"It turns out that when the rock size is set to about 3 centimeters in the simulation, it passes the skydiver at 12 seconds. This rock size just happens to have the same terminal velocity as the solution we found by matching the velocity seen in the video."
Hm. Poking around[1], drogue/pilot chutes seem to be around 30 inches or 75 centimeters in diameter. I wonder how you'd get a 3cm piece of "gravel" mixed up in that?
The pilot chute can be hastily scrunched up and shoved into the bottom of the container ("backpack") without any adverse effects to parachute deployment, so it's plausible that the rock was stowed by accident.
Hm. Poking around[1], drogue/pilot chutes seem to be around 30 inches or 75 centimeters in diameter. I wonder how you'd get a 3cm piece of "gravel" mixed up in that?
[1] http://www.chutingstar.com/skydive/chernis-collapsible-main-...