Simulation of Rotorcraft Response Including the Possibility of the Vortex Ring State

It is imperative during training that new pilots are taught about the unstable condition called the vortex-ring state which can occurs during a vertical descent. They should be made aware of what it is, how it is induced, what is occurring aerodynamically, and how to react and recover. This paper demonstrates what occurs to the rotor inflow during a purely vertical descent and also illustrates how the addition of collective pitch can further excite the vortex-ring condition. Two sets of scenarios are simulated. The first scenario places a rotor in a purely vertical descent, linearly increasing the rate of descent from the initial condition, while viewing the total inflow radially for each blade segment. It is illustrated in this first test, that the rate of descent plays a large role in how well the instability of the vortex-ring condition establishes itself and how long the condition lasts. The second scenario is a duplicate of the first with the exception of introducing collective pitch shortly after the onset of the vortex-ring condition. This second scenario clearly demonstrates how easily the vortex-ring condition and inflow through the disk can diverge making it an extremely difficult condition from which to recover.