On The Role of Cable Curvature in Rotorcraft-based Tow Operations for Submerged Loads

This paper discusses mathematical modeling of helicopters towing loads that are submerged in water. Special attention is paid to the role of cable hydrodynamics and effects of curvature. Analytical predictions for a four-bladed conventional utility helicopter towing a representative load with fins for passive stabilization and depth control are shown for steady and level forward and turning flight conditions. As the lengths of the cable increase, the total drag from the tow cable is comparable to that on the submerged load and cannot be ignored. The role of hydrodynamic fairings is critical for reducing rotor power requirements. In turning flight, drag on the cable causes the towed body to turn with a radius that is smaller than the helicopter, and asymptotes to the center of the turn with increasing turn rate. Engine power may be limited by straight-line tow speeds, and not the peak turn rate.