Effects of Uncertainty on Slung Load Divergence Speed Determination

Azimuth-resolved 6-DOF loads data are now available on objects of arbitrary shape and attitude as discrete series. Divergence speeds of single-point slung loads are determined using simulation from these airloads, for flight at constant speed. The effects of various types of uncertainty on the divergence speed are studied. Scale-model divergence speeds for a cylinder of L/D 1, and a porous box are obtained. Three types of uncertainties are examined: measured or predicted air loads, poorly-resolved load variations, and gusts. Results show that typical uncertainties in wind tunnel data from continuous-rotation testing have little effect on divergence speed prediction. Poorly-resolved data cause significant uncertainty in the path towards divergence, but not the actual divergence speed, for some shapes. A robust control approach shows that the effects of gusts and maneuvers can be alleviated to some extent by flight control, so that safe flight near predicted divergence speed appears to be feasible.