simonmm said...
Without being an expert on the theory, I can only speak from practical experience and say that having flown many different kites on fixed and customised bars, there is an absolute world of difference in the ability to depower through edging with different kites. Even in the C kite only realm, some Cs are almost impossible to fly on a fixed bar whilst others perform like a dream. Actually, even different sizes within the same line of kites sometimes have vastly different performance characteristics (eg you may be able to fly one size fixed on really short 10m lines because of its great stability and performance, yet another size in the same line of kites is an absolute dog fixed on any line length).
My speculation would be that it is a combination of increased line tension and slowing the board down forces the kite forwards in the window. Again from experience, it is easy to see the kite surging forward even if you walk straight backwards in to the wind. Alternatively, imagine a model train on a circular track. Attach a string from the caboose to the centire of the circular track. Now pull on the string and the caboose will have to travel forwards or backwards on the track even though the direction of pull is almost perpendicular. A similar principle seems to apply to kites except that given they are designed to fly forwards, they have a propensity to head in this direction. It is just that some kites want to travel further forwards than others. The thing with the bows (and some poorly designed Cs) is that they seem to be much more sensitive to hindenburging or back stalling. From what I have seen, when you use a fixed bar with a bow it is difficult to get the kite to just sit there with minimal pull without hindenburging. When a gust hits, the kites seem to have a greater tendancy to overfly, hence needing to trim them further back in the window. The problem then becomes that they pull more and can sometimes backstall. The best Cs tend to surge forwards to a point then just sit there. Additionally, different kites do travel through the window at very different speeds. To me, at least, it definately feels like the faster kites fly through the window, the more reactive they are to edging (don't really have any theory to back this up, it is just how it feels).
I guess you can ping pong the theory all day, but nothing beats hooking up a bunch of kites to a fixed bar and giving it a go (this obviously applies only to advanced riders who are very competent in tuning and setting up kites). Some would label it a waste of a good windy day, but for the kite nerds out there it may be an interesting excercise (and going back to the origional thread might even improve your flying skills).
I'm not an expert on the theory either, or the practice, but just find it interesting to try to understand this.
I don't think your analogy of the circular train track holds. If the direction of pull is truly perpendicular to the track the train won't budge forward or back. And it doesn't matter how hard you pull. Just as tightening spokes doesn't make the wheel spin.
However I think you may be onto something regarding the Hindenburging. Increasing the load on a wing and increasing its angle of attack both make it tend to stall. Slowing your board down does both, and the more abruptly you slow it the more likely the stall. Different wing sections are more or less prone to stalling. But assuming a bow and a C both use the same section it's possible that the C might have an advantage here. On any curved kite the stall will start at the middle of the kite and work outwards because the affective angle of attack is highest at the middle and decreases towards the tips. On a C kite, when the centre starts to stall the tips will still be working because their angle of attack doesn't really change at all. The flatter the kite the more the tips will also start to stall at the same time. It seems reasonable to think that because a C kite maintains a strong vortex around its tips this helps keep the vortex at the centre of the kite from detaching as soon as on a flatter kite.
If this is right, it would explain what a few people on this thread have said: flying a bow without stalling it requires more active attention to the bar pressure and flying a C requires more active attention to controlling the speed of the board with edging.
