This is just a bunch of random jottings about the development of the 'Phaze' power kite. I've pretty much discontinued work on this, due to the fact that there are better hybrids out there, and I'm concentrating on valved foils. Use the information herein if you want. Just don't blame me if it doesn't work for you. It might help you avoid some of the dead ends I've reached. Or not. Enjoy.
I had been playing with power kites for some time, mainly stacks of flexis, a Sputnik 2 for *really* high winds, and a no-name quad built from a friend's plans. I'd been having a right old laugh. Then I built a 2.5m2 NPW5 from this plan. On the first test flight, it dragged me half way over Richmond Park in winds I'd happily have flown a 3-stack of flexis in. It was awesome. It was scary. It was totally bloody uncontrollable.
Quadlining the beast tamed some of the madness out, and allowed me to actually see what was going on with it, and I now have a Nasa which flies in a reasonably civil manner.
Anyway, I got to chatting with the friend who designed my other little quad, and we were talking about the drawbacks and benefits of the Nasa kite. Roughly speaking the list we came up with looked something like this:
Pro:We figured that some of these drawbacks could be removed by increasing the aspect ratio of the kite. We reckoned that by reducing the depth of the kite, we gould get a greater lifting area with less bridling (and hence less drag, therefore more speed), slow the turning somewhat and make it somewhat less susceptible to collapse.
And thus was born
Phaze 1 didn't really have a name. It was a toy kite, really. About 1m2 with an aspect ratio of 5, it was a bastard hybrid of a Nasa and a 'standard' power quad. It had a single skin, with the 'roll' nose of the NPW, but was bridled in roughly the same way as a standard quad (more primary bridle lines - 6 per 'rib'). It was horrible. It flew, but the slightest gust would collapse the nose. The collapse would then propagate for the length of the kite and it would plummet. It was also hideously slow, something I attributed to the spanwise folds that appeared in the skin as it billowed. All in all, not a success. I didn't get any photos of this.
Then we bunged a piece of foam pipe lagging into the nose to get it to hold its shape. The improvement was rather dramatic. It was still slow, and without high winds the weight of the lagging made it drop, but it flew. Without collapsing. And at that, it was retired. I could see that sparring the front of the kite would improve matters drastically, and that I needed to improve the aerodynamics of the rest of the kite, but I couldn't see how to do it.
Development stopped
Then, a number of things combined. Inspiration comes from strange places. I was making pop-up Christmas cards for friends, inflatable ripstop Christmas trees, and a 'Croissant de Lune'. Thoughts began to coalesce. I went on holiday to Corsica, took some kites with me, and discovered that both NPWs and ram-air foils are a pain to get out of the water once you dunk them. I talked to some windsurfers and took a close look at how their sails work. Particularly the battens. And when I came back, strange rumours of a new Peter Lynn kite were surfacing.
Phaze 1 was pulled out of the scraps bag, the bridling was junked, and I sewed strips of foam camping mat along the 'ribs' to provide some stabilising effect. I lost the 'roll' nose, sparred it with 3mm grp along the leading edge, and went to a standard 4 line primary bridle. I put more darts in at the front to give some shape to the skin. It was now so heavy, due to the foam, that it needed a lot of wind to fly. But it held its shape a lot better than before. It went upwind about as far as my inflatable foils, didn't collapse, and produced a reasonable amount of pull for such a small kite. The shape of the skin and the foam 'battens' improved aerodynamics, reducing the size of the ripples in the skin.
Losing the pipe lagging in the front meant it didn't drop like a stone when it luffed. Matters were improving. Oh, yes, and the foam meant it floated.
And I didn't get any photos of this one, either.
I was thinking about ways of stabilising the foil shape further. I'd worked out a way of shaping the skin so that it fell naturally into the foil shape. I needed a way of reducing weight, retaining flotation, and reducing bridling (and therefore drag). Inflatable mylar bladders came to mind. The design for the 'rib' bridle attachment points I came up with looked roughly like this.
I never got round to making a kite with this design. I suspect the mylar would make it just as heavy as the foam previously used, puncture easily, and the big bulbous bridle attachment points would cause more drag than a standard bridle. Plus, I'd worked out how to stabilise the foil shape properly. GRP battens.
By this point, I'd seen photos and discussion of the Peter Lynn C-Quad, which is also battened. As I understand it, the battens on the C-quad run flat, with the skin shaped to billow to a foil shape. I figured that if you batten to a foil shape, the skin needs to be less radical, skin flutter would be less important, and more of the surface would be lifting. At the time, I'd never seen a C-Quad flying (I saw one in a stall at Blackheath 99 after I built Phaze 3, but didn't get a chance to inspect it closely), let alone flown one.
One evening, I was chatting to my boss, who is, among other things, a windsurf freak. He explained to me in more depth how windsurf sail battens work. They're attached to cams, which pre-stress them into the foil shape. I figured that if I could work out a way to pre-stress 3mm grp rod (which I had decided to batten with) into the required shape without the need for cams and other metalwork, I had it cracked. Even if I couldn't pre-stress, the only problem would come with 0 wind, where your kite would tend to spring flat, lose lift, and drop.
In the end, it was relatively easy. Compress the end of a grp rod, and it bends. You can do this by forcing it into a sleeve which is too short for it. Pre-form that sleeve to the shape you want, and that's the way the grp will tend to bend. If you then bridle off the bottom of the sleeve, the bridle lengths (carefully chosen) will make any final adjustments you need. Combine this with a shaped skin, and you should have an aerodynamically clean single skin kite. So I started designing.
On good Friday, I started with Lotus 1-2-3, a web browser, and a copy of plotfoil. Design took about a day, including the time it took to get plotfoil to compile on my mac. I decided on the Eppler E377 foill shape, as it's basically single skin anyway, then doubled the thickness. I worked out the measurements I needed, marked out on a single sheet of 165 cm white ripstop, and started cutting and sewing a 5.5m span prototype (dual elliptical shape, shaped skin, approx 4:1 aspect ratio, just under 7m2).
The kite was ready for a test flight on Sunday night. 2 days to build, from design to packing it into a makeshift bag. I was proud of myself.
So, on Easter Monday, I went up to Blackheath kite festival and gave it a try. Winds were around 5 knots, by my guesstimation.
Eeeagh! A combination of beer, haste and running out of spectra had resulted in an almost totally useless brake bridle. I had to cut 4 lines off entirely to get the damn thing to fly.
The primary bridle was mismeasured, resulting in an AoA which was way too low, and not easily adjustable on the field. However, despite the bridling problems it seemed pretty good. Turning, upwind performance and speed were all very poor due to the bridle.
But it was pulling me out of my boots in the whole of the window it would fly to. Other minor problems included the batten pockets which didn't work properly (the battens were falling out), and the 6mm excel leading edge spar, which proved not to be up to the job of being repeatedly smacked into the ground. Also, the spar tips slipped their bungies and dropped out, resulting in very floppy wingtips.
Sadly (or maybe not) my photographer friend hadn't turned up due to excessive beer and whisky consumption the night before. So, again, no photos. Still, a promising, if flawed, start.
A week later, after a minor redesign of the batten pockets, replacing the leading edge spar with 4mm grp and a new brake bridle, it was ready for another test flight. Winds were around 6 knots, varying from 0 to 10 or so. Gusty, and changing direction over a 30 degree range. Not great weather for testing, but at least it wasn't raining.
The results were more encouraging. Turning and speed had been drastically improved by the new, improved brake bridle. While not as fast 'flat out' as my ram-air foils, it was a distinct improvement on the NASA. Turning was still a little sluggish, but this time it turned. More bridle improvements required there
The battens didn't fall out due to the new, improved batten pockets. No more need I fear impaling innocent passers-by. Handy, as I was testing on Parliament Hill, and it gets a little crowded there.
By this point, upwind performance was fairly awesome. It went as far as my ram-air foils and further. It was quite easy to overfly at the top. And it pulled hard at the edge.
'In the window' I couldn't hold it. 15m+ slides before I could get the kite out of the max power zone were commonplace. Heh. Even parked at the top, it was threatening to lift me off the ground.
And on the down side......
Improving the brake bridle pointed out the woeful inadequacy of the primary bridle. Still too low in AoA, too much anhedral, and TOO MANY LINES. I improved it further on the field, but a redesign was needed. Sigh. The 'b' lines weren't even under tension, while I ripped a couple of seams on the central 'c' and 'd' line attachment points (Which needed some work as well)
The 4mm grp spar was rather too floppy, IMHO. I might scale up, or go back to carbon (ouch, wallet hit). Also, when the kite luffed, the spar had a tendency to spring flat, and the kite plummeted in 'dead leaf' mode. A new bridle should help with this.
My new, improved, batten pockets also needed a little more improvement. Well, OK, a lot. They stuck out a bit at the front, and this caused some fairly major line tangles at launch, when the wind dropped, if I crashed it, etc. Similarly, the spar ends need to be kept inside the leading edge pocket. They were another bridle tangle blackspot, as they protruded about half an inch on either end, with bungie cord knots and the like adding to the problem.
My photographer friend turned up this time, and got some photos early in the session, before I had a chance to futz with the bridling too much. Hence the kite looks like a sack of shit.
PhotosSo. A completely new bridle, redesign of the bridle attachment points and leading edge batten pockets. Plus sewing up the ripped seams. I'll try to get that finished within the week and we'll see what happens then.
The new bridle design has two parts. A 'structural' element, designed to keep the kite in its natural curve when luffing, and a 'flying' bridle with a two-point primary.
This sort of worked. It didn't spring flat, but it's all extra line. Upwind performace is still good, but I've done something to the bridling that stops it pulling quite so hard.
Like so many prototypes, the phaze now sits, rolled up, in a bag in the cupboard. I occasionally look wistfully over in that direction, but the thought of rebridling it again strikes fear into my heart. It's too damn big to move around easily, and it really needs reworking.
If you want to make a hybrid, I'd really recommend the Trident, which is probably better in all respects. I'm moving back in the direction of ram-air foils, possibly hybrid hybrids (ram-air/single skin bastardisations) and all sorts of other things.
Given that it was the bridling that got to me in the end, some kind of simplification seems to be required. Of course, Peter bloody Lynn has it all sorted with the C-Quad. A year on from the Phaze's first outing, I finally got to fly a C-Quad. They're lovely. But I still say they'd be better with a higher AR.....
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