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Speed system / mixer test explanations

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foilholio
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Re: Speed system / mixer test explanations

Postby foilholio » Sun Apr 22, 2018 9:02 am

Adjusting Z is the same from a camber point as C and B in their correct ratios, which B does automatically on flysurfer mixers when you adjust C. Flysurfers standard advice is to adjust B and C in their correct ratios, why they don't just add a Z adjustment and make it simpler? The main differences between adjusting Z versus BC is BC has some extra tricks having two separate adjustments,and BC moves the bar sheet vs kite sheet point which I am not sure is a good thing considering shortening B will move the camber and bar both to more stall, and finally adjusting B or BC without adjusting Z changes the AB depower point, which can create a strange quagmire when trying to adjust kites where certain characteristics associated with lower AOA , depower, speed, float, hangtime, lowend are all unnecessarily affected.

Aging kites tend to need Z shortened but I have seen the opposite. Two factors involved are bridle shrink and pulley line shrink. Pulley line shrink always reduces camber so to correct shorten Z, bridle shrink tends to be in ratio i.e. B for 2cm C for 4cm Z for 8cm, but can be outside that a bit requiring at least 2 adjustments to fix, BC or BZ or CZ. The AB depower point is always reduced with any shrink. To fix that you only need to adjust B but to keep the correct camber you will need to adjust also C and Z. So the only way to truly adjust a kite is with BC and Z. Then there is the sewn canopy shape and porosity...which both change with age... Welcome to foils.

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Re: Speed system / mixer test explanations

Postby Regis-de-giens » Sun Apr 22, 2018 10:22 am

Sandras wrote:
Sat Apr 21, 2018 5:28 pm
A picture is a thousand words!
Regis many many thanks for your drawings and explanations.
One of the most useful posts in this site!

I understand that playing with the Z line has 2 advantages for someone that does not want to mess around a lot. 1) adjusts both B&C proportionally at once. 2) looks easier accessible than spl-C

An aging kite is more likely to need extending or shortening of Z?
Thank you. Very happy if it helps.
I agree with Foilholio : A used kite GENERALLY needs Z shortening.
Z shorening is indeed a bit easier to modify on a kite without any settable speed system included in the design. But as shown in drawings and also because you will gain some power, you may need to trim a bit on the bar to maintain the same overall AoA (not compulsory , just to keep the same compfortable bar position in ride).

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Re: Speed system / mixer test explanations

Postby Sandras » Sun Apr 22, 2018 11:02 am

Thank you both for the clarifications.

I've made a bar with lots of trim adjustment but if I understand correctly, shrinkage of spl limits the depower IN the mixer. (i.e the pulley will be at the end of the spl earlier because the spl is shorter)

So we can say that as kites age, backstall more and hindenburg less (in general)

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Re: Speed system / mixer test explanations

Postby Mossy 757 » Sun Apr 22, 2018 11:20 am

Yeah, as kites age they become increasingly "football shaped" meaning they acquire negative camber on the bottom of the airfoil to create a symmetrical shape that is less likely to front collapse but more likely to fly backwards.

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Re: Speed system / mixer test explanations

Postby kitexpert » Sun Apr 22, 2018 11:25 am

foilholio wrote:
Sun Apr 22, 2018 9:02 am
Adjusting Z is the same from a camber point as C and B in their correct ratios, which B does automatically on flysurfer mixers when you adjust C. Flysurfers standard advice is to adjust B and C in their correct ratios, why they don't just add a Z adjustment and make it simpler?
How could changes to very different part of chord (rib, airfoil) have similar effect? If pulley line has shrinked and pulls B-C area to low camber adjusting Z tighter doesn't affect it at all. It is a hack fix at best.
foilholio wrote:
Sun Apr 22, 2018 9:02 am
Two factors involved are bridle shrink and pulley line shrink.
That is correct. Due to different loads and line lengths bridle lines don't shrink equally.

To not make it too difficult it is perhaps best to remember basics:

1. Check and adjust flying lines to equal length with usual method

2. Check and adjust mixer. Replace pulleyline if it is too shrinked, I've seen 10% shrinkage in worst cases.

3. Check the bridle. This is the hardest part, because bridle has so many lines. However making some measurements here and there is enough - and if something is wrong you can always make more measurements. Most suspicious lines are those which are the longest and of course if there is a wingtip problems there is something wrong there. Usually loaded lines keep there length and less loaded tend to shrink.

With aging kites there is porosity problem which of course can't be helped much by tweaking the bridle.

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Re: Speed system / mixer test explanations

Postby kitexpert » Sun Apr 22, 2018 11:39 am

Sandras wrote:
Sun Apr 22, 2018 11:02 am
Thank you both for the clarifications.
...I understand correctly, shrinkage of spl limits the depower IN the mixer. (i.e the pulley will be at the end of the spl earlier because the spl is shorter)
No, it is not about line being to short for bar movement. Pulley lines are usually 100cm upwards (1:2 line has most movement and should be the longest one), so unless bar sheeting range is unusually long it is enough. Kite would backstall before pulleyline lenght is used. it should be remembered "neutral" position in mixer is with equal line lenghts (which is when bar is against the chickenloop).
Sandras wrote:
Sun Apr 22, 2018 11:02 am
So we can say that as kites age, backstall more and hindenburg less (in general)
That is true. Lowered camber makes kite slow and backstally.

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Re: Speed system / mixer test explanations

Postby foilholio » Sun Apr 22, 2018 12:43 pm

Honestly kitexpert you contradict your name at every turn. I often don't reply to you because well what they say about arguing with an idiot and all.

How can adjusting Z work when it's B and C that have shrunk? Well if you had read everything I had written that is not what I said. You would need to adjust BC and Z to get everything back to normal. Adjusting Z alone though can return the camber to normal though ( yes I know you believe you can't change camber with bridle tension "calm down" :-) ). Adjusting BC has with it the same problems of Z both won't correct the AB depower limit alone. If a kite was designed to have sufficient slack from the start on B that "any" amount of shrink wouldn't see it go tight, then adjusting BC or Z alone could be used. But I have never seen such a kite even though it would seem modern kites that can fly solely on A could be designed like that.

Replacing pulley lines well before wear would require seems well stupid. Factor in NEW pulley lines can be shrunk close to 10% and shrink is a continual problem, that after 1hour of use "technically" an adjustment could be used then why not have an adjustment?, either on the pulley line or on BC and or Z.

As to the range of mixers... here your lack of understanding shines through. Well you will find the 1meter C pulley line on most flysurfers gives roughly 1m up and 1m down. From the 1m up down to about level is the normal flying range, the 1m down is more advanced flying, landing and relaunch or reverse flying. What you seem to stumble past is a mixer needs to do a few more things than are simply labelled as "AoA changes", the same as a kite needs to do a few more things than are simply labelled as "lift". You will find a bar is quite capable of having a trim range of 1m or even a bit more, and with the manual use of hands on lines like in relaunch another meter is close near achieved. As to whether 2ms of range is needed on foils kites? Well on the larger 21+ sizes that is perhaps a bit short, but on a smaller 6m then 1/2 to 2/3 of that would be enough. I think manufacture, design and support dictates a standard mixer size.

Porosity can induce instability, can be countered a bit with mixer. But also there is performance loss I guess from increased drag so overall there is no real win there. A punctured tire you can drive slow but best to patch it up.

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Re: Speed system / mixer test explanations

Postby kitexpert » Sun Apr 22, 2018 4:44 pm

foilholio wrote: Honestly kitexpert you contradict your name at every turn. I often don't reply to you because well what they say about arguing with an idiot and all.

How can adjusting Z work when it's B and C that have shrunk? Well if you had read everything I had written that is not what I said. You would need to adjust BC and Z to get everything back to normal. Adjusting Z alone though can return the camber to normal though ( yes I know you believe you can't change camber with bridle tension "calm down" :-) ). Adjusting BC has with it the same problems of Z both won't correct the AB depower limit alone. If a kite was designed to have sufficient slack from the start on B that "any" amount of shrink wouldn't see it go tight, then adjusting BC or Z alone could be used. But I have never seen such a kite even though it would seem modern kites that can fly solely on A could be designed like that.

Replacing pulley lines well before wear would require seems well stupid. Factor in NEW pulley lines can be shrunk close to 10% and shrink is a continual problem, that after 1hour of use "technically" an adjustment could be used then why not have an adjustment?, either on the pulley line or on BC and or Z.

As to the range of mixers... here your lack of understanding shines through. Well you will find the 1meter C pulley line on most flysurfers gives roughly 1m up and 1m down. From the 1m up down to about level is the normal flying range, the 1m down is more advanced flying, landing and relaunch or reverse flying. What you seem to stumble past is a mixer needs to do a few more things than are simply labelled as "AoA changes", the same as a kite needs to do a few more things than are simply labelled as "lift". You will find a bar is quite capable of having a trim range of 1m or even a bit more, and with the manual use of hands on lines like in relaunch another meter is close near achieved. As to whether 2ms of range is needed on foils kites? Well on the larger 21+ sizes that is perhaps a bit short, but on a smaller 6m then 1/2 to 2/3 of that would be enough. I think manufacture, design and support dictates a standard mixer size.

Porosity can induce instability, can be countered a bit with mixer. But also there is performance loss I guess from increased drag so overall there is no real win there. A punctured tire you can drive slow but best to patch it up.
I don't know, I've been working, designing, building (incl. mixers, many different kinds of them) and using depowerable foil kites for over 15 years now (I still occasionally do) and never I've had any special problems with speed systems or bridles, I mean nothing that would make me think there is something I don't understand. But I must say when I'm reading your posts foilholio I quite often find it hard to follow what do you mean.

1) Yes, you can adjust if there is possibility to do so and you take care of all line rows which are affected. Length of pulley line is not so critical as long as it isn't too short. Like Regis wrote this general shortening should be compensated on flying lines also (or making A shorter too).

2)Badly shrinked pulley lines which I've seen are also more or less worn out. It is a cheap line, not worth playing with.

3)These "advanced flying" things are possible because pulley lines have some practical length. 1m range on C is much more than any (available) kite or depower line length (sheeting range) allows. Relaunch (LE down) happens when back lines are pulled, other line rows don't matter that much as long as they are pulled less.

Your opinions on line lengths ("1m up and 1m down", "2ms range" etc.) are those hard to understand things. Only biggest kites benefit long sheeting ranges, and because modern big foil kites have high AR (relatively short chord) it isn't that relevant even for them.

I suggest to keep different component adjustments away from each other as long as possible. Then it remains possible to follow and isolate changes and fix them more at where they exist. FS mixer adjustment is ok though, but when it is used to correct bridle line changes results are less than perfect.

For me adjusting kite is not difficult because I feel and and see what should be done. But if you have less experience and read instructions from here it can be overwhelming task. Endless bridle/mixer tweaking is 99% nonsense.

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Re: Speed system / mixer test explanations

Postby foilholio » Mon Apr 23, 2018 3:07 am

Lets just put the understanding thing down to a language problem and perhaps my lack of paragraphs( but that was intentional :-) )

Having run many a pulley line to destruction, replacing them for shrink is wasteful. Sheathed line has a wonderful soft failure where the core can remain intact for quite a while after sheath failure, noticeable as a rough point when sheeting. You can get stuck pulleys and other bad things happen or even full failure, best avoided if you can. I know the furry and thinning signs of a pulley line that is about to go so I usually replace them. But even with full failure I have ridden the kite in. Kite still works somewhat with just A and Z intact, another safety advantage of foils over tubes.

You have 15 years designing making kites, congratulations. There is many many kite designers/makers who once made for some well known brands, now they don't and most just do repairs. Ever wonder why that is? I can see you are knowledge in kite construction techniques, somewhat in design, but adjusting kites particularly old ones not so much. Also your understanding of fluid dynamics is well flawed, and that's a hint to the previous question to think on.

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Re: Speed system / mixer test explanations

Postby Kamikuza » Mon Apr 23, 2018 1:16 pm

foilholio wrote:
Mon Apr 23, 2018 3:07 am
Sheathed line has a wonderful soft failure
What? Mine snapped mid-jump and I got dropped like a rock from a decent height and had a very long trudge back to shore. I replace "early" to avoid that.


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