# The second, most important, law of tether drag

Hi. This was my poster talk. I’d be happy to comment it here, and also uploaded the PDF

Based on feedback, I should mention that the title is humorous (though probably only I find it funny). The «most important» should be read like «very important».

There is no «first law of tether drag». What I meant was that one assumes tether diameter and aerodynamic drag is the problem with tether drag. I am stating that there is a second thing about tether drag that we should be aware of, one related to only tension, mass and rotary speed. If this law is violated, tether drag will increase indirectly as a result of the «jump rope effect».

Based on the 3D shape equations, I also devised a method to measure tether drag quite simply bu measuring phase angle difference between tether at the winch and the kite looping (remember that the tether is kind if spiral shaped)

Last note: The equations have not been shown completely on the poster due to space restrictions. I might add these later if there is interest.

Second last note: The equations may be used to calculate the tether shape using a numerical solver (time simulation). Just replace time t with tether position s and simulate from zero to l

Third last note: The actual drag may be easily calculated by using T and the derivative of \alpha(s) at l.

Oh, and the second law states:

T > \mu \left( \frac{v l}{R} \right)^2

T - tether tension
l - tether length
v - kite speed relative to ground