Building a state-of-the-art foil kite

[downunder]

The question is why?

Why building it when one can potentially find used race foils quite cheap. The only negative for race foils is depreciation. It's huge. The materials are not that cheap either, when buying small batches.

I did see a lot of passionate builders over the years. It takes more than a passion to actually improve from the first build. There is no guarantee that the first one will be any good.

That is why no one is doing it. I would do it if there is a described process for it. But this is the only one I know off:

http://www.zeroprestige.org/sewakite.pdf

[kitexpert]

I strongly disagree with Kitexperts outlining of state of the art. First you need to select into which style of riding the kite will be used. Because for somethings they may be less important and for others they are more important. For example in Race stability is less important to L/D, off which high AR is a help. Where as for wave it is opposite.

In foils we have state of the art technologies, being seen in single skins, hybrids, the various race kites and various other kites. Things like semi rigid LE, unsupported tips, 3 row bridles, mixed ratio wing, PA change, changing bridle cord locations. I think if you could get your head around them then you could truly make something very interesting.

You have some point there, I agree defining "state-of-the-art" for kites is at least to some degree subjective. For me it is that wow-effect some kite are able to deliver because of their high performance (for me at the top of the list is one very high AR 6m race kite, but it has of course problems/difficulties of its own). For sure I'm not impressed by any low AR wave foil kite no matter how light material it has or how stable it is (trivial for low AR kite, like it is using expensive light weight material).

If we look most advanced ram air wings they are PG's, most interesting are like this:



Actually contemporary foil kites are quite bad, all of them. They are not clean wings. I can design one that is better but it is not an easy project because increased cell count affects to so many things and there is a lot of work and also more material costs. There is however some solutions to keep these challenges within reason.

Then why? IDK, some people like huge challenges, to go where no one has gone before or to do new things

[kitexpert]

As a corrective: my goal or inspiration under this topic is not to reinvent foil kite but to develop a new combination of high end specs and moderate AR. Something like AR 5 to 5.5 and cell counts between 40 and 80 with fully supported structure and low drag bridle. There will be also size limitation because all big foil kites are so slow - limit could be about 10m, preferably much smaller 5 to 8m.

[foilholio]

I would suggest for that AR 3 bridle rows, as I have had success with that on the A15 (being a similar AR) with no down side. I wonder given the higher AR of many foils on the market why they still use 4 bridle rows.

[kitexpert]

I would suggest for that AR 3 bridle rows, as I have had success with that on the A15 (being a similar AR) with no down side. I wonder given the higher AR of many foils on the market why they still use 4 bridle rows.

I have some some bad experiences with three line rows with Speed4dlx. When I worked with one I couldn't get wingtips smooth like there just wasn't enough support with three line rows, and when I observed one other Speed4dlx I saw it there too. So I'm not sure if it has ever been good even on a new kite. Also possibilities to adjust kite and to have variable camber is more limited with three line rows. For high AR (short chord) three line rows is more natural, but even with them only FS uses it.

One possibility might be to have usual four line rows and to cascade B-C together, then speed system could be simple 1:2 and there would be possibility to do more adjustments or to go back to normal 1:2:4 speed system. Too bad line row locations on chord for different configurations are not very compatible, so I think it should have to be designed for 1:2:4 and then just try how well 1:2 would work. Other possibility for 1:2 speed system is to cascade A-B, but it may limit depower, and again line row locations should be different.

Four line rows is just proven concept, it works. For moderate cell counts it is also stronger because it has more line attachment points. High cell count race kite has so many bridle points there is not that issue even with three line rows.

Anyway this is essential design parameter. It must also be remembered that line row count and locations affect directly to inner structures of kite. To have more is better for structure, less is of course lighter in weight and less laborious to make.

[foilholio]

I have some distortion at the tip on the A15. It is mainly at the transition from C to B as that is quite large. I use the C positions for B at the tip because they work much better. The positions I think are definitely not optimal and I think I will move at least the transition bridle attachment so it is smoother.

Despite the slightly off look of the tip, the increase in performance is considerable and as I said I have no downside, but actually considerable upside. The fact is I have removed 1/4 of the entire bridling and a pulley line. That has to definitely offer some L/D improvement, which is what I observe. Then also my changes to Z also improve that as well. Improvements to turn I put mainly down the change of ratio on B from 1:4 to 1:3.

I think the speed4dlx at AR 4.85 vs A15 which I guess at 5.5 might be the difference to the effectiveness or even viability of 3 rows. My thinking from a mechanical perspective is the shorter the cord the less need for 4 rows. Hence why I am surprised that with all the race foils it is not seen more. The thickness of the structure surely plays a part too.

I read it mentioned that 3 rows is quite common on high performance paragliders. I have seen paragliders with 3 rows, but I think there AR is even higher than kites.

You are correct about the camber advantage that 4 rows offers. I think the sole play between A and B give a lot of the good depower behavior that foils have. I have previously played with pulleys on B C together and that did not work at all, huge stability problems and bit weird as I remember. Maybe static links would work, but I have seen that done and the kites were not successful. I think you just have to weigh advantages vs disadvantages, it may seem worse in someways visually but overall is it better?

Sure Flysurfer abandoned the speed4dlx, but that may be because it was too ambitious having both high PA change and just 3.1 rows. I hope designers start at least trying some of these things out. They are at least somewhat proven and having extra attachments on prototypes seems common. From my experience moving bridles and altering their lengths is a cheap way to test things out. My higher hopes are with hydrid foils. Perhaps kites with just part of the TE single skin. My ideas are to improve depower ,weight and drift. I know it most likely is out of your realm of interest but I know I am not the only one interested in kites with these properties.

[Rein de Vries]

Thank you all for sharing ideas! Quite clear also that since so many parameters influence the end result it is not trivial or even personal what a state-of-the-art kite should be.

Despite this however I think and hope we should meanwhile be able to define some baseline plans which approach commercial state of the art. I remember from years ago allready a book that presented plans of the kites from those days. The authors made some educated choices I think, and I had a lot of fun with it!

So to answer the why question. For me because it adds significantly to the fun surfing around using a DIY kite.

I was thinking about trying a 6m2, in performance similar to e.g. Sonic 2. So using similar AR, canopy, bridles, etc. Would be a sensible starting point I think, since the succes is obvious. A plan for something like that could become a baseline I guess. But how to get it in detail, would be my next question.

[kitexpert]

I have some distortion at the tip on the A15. It is mainly at the transition from C to B as that is quite large. I use the C positions for B at the tip because they work much better. The positions I think are definitely not optimal and I think I will move at least the transition bridle attachment so it is smoother.

Despite the slightly off look of the tip, the increase in performance is considerable and as I said I have no downside, but actually considerable upside. The fact is I have removed 1/4 of the entire bridling and a pulley line. That has to definitely offer some L/D improvement, which is what I observe. Then also my changes to Z also improve that as well. Improvements to turn I put mainly down the change of ratio on B from 1:4 to 1:3.

I think the speed4dlx at AR 4.85 vs A15 which I guess at 5.5 might be the difference to the effectiveness or even viability of 3 rows. My thinking from a mechanical perspective is the shorter the cord the less need for 4 rows. Hence why I am surprised that with all the race foils it is not seen more. The thickness of the structure surely plays a part too.

I read it mentioned that 3 rows is quite common on high performance paragliders. I have seen paragliders with 3 rows, but I think there AR is even higher than kites.

You are correct about the camber advantage that 4 rows offers. I think the sole play between A and B give a lot of the good depower behavior that foils have. I have previously played with pulleys on B C together and that did not work at all, huge stability problems and bit weird as I remember. Maybe static links would work, but I have seen that done and the kites were not successful. I think you just have to weigh advantages vs disadvantages, it may seem worse in someways visually but overall is it better?

Sure Flysurfer abandoned the speed4dlx, but that may be because it was too ambitious having both high PA change and just 3.1 rows. I hope designers start at least trying some of these things out. They are at least somewhat proven and having extra attachments on prototypes seems common. From my experience moving bridles and altering their lengths is a cheap way to test things out. My higher hopes are with hydrid foils. Perhaps kites with just part of the TE single skin. My ideas are to improve depower ,weight and drift. I know it most likely is out of your realm of interest but I know I am not the only one interested in kites with these properties.

For me state-of-the-art kite has to be very high performance kite in a traditional sense. But because I don't want to start competing race kites (like FS 13-13-13 kite) because of many reasons I see now a mid AR kite with very high specs most interesting try. Goal is to have very high performance kite with good usability.

Because main objective would be to decrease drag by trying to make very clean wing I see now 3 line row bridle not so suitable. Like I wrote it also affects to inner structures of the kite and this is actually part of the design I am working mostly now (together with cell count and bridle spacing). Wider chord wise gaps between attachment points of 3 line rows is a challenge there.

I'm not sure if I got it right but you have experimented some sliding system between cascaded B-C? This should help it to adjust when AoA changes but it makes bridle a bit more complex and and adds wearing lines to it. Perhaps with some small steel rings as a pulleys it could be done neatly/lightly enough and range of movement perhaps limited (after which B-C would be fixed). Possibly then 1:2 speed system would suit better to 4 line rows.

I have several hybrid designs going on, actually I have had difficulties to decide which kite type I should concentrate. Also problem is I'm struggling to have enough time to make kites nowadays.

[kitexpert]

Thank you all for sharing ideas! Quite clear also that since so many parameters influence the end result it is not trivial or even personal what a state-of-the-art kite should be.

Despite this however I think and hope we should meanwhile be able to define some baseline plans which approach commercial state of the art. I remember from years ago allready a book that presented plans of the kites from those days. The authors made some educated choices I think, and I had a lot of fun with it!

So to answer the why question. For me because it adds significantly to the fun surfing around using a DIY kite.

I was thinking about trying a 6m2, in performance similar to e.g. Sonic 2. So using similar AR, canopy, bridles, etc. Would be a sensible starting point I think, since the succes is obvious. A plan for something like that could become a baseline I guess. But how to get it in detail, would be my next question.

6m2 size is good for diy. But to try compete against kite like Sonic2 is very very ambitious. And to make very similar kite I don't think it is worth it, some own idea/concept should be had. Trying to copy existing kite just by making it to look same is not at all guaranteed to be a success, for a high aspect kite far from it. Only way to copy a kite reliably is to undo it completely and make precise copies from every part of it and so on.

[Regis-de-giens]

We are asking this to Kiteexpert for month, and unfortunatelly we have nothing real now, that is regrettable.

Of-course a mid AR kite cannot reach the same level of LD ratio than high AR kites. Otherwise all designers from all brands around the world and among years would be idiot developpers ? And even assuming this point ... then the same super-ideal kite would have an even better LD ratio and race performances with a bit higher AR (induced drag would mathematically be reduced, hence better in race..) Come-on ...


Foilholio is naturally right, there are different kites for different use, and some design feature like arch of the profile have to be increased or decreased depending on speed or wave wish for example.

Big respect for Stephano Moris for its impressive work and hope that people will continue do diy kites.