Freefall Drift Simulator Details

This 3D Freefall Drift Simulator was written by Dave "Juggler" Blumenthal, based on John Kallend's 2D simulator and his math and physics code.

John maintains a nice collection of freefall drift resources at his website, http://www.iit.edu/~kallend/skydive/.

Permission is granted to use this Freefall Drift Simulator for non-commercial purposes, provided that this page, or a link to http://www.skyjuggler.com/drift, accompany the simulator program. If you copy the simulator to another website or some other medium, please let me know so I can inform you of any updates.

What it does

Simulates the most likely trajectories of groups of skydivers in freefall with different fall rates, given the fall rates, airplane speed, and winds.

Assumes the following...

about the world:

ICAO standard atmosphere.
Ground is at sea level (0 MSL).

about the skydivers:

The first group of jumpers exits when the plane is directly over the "spot," which in this case is the red ball on the ground.
Skydivers maintain a constant attitude with respect to the relative wind, from exit to breakoff.
Exit altitude is 13500 feet MSL.
Breakoff and tracking is at 4000 feet MSL.
Canopy deployment is at 2500 feet MSL.
At breakoff, all jumpers maintain a flat track with a fallrate of 110 MPH and a horizontal true airspeed of 35 MPH, which is held until opening altitude is reached. For large formation skydive groups, this may not be enough to ensure safe separation of the jumpers within the group. Be sure that the horizontal separation between groups is enough to account for the additional tracking a large group will need to do.

about the plane and the wind:

The airplane airspeed readout shows "indicated" airspeed (IAS) which, at 13500 feet MSL, is about 81% of the airplane's true airspeed.
The windspeed readouts show true airspeed. The wind direction readouts indicate the heading the wind is from, as is conventional in aviation.
The airplane will do its best to make jumprun due north. If there are upper winds from the east or west, the plane will turn into the wind just enough to maintain a northward jumprun. If the winds are too strong, the plane may be blown to the south. If the eastward or westward component of the wind is stronger than the plane's true airspeed, the plane will be blown to the east or west.
If the plane's airspeed is set to 0, it will behave like a balloon.
The SR71 is a common skydiving jumpship. Really.

What's Next?

I have a number of improvements that I'd like to make to this simulator, both in terms of features and performance. However it's not likely that I'll get to it any time soon - I'd rather be jumping :-)

If there are specific features you would like to see added, please email me and I'll be happy to consider them.