Schietwedder wrote: ↑
Fri May 10, 2019 4:28 pm
Hi, thanks for the feedback.
Yes I know with the tip air intakes i actually don´t know anymore why I put them there but it wont have a negative effect I think/hope. It had something to do with that the blue cloth (because it was a recycled reserve parachute which has not been used) It was so hard to sew (silicone coated and very thin) that I put vents in the orange cloth which was 41g and a lot more stiff. But could have put it on cell 4 indeed. Is there any point why most production kites have them more towards the center other than that the tip cells are comperatvely small so a vent there would not be as efficient in area, and maybe that the flow is more spanwise towards the tips than towards the center-though that should be a relatively small effect on LE.
I made some material test before with the strap, so I put 20Kg on a 100mm long section of the internal strap and measured the strain (delta). It was 3mm (3%) so I think i went to that value + a millimeter safety. So under no circumstance the strap would have more strain than a 25cm wide section of the lower skin which I also tested. -> Strap takes the load always induced by the bridle.)
The lower skin is not the same width- chordwise of course with skin tension and canopy curve so I went to different strap lengths on A,B and C straps but 4% is the delta.
I then also calculated the angle of the D-Ribs and the resulting shortening of the D-Ribs so that it is in tune with strap tension which was also some millimeters. Otherwise it could have happened that the D-Ribs don´t transfer so much loads or the kite would get a bit zick-zack shaped in the air.
All these calculations are quite simple to do on a rectangular/constant canopy curve kite but get really complicated and confusing in more complex geometries, so I like this concept very much.
For the bridle configuration of your kite better (or more elegant) location for wingtip air intake is cell no 5, because that is free from dribs which can even interfere how valve works. Just a detail but if you can choose why not to choose better one. But like you wrote you had your own reasons because of the fabrics you used.
Usual locations of air intakes work well, wingtips inflate without problems from quite far away located air intakes. If it is not needed it saves weight and costs to not have them closer to wingtips.
I'm afraid you didn't consider billowing of the cells in your strap length calculations. Value of 3% is very low tension, it should be perhaps twice or triple of that. But these values depend on cell width and are AFAIK quite a lot results of practical tests. Cell shape control is certainly one of the most difficult things in foil kite (and PG) design. Too long straps don't do much, fortunately there is not harm either.
Your worry with the length of dribs is in principle correct but in practice some mm deviation is insignificant. If there wasn't dribs at all there would be many cms of deformation with bridles on every three cells and your cell width, that would be easily seen and it'd have a bad effect to how kite flies.
Lower (and upper) skin shapes come from the double curvature of your wing. The more you have canopy curve and air foil camber, the more shape upper and lower skins have and more they differ from each other.