kite.
Having understood the problem, I could now calculate how much each bridle was short by and build a set of extensions to bring the rear bridles out to their correct length. We set about cutting and tying lots of little bits of Spectra in the caravan, but it soon became aparant that this wasn't going to work - the process was prone to error.
Next, I decided to simply replace the rear half of the primary bridle, but this didn't work either - I had managed to change the overall length of the bridle at some point, so this bridle was hopeless too.
As you can imagine, I was becoming increasingly frustrated. In my head, I knew exactly what the bridle should look like, but I was repeatedly failing to calculate the right dimensions. So damn the computer, I'll do it by hand. I just sat down and worked my way through the entire bridle, setting it to something that *looked* right.
This bridle flew first time, It looked a very ragged to me in places, but everyone else was impressed... There is an important point here. As soon as the kite was launched, I could see things that would need fixing in the tuning of the primary bridle - due to the hand-eye guesswork, there were glaring inconsistancies all over the canopy, but while these were obvious to me, they were invisible to everyone else.
A noteable issue was that there was a crease on the skin between the A-line and the B-line, so I tuned this out, to make the kite look nicer. Although the skin was looking prettier, the kite was not performing as well. I ended up deliberately tuning the crease back in, ending up with a setting for the entire bridle that was considerably different to what I had done before.
When properly sorted, this tuning was hugely successful. I had stumbled across a much improved setup. The power available was considerably higher than would be expected - the kite felt more like 10m^2 than 7.7, yet the canopy was small and zippy due to the smaller 6m span and reasonable aspect ratio.
Not only was this bridling breakthrough important of it'sself, but it was important in the light of the experience in Scheveningen. A small adjustment in tuning could makde a 10m kite feel like a 5m or make a 7.7m feel like a 10m. This is just the technology that I need to build a reefing kite - the ability to switch from low-power to high-power with just a small adjustment.
Having seen the machine, I sat down with my computer and changed the plans to work with it. Not only must I now design the shape of the components, but I must decide how they are to be assembled on the fabric, for the laser to cut them.
I ended up with three plans. One was all ribs, with the ribs carefuly hand-alligned to squeeze as many on as possible. Another had the 4 light-coloured triangular panels that make up the trailing edge, together with some left-over ribs. With careful juggling, this fitted all of the light-colour components precisely into two 7.7m strips. Symetry means that the for the 4 dark panels, I made one plan that held two panels, with instructions to cut it twice.
I wanted to see the machine in action, so I arranged a day off work to do the cutting. The first thing we tried was the ribs. It was clear that something was badly wrong. The machine would do a small section of the top of the rib, a small section at the bottom, then back again. I looked at the code and realised that this was exactly the way that I drew it - since there is a relationship between the top and the bottom, I was drawing the top and bottom at the same time. Something that's easy on a computer screen, but difficult with a single mechanical laser.
I sat down on the spot, changed the program to draw one side *after* the other and gave him a new set of plans and we set about plotting and cutting them. It took around 90 minutes of very expensive machine time to plot and cut one plan.
I took the panels and went off to build the kite, but I also went back onto the computer to work on optimising the plans for the machine. I came up with an extensive list of improvements:
After making these improvements (and many others besides - I had a checklist with nearly 20 items), I returned to the lasershop with 2 rolls of fabric and an order for 8 kites-worth of cutting. With the improved plans and the a decision to cut more than one layer of ribs at a time (there is no marking on the ribs), we saw a marked improvement - the time budget for 8 kites was cut from 12 hours of machine time to 5:30 hours, which makes the difference between the cost being too much and it being worthwhile.
Even then, there were still things to work on, little ways to improve it further. I hope to get the time for eight kites under 5 hours.
The principle I wanted to use was quite simple. Build a kite with two *complete* bridles. One is tuned for maximum power, the other tuned for minimum power. The high-power bridle is connected through a bungee, but on a shorter line than the low-power bridle. When the pull is low, the bungee is short and the kite flies entirely on the high-power bridle. as the pull increases, the bungee stretches, until the canopy is stopped by the low-power bridle. Thus the performance of the kite is changed to the performance provided by the low-power bridle.
All that needs to be done is to find a suitable bungee. I use a loop, made from 1m of bungee, folded over several times. The lines attatched to the bungee are attatched by a larks-head, so it is easy to adjust the bungee from 5 loops to 4 or 6 as required. Idealy, you would set the bridle adjustment once, and fly it the same in all wind, but in practice you set the bridle to something appropriate for the day, because the automatic system is imperfect and not capable of maintaining the same pull in all possible cases. Thus you set towards high power during less wind and set the bridle softer in strong wind, thus changing the range within which the reefing mechanism works.
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