Generally, the rope dart is made of 4 components: the dart/throwing knife, rope, rings and the rope dart flag. While the purpose of some of these components are obvious, I have not come across anyone who sees the flags purpose the way I do.
A quick search of the internet will have various authors describe the rope dart flag as a means of wind resistance or drag. Others describe its use as a means for distraction or to hide the dart. Before we explore both ideas and get to my own rope dart flag theory I would like to point out that I agree with the former theory (resistance) and whole heartedly disagree with the latter theory (distraction).
Any practitioner of ample time can feel an apparent difference between having a flag and not having a flag attached when playing. The dart is easier to control when it has some form of wind drag, which the flag provides. If you have never played the dart without a flag, try it. The difference in feeling is outstanding as the dart moves at a much faster rate and is more difficult to control, which is great for conditioning. Some feel that the flag serves as a distraction to hide the dart and/or confuse enemies. Â Sigh. Not really. If anything the flag could be looked at as counterproductive for this theory. Wouldnâ€™t, if anything, a bright red flag (or any color for that matter) alert an enemy that something is coming at them? Sure, they may not know it is a dart, but it is something, right? Are they going to stand there and wait to see what it is? Hardly. I mean, whose eye doesnâ€™t immediately follow this flag at the end of a rope? If anything the flag would alert someone of danger â€“ who wouldnâ€™t get out of the way of danger?
Now to the theory that no one is saying (so far as I have ever seen/read). First, lets look at other bladed weapons in Kung Fu to establish an overall theme. Weapons are used to kill an enemy in time of battle and efficiency for these weapons are a must. When one looks at, say, a spear, they will notice the hairs (originally horse hair) just under the spear head. When one looks at a saber, they will notice a bell guard, or rather, a blood cup. These components are used to absorb/catch/redirect the blood of an enemy so that it doesnâ€™t get on the weapon handle, and ultimately your hands making it a slippery mess.
So, if the horse hair on a spear absorbs blood and the bell guard of a saber provides hand protection from other blades and acts as a prevention for enemy blood getting on the hands then doesnâ€™t it seem likely that the rope dart flag serves the same purpose?! The flag absorbs the blood of a pierced enemy so that the rope doesnâ€™t get bloody. Same goes for the whip chain and other weapons with flags or â€œhairsâ€ on them.
In conclusion, the function of the rope dart flag (so far as I can tell) is used for wind resistance (more control) and catching blood.