Empirical models of the magnetic field structure of flux ropes found in the Venus ionosphere indicate that ropes are unstable to long wavelength (>100 km) helical kink perturbations. The onset of such an instability can explain the apparent volume distribution of flux ropes with altitude, and their orientation as a function of altitude. In the subsolar region, the fraction of volume that is occupied by flux ropes increases from roughly 20% at high altitudes to more than 50% at low altitudes, which is a greater increase than would be expected if ropes convect downward as simple straight horizontal cylinders. The helical kink instability increases the fractional volume occupied by ropes by turning the originally straight, horizontal flux tubes into corkscrew-shaped structures as they convect to lower altitudes. This instability also explains why high altitude ropes tend to be horizontal and low altitude ropes appear to have almost any orientation. Specifically, the orientation distribution of low altitude subsolar ropes suggests a 70¿ average helical kink pitch, which agrees with the pitch obtained from the fractional volume increase.