Certifying the highest safe speed for an aircraft with a slung load, is life-critical yet daunting. Two flight cases are considered, to test an iterative procedure that predicts the divergence speed from experimental scale model data and simulations. The first is an empty engine canister. The second is a segment of a water-floatable military Ribbon Bridge. In each case, mass, geometry, tether length from a single rotation-bearing attachment, and moments of inertia, come from flight preparations. An initial aerodynamic load map is interpolated and synthesized from a growing library on bluff body aerodynamics. Dynamic simulation with these data predict maximum roll, pitch and yaw angles reached as functions of freestream speed. This yieldw a good initial estimate of critical speeds and dynamics. Model-scale wind tunnel data using our Continuous Rotation method about the required axes, refine simulation. For the engine canister, simulations matched detailed flight test data on maximum trailing and rolling amplitudes over the operational speed range. Trail angle data showed that Reynolds number errors are not significant. In this paper, model-based results explained the correct speed where the ribbobn bridge flight test was stopped. While flight test oscillation amplitude histories depend on initial perturbations of the load, a 15-degree initial amplitude gives conservative results. Ribbon bridge airloads resemble those on a long container but with asymmetries. Dynamic behavior follows the general pattern of an intermediate hump in roll amplitude followed by stable operation at higher speeds until divergence occurs.

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