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When I was a little nipper I had an argument with a garden rake. It was propped against the wall of the garden shed and, in the vernacular of the time; 'fetched me a stunning blow' when I trod on the points.
While my desire for revenge didn't abate, still hasn't actually, as the world swam back into focus, I soon analysed and solved this problem, so I thought, by turning it around.
But yep, it had another go at me the next day when I trod on its heel.
Slow learner!
Actually that tiny brick garden shed has other memories- like as an 11 year old when I pounded a .303 calibre rifle round with a hammer until it exploded- I still have the ringing in my ears.
And brain damaged!
Probably now exacerbated by incipient Alzheimers.
Which goes some way to explaining why it's taken me 12 months, more than a 1000 hours and 31 prototypes to get to a generally useful single line single skin kite (SSSL) and even then I've had to pull back from the latest, simplest and best looking, to an earlier complicated wrinkly prototype that actually flies well.
But rewinding the clock for a bit;
I started on SSSL development a year ago as a new challenge when single skin traction kite development entered the (boring) commercialisation phase.
So where are these amazing new SS traction kites that I've been rabbiting on about since forever- are they all just talk and dreams?
They're real; the Peter Lynn brand's top designer (Michel Dekker) has been working on an SS range for a few years now.
Are they as good as rumours suggest?
They are, better even- truly world changing. Michel had breakthrough traction kites 2 years ago, but these weren't marketed then for reasons I don't yet fully understand- maybe it's that they expected Ozone (brand) to trump them as soon as went public, or maybe they were waiting for the market reaction to the Flysurfer "Peak" (like the Curate's egg- good in parts). Or perhaps it was a purely business decision from the Peter Lynn brand operators (Vlieger Op bv)- that these new kites would destroy their current market for 'foil style traction kites.
On their recent trans-Mongolian buggy expedition, Craig Hansen and Gavin Mulvey took only single skin kites- they didn't pack any conventional 'foils or LEI's at all. A reason is that they were, as usual, straining their baggage limits. SS's will fit in your jacket pocket and weigh almost nothing; not just because they only use half as much fabric for the same area but also because they're 50% to 100% more powerful size for size.
In the event, the SS's were faster, easier and safer- upwind and downwind. A defining characteristic is that unlike 'foil type kites they don't overfly, ever. SS's won't collapse, drift back then re-inflate and rip your arms off- they just don't do this. Craig and Gavin have both declared that with the 'old' style kites they would have been lucky to survive the difficult Mongolian winds and terrain uninjured and wouldn't have been able to cover half the ground they did.
But, I hear you asking; when can you buy these kites- and for how much, and what models, sizes, graphics? For all of this you'll have to ask your dealer as I'm under strict instructions to keep my big flappy mouth shut.

I started single skin single line kite development in late 2013. Within a few months (prototype 7) they were as reliable in some winds as standard pilot kites- while being less than half the size for the same pull, flying at a lot higher angle and being ridiculously cheap and easy to make.
Unfortunately the operative phrase here is "in some winds"- because then the development stalled.

And here's a metaphor:
Developing very complex things is like blundering around in a mist enshrouded swamp searching for hills. When you encounter rising ground, you can eventually feel your way to its highest point- but what you can never easily know, is whether there may be a higher hill somewhere nearby. To have a chance of finding one, if it exists, you must go back down into the swamp and blunder around some more.

By June 2014 (prototype 19), while they would hang on well in light winds, matching the best 'foil type pilots, when they did stop flying, even momentarily, the result was inevitably terminal. And in strong winds they tended to fold a corner and go into a death dive.
Which seemed like easy problems to solve.
But they haven't been.
I eventually (slow learner) figured that the hooked trailing edge of the prototype 19 type kite (similar in this respect to an NPW power kite) was a cause of these problems.
Why a hooked trailing edge makes single line stability more difficult to achieve is easy to understand when you know what to look for. Camber near the trailing edge moves the kite's centre of pressure (where the lift forces act) closer to the kite's centre of gravity (where the weight forces act). If these points get too close together, the kite will have difficulty deciding where "up" is. If they even momentarily reverse (the centre of pressure moving to below the centre of gravity) recovery becomes unlikely and a crash is imminent Which is exactly what happens when kites with hooked trailing edges like SSSL 19 drift backwards in light winds and also what happens to this style of kite when the leading edge folds back a bit.

So I then went back down into the swamp for a while, struggling up a new hill- trying flat profiles and open trailing edges (like the SS traction kites that are about to explode onto the power kite stage).
A difficulty is that flat profiles require a slightly higher flying speed than cambered profiles. The lightest wind I've been able to get a cambered SSSL to hang on in is just under 5km/hr (and 'Skins'- which have lots of camber and hooked trailing edges- will fly even slower than this) while the best flat profile SSSL's (and Michel style SS traction kites) need a km/hr or two more. On the other hand, a single line kite that gets confused as to where "up" is when it's close to stall speed, is not a useable kite.
Unfortunately, flat profiles also require more cells spanwise and more bridles per cell (chordwise), so these new direction kites generally have 24 or more bridles (just 9 bridles for prototype 19, the best of the high camber series). But they still hang in there in winds too light for 'foils, albeit not quite matching SSSL19 and its cohort - and crucially, they recover from light wind collapses with aplomb and panache (finally, an excuse to use these two words).
But after an intensive development period last week, averaging 2 new prototypes per day, testing refining and simplifying, by Friday 28th they were still not flying well enough for general use.
This became difficult to deny when we had a few days of really bad winds- occasionally gusting above 100km/h- and the best SSSL's I had then (prototype 31 being the new benchmark) couldn't handle it. They tramped, pulsated and collapsed, or dived off to one side terminally within seconds of launch.
By comparison, a latest Airbanners 12 sq.m 3 bridle Lifter just sat up there mocking everything below.
A pretty tough test; but until SSSL's can handle the extremes, they're curiosities not kites.

Introspection on Saturday: Yes, I have screwed up the development process by too much stupid 'artist' stuff- appearance, simplification and aesthetics - and not enough engineering thinking, which is; 'whatever works'.
So what if SSSL's, for now, have numberless bridles and many intricate panels? Once they're flying well, there'll be plenty of time for whatever refinement and simplification is possible- and artist types can then have their day (which will confirm their self-view that they're useful and important, which is all to the good). So later on Saturday I took a selection of prototypes down to the beach and flew them again, one by one. From which I've settled on SSSL24 as being the most promising re-boot point. Sure, it's complicated and wrinkly, but it's stable across the range- to 60km/hr at least- doesn't show any inclination to dive off to either side in gusts, and recovers well from lulls.

Actually it's there; so what have I been obsessing about?
Calling all artists!

Peter Lynn, Ashburton, New Zealand, 1 Dec '14.

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