Hydrodynamic Characterization of a Sonar Body for Rotorcraft-based Towing

This paper describes experimental measurements of a fully submerged body designed to be towed by a helicopter. The goals of the tow tank testing program are (1) to characterize the towed body model so that a hydrodynamic lookup table can be constructed for a simulation, and (2) to provide measurements and observations that can validate the simulation. In this phase of the experimental investigation, the towed body model was first mounted on a rigid sting, and hydrodynamic forces were measured for a range of speeds, pitch angles and yaw angles. It was shown that using the mechanically practical Froude scaling method can produce reliable force coefficients for the range of Reynolds number at which the full scale towed body is likely to operate. A second series of tests towed the model from a cable, and demonstrated that cable slack will produce transient motions of the towed body in the two directions measured, while gradual increases in cable tension do not disturb the equilibrium of the body.