OBSESSION?

For now, let's call it a goal shall we?
Which is to develop a better pilot kite.
And this project ticks all my boxes:
It's difficult enough to provide a real sense achievement if it is successful.
But probably not so difficult as to be impossible.
Will provide the world with something useful (not just for kite fliers).
And creates many opportunities for attacking trees with chainsaws.

Starting point is the single skin design - the Boomers that John and Irene Tan make, the 1Skins from Kaixuan- and various copies in China, Indonesia, Europe and elsewhere.
They showed great early promise, but as for many breakthrough ideas (Diesel's engine for example), then became bogged down by various practical difficulties that only persistence beyond reason by some obsessional person- persons now, in this case- can surmount, and not even always even then.

Their advantages over traditional ram-air Pilots are; immediate launching, delightfully responsive flying, luff resistance, easier retrieval from water, much more pull for size and higher flying angle. And all this for less than 1/3rd the cost and weight. They have the potential to be truly throw-away kites that will encourage more people to fly more show kites more often by removing much of the dollar risk of losing expensive pilot kites when flying in difficult places and when the wind is tricky.
Their disadvantage is (or has been?), that they tend towards superstability (diving off to one side or the other inexorably) in stronger winds. After 3 years, 77 prototypes and a thousand or more hours of stuffing around, I'm now pretty sure that the primary cause of this behaviour is insufficient air pressure behind the leading edge to hold it in shape as the kite flies progressively flatter in stronger winds.
Which seems a banal and obvious explanation of course- so how come it's taken me 3 years to figure this out you might reasonably ask? Well, it's always been apparent that leading edge stability is a function of angle of attack, but that it hasn't yet yielded to the very many work-arounds tried by myself and many others puts it on a more fundamental level.
A first response is to just pull in the back bridles a bit more so as to keep the leading edge pushed out, but this doesn't work because single skin kites are already bridled back as far as they can be without stalling in order to do this. Even a teensy bit more costs whatever light wind flying they have and enough more to keep the leading edge nicely puffed out no matter what, stops them from flying at all.

The light wind end was solved a few months ago, albeit with an ugly solution; providing different bridle settings for different winds. At Petra and Craig Knight's wedding-on-the-beach in Dunedin a few weeks ago, a 3 sq.m 1Skin lifted two large heart kite inflatables (one German, one Kiwi!) in wind that was less than marginal. Even a much larger conventional ram-air pilot would not have been able to do this.
But alternative bridle settings are an unsatisfactory solution because what do you do with a stack of maxi inflatable kites under a pilot rigged this way when the wind increases and the pilot misbehaves, except pull everything down and re-set the bridle? And you may need to do this 3 times for a 7km/hr to 50 km/hr range. But, though far from ideal, this has demonstrated unequivocally that these kites are capable of superior light wind performance. Eventually, a reactive bridle with pulleys and springs can make the setting function automatic- though there will be many devils in the details of this that I'm not looking forward to working on. It will be slow boring sort of work too, not exactly my forte', if I have one that is (I know I used to have one, it's probably still in the workshop somewhere).

As for the other end of the wind range, I've been hiding away from kite events since Dieppe, making refinements in the leading edge panels to eliminate wrinkles from which the dreaded leading edge collapse initiates. Which is now achieved; a few tedious months (much relieved by the US election) which could have been short circuited by what I know now; that it's mainly the width of the lower leading edge panels rather than their precise shaping that causes these wrinkles/folds in strong winds, and leads on to inevitable and usually asymmetric leading edge collapse. All I really needed to do was cut excess fabric away, but I went through 5 or 10 leading edge panel iterations before getting to this, though the rib leading edges had some necessary discipline applied to them during this process also.

The final iteration in this, 75 (pink/orange), was reasonably reliable in strong gusty winds by mid-November and 76 (yellow) in its second iteration (with the rib fronts cut away more) flew pretty well in the stupidly strong winds we've been getting here for the last week (198km/hr reported from South Westland, 126km/hr in central Wellington), albeit with a tail ( no I'm not in the slightest embarrassed by using a tail; in this wind it's 'whatever works'- and 'stand well clear'). I had to move up to 4mm diameter Dyneema because the 3mm broke (nominal 300kg, though with knots and nicks, it can break at less than 50 I think).

So, by the 26th Nov I was at last free to try something a bit radical again; which was to use gauze instead of fabric for the rear half of the main skin. The idea behind this is that the higher the pressure difference, the more air porous fabric lets through. I was hoping to use this characteristic to tame the kite in stronger winds, while not losing too much (hopefully nothing noticeable) at the light end.
Didn't work though, the finest gauze I could get (<1mm holes) let so much air through in light winds and when at higher angles of attack, that the kite would barely fly. It did show signs of being more docile in strong winds though.
Changing from gauze to uncoated fabric for this rear panel was the next step. I'd figured by then that it needed more fabric and less holes- and that the maximum hole size to get the sought after effect would be in the order of 0.1mm not 10 times this. I'm not sure why I ever thought gauze would work, but trying it did at least demonstrate that the principle was sound.
And using soft fabric for the rear panels does work; 77 (orange/purple) flew really well in light winds, and then showed every intention of staying up in the wildest patch of wind we've had hereabouts for some days (and without requiring a tail). Until the line broke, and its young life was tragically terminated in a tree. I'm wracked by guilt over this too, having dropped back to 3mm line again, thinking that rear panel porosity had knocked off some of the pull. It probably had, but there was even more wind by then.

I feel a chainsaw coming on.

And while all this has been happening here, my fellow obsessional, Simon Freidin, has been squirrelling away on a parallel single skin development in Melbourne. His prototypes are 0.75sq.m, which in itself yields useful data (smaller kites tend to more volatility and for single skins, are less subject to leading edge collapse because fabric stiffness has a proportionally greater effect).
And when I say squirrelling away, this is not accidental word use. Simon has some really secret squirrel stuff going on over there; an approach which looks very promising, not just for single skin single line kites but also for single skin traction kites- which suffer problems deriving from the same leading edge collapse cause. While my current direction (using porous panels in various arrangements) is unlikely to have applications for traction kites because porosity always costs high end performance, Simon's 'special features' should be able to be disposed so as not to have this disadvantage.
To keep open the possibility of IP acquisition, for now he can't disclose what's going on over there, but it'll be coming to a kite field near you some-day soon I'm sure.

PETER LYNN, ASHBURTON, DEC 1 '16