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Flysurfer back stall

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Flyfish
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Flysurfer back stall

Postby Flyfish » Mon Oct 31, 2016 12:43 am

I recently re-tuned my quiver of pulse 2's and Psycho 4's. I changed all spare parts lines and made sure A B C and Z lines were all equal. Then I changed all of my depower lines and made sure all four line lengths were equal. But I still have some pretty bad back stall happening on the kites. I did not streatch any bridal lines on any of the kites. I can trim the back stall out by full depower strap pulled down. Other than the back stall, kites seem fine performance wise.

My question is:
1) Should I streatch my bridal lines?
2) Simply add pig tails to stearing lines?
3) Or would shortening just the A line a couple cm in the mixer reduce the stall?

Thanks

windrider1
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Re: Flysurfer back stall

Postby windrider1 » Mon Oct 31, 2016 1:27 am

ABCZ all equal does not really work sometimes instead try A and Z a little longer than B and C.

Jzh_perth
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Re: Flysurfer back stall

Postby Jzh_perth » Mon Oct 31, 2016 1:31 pm

You are certain it's related to the canopy profile and not the flying lines ? Have you got line plans ? You could measure everything...

Flyfish
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Re: Flysurfer back stall

Postby Flyfish » Mon Oct 31, 2016 3:14 pm

Jzh_perth wrote:You are certain it's related to the canopy profile and not the flying lines ? Have you got line plans ? You could measure everything...
Good question.
I definitively made sure all four flying lines were equal. So I'm pretty sure that's they are equal. I tie them off just before the mixer and pull with the bar fully powered. I even make sure the flying lines are a touch tighter than stearing lines.

As far as lengthinging B and C in mixer, would i lengthen B and C even?

windrider1
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Re: Flysurfer back stall

Postby windrider1 » Mon Oct 31, 2016 3:36 pm

No i said lengthen A and Z even in relation to B and C see if tht helps.


Flyfish wrote:
Jzh_perth wrote:You are certain it's related to the canopy profile and not the flying lines ? Have you got line plans ? You could measure everything...
Good question.
I definitively made sure all four flying lines were equal. So I'm pretty sure that's they are equal. I tie them off just before the mixer and pull with the bar fully powered. I even make sure the flying lines are a touch tighter than stearing lines.

As far as lengthinging B and C in mixer, would i lengthen B and C even?
Last edited by windrider1 on Mon Oct 31, 2016 4:45 pm, edited 1 time in total.

Mossy 757
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Re: Flysurfer back stall

Postby Mossy 757 » Mon Oct 31, 2016 3:44 pm

Jzh_perth wrote:You are certain it's related to the canopy profile and not the flying lines ? Have you got line plans ? You could measure everything...
The whole bridle shrinks on these kites very quickly, so taking individual line measurements and comparing them to the line plan will probably be more confusing than anything; the line plan is almost certainly inaccurate by the time the kite ships from the manufacturer to the retailer, just knowing how quickly Dyneema can shrink. I think you can find problems in the canopy bridles by making comparisons left side versus right side trying to find irregularities. That, of course, doesn't really account for back stall problems, but it's less frustrating than measuring from a line plan and realizing that literally ZERO of your bridle lines are the same length Flysurfer says they should be.

Since backstall is sometimes a factor of Z being shrunk or B and C being too tight, but you said your mixer is level, I'd measure Z and A from your line connectors all the way to the canopy at a main power rib and compare them RELATIVE to each other compared to what the line plan says. If the line plan says, for example, that Z should be 40cm longer than A but you find that Z is only 20cm longer than A, shrunken Z is your problem. You can add pigtails to the Z main above the speed system to account for that shrink so that your mixer test will still work. If the RELATIVE ratios of Z to A are close to what the factory line plan says, I'd investigate your B and C settings and see if extending them a bit improves the handling of the kite.

Flyfish
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Re: Flysurfer back stall

Postby Flyfish » Mon Oct 31, 2016 9:14 pm

Mossy 757 wrote:
Jzh_perth wrote:
Since backstall is sometimes a factor of Z being shrunk or B and C being too tight, but you said your mixer is level, I'd measure Z and A from your line connectors all the way to the canopy at a main power rib and compare them RELATIVE to each other compared to what the line plan says. If the line plan says, for example, that Z should be 40cm longer than A but you find that Z is only 20cm longer than A, shrunken Z is your problem. You can add pigtails to the Z main above the speed system to account for that shrink so that your mixer test will still work. If the RELATIVE ratios of Z to A are close to what the factory line plan says, I'd investigate your B and C settings and see if extending them a bit improves the handling of the kite.
That's interesting. I will compare A bridal to Z bridal. Thanks

axel_lotta
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Re: Flysurfer back stall

Postby axel_lotta » Mon Nov 07, 2016 1:28 am

Mossy 757 wrote:
Jzh_perth wrote:You are certain it's related to the canopy profile and not the flying lines ? Have you got line plans ? You could measure everything...
The whole bridle shrinks on these kites very quickly, so taking individual line measurements and comparing them to the line plan will probably be more confusing than anything; the line plan is almost certainly inaccurate by the time the kite ships from the manufacturer to the retailer, just knowing how quickly Dyneema can shrink. I think you can find problems in the canopy bridles by making comparisons left side versus right side trying to find irregularities. That, of course, doesn't really account for back stall problems, but it's less frustrating than measuring from a line plan and realizing that literally ZERO of your bridle lines are the same length Flysurfer says they should be.
Having gone down the path of painstakingly measuring the entire bridle, I can 100% agree with this statement. The company who makes the lines (LIROS) claims a maximum shrinkage of 1-2% but this is complete BS. The maximum shrinkage I have measured on the small white brake lines was up to 9.5% (in real terms that equates to over 50mm on a half meter line) and that is only for the very upper bridle. I had to add 60mm to just the Z main and Z main extension to bring it up to the stated line plan... That said, my kite also has backstall problems with a 100% correct (as per the line plan) bridle, and that is just apparently a feature of these kites due to the aspect ratio. I was flying it yesterday with a very experienced landkiter who always has his trim strap depowered about a third as a baseline. After all of the stuffing about that I have done getting everything perfect, it appeared the way to get my kite flying nicely was just to reduce the length of the front lines (by shortening the black rope between the trim strap and small alloy block) by about 3 inches (75mm). I also added about 3 inches to the safety line with an small extension. This was done because when fully powered up, this line was as tight as the normal front flying line beside it (this won't cause back stalling but is nice to have right anyway).

My advice is to spend the time to understand how the bridle lengths actually work in shaping the wing and what changing the lengths is actually doing as far as performance (giving the wing more or less camber etc). There is a Facebook tool floating about somewhere from Flysurfer that explains the mixer adjustment quite well. In short, flattening the wing (less camber) will cause a stall earlier in low wind, but makes for a much more stable (if less powerful) wing and will allow for better upwind ability due do the reduced drag. Increasing the camber will increase the low wind performance (to a point, too much will introduce massive drag which will cause stalling), but will lead to a very grunty and unstable kite at a higher windspeed. Also due to the increased drag, it will sit lower in the wind window and reduce you ability to go upwind.

One last point on this that not too many people are aware is that these kites actually have what is known as a 'reflex camber'. That is by their design, the shape of the airfoil is such that the about 3/4 of the profile from the nose back acts like a standard wing giving lift, whilst the last 1/4 to the trailing edge acts in the opposite direction effectively pushing the trailing edge downwards. This is why, you can sometimes get very good results by moving B towards to kite (increasing the camber and lift) whilst leaving C where it is allowing an amount of reflex camber to remain, effectively stopping the kite from wanting to tuck it's leading edge under itself.

I hope my comments have in some way helped, rather than added to the confusion..

Cheers,

Axel.

axel_lotta
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Re: Flysurfer back stall

Postby axel_lotta » Mon Nov 07, 2016 1:37 am

Flyfish wrote:
Mossy 757 wrote:
Jzh_perth wrote:
Since backstall is sometimes a factor of Z being shrunk or B and C being too tight, but you said your mixer is level, I'd measure Z and A from your line connectors all the way to the canopy at a main power rib and compare them RELATIVE to each other compared to what the line plan says. If the line plan says, for example, that Z should be 40cm longer than A but you find that Z is only 20cm longer than A, shrunken Z is your problem. You can add pigtails to the Z main above the speed system to account for that shrink so that your mixer test will still work. If the RELATIVE ratios of Z to A are close to what the factory line plan says, I'd investigate your B and C settings and see if extending them a bit improves the handling of the kite.
That's interesting. I will compare A bridal to Z bridal. Thanks
A quick tip on this from someone who has spent more hours on measuring a bridle than his girlfriend thinks sane, get yourself a cheap scale (the type with the gauge between the handle and a hook, sometimes known as 'fishing scales') and ensure you pull equal tension on your lines when measuring. I used about 5 pounds (about 2.5kg) with each measurement and it was very consistent for my readings without stretching the lines (oh boy, thats another topic sure to ignite some passion on forums such as this..).

windrider1
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Re: Flysurfer back stall

Postby windrider1 » Mon Nov 07, 2016 3:28 am

If youre coming from an LEI it takes a little bit of practice to understand flysurfer kites they are high tech kites and will backstall if you dont know how to trim the kite. The different speed series have more or less tolerance for this . Most guys I lend my kite to the first thing they want to do is let the strap out and I always have to tell them a foils is different u adjust the trim strap based on the wind conditions and feel of the kite if its not too windy then u actually want to depower the kite a little more so as to let it move through the wind window faster and generates apparent power. Some common problems are if your bridle lines or flying lines are mismatched as far as lengths then u may have issues depending on the severity . Sometimes small bridle line mismatches will not produce any problems. In general I never fly with the kite trimmed for full power or strap all the way out as I noticed I can go upwind better and the kite moves through the window faster generating full power with the strap pulled in just a tad bit . Any issues with stalling I check my line lengths from the bar then check bridles ABCZ. If all is ok then I lengthen AZ in relation to BC. But most time just depowering the kite a little bit solves most backstall issues.


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