Vortex Ring State Vuichard Recovery Technique Settling With Power

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Vortex Ring State Or: How I Settled With Power. Dan “Taz” Christman
2018 FAA Flight Instructor of the Year. Often considered as the equivalent of the fixed-wing stall, Vortex Ring State is a aerodynamic condition of powered flight where the helicopter “settles” into its own downwash. History of Vortex Ring State. What is Vortex Ring State? Conditions necessary for Vortex Ring State. Flight conditions leading to Vortex Ring State. Symptoms of Vortex Ring State. Recovery from Vortex Ring State. Settling with Power, all included in this presentation, and more. The insidious nature of Vortex Ring State makes it vital that pilots understand and avoid the conditions that lead to its development. George de Bothezat first recognized the vortex ring state in 1922 with his “flying octopus,” a machine with four massive, six-bladed rotors (similar to todays quadcopters). Since then, numerous flight tests, wind tunnel experiments and mathematical modeling efforts have refined our understanding of the vortex ring state. It is understood that the number of rotor blades, rotor rpm and rotor diameter have little effect on the vortex ring formation, but helicopters with higher disk loading and increased blade twist are more susceptible to it. In the U.S. there is a lot of confusion on whether Vortex Ring State should be (properly or improperly) called Settling With Power.

The controversy stems from a condition completely different from VRS, in which engine power required exceeds engine power available. Over the years, aviation organizations have used conflicting terms in discussing these different conditions. In the 1950s, the U.S. Navy referred to the vortex ring state as “power settling” and used the term “settling with power” for the power-available-vs.-power-required situation. In the 1960s, U.S. Army pilots in Vietnam used the term “settling with power” to refer to the vortex ring state and “power settling” when they were trying to get out of a landing zone while being overloaded with troops. The FAA uses Settling with Power and Vortex Ring State interchangeably in the Helicopter Flying Handbook and the Practical Test Standards (as do several other authors). Most of the rest of the worlds aviation agencies differentiate between Vortex Ring State and Settling with Power and treat them as two separate issues. That being said, when it comes to the written tests most of these countries still use the terms interchangeably. Since the general consensus in the helicopter industry is leaning to the separation of the two terms, we will do the same. For now I’ll discuss Vortex Ring State as it is currently understood by the industry and then at the end of the presentation, I’ll explain a little more on the specifics of Settling with Power. Engineers analyze vertical flight dynamics using basic aerodynamic states of flow at the rotor during vertical flight.

Three of these being:
Propeller State
Vortex Ring State
Windmill Brake State The Vortex Ring State is only one of these three distinct working conditions for a helicopter’s rotor.

In the Propeller working state (normal working state), airflow is directed downward through the rotor and the rotor disc moves in the direction of rotor thrust, as in a vertical climb. Hovering is the static thrust condition in this state. The Vortex Ring State is only one of these three distinct working conditions for a helicopter’s rotor.

If the helicopter descends at greater than 300 fpm, upward-flowing air is drawn in and down through the rotor. This forms the large circulating pattern called the vortex ring state.
The Vortex Ring State is only one of these three distinct working conditions for a helicopter’s rotor.

The windmill brake state is encountered if the descent is allowed to continue to greater than 2,000 fpm. The flow of air is pushed entirely upward through the rotor. The force generated by the rotor is equivalent to that produced by a parachute of the same diameter.
Flight in the vortex ring state is characterized by very unstable flow conditions, which produce vibration and erratic thrust variations.

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