Aerosoftware - skydiving

Group Separation

Here is an explanation of what group separation means. This explanation applies to any type of freefall: RW, vRW, AFF, tandem.

This first explanation assumes no wind. The effect of wind is illustrated later. All figures show trajectories from the point of view of someone standing on the ground.

The figure shows jump run from left to right. There is a horizontal brown line drawn at the exit altitude and at the opening altitude. The ground is represented by a thicker black line. A large X marks the perfect spot.

In the *ideal* case each group would exit at the top of the red line running inside the purple cylinder.

Groups need some space to do their RW or vRW. This space is represented by the purple cylindrical column.

At break off, groups need space to track away from each other, this is represented by the black cylindrical column around the purple column.

Some room for error is represented by the space labeled buffer zone.

When you add these distances together you get the separation distance between groups, that is desirable to ensure safety.

What about the forward throw from the aircraft?

This figure illustrates how the forward throw of the aircraft changes the trajectory of each group, (no-wind condition).
As you can see the significance of the aircraft's forward throw is relatively small compared to the separation attained by waiting for the aircraft to travel across the ground.

What About Winds?

Here is how high upper winds will change the trajectories and the safety columns of air. Jumprun is into the wind.
The forward throw is still there. but then the wind pushes jumpers down wind as they descend.

What Does This Mean?

These illustrations show that an optimal safe separation distance between groups, as viewed from the ground, is the same regardless of wind speed.

In higher winds, an aircraft will take a longer amount of time to travel across the same distance. This means you must wait longer before exiting behind another group. An alternative gauge (besides counting) that you can use to figure out when to exit is to observe the ground track of the aircraft from when the group in front of you exits to when you start your climbout. (Remember, as a courtesy to the folks behind you, to account for the time it takes your group to exit.)

What About the Exit Order Controversy?

The reason it is generally safer to put belly flyers out before free flyers is because of what *might* happen under canopy. The groups leaving early or late do not get an optimal spot. They are either upwind or downwind of it. Once under a canopy, these jumpers tend to fly back to the optimal spot. They don't want to walk;)

If free flyers go out before belly flyers:

  • the free flyers reach pull altitude (sooner than a group of RW in the same exit order) before the belly flyers behind them
  • the free flyers would tend to fly their canopies up the windline, underneath the belly flyers that followed them out
This is the reason most DZs have belly flyers go out before free flyers.

(This article is very incomplete, but I have some other stuff i need to do.)

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