Wind Drift & Exit Order Graphic (Visit this link)By Tim Wagner on 2003-08-19
This graphic is based directly on the output of John Kallend's freefall simulation program set to the following conditions:
To view a graphic of the same conditions but the exit order reversed, click here.
This is what CAN happen under THESE conditions. It goes without saying that there are endless possibilities and variables besides those presented here.
I believe it is important to note Kallend's remarks regarding the creation of his program:
Most of the belly fliers I know maintain an essentially constant attitude unless they funnel. I suspect the head downers may vary (I don't freefly).
Also missing are such things as systematic backsliding, freaking around, etc. I believe these will impose a random spread on the calculated paths."
-John Kallend, Ph.D.
Many people have assumed, based on the arguments posed by this graphic, that it is a case for making fast fallers always exit after slow fallers. This is not the purpose of the graphic. There are instances where, as a DZO, I would have the fast fallers exiting first. An example might be if I had a DZ on an island and the spot was critical; I might consider the risk caused by a premature deployment to be less than the risk posed by drowning skydivers. At a wide-open DZ (like Skydive Arizona), out landings are less of a hazard, and the horizontal separation ensured by putting fast fallers out last becomes the deciding factor.
The bottom line is that there is much more to consider than wind drift and fall rates. Every drop zone needs to adopt a policy that provides the best safety under the conditions and types of skydiving that take place. There is no single solution that works for everybody all the time.
Perhaps most importantly, skydivers need to be educated about the effects of wind drift, fall rate, and time. Time is the key to understanding freefall drift; it is a basic observation that a slow falling group will experience more drift because it is drifting for a longer period of time than a fast falling group. While they are in the same moving air mass, they are drifting horizontally at the same rate, but they experience different periods of time in that air mass (in the above example, 29 seconds for the fast faller and 36 seconds for the slow faller). In conditions where there are extremely high winds aloft, it is possible for a slow falling group, exiting well after a fast falling group, to open up several thousand feet downwind of the first group.
-Tim Wagner, D-10552
Winsor Naugler's Another Look at Descent Kinematics
John Kallend's Interactive Java Freefall Simulation
More articles in this category:
- Launching 2, 3 and 4-Way Stars for Recreational RW - by Ed Lightle (Posted: 2010-09-14)
- Exit Separation Revisited - by Bill von Novak (Posted: 2006-05-10)
- Essay on Exit Order - by Bryan Burke (Posted: 2003-08-19)
- Another Look at Descent Kinematics - by Winsor Naugler III (Posted: 2003-08-19)
- Freefall Simulation Program - by John Kallend (Posted: 2003-08-19)
- Wind Drift & Exit Order Graphic - by Tim Wagner (Posted: 2003-08-19)