Tuning adaptive canopy curve

[jakemoore]

The speed 4 8 is getting old. It's not porus. I have stretched the bridles, checked lines, replaced spl and tuned the mixer. I did the long mixer test on every lines

She flies great depowered with a nice c shape and stable tips. The drift behavior is unbelievably good. And if I'm looping the kite to power downwind it flies great.

When I'm trying to head upwind in good winds or keep speed on a beam reach at the lower wind limit it hits me: tips collapse and fold so the bottom skins touch.

It takes three to five seconds to establish air flow and open the kite by powering and de powering. Just enough time to need another water start for sure.

I've tried empirically shortening or lengthening B or A at the tips with knots or lcl. No satisfaction.

I can't decide if the tips are front stalling or back stalling. It happens in powered flight, usually with a brief lull, or momentary slack from riding over a wave.

Who would share wisdom regarding tuning the wing tips.

[alexrider]

T...
When I'm trying to head upwind in good winds or keep speed on a beam reach at the lower wind limit it hits me: tips collapse and fold so the bottom skins touch.
...
Who would share wisdom regarding tuning the wing tips.

Shorten B lines on the mixer a cm a a time in order to reduce de camber of the profile (depth). The tips collapse should be significantly reduced and
you might end up going better upwind, with possibly slower turning speed. If it's a Speed 4 DL, there is only B lines. On the Speed 4 Lotus, there is B and C. In that case, you've got to shorten C (and if you wish B as well remembering shorting C will shorten B by half the amount)...
Cheers
Alex

[foilholio]

I did the long mixer test on every lines

What is that long mixer test. I always remember reading about it but never exactly what it is.

She flies great depowered with a nice c shape and stable tips. The drift behavior is unbelievably good.

Flysurfer are such cock teases. They release 2 sizes and then! All gone FFS! The Psycho4+ platform has so much potential especially for freeride/style and surf.

When I'm trying to head upwind in good winds or keep speed on a beam reach at the lower wind limit it hits me: tips collapse and fold so the bottom skins touch.

What is the powered state? Bar fully in/out? rear lines tensioned? just or a lot? Are you moving the bar in and out when it happens? Like depowering for a short gust etc?

Also what is tips collapse and fold so the bottom skins touch? Do they collapse in perfect symmetry? Do they collapse into the rest of the kite? or do they collapse together like two hands clapping??

It takes three to five seconds to establish air flow and open the kite by powering and de powering. Just enough time to need another water start for sure.

I have some ideas but it does sound weird.

I've tried empirically shortening or lengthening B or A at the tips with knots or lcl. No satisfaction.

So shortening B didn't even have an effect on it? how much did you shorten it?

I can't decide if the tips are front stalling or back stalling. It happens in powered flight, usually with a brief lull, or momentary slack from riding over a wave.

Who would share wisdom regarding tuning the wing tips.

You'll need to answer my questions but it sounds like a problem ARCs develop, canopy stretching and becoming porous is the cause. top skin tuck was a solution. I think my pleats would work better and maybe recoat it. I am surprised adjusting the mixer didn't affect or fix it, I know my Pyscho4s behave nasty if Z becomes too tight. With them collapsing similar to what you describe.

[jakemoore]

https://vimeo.com/170791814/9529520c52 I made a short video of some tuning flights to illustrate. Its 1080p on vimeo for those curious.

BarPic.jpg (114.99 KiB) Viewed 1805 times

[foilholio]

Interesting video. My pyscho4s get similar when Z is too tight, I use a Zmod to extend Z 7 to 10cm. It looks like you have shortened B a bit as the wing tips are starting to pinch or V a bit. Lengthening Z will have the same effect maybe you just need to do it more. Great video though I can really see how the tips are hollow profiling and wanting to close in. If playing with the mixer doesn't work you could use my pleats to alter the profile. I would do 2 one at each 1/3 then 2/3 cord or 1/4 and 3/4. You can then come back and add another at the middle. or you can be conservative and just add one to the middle and add more later. I would do it from the tip cell to the cell just before the first inlet near the tip, it looks like the fold initiates there. In reality though making adjustments to the outerskin any where on the tips will increase the outward force on the tips. I.e you could just do a couple cells and you will already notice a difference. At the end of the day you will only have some needle holes if you don't like it. Looking at your kite though I think you would be happy with anything better. It looks unflyable. As I said though my pyscho4s do similar and lengthen Z fixes it, so try that first. It could be though the lack of a more forward B position on the oldspeed4 prevents a simple fix like that.

I will say as well ARCs do the exact same thing. It was described to me as the fabric stretching. I think it's porosity related as well. I remember a top skin tuck being talked as a solution. I think the pleat will handle it better. It is interesting though, further evidence of how flysurfers c shaped depowered profile works and one of the fundamental problems of doing it that way. I don't think flysurfer should scare just because of that, it works well on the pyscho4. There is other ways of doing it too.

[Johhnn]

Hahahahaha! Great video showing the problem! My S4 10 m dlx behaves a lot like this, though not quite as bad. Except when fully powered up, it flies through the air in kind of an inverted U shape. Haha. Very ugly. On mine the fabric is definitely porous, so I got the S4 10 Lotus to replace it. Except for this problem, the 8 m and 10 m were/are great kites. I'm just waiting for the day when my S4 8 m dlx which I love starts to do it.

I will be very interested in seeing if you can find a solution.

[jakemoore]

The win tips curl down nicely without dramas when depowered.

Foilholio:

Long mixer referrs to checking relative line lengths. If you put the bridle plan into a spreadsheet, you can calculate relative lengths. So for example its easier to see if one line should be 20 cm longer than the next than to see if its exactly 192 cm long. Originally described for Speed1 and the 1.5 mod, because the mixer knots were not aligned. Also, it accounts for bridle stretch above the mixer.

In the video above, the entire flight was performed with the stopper ball as shown, sheeted just to the point the kite opens up. I think this should be the maximum upwind position for sheeting the bar and obviously we don't want collapsing tips drag. Windspeed was about 10 mph. If I made a quick step toward the kite, a momentary loss of tension that might happen for example after going over chop the tips collapse.

3 different tests to increase AOA and reflex: Each time I changed only one side to compare to the other in flight. I shortened the 4 B lines near the tips by as much as extra loops on the larks head. At the extreme, collapse was worse. I lengthened 4 B lines near the tips by 1 LCL. Not much change. I lengthened A near the tips by 1 LCL. Not much change.

Interestingly increasing Z by 1 LCL did make very tiny improvement. I may follow that path first.

I have 2 ideas. 1) Short Z reduces tip reflex in the tips, causing the kite to be unstable. This may be worse with the bar in. 2) There are dimples on the topspin only where there are no LE stiffeners. This might also contribute to collapse. I might try to insert a stiffener. Somebody suggested weed eater line. I wonder how to temporarily add so as to test, and how to permanently add if I like it.

[foilholio]

It looks like you are depowering it when it collapses. If it is doing that only when powered it should be the bridles, so lengthen Z.

So for the long mixer test, you first calculate what the difference for some bridles should be at the kite with the mixer even? So A0 B+15 C+13 Z+5 etc. Then you lock the mixer even and measure the bridle differences at the kite and then adjust the mixer to compensate?

[Mossy 757]

It looks like you are depowering it when it collapses. If it is doing that only when powered it should be the bridles, so lengthen Z.

So for the long mixer test, you first calculate what the difference for some bridles should be at the kite with the mixer even? So A0 B+15 C+13 Z+5 etc. Then you lock the mixer even and measure the bridle differences at the kite and then adjust the mixer to compensate?

That's what I do with my Elf since its modified speed system doesn't allow me to use the ABCZ knots anymore as a reference point. Fix the ELC's and then make sure your relative measurements are clean at the canopy with A row as the zeroed out reference. This works really well if you've ever cut/spliced/pigtailed a part of your speed system and have no fixed point of reference below the bridle/speed system interface.

[jakemoore]

Exactly.

And for kites with no line plan, consider marking the bridle with the kite bedded in near new.

After the first few flights if you are happy fix the line attachment points so they are even. A Sharpie marker works well.

Use one color to mark the bridles front to back chord wise. Mark Z where the C connects to the kite. Mark B where C connects to the Kite. Mark B where A connects to the kite.

Use another color to mark the bridles span wise along the A so you can reproduce canopy curvature.