Sokol - greetings
The lighter helo has to decend faster to get in the same state as the heavier helo, right?
No.
If the heavy helo has to displace more air (same size disc) quicker to balance the mass (in the hover) then the speed of the downwash must be higher. That is where F = MA comes in.
If you require a rate of descent of at least half your downwash speed to get into VRS, then the heavy helicopter must have to descend at a faster rate than the lighter one.
If your Vi is higher (as it is in the heavy helo) then your Vd has to be higher to reach the required ratio for VRS.
