The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid.
it's not a smaller envelope to avoid - it means you can get into VRS easier (ie with lower RoD) in an aircraft with a lower disc loading. You have to have a higher RoD to get into VRS in a helo with a high disc loading.
Hence, smaller and lighter helicopters are more vulnerable to VRS since you can encounter it at lower RoD than in a big, heavy powerful military helo.
Much higher than 1700 FPM???? There are actually graphs and formulas for VRS, yeah know?
no. really??? The graph you are referring to was posted on here many years ago by Nick Lappos - it shows that you need to have a RoD around half to 0.6 of your downwash speed to encounter IVRS and around 0.7 to be in fully developed VRS,