Passive Stabilization and Stability Quantification of Helicopter Sling Load Payloads

Helicopter Sling Load, while the most accurate form of aerial delivery, can be the most costly and inefficient materiel delivery option due to payload instabilities. These instabilities cause a reduction in airspeed and, therefore, increase the risk of being exposed to enemy fire while in hostile areas, increase the time of delivery, reduce the effective mission range, and increase the mission cost. This paper describes the design, wind tunnel, and half-scale flight testing of several flexible (fabric) passive stability concepts, including rigging changes and materiel prototypes. The most successful device demonstrated was a fin attached between the aft two sling legs. This fin was simple to attach to the payload and could be compact enough to store in a pocket. A method of quantifying stability of tethered bluff bodies was also demonstrated as the integration of the Fast Fourier Transform in three primary load instability motions. This stability coefficient showed excellent correlation with qualitative data, and therefore could be used to rank effectiveness of stability devices.