A Qualitative Introduction to the Vortex-Ring-State, Autorotation, and Optimal Autorotation

The main objective of this paper is to provide the reader with some qualitative insight into the areas of Vortex-Ring-State (VRS), autorotation, and optimal autorotation. First this paper summarizes the results of a brief VRS literature survey, where the emphasis has been placed on a qualitative description of the following items: conditions leading to VRS flight, the VRS region, avoiding the VRS, the early symptoms, recovery from VRS, experimental investigations, and VRS modeling. The focus of the paper is subsequently moved towards the autorotation phenomenon, where a review of the following items is given: the maneuver, the height-velocity zones, and factors affecting autorotation. Finally the paper concludes by providing a literature survey relative to single-engine helicopter optimal autorotation, and its associated problem formulation as a nonlinear, constrained, optimal control problem.

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