Date: Sun, 27 Jun 1993 20:02:18 -1000 From: tanaka_be@swam1.enet.dec.com Message-Id: <9306280601.AA07928@enet-gw.pa.dec.com> Organization: Division of Applied Sciences, Harvard University Subject: Fine tuning an NSR Fine tuning the NSR. WARNING. Long winded post follows. In an earlier post, I suggested to a flyer that he adjust his clips down in order to reduce forward drive on his NSR (North Shore Radical), to make the stall and landing maneuver easier to do. He then asked if shortening the outhauls would have the same effect as moving the clips. In the context of the original post, I responded, yes. And, that the adjustments were interactive. Jeff Burka responds: >No, shortening the outhauls does *not* do the same as moving the clip up >and down. >Moving the clip changes the kite's angle of attack, whereas the outhaul >changes the amount of dihedral in the kite (in fact, on the NSR and NSE, >you can adjust between an anhedral and a dihedral). >When you move the clip down (marks up), you "let out the nose." This makes >the kite flatter to the wind. The kite becomes slower, pulls harder, and >turns faster. As you might guess, though, this also can hurt the kite's >low-wind abilities. Some folks adjust a kite for the wind they're flying >in. Some folks have different kites with optimal settings that they >pull out depending on wind conditions. And some kites need virtually no >bridle adjustment once the sweetspot is found (the Tracer and Pro both >fall into this category). Some kites will need the bridle adjusted a bit >as the sail stretches. >Changing the outhaul will, amongst other things, vary the amount of >oversteer your kite has. I have spent some time trying to figure out exactly what the outhaul adjustment is supposed to do and would like to share my conclusions with you all. It might be helpful to imagine a kite, superimposed upon a graph, so that the spine is the Y axis, and that the clips are on the X axis, equidistant from the Y axis. Y axis / |\ / | \ / | \ / | \ +=clips / | \ / | \ X ----------+---------+-------axis / | \ / | \ / | \ / | \ / | \ /=====this is a kite=======\ Be sure to make that a real crummy looking kite. What I've deduced is that moving the clips up and down (vertically), affects forward drive. Raise the clips, and the kite will have more forward drive. Lower the clips, and the kite will slow down. Moving the clips along the X axis so that they are both closer, or further from the spine (Y axis) affects turning characteristics. With the clips close to the spine, the kite will turn faster, and tighter, even to the point of oversteering. It will spin relatively flat. With the clips positioned in a "wide grip" position, away from the spine, the kite will spin slower, and much wider, but will track straighter, and will be more stable in slides. It will spin in a more "layed back" attitude with one tip closer to the pilot than the other. These are the two effects, generalized somewhat, that I believe we are trying to fine tune. Let's see what happens when we only move the clips on a real kite, an NSR, i.e. On a real kite, when we move the clips up, we increase forward drive alright, but we lose turning sharpness. When we move the clips down, we decrease forward drive, but increase turning ability. Why both effects? The bridle line that we are moving the clips on is tied on each side, to the end of the top spreader, and at the bottom, to the spine. When we move the clip up, it is moved toward the end of the top spreader, AWAY from the spine, in a radius described by the outhaul. When we move the clip down, toward where it is tied to the spine, the clips move simultaneously, TOWARD the spine in a radius described by the corresponding outhaul. If you have trouble picturing this (I can't imagine why with such a great diagram to use), try it on your NSR, or any other kite with a standard bridle system. The effects are interactive. Now, let's move only the outhauls. Theoretically, the outhauls should only affect kite turning radius. But, here's a little experiment you can try yourself if you have a kite like the NSR. First, adjust your NSR so that the outhauls are on the short side, and the clips are low enough so that when you try to launch with a nice firm snap, the kite only pops up 5' into the air or less. Without touching the clip adjustment, lengthen your outhauls 5" or more. Now relaunch using the same force as before to snap your kite up into the air. You should get a height of around 15' or so. More forward drive. So, it isn't really a question of whether or not the two effects are interacting, but why? Ok, when you lengthen the outhauls, observe the clips carefully. You will notice that they not only move closer to the spine, but also RISE in a radius described by the part of the bridle that is attached to the spine. Shortening the outhauls on an NSR gives it a wide grip, and if you observe the clips carefully, you will note that the clips also move relative to the kite, downward. Less drive. Interactive effects. When the original question was posted, the noter said that he was having difficulty doing a stall landing. I suspected two things. First, that his outhauls were longish because he was still rising even on the edge, typical of an NSR, and that two, I sensed that his kite was acting tippy, also characteristic of the "close grip". So in the context of that question, I responded, yes, that shortening the outhauls would produce more or less the same effect as lowering the clips. This is because that it will reduce forward drive, AND make his NSR more stable in the float position (otherwise known as a SWAG scientific-wild-a$$-guess). I also suggested that he adjust his kite to fly with short outhauls, and, for low winds, (you can also demonstrate this for yourself) lengthen the outhauls only. Try 4 inches. What you'll find out, is that the NSR will be able to fly in low wind just as well, if not better, than if you just raised the swivels. With the bonus that the original tight turning characteristic you have it adjusted for in normal winds will be better preserved in low wind (remember, the clips also move toward the spine) and at least you won't be stuck with those 20'radius circles that raising the clips high up often give you. I flew a kite in Hawaii once, which I believe was Kathy Goodwind's Zephyr. I hope this is right. At any rate, this kite had the long bridle running from the end of the top spreader, to the end of the bottom spreader instead of the spine. The "inhaul" ran from the clip to the spine. Raising the clips on this setup increases forward drive with no deterioration of turning radius. This is because when you raise the clip, it is forced to describe a circle around the inhaul, which positions the clip closer to the spine as it is raised and produces the "close grip" characteristics. Great kite. Outstanding in low wind. This interaction is slight. For large adjustments you would do just as Jeff suggests. Clips to control forward drive. Outhauls to control steering characteristics. My experimentation has shown me that the interaction is roughly 1/8" on the bridle = 1" on the outhaul (this isn't real accurate, but its the figure I use to help me guesstimate where I want to set things up at). If you have a favorite kite you want to fine tune, you might consider the "interactve effect" and get the combination of drive and turning radius you really want and what that kite is capable of. In summaray, I fully agree with Jeff in that the two adjustments are not identical but due to the interactive effect, can be used in a compensating manner in specific instances. Plus, this explantion could prove to be confusing to some. Plus, I might be all wet (oh well, it won't be the first time). Whether or not this theory is really correct, (I don't even know what an anhedral is...) I have been using it as if it were, and its been pretty helpful to me, hope it is for you, too. Good Winds, Bert Tanaka = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =