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Sail Billow.
Sail Billow or close up angle all mean the same. They refer to the amount of sail depth. Some people refer to the length of the inboard standoffs but more properly it is the difference between the nose angle you cut the sail and the frame angle as set by the spreaders. Typical values of close up angle are 10 to 15 degrees in most kites, although I have used values of as high as 20+ degrees with good results. Large billow has some advantages.
The sail induces less crushing loads on the frame (less tendency to try and close the basic frame triangle).
The kite will usually be more stable and precise.
The kite will fly slower, this may be an advantage or disadvantage depending on your point of view.
Sail Camber.
Sail Camber refers to the curve in the sail along the sail chord. Camber enhances the lift of the kite when it acts as an airfoil. In my experience the best way to increase lift on the kite sail is to provide a substantial amount of camber and position the largest depth near the leading edge. If the kite sail were to contain two separate surfaces with space in between then moving the greatest depth point rearward would probably be in order.
My theory on having the camber positioned forward and having it so abrupt is that a separation bubble forms just behind the leading edge spar creating a virtual lower surface. In any case kite wings built in this manner exhibit large amounts of lift. I have made kites with other camber configurations and they did not come close to exhibiting the dramatic increase in lift.
The third kite on the gallery page is an example of large camber at the leading edge. The enhanced lift of such a design results in a forward pitching moment as theory predicts. This must be reacted by a lower bridle setting or the kite will pitch over once it starts to pick up speed (the apparent wind vector has moved around far enough to cause the wing to behave as an airfoil). The lower bridle setting makes the kite difficult to launch, it wallows from side to side until it gains some forward speed then it locks in to stable flight that is fast with greatly increased pull.
Center of Gravity.
Center of Gravity or CG is the static balance point on the kite. For most delta designs it is just in front of the "T" connector that joins the lower spreaders to the spine. For most of a kites flight regime the CG has little effect since the aerodynamic forces are much greater, but during a stall or a float the gravitational force on the CG is comparable to the aerodynamic forces.
There are some ways to move the CG. You can use ballast but that will seriously degrade kite performance if enough is used to make a large change in CG. Shifting the location of the spreaders will also move the CG. Use only one set of spreaders and move them well up the leading edge. The most forward CG I have ever seen in a stunt kite was the "Scimitar" designed by Skip Parks, the same fellow that designed the large version for the "Kiteski" system. The kite has only a leading edge and a spine and a few battens. The leading edge is held in a curved shape with a line between the wing tips.
I don't generally give CG much thought unless I am designing an ultra light kite. Then I try to keep it forward as much as possible for gliding stability. If I were to design an ultralight today I would probably use only one set of spreaders and experiment with the location along the leading edge to obtain the best CG location for performance as an ultralight kite.
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