In looking at a handful of rockets which use canard type fins one half to two thirds the rocket's length forward of the rearward fins, and in the same line, I've noticed some behave nastily. Is there a formula for the air disruption a canard induces? Or a seperate design form for a canard? Is there a likewise formula for the cure? Let's say a .08" canard can be followed by no less than a .25" thick rearward fin.......or maybe a canard one half the size of the rearward fins must be twice the thickness......or maybe a canard must have a leading and trailing edge sanded down to one half the thickness of the center chord of the fin.
Chuck