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Speed 3 21m Upwind adjustment

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Regis-de-giens
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Re: Speed 3 21m Upwind adjustment

Postby Regis-de-giens » Sun Jul 24, 2016 11:48 pm

The Captain wrote: what is the symptom of shortening them?
More backstall in low wind (i.e kite flying backward toward ground) and less pull force (i.e more difficult to waterstart and planning).
Changes in length of yellow spare lines through pulley has no significant impact since you can replace the ring to align the mixer. If you want to do a complete check, you need to measure all final bridles to the intrados and compare to original. You can indeed first try the 0/0 or -1/-2 mixer test which is more easy to do first. This is not a negative camber but rather a more flat camber.

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Re: Speed 3 21m Upwind adjustment

Postby Kamikuza » Mon Jul 25, 2016 2:52 am

foilholio wrote:You have lost me. Going up to the pigtails for what, mixer test or measuring or...? The length of the pigtails is just line trim.

So it looped, but it didn't loop hard? and of course you could back stall it on to the water or flag it? I would think an A main going would be enough to make it collapse and not be relaunch able. With a short wac line you could probably still fly it.
For line tune. Beacause OCD :D

The wind had picked up which was good, but the gusts were brutal. I'd just got to the shore, about waist deep in water when a gust hit. Kite surged, drifted back, powered up lifted me, and I felt the "twang" of something breaking and the kite looped--hard. Pulled me up out of the water and at the beach, the same as when I broke my wrist :lol: this time I went in feet first and the sand had been fluffed up, so it was like a little jump. Went for the QR when it twanged but missed it, but the kite looped into the beach and stayed put so I ejected then and easily recovered the kite.

Now I think of it, I blame the Dynabar for missing the QR. Kite at the zenith, so the QR was against my body. One and only example of a regular spreader bar advantage . . . ?

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Re: Speed 3 21m Upwind adjustment

Postby Jzh_perth » Mon Jul 25, 2016 4:28 am

I don't think anyone else has suggested this - apologies if you have - but does the kite perform better with more trim (depower) on ?

I had the same kite and found as the rear lines shrunk, upwind performance became compromised as the kite can't fly far enough forward in the window. Depowering the kite is a simple way to check. Above the trim strap you have the 2 black lines with a figure 8 knot that you use to shorten the front lines to counter this.

I suspect if you checked, you may find your rear lines are shorter than the fronts when the bar is fully sheeted in ( and no trim on). They need to be equal.

If you can't shorten the fronts any more because this has already been done, you may need to add pigtails to the rears (or invest in new flying lines. )

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Re: Speed 3 21m Upwind adjustment

Postby foilholio » Mon Jul 25, 2016 5:45 am

Kamikuza wrote:but the kite looped into the beach and stayed put so I ejected then and easily recovered the kite.
Good it stayed put. I feel foils don't really have a tendency to deathloop. They can but the circumstances are much rarer compared to an inflatable. A slight imbalance in the system and they don't want to fly or end up stuck on the ground/water. You can also easily disable them by pulling on any line and they won't want to fly.
Regis-de-giens wrote:Changes in length of yellow spare lines through pulley has no significant impact since you can replace the ring to align the mixer.
Realigning the mixer only accounts for half of pulley line shrink. As explained viewtopic.php?f=197&t=2392205. As to the significance that depends on the user and use. For someone chasing absolute lowend or highend or performance it matters.
phpBB [video]
In this video he is failing to get a speed3-21 to fly forward, pulley line shrink and no adjustment to fully correct it would be one of the reasons why that was happening.(inept piloting would be another:-) Sorry Hawaiis love yay bro but....
Regis-de-giens wrote: If you want to do a complete check, you need to measure all final bridles to the intrados and compare to original.
For the first time I tried this "long mixer test", while the results where ok they were far from great. I suspect the problem is as I have measured on kites the span wise changes are different, so if you measure and adjust because of the tip, the center will not be correct and vice versa. I think hand tuning produces better results but the damn flysurfer C adjust B makes that difficult plus no adjustment for Z. I actually think just adjusting C and Z mainly and the AB depower point and not B in the profile is the simplest complete way to adjust a mixer, but I will still think on it some more.
Regis-de-giens wrote: You can indeed first try the 0/0 or -1/-2 mixer test which is more easy to do first. This is not a negative camber but rather a more flat camber.
Well it will be more reduced, it may or may not be negative. Depending on the amount of sheeting the kite will still go positive at some point, you need a much bigger adjustment to prevent that. I would actually say most of AB or C transition state is negative until Z engages.
The Captain wrote:what is the symptom of shortening them?
worse upwind and better upwind:-) The profile will be better for upwind but you are limiting the depower more by shortening B, so worse upwind when the wind is stronger. You will need to use a ZMOD to get the results you desire. You can counteract the less pull for waterstart etc by setting the WAC(hard soft) line to hard or AB even.
kitexpert wrote:No. Best upwind needs high L/D ratio and enough pull to counter the drag of the kiter. If kite has negative camber and low AoA these values become very low, even 0. Then kite doesn't pull at all. At higher AoA negative camber is not as effective as cambered one.


From my understanding slight negative camber or reflex has the best L/D.
kitexpert wrote:Apparently you foilholio mess things up when you think mixer adjustments could result "negative camber". It would need huge amounts of adjustment and kite would distort badly. There is no kitesurfing kite which has negative camber and it would be foolish to try to distort kite such by tweaking the bridle. Reflexed airfoils are used, but not always.


Nope all depower foils like this produce negative camber until Z engages. Preventing positive camber actually requires large adjustments to disable Z being tensioned or tensioned much.

Yes the wing can distort, how much depends how much the bridles adjust away from the sewn shape. Ideally to achieve maximum efficiency the sewn shape and bridles should align for a good flight profile. But depower foils are trying to do many things, depower a lot and still remain stable, power a lot for water starting or jumping, have good L/D for glide and upwind. turn tight and fast, reverse flight for relaunch and other uses. From a relatively fixed bridle parafoil, like simple kites or paragliders, to this the design paramaters are huge and present a lot of complication. It's no wonder failed kite designers with a large lack of riding experience posing as "experts" can't seem to grasp many of these things. It is possible the have a foil change from its sewn shape quite a bit before creases are produced but they are inevitable given the wide use the wing must go thru.


kitexpert wrote: In practice best upwind is achieved when kiter takes out maximum pull of the kite when still able to hold the edge.
This a bit of a complicated subject but I will try explaining it more from my experience and knowledge. I think you need to look at the speed where minimum drag is produced. You need to look at both kite and board. The board needs to overcome the fat arse on it and do this efficiently it needs some speed , especially to plane. it will have an ideal speed where it does this with the least amount drag and so force to overcome that drag. The kite then needs to produce this force for the board. But it too has an ideal speed that it can produce that force with minimum drag. Benefit of a kite though is if the speed is above board speed you can fly the kite on it's lines in an S pattern or sine it, but if the board speed is below the kites... well then I guess some compromise must be reached between them. Speeds outside this will be less efficient and I would guess not go upwind as well. This aligns with my experience that in the lightest of wind (for the kite size, so power) I need to fly the kite up and down just to go or go upwind. In a moderate amount of wind/power I can effortlessly power the kite and ride upwind. Outside this it becomes harder work. The same with board speed, go too fast and I stop going upwind go too slow and I also stop going upwind, this I guess is the compromise territory. To say the maximum pull goes best upwind is really far from the truth like a lot of thing you write. First maximum pull is directly associate with maximum speed! Now although sailing boats claim they can get maximum speed going upwind the world records for speed like on Lüderitz are achieved at 140degrees off the wind which is way downwind. As to my own experiences going fast, going downwind off the wind is the trick, and both the speed and pull from the kite gets truly immense. Sometimes you are barely worth replying to kitetwit as you are so wrong so much but I found this interesting to explore on the keyboard again. Thanks.

Image

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Re: Speed 3 21m Upwind adjustment

Postby kitexpert » Mon Jul 25, 2016 10:57 pm

foilholio wrote:I found this interesting to explore on the keyboard again. Thanks.
Absolutely. These are complicated questions. There is so much changing parameters and feedback loops etc. :thumb:
foilholio wrote:From my understanding slight negative camber or reflex has the best L/D.
Airfoils with negative camber are inefficient, they have low L/D. Negative cambered airfoil has negative to zero lift at low AoA, then L/D is also 0 or below. At higher AoA's they work but are inefficient.

Reflex airfoils may have quite a lot camber, they are a compromises between efficiency and stability. They are often called auto-stable airfoils, because they resist low AoA's which otherwise may lead to front stall, with kites it means frontal collapse of the wing.

Best L/D is achieved with high camber airfoils. However there is two main reasons why they are not suitable for modern (depowerable) kites. 1) they are too unstable, kite with high cambered airfoil can not be used at low AoA. If wind is gusty it behaves aggressively, overflies and collapses. 2) they produce a lot of lift even at low AoA's. So kite with high cambered airfoil does not depower.

If high cambered kite is forced to low AoA by the bridle, to get it depower, it collapses. So they are made fixed AoA kites, at stable enough AoA. Then they produce very strong pull, stronger than depowerable kite at same AoA.

It is interesting question when kite has highest L/D, at which AoA. According to Peter Lynn it is near 10 degrees, so very well powered up. It is remarkable that it goes down slowly, it is still high at 20 degrees, near or past stalling. I don't know how much this changes for different kites but my own experiences (very long snowkite upwind legs) do support it.
foilholio wrote: Nope all depower foils like this produce negative camber until Z engages. Preventing positive camber actually requires large adjustments to disable Z being tensioned or tensioned much.
Like Speed? Produce? You can trust me, foilholio: there is no traction kite with negative cambered airfoil. I have studied several of them and designed some 8) Speed has cambered airfoil, actually I was surprised how much of it it has. Airfoil shape can be seen roughly from the inflated kite.

When kite is depowered fully it flies mainly on A-lines. Then airfoil shape is the designed one and undistorted. It usually has moderate camber and some reflex, to allow enough depowering and for the needed stability. When kiter wants more power he sheets in and kite turns to higher AoA, increasing lift and L/D. Quite often kite is designed to increase camber simultaneously when AoA gets higher. This distorts kite, but at higher AoA's benefits are greater and there is no fear for instability.

For example, you have a new FS kite, correct lenght bridles and even mixer setup. Then you have an idea: "I want to make it more stable, let's pull more B-C". This means you disagree with the designer how cambered kite's airfoil should be. Now when fully depowered some B-C pull may exist and really decrease the camber, but then does the kite fly as low AoA than before? Is there any gain in depower? When starting to sheet in adjustment kicks in: kite has less pull, it is slower, worse upwind, it does not fly as far in the window and is more stable and has softer feeling. There is some more distortion also at low AoA's. Overall result is lower performance, but in very gusty conditions it may be ok.

It makes more sense to try to increase the camber for the final sheet in like Diablo-line does. At high AoA distorsions don't matter much, later stall and increased lift are valuable then. But this comes at the cost of increased bar pressure.

Increasing camber universally makes kite unstable and harder to depower.

Remember foilholio that primary function of the mixer is to change the AoA of the foilkite, because it does not have chordwise rigidity to do it without it. Depowerable kite works very well without any adjustments or designed changes to camber there, but they are useful options of course.

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Re: Speed 3 21m Upwind adjustment

Postby foilholio » Tue Jul 26, 2016 1:47 am

kitexpert wrote:Airfoils with negative camber are inefficient, they have low L/D. Negative cambered airfoil has negative to zero lift at low AoA, then L/D is also 0 or below. At higher AoA's they work but are inefficient.
Nope I disagree depends how much , with a tiny amount they are more efficient, with any more they are less efficient. Depends where the negative camber is and obviously a none zero AoA is needed otherwise the lift is negative. Lets try not be stupid.
kitexpert wrote: Reflex airfoils may have quite a lot camber
They don't have to. Obviously some positive is needed to be called "reflex", but I don't think that is the most efficient shape, I think a slight negative over the whole airfoil is, emphasis on slight.

I know it's Wikipedia [url]https://en.wikipedia.org/wiki/Camber_(aerodynamics)[/url ]and it's about near supersonic speeds but "Some recent designs use negative camber. One such design is called the supercritical aerofoil. It is used for near-supersonic flight, and produces a higher lift to drag ratio at near supersonic flight than traditional aerofoils."

kitexpert wrote: Best L/D is achieved with high camber airfoils.
Not true, high cambered airfoils positive or negative have horrible L/D. Low cambered( and I think negatively so) airfoils that are thin produce the best L/D. This is one reason inflatable designers fail at designing flying things well, fat tubes and puffy(poofy:-P) profiles do not have aerodynamic benefits. What is difficult though is building a thin structure that is structurally stable. I.e. doesn't collapse, but also doesn't flap or vibrate making drag.
kitexpert wrote:If high cambered kite is forced to low AoA by the bridle, to get it depower, it collapses.
Yes and this would be why more reflex is used and more arc in the span, to increase stability so depower can be increased too.
kitexpert wrote:It is interesting question when kite has highest L/D, at which AoA.

Refer to the picture above sigh.

Highest "usable" L/D is at the lowest airspeed(wind) that can support the weight of the kite at a very LOW AoA which would be basically flying off A. You can observe this in light winds when the kite will start to overfly or fly really forward in the window. With some kites that really reduce AOA some times some bar can help but usually the weight of the bar is enough. BUT! to ride the kite needs to pull your arse so the airspeed for lowest L/D is higher. From experience gliding, best L/D is always achieved at low AOA's where more speed can be achieved, sometimes some negative camber works sometimes some positive camber but it is always very slight. Depends on the airfoil/wing too. Thin ones always have better L/D but need more speed to achieve it. This is all besides usability, fat airfoils are easier partly because they are more rigid and stable but also because they don't need to be flown fast to perform.
kitexpert wrote:Like Speed? Produce? You can trust me, foilholio: there is no traction kite with negative cambered airfoil.
There is plenty, ARC's are famous for it, it's in the fucking PATENT for fucks sake. Reflex is negative camber but at one section of the Airfoil.
kitexpert wrote:I have studied several of them


Obviously not enough though. HAHAHA
kitexpert wrote:Airfoil shape can be seen roughly from the inflated kite.


Get some glasses.
kitexpert wrote:It usually has moderate camber and some reflex


Doesn't disagreeing with yourself get tiring. No reflex some reflex, which is it.

kitexpert wrote:This means you disagree with the designer how cambered kite's airfoil should be.


No shit, nor is it possible for them to design a kite exactly for everyone or for every use, or to stay perfect forever. In all cases a foil can be adjusted to change it's behavior, inflatables too but much less so.
kitexpert wrote:Remember foilholio that primary function of the mixer is to change the AoA of the foilkite


I disagree, well it may be thought of to do that, but in reality I think it is debatable if a foil can change AoA at all. If it does change AoA it does very little. The majority of changes are in camber. Yes it can change AOA by changing position in the window like all kites!, but I am talking about AoA say with some line referenced off the tow point. What a mixer does is make the kite more usable, my big revelation was that the majority of use is merely playing with A and B. I don't think it is possible for B at it's position to really change AoA. If it did it's effects on power would be much much more noticeable. Instead it bulges the front or where ever it is on the kite changing the airfoil, not dramatically increasing power but dramatically increasing stability.

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Re: Speed 3 21m Upwind adjustment

Postby kitexpert » Wed Jul 27, 2016 7:28 pm

foilholio wrote:Nope I disagree depends how much , with a tiny amount they are more efficient
No, they are not more efficient, but significantly less.
foilholio wrote: I don't think that is the most efficient shape, I think a slight negative over the whole airfoil is, emphasis on slight.
Reflexed airfoils are not as efficient as traditional cambered ones. Slight negative camber is very inefficient airfoil shape. It has low lift and low L/D when there is usable amount of lift. It also stalls earlier.
foilholio wrote: it's about near supersonic speeds
Rare exeption, which has nothing to do with kites.
foilholio wrote:more reflex is used and more arc in the span
Yes, more reflex is used for more stability. Increased canopy curve has other design goals than adding stability.
foilholio wrote: There is plenty, ARC's are famous for it
In lift area arcs use cambered and reflexed airfoils. Traction kite with negative cambered airfoil is a very stupid idea, I have not seen one.
foilholio wrote: Obviously not enough though. HAHAHA
You are ignorant, foilholio. Actually this is quite ridiculous when you don't know even the basics of the kite design.
foilholio wrote:
I disagree, well it may be thought of to do that, but in reality I think it is debatable if a foil can change AoA at all.
This is just stupid. I am not going to explain how foil kite changes its AoA when bar is sheeted in.
foilholio wrote:The majority of changes are in camber.
False. Mainly AoA changes, camber possibly not at all. In many kites there is some more camber when powered up, but kites work just fine with constant camber. Changing camber is one third of the FS's "triple depower" system. It is ok invention, but not very original or essential for the performance of the kite. Any kite desigher can use it if he wants to.
foilholio wrote:I don't think it is possible for B at it's position to really change AoA.
This does not make any sense. There is nothing wrong with generally used locations of B for AoA change, nor locations of C and D.

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Re: Speed 3 21m Upwind adjustment

Postby foilholio » Thu Jul 28, 2016 12:00 am

You are not an expert and are very poor at observing things in the real world, just about everything you wrote is incorrect.

Low AoA, Low Camber, thin airfoil is where maximum L/D is. If you are talking about high lift you are talking about High AoA, High Camber, and yes stall is at it's lowest. If as you bring up talk about "usable lift" wtf is that? in use all profiles have a use, If you are talking about good/some more amount of lift where the L/D is still good then the amounts for camber/aoa/airfoil thickness are somewhere less than extreme all depending on airspeed.

There is more data out there on negative camber but not a lot. I base my statements on personal experience, hence I believe best L/D is with a slight negative camber. You know one the most high tech aircraft in history has a negative camber wing right? Known for it's incredible range, you don't get that without good L/D. Maybe it's a closely keep secret among glider pilots and thats why it's less known, or maybe just maybe you're the one who is ignorant. LoL the ignorantexpert it shall be your new name.

Looking at parafoils merely changing AoA is 100% incorrect, looking at them changing AoA at all may be partially incorrect or correct. I think the majority of change comes from wing distortions i.e. camber change. I base this on observations, i.e. functioning eyes and brain unlike a pompous prick like you.

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Re: Speed 3 21m Upwind adjustment

Postby kitexpert » Thu Jul 28, 2016 11:07 am

foilholio wrote:You know one the most high tech aircraft in history has a negative camber wing right?
It is not reasonable to value aircrafts by their "high tech" status. There is very different uses for aircrafts and they are designed for that point of view. Low speed airplanes (which are closest to kites) use high cambered airfoils.
foilholio wrote:as you bring up talk about "usable lift" wtf is that?
Low camber airfoil may have decent L/D at some AoA (not as good as higher camber airfoil though). But if it then does not produce enough lift, it is not a good choice for traction use.
foilholio wrote:I base my statements on personal experience, hence I believe best L/D is with a slight negative camber.
This is misunderstanding. You have never even used a foil kite which has "slight negative camber" - or do you want to tell what kite is was?
foilholio wrote:Looking at parafoils merely changing AoA is 100% incorrect
There is nothing strange if foil kite changes only its AoA when powered/depowered. Of course it can increase or even decrease camber if it is designed to do so. I'm afraid you foilholio still don't get how this is done, even though I have explained it earlier :roll:

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Re: Speed 3 21m Upwind adjustment

Postby Regis-de-giens » Thu Jul 28, 2016 2:49 pm

I'am affraid I cannot sort out your debate , but let me bring some biscuits and opinions, sorry for the long-bothering details:

- One way I found to get an estimation of L/D is measuring its angle "alpha" to the vertical when static at the zenith : L/D ratio = arctan(90-alpha). Even if hard to measure you can use this to check the impact of sheeting-in or out or check the impact of any speed system tuning if you have a good "neck" memory. It is also a good way to compare the performance of two kites if you have two synchornized pilots to put the two kites side by side. Another way to measure the L/D is to measure the speed of the kite "s" when crossing in the middle of the wind window ; L/D ratio = s / wind-speed

- L/D ratio decreases rapidly when AoA increases (of course after a minimum AoA otherwise lift is zero, hence L/D poor), as it is the case for most "Naca" profiles ; you can see a lot of curves on Google like this Image . ... knowing that the maximum AoA of a kite in15-20 degree.
So when AoA increases, Lift is indeed better (good for jumps, waterstarts, plannings) however traction direction points less upwind, hence to ride upwind with maximum speed, the rider shall find the optimum balance between pure traction value (high AoA) but better upwind traction angle (low AoA) ; this explains why it may sometimes be beneficial to sheet-out to save some upwind angle (depending on your support : TT , hydrofoil ...). Consequence in HF foil race : for speed and upwind, it should be better to have a larger kite a bit sheeted-out rather than a smaller kite more sheeted-in.

- Foilholio, AoA is not the angle of the line AB against the wind, but rather the line AZ (assuming that bridle were connected between intrados ad extrados) ; therefore when you pull on Z, even if A and B and C had been unchanged, then AoA will increase;
Image

... so yes the AoA will change as soon as you pull on the bar, even on a 4-line-handles-traction-kite without speed system and keeping ABC unchanged !

- As kitexpert said, the speed system 's primary function is to change the AoA without impacting too much the camber. It iaims at counteract the lack of rigidity of foil kites ( vs LEI rigidity that need no speed systems). If you remove it, you are on the case of a paraglider or a 4-line-handles-traction-kite, where camber increases hardly when AoA increases. If you add a WAC line or a diablo line on the speed system, it is a kind of physical limitation of the speed system impact, and you come closer to a paraglider mode. It could be an optimisation for a fine tuning, but not the overall principle of a speed system that act as a rigid frame.

- I agree with Foilholio that generally speaking, a higher camber may be in detriment of the L/D ratio (as for the AoA); this is why the speed system not only allows to depower the kite (in opposition to a 4 line traction kite which keeps ABC unchanged, therefore D will align with C when depowered, so less change of AoA , so it remains powered), but it also allows a better upwind ride. PS : that is why I have always thought that when we ( in france) say we put a "performance set-up" by extending B and C for more camber, it is a wrong expression ; we should rather say "power set-up" for more camber and use "performance set-up" for the opposite tuning (flatter camber = shorten B and C) as it should increase L/D ratio which is the definition of performance.


Foilholio, except ARC that are known to have poor L/D, I do not know which "standard" foil kite has a negative camber, so I am also interested to know which kite you tested has a negative camber with a positive impact on L/D ratio

BTW about the yellow spare lines, I maintain that extending B and C using the 2*2 inox rings on the MT of the speed 3 allows to counter act the totality of the Spare lines shrink (not all the bridles of course) until the ring touches the pulley ( then SPL have to be replaced)


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