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.
Airflow through helicopter rotors in vertical flight
In this report an attempt is made to describe the field of flow through a helicopter rotor, in various working conditions in vertical flight. The limitations of the momentum theory are discussed. The spread of the slipstream explains the existence of an airbody around a rotor, working in the vortex ring state. By considering the proporties of this airbody, the working conditions and the rough behaviour of helicopters at moderate rates of descent can be more clearly understood.
Technical Note: Accuracy of Straight-Line Segmentation Applied to Curvilinear Vortex Filaments
Electrical drive apparatus for a vehicle comprising a detachable battery pack and a further unit comprising an electric motor, a differential with output shafts to respective vehicle wheels and a transmission from the motor to the differential including a universally jointed shaft, the axes of the motor differential output shafts and the shaft being substantially parallel and the motor being on the sprung and the differential being on the unsprung part of the vehicle.