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Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Tue Oct 03, 2017 11:17 am
by stefFZ
Nice to hear that there are new people trying these kites! Happy for Benoît in particular because he always told me that these kites were often one of a kind because I was the only kite surfer asking him to build that sort of kitez. It took us 5 years of exchanges and tests to get there thanks to the continued interest of Benoît for this bizarre idea.

@jannik: Hi. Good question. My problem is that I use the same bar for several kites and I always need to adjust (even minimally) the trim at the start of the session and I fine tune when I am in the water (I like to be at the very limit of stalling the kite with the bar completely pulled in). Difficult to tell you if I am using the trim in the session because I never really asked myself the question, but I would say it is more on the "only a few times" side. In any case, I would start to fly the kite with the trim in order to find the correct tuning and then think about removing the trim - if you have no trim maybe add short lines with knots to your flying lines to find out your best tuning.

@Sergio: If you liked the PS4, I am nearly sure that you will like the Concept Air Waves. I used to fly and travel with my Psycho 4 (4m,6m and 10m DL) and I liked them in waves. When I started to fly the first Concept Air prototype in Australia however, I understood that this was the way to go and I don't fly my psychos 4 anymore. The early prototypes showed us the route. They were not perfect for sure but the feeling was already there and it took us some time before getting there (not only because work on design and testing were needed but also because Benoît has to earn money on projects with an actual demand + I pay for my kites and I am not really on the rich side).

Stef

PS: I created a new account, I don't like using the LesFoilZ account anymore as it is a community forum and I don't want to misled people.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Wed Oct 04, 2017 8:16 am
by jannik
Yes, I will have to test and see. I have bars both with and without trim so no problem.

I left foils for leis only because the leis where much better in waves in my experience, so this kite came as a plessant surprise (I hope it lives up to the expectations).

I never understood why foils always had to be so high AR. My leis are 1.77 in projected AR and the lowest AR foil I ever had was 4 (Flat AR so less projected) just to make a comparison. That foil was also the most fun.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Wed Oct 04, 2017 10:01 am
by kitexpert
jannik wrote: Yes, I will have to test and see. I have bars both with and without trim so no problem.

I left foils for leis only because the leis where much better in waves in my experience, so this kite came as plessant surprise (I hope it lives up to the expectations).

I never understood why foils always had to be so high AR. My leis are 1.77 in projected AR and the lowest AR foil I ever had was 4 (Flat AR) just to make a comparison. That foil was also the most fun.
Yes, isn't that an interesting (even trivial) observation: LEI's have much lower projected AR's than foils and even though they are most widely used kites.

Some explanations, not in any particular order. LEI's have some advantages in flight:

1) Lower inertia, because of smaller total weight. This advantage is greatest on big LEI kites, because volume (of foils) increases more rapidly than area. This is why big foils are so slow to turn (accelerate). You can consider added weight as a drag, so in that sense LEI's have higher L/D

2)LEI's are single skins. This has some advantage in low winds, single skin kite tolerates higher AoA before backstall. Difference in practice is you can just sheet in a LEI to get some power (with very low airspeed), but you must get some flying speed to a foil kite. Just sheeting in without speed usually chokes foil kite.

3)LEI's have sharp TE. Some aerodynamical advantage.

4)LEI's are more rigid. This helps to give precise handling.

Foil kites compensate these advantages by having higher AR and more PA. Low AR is ok for small foil kites, but if you make a big foil kite with low AR it becomes very slow tractor. High AR respectively makes foil kite lighter in weight (less volume) and by increasing L/D there is double benefit. However high AR means big wingspan, which make turning radius big - so completing a turn is not very fast. In park-and-ride high AR foils are the most efficient kites like everyone knows.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Thu Oct 05, 2017 12:17 am
by Regis-de-giens
Kite-expert,
Some of your analysis need correction. It is not linked to this topic so sorry for the disgretion. But among errors the main one is that inertia and weight have no direct impact on L/D ratio. It will rather decrease agility (but can increase stability in drift or light wind) . Hence saying that a low AR LEI has same drag or performance than higher AR foilite is just non-sens.

Higher AR of foilkite is more linked to history and demand : before hydrofoil , Ram air where mainly interesting in lighter winds, where high AR was needed to stay upwind (Very important before hydrofoil). Then Hydrofoilers "Re-discovered " foilkite advantages for their better speed : they gained precious seconds in competition. Now that hydrofoil practices evolve , mid or low AR foilkites allows to combined low end, stability and drift for wave surfers, while upwind is not an issue anymore on Hydrofoil. But believe it or not the very low end (In the sense of riding just upwind) is lower with a middle AR kite, folkite a-fortiori. And Stephane will tell you that relaunch is often easier and quicker in wave (for simiar low AR kites).

With all the respect I can have for you, i wonder how you could have the pleasure to develop your own low ratio foik kite , with so much negative aprioris on ram air kites !
Just look at the video from Stephane Goffinet above in this post (From 1 : 30 approx) and you will notice what is the incredible level of stability at drift with slack lines. Struted LEI will not offer that I'm affraid. Regarding the agility, it seems to be sufficienty quick turning !

Just as reminder : I use (and like) both LEI and foilkites, so no religion to defend on my side.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Thu Oct 05, 2017 11:05 am
by kitexpert
Regis-de-giens wrote:
Thu Oct 05, 2017 12:17 am
Kite-expert,
Some of your analysis need correction. It is not linked to this topic so sorry for the disgretion. But among errors the main one is that inertia and weight have no direct impact on L/D ratio. It will rather decrease agility (but can increase stability in drift or light wind) . Hence saying that a low AR LEI has same drag or performance than higher AR foilite is just non-sens.

Higher AR of foilkite is more linked to history and demand : before hydrofoil , Ram air where mainly interesting in lighter winds, where high AR was needed to stay upwind (Very important before hydrofoil). Then Hydrofoilers "Re-discovered " foilkite advantages for their better speed : they gained precious seconds in competition. Now that hydrofoil practices evolve , mid or low AR foilkites allows to combined low end, stability and drift for wave surfers, while upwind is not an issue anymore on Hydrofoil. But believe it or not the very low end (In the sense of riding just upwind) is lower with a middle AR kite, folkite a-fortiori. And Stephane will tell you that relaunch is often easier and quicker in wave (for simiar low AR kites).

With all the respect I can have for you, i wonder how you could have the pleasure to develop your own low ratio foik kite , with so much negative aprioris on ram air kites !
Just look at the video from Stephane Goffinet above in this post (From 1 : 30 approx) and you will notice what is the incredible level of stability at drift with slack lines. Struted LEI will not offer that I'm affraid. Regarding the agility, it seems to be sufficienty quick turning !

Just as reminder : I use (and like) both LEI and foilkites, so no religion to defend on my side.
Me too like both kite types and use them, but nowadays I use foil kites almost only in the winter. I have huge amount of all kinds of kites and I've tested much over 100, perhaps 200 different kite models through the years. I'm familiar to every kite type, from C-kites to strutless kites, from arcs to high end foil kites. I also know single skin kites (Peaks) and I have made them also as well as arcs. BTW these two are much more difficult concepts than foil kites, which always work better or worse.

I wrote "you can consider..." meaning added weight is a kind of drag. I'm a bit surprised it was you Regis who picked this up, because you have praised the light weight of the kite so much. Added weight has quite similar effects to kite than added drag, but not exactly same of course.

I would have liked to give two different L/D ratios, one for dynamic and one for static flight. But I felt it difficult to describe better so I didn't.

In Pulsion line drag is compromised for light weight. For light wind use I see it a good compromise, because then airspeeds are low and excessive line drag is not so bad thing. Added drag keeps kite also further from the edge of WW, this limits how easily it overflies and then collapses.

I have longer experience than anyone with hydrofoils in extreme low end kiting, I mean kiting in the winter. Then conditions are also more uniform than with hf and kiter skills/weight are of lesser importance. Order of efficiency and how low it is possible to go is very much in line how high AR kite has. What I have seen/used, in order of efficiency: russian extreme high AR experimental foils (AR 9 to 10)>Ozone Chrono, Sonics>Speeds>race LEI's>Peak, mid AR foils>low AR foils, most LEI's>beginner foils, arcs.

Worth noting is that extreme high AR kites are much superior, they can go upwind when everything else is struggling to keep in the air. Second point is how good performance Peak has, except for performance to jump which isn't there. Most LEI's are roughly in par with Frenzy type kites, but their feel and handling is more dynamic. Arcs are worst, they are a bit like C-kites but with less dynamic performance - although I haven't use high AR versions of them which of course have higher performance.

I don't see my views for ram air kites "apriori", because I've been using them last 15 years and more than other kite types. Personally I don't see developing low ratio foil kite very interesting, but I can still try to find out what there is to do.

I see you Regis understand quite a lot how kites are. However I woudn't say it is nonsense to say (low AR) LEI has same performance than higher AR foil kite. Performance is not easily defined, for example LEI having faster turning and acceleration it jumps more easily and higher than a foil kite with higher AR.

Finally a youtube video showing modern high AR foil kite performance in very low winds.


https://www.youtube.com/watch?v=wuTC9REz0xU

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Thu Oct 05, 2017 1:14 pm
by jannik
kitexpert wrote:
Wed Oct 04, 2017 10:01 am

2)LEI's are single skins. This has some advantage in low winds, single skin kite tolerates higher AoA before backstall. Difference in practice is you can just sheet in a LEI to get some power (with very low airspeed), but you must get some flying speed to a foil kite. Just sheeting in without speed usually chokes foil kite.
Could you please elaborate on the above?
Are you saying that a twin skin will lose laminar flow before a single skin or are you saying that a twin skin requires more pull to create enough forward speed(maybe because of inertia)? Both of these statements does not conform well with the fact that it is possible to launch a twin skin in very little wind even though the kite is uninflated and out of shape which can't be good for laminar flow and also the kite will keep flying in very little wind (static, so not moving inertia).

To my limited knowledge low AR has higher AoA tolerance than high AR which could explain something when comparing kites with projected AR under 2 with foils having much higher proj. AR.

I fully know what you mean about generating power by sheeting in. But why is that often lacking in a foil kite? Again I'm blaming high AR for some of it.
A high AR kite will fly very close to the windows edge when you lose ground speed which means the kite flies further out of the power zone. Sheeting will not have as much effect here and trying to stall the kite back into the window of cause does not help with power. The lower tolerance for AoA makes it even worse.

Furthermore, You now want to dive the kite but you are trying to turn the kite where there is not much room to turn and the high AR does not help here either because it requires room. So the turn will likely involve some stalling resulting in a slow guttless turn. The kite is now diving and needs to accellerate but if you made a normal down turn you are already flying close to the edge and do not have a long way to fly before hitting the edge again. So you move the kite back past zenith before diving or even loop back to make distance to accellerate. You still need to turn up again well before the edge.

I don't see these things relating to foil vs lei, or even twin vs. single skin, as much as high vs. low AR. I'm not saying you can get a foil and a lei to fly the same but I do believe that a lot of what we are seeing is difference in AR.
And as the Wave is low AR, this was my attempt to bring the above back on topic :oops:

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Thu Oct 05, 2017 5:42 pm
by kitexpert
Wave is a simple low AR kite, small sized and for higher winds. More than kite for performance it is kite for stability and good handling to fill known requirements for a wave kite.

Small foil kites have small volume and therefore inertia is not a problem. Big foil kite can have over ten pounds of air inside to accelerate - and lower the AR bigger the volume.

If you think lowering AR is an answer to foil kite performance you are mistaken. It is ok only for small foil kites. Larger sizes become slow and heavy tractors. Also it is a challenge to have enough AoA change if kite has huge chord lenght, in which low AR leads to with big sizes. Then power/depower ability suffers.

Single skin efficiency in low air speeds and high AoA's is widely known. It should't be too difficult to understand how concave bottom surface is then better than a convex one.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Fri Oct 06, 2017 3:37 am
by Horst Sergio
Hi kitexpert,
first respect for your kite build project. :thumb:
I think the point that some like mid AR kites for low end, especially on the hydrofoil, is that those kites are typically more easy and stable to fly in light winds, not just but also by construction have less cells and therefore less weight. On the other hand I prefer myself high AR kites for low end as I don't want to stop for maneuvers, but keep riding and jumping which also on a hydrofoil just requires better performance kites in the absolute low end.

But all this is not about Smart Wave, which just have to be stable, stable and easy to control. In 30 knts you can also foil with an umbrella :wink: no need for performance. Will report and also excited how much I like the 4.5 m² as I will directly change to it from a 6,4 m² sonic² which for sure will be some cultural shock :o . But on the other hands winds above 30 knts can get nuclear on our small lakes and here I need just something that helps to survive :D . Have good confidence that Ben is able to help me in this conditions with his experience and constructions.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Fri Oct 06, 2017 5:37 am
by Regis-de-giens
I mostly agree with you Jannik. (EDIT : and you sergio as your message arrived while i was writting :roll: )

Kitexpert, I never said that low AR LEI have same performance than high AR foilkite (i hope by "Performance" you mean speed and upwind angle, and not just "Power" ). I actualy say that riding in extreme low end with a HF does not need an extreme high AR kite and can benefit of a lower AR for extreme low end.

You are right I indeed deeply believe that light weight of the kite is a master key in light winds (for years and years and even when it was fighted by some "Experts" time ago) : most everything is improved, I won't detail here. Most except one thing : the drag (and L/D ratio hence upwind angle consequently) ; even "Kind of " or "Quite similar effect than drag " is inapropriated actually. Drag is not or few affected. I say few because if we want to go deeper in the secondary consequences, lighter cloth could even BADLY affect the drag in high winds (Profil defomation due to light cloth softness) ;

Now on the drag of the line
kitexpert wrote:
Thu Oct 05, 2017 5:42 pm
For light wind use I see it a good compromise, because then airspeeds are low and excessive line drag is not so bad thing. Added drag keeps kite also further from the edge of WW, this limits how easily it overflies and then collapses.
Ok for the second part on stability which is important on "Real life" hyperlight wind ride on the water. However in light winds, even more than in strong winds, we need to reduce drag as much as possible because it is not the value of the drag itself that really matters but its ratio with lift (called L/D ratio for everyone to understand) . This ratio will drive your upwind angle (Not the drag alone). So since the Lift reduces a lot light wind, you need to decrease also a lot the drag, so thick briddles (and lines...) are detrimental to expreme light wind .
I am speeking here about the general impact on rider speed and upwind angle. Now If we consider the special case of the hydrofoil which has intrisequely a huge upwind ability, we can accept to loose some drag (still stay upwind but with less speed), against more agility and power in the window or during loops to gain some waterstrat ability (transient part of the ride). On this quick and powerfull turn/Loop need, a lower AR will be more efficient in extreme light wind. This point may not be obvious with your snow experience (which I also practice) because there is no need to waterstart.

I hope I'll have changed a bit your view on this drag matter, but if not , I won't react again here (to keep this topic tight to the conceptair Wave). Maybe on your low AR kite design topic this discussion would be more appropriated. Thanks kitexpert for having kept the tone respectful :remybussi: .

BTW I wonder how a 15m2 wave would be in extreme light winds with HF, but think that upwind angle will start suffering too much.

Re: Concept Air Smart Wave 6.5 & 4.5 & 3

Posted: Fri Oct 06, 2017 8:23 am
by jannik
kitexpert wrote:
Thu Oct 05, 2017 5:42 pm
If you think lowering AR is an answer to foil kite performance you are mistaken.
I don't. I'm offering an explanation to some of the differences people experience when they compare kites other than "it's because it's a foil/LEI/single-twin skin/ARC/other....!".
kitexpert wrote:
Thu Oct 05, 2017 5:42 pm
Single skin efficiency in low air speeds and high AoA's is widely known. It should't be too difficult to understand how concave bottom surface is then better than a convex one.
So another important point: upper and lower camber. The answer is not "because it is a twin skin". Rather the question is: why is lower camber not build convex in foil kites? I bet there is a good explanation.

Concept'Air should receive kudos for doing active development in a lower AR closed cell ramair. I never use a bigger kite than 7m2 but with some success it wouldn't be long before people start asking for something like a 9 and then if would be fun to see how Benoit would scale the design.

For now I can't wait to receive mine :jump: