Also, it looks like Nick's example of the R22 for vertical and horizontal velocities assumes a level rotor disc which of course is not always the case.
So here is a scenario: I'll use a disc load of 4 which is close for light to medium turbine helicopters at reduced weights of pilot fuel and longline. This would give a downwash velocity, according to Nick's rule of thumb, sqrt(4*210)=29ft/sec = 1740 ft/min
At the 75% horizontal velocity this would be about 13 kts fwd and translates to a descent angle of about 37 degrees from the vertical or 53 deg below level and a total velocity on this path of 1740/cos37=2175 or about 22 kts.
So if we put the helicopter in a 15 deg nose up attitude descending with longline to pick up a load, the new flight path that would provide the same disc angle of attack and velocity would be 52 deg from the vertical or 38 deg below horizontal with vertical velocity at 2175*cos52 = 1340fpm and horizontal velocity of 2175*sin52=1714fpm or about 17kts. Then lets say that he is coming in cross slope and crosswind to the sling site of 14 kts blowing up a 45 deg slope, this is about 1000fpm of vertical airflow. Since this 1000 fpm flow is not moving atmospheric pressure gradient lines past the helicopter then it will NOT show up on the VSI. So here we have a situation where the velocity component normal to the rotor disc is 1740fpm and a VSI that will only read about 340 fpm and this is a 100% downwash velocity descent rate and Nick says you only need 50% to start seeing VRS.
Yes I know I neglected to factor in the horizontal wind component but I think the point is still valid.