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.