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.
A Small-Scale Tiltrotor Model Operating in Descending Flight
A small-scale tiltrotor model was tested in the 7- by 10-Foot Wind Tunnel at NASA Ames Research Center with the goal of further investigating the aerodynamic environment of a tiltrotor operating in the Vortex Ring State (VRS). Test objectives were to obtain performance data of a 3-bladed tiltrotor model over a range of descent and sideslip conditions and to compare mean thrust results with a previously reported 2-bladed tiltrotor model investigation. Three sets of rotor blades, twisted and untwisted, were tested in a dual rotor configuration. Results of this investigation are presented, showing mean thrust reductions, a reduction in the effective lift curve slope and an increase in required collective pitch in the region of VRS. There was no consistent trend between the 2-bladed and 3-bladed untwisted blade sets or the two sets of twisted blades. Sideslip did not appear to significantly effect mean vehicle thrust.
Persius and the Programmatic Satire: A Study in Form and Imagery
Introduction 1. Style and expression in Persius' fifth satire 2. The programmatic satire and the method of Persius I 3. The nature and sources of Persius' imagery 4. Persius' first satire: analysis 5. Grandeur and humility: Juvenal and the high style Appendixes Text Translation Index of modern authors Index locorum potiorum Index of images, topics and words.