Conclusion 1 (cont.)
Why, then, do the common groundspeed (or ground-distance) based methods
work? Basically, because the windspeed at opening altitude is usually
small compared to the airspeed of the jumpship, and can be fairly safely
ignored. If the lower level winds are opposite the uppers, then extra
spacing is needed.
We now need to use a freefall trajectory simulation program to investigate these and other effects. This can be downloaded from www.iit.edu/~kallend/. Since it is an interactive program, you can put in typical jump plane speeds from your DZ, (70kts IAS might be typical of an Otter) and check out the effects of fall rate, windspeeds, etc. I suggest that you try various combinations of upper and lower windspeeds to check out the previous conclusions.