In the old days we’d make this kind of effect by placing a circular emitter underneath the helicopter, but locked in Z to the ground (so the emitter stayed stuck to the ground underneath the helo). From this point particles would be emitted outward (ie laterally) from the emitter, the speed and quantity proportional to the distance of the helo to the ground.
Rotorwash is a subtle effect until the rotors get closer to the ground, then it’s more pronounced. The particles get shot out laterally, then become effected by turbulence and drag (and depending on the medium - gravity). If you’re doing dust, you can get away with different shading/rendering options. FumeFX would be good but might be tricky to control in this situation AND you might be stuck with a long translation on the helo, requiring a large grid. I’d done the dust (or snow) effect by using Afterburn for shading with good results. If doing snow, it always helps to render a second pass with just tiny particles to add that icy shimmer. If it’s water you’d dealing with, rendering LOTS of little tiny particles seems to be the best solution. I would do that with Krakatoa these days. FumeFX could be used to do a simple velocity field to advect the bulk of the particles and give you a good subtle but natural effect.
