Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics
The influence of vortex ring state (VRS) on rotorcraft flight dynamics is investigated, specifically the vertical velocity drop of helicopters and the roll-off of tiltrotors encountering VRS. The available wind tunnel and flight test data for rotors in vortex ring state are reviewed. Test data for axial flow, nonaxial flow, two rotors, unsteadiness, and vortex ring state boundaries are described and discussed. Based on the available measured data, a VRS model is developed. The VRS model is a parametric extension of momentum theory for calculation of the mean inflow of a rotor, hence suitable for simple calculations and real-time simulations. This inflow model is primarily defined in terms of the stability boundary of the aircraft motion. Calculations of helicopter response during VRS encounter were performed, and good correlation is shown with the vertical velocity drop measured in flight tests. Calculations of tiltrotor response during VRS encounter were performed, showing the roll-off behavior characteristic of tiltrotors. Hence it is possible, using a model of the mean inflow of an isolated rotor, to explain the basic behavior of both helicopters and tiltrotors in vortex ring state.
Numerical investigation of vortex ring state of tail rotor and uncontrolled rotation of helicopter
Vortex ring state, or settling with power condition, of tail rotor of helicopter Mi-17 is investigated by numerical methods of Computational Fluid Dynamics (CFD). Distinct shape of inflow-thrust curves is described and various flow patterns at different locations of the curve are identified. The shape of the curve is identified as a feature responsible for uncontrolled rotation of helicopter at the onset of vortex ring state at the tail rotor.
Gender and History in Medieval English Romance and Chronicle
New York, Bern, Berlin, Bruxelles, Frankfurt/M., Oxford, Wien. This reading of canonical texts of medieval English literature - Sir Gawain and the Green Night and Chaucer's Man of Law's Tale - alongside Geoffrey of Monmouth's Historia regum Britanniae and other Anglo-Norman and English chronicles offers a broader context for reading the romance narratives and re-evaluates romance conventions in light of the genealogical priorities of these chronicles. By arguing that maternity is featured as a position of power, Gender and History in Medieval English Romance and Chronicle adds to our understanding of women and sovereignty, and the ways gender and authority were rhetorically linked to medieval texts.