Dynamic modeling and simulation of a cable/tow body system of a helicopter

Abstract

For cases involving a helicopter involving a towing cable with an end mass, when the mass of the towed body is of the same order of magnitude of the towing cable mass, the dynamic analysis and simulation of the resulting system can become quite challenging, especially in cases that involve large cable lengths. This paper develops an approach utilizing the natural modes of a hanging string with tip mass in free vibration. With a modal representation of the cable deflection, the problem solution reduces to response to applied aerodynamic forces on the cable and the towed body. The aerodynamic forces acting on the cable are calculated using the cross-flow principle and the aerodynamic forces on the towed body are included using a table look up variations with angle of attack and sideslip angles, which are pre-computed using a comprehensive CFD analysis. The resulting equations of motion in generalized coordinates are numerically integrated for determining the cable transient deflections due to helicopter maneuvers. Results from transient simulation of the cable/tow body system for selected cases of helicopter maneuvers are presented. Further, the impact of variations of cable/tow body system parameters on the tow body transient motion are analyzed.