vortex ring state for eggbeaters

[GregLocock]

A nice look at trying to figure out VRS, with a rather glaring disparity between real world and maths.

https://www.mdpi.com/2226-4310/9/2/61

Cheers

Greg Locock


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[Sparweb]

All flows that are unstable and/or turbulent are inherently a challenge to mathematical models. Note the many examples of helicopters in production and in service, that were flight tested in the vortex ring state, with no mathematical predictions to guide the pilots before they tried it.

IIRC, older helicopter design textbooks (Jacobs, Johnson) describe the VRS in detail and provide empirical charts to allow designers to select parameters that minimize it so that pilots are less likely to operate in ways that can enter it.