Just came across this post. One of the biggest misconceptions about line drag is that the smaller the line the less drag it will create. This is not always true and in most cases, exactly the opposite. Line drag is created by the resonating frequency of the lines. The lower the resonating frequency the more drag the line creates. Most everyone has heard their lines "sing" to them in the stronger winds. This singing is the resonating frequency being produced by the lines as it moves through the air. The higher the frequency the shorter the resonating wave length of the lines and the less drag the line will be creating. All lines resonate whether you hear it or not. Most of the time the resonating frequency of the lines is below the normal hearing spectrum of your ears, but the line is still resonating.
As the line resonates, it "waves" back and forth very fast. You can re-create this phenomenon by taking an extension cord or Jump Rope and wiggling it back and forth really fast. The total distance created by the "wave" of the line is what creates the total amount of wind resistance - NOT the actual diameter of the line. So having a line that is less than 1/8" in diameter, but is resonating at a distance of 2" will create the same amount of wind drag (or even more) as a 2" diameter pipe. The reason that the wind resistance can even be more than the same size pipe is that the wind flows evenly and smoothly over the roundness of the pipe but is abruptly disturbed as it flows around the "wave" of the line, making the line appear to be even larger in the eyes of the wind.
Powerline Sports is a manufacturer of Q-Power line, similar to that of Shanti and Laser Pro and also produces line for many military and commercial applications. Powerline Sports created a specialized spectra line that has a linear wrap around the entire length of the spectra line - called Q-Power line. This extra wrap nearly doubles the overall diameter of the line compared to the same test line produced by other companies. Q-Power line has been wind tunnel tested against other lines including LPG and Shanti and has proven that the larger diameter line with the specialized linear wrap actually produces less wind resistance and overall line drag than any other line on the market (as of 3-4 years ago anyways). The reason is that the linear wrap of Q-Power line allows the wind to flow smoother around the line and the extra stiffness of the line reduces the amplitude of the resonating frequency. One of the most noticeable feature of Q-Power line is that it "sings" much louder and higher pitched than other lines.
I am not pushing or pimping Q-Power line, just using their line as an example to show the differences in diameter and the effect it has on line drag. We use a ton of Q-Power line for our power kite sports, especially kite surfing and snow kiting. The line is pretty awesome in that the extra linear wrap means that you never have to use sleeving, just fold and tie. The line seems to last much longer than other line as well. I have some Q-Power line sets that I have been using on my traction kites for over 8 years with no show of wear (other than they are quite dirty now).
The biggest reason that light weight line is used is not because of the smaller diameter and less line drag (myth), but more because of weight savings. Trying to fly an indoor Rev on 200# Q-power line will just be silly. You will have nearly zero line drag but the weight of the line will kill the flight of the kite. Weight savings would be much more important than that of line drag, especially when flying indoor or in SUL conditions where kite speed is so slow anyways. When flying my Focus Manta in zero wind conditions we can see the difference in line weight. Right now it has 130# waxed line on it which is easier to feel, see and grab than the thinner 50# Spectra line. You can see the heavier line actually pull the nose of the kite down more than the lighter weight 50# line. The reason I like the heavier line is because it is easier to grab when pulling the line in, pays out easier when you set the Manta into a glide and it rarely ever tangles up. Tangles were a constant pain with the 50# line but the glide was slightly better.
Anyways, just wanted to add some food for thought. Not that it means anything at all, but it may give you something to BS about the next time you are sitting around waiting for the wind to pick up.
As always, this post is worth exactly what you paid for it.