Do You Make These 6 Mistakes When You Pack?

You Might Be Setting Yourself Up for Hard Openings

Mind your slider when you pack. Image © Joel Hindman

Usually, it’s an excellent sign when your parachute opens overhead – cause for a bit of celebration, really – but sometimes, it can kill you.

Yes. That.

If your canopy deploys with sufficient force, it can break your neck, break your back, or even rip open your aorta and end your skydiving career very abruptly. Here's how to pack in a way that minimizes your risk.

Slider Placement

When a ram-air canopy opens in freefall, the dynamics of that opening are controlled by two processes:

  • Cell inflation: the process of air entering the cells through the inlets along the canopy’s leading edge and pressurizing the airfoil
  • Bottom-skin Spreading: The side-to-side spreading action of the canopy as the relative wind hits the bottom of the canopy. This process is very efficient, since a skydiving canopy is “anhedral” (sides tilted down) rather than “dihedral” (sides tilted up) and is designed with stabilizers that additionally cup the air under the canopy.

Bottom-skin spreading is so efficient, in fact, that the canopy will open entirely by this method if there is no slider -- and it will reach full extension before the cells have a chance to inflate and pressurize. Such an opening exerts enormous forces on the jumper. In one test by the Parks College Parachute Research Group, a sliderless jumper was subjected to 18 g. To put that in perspective: before WWII, the US Air Force did not consider those g forces survivable.

A slider, therefore, has one main function: to put a damper on bottom skin-spreading, removing it as far as possible from the canopy expansion process. A correctly packed slider stays at the very top of the lines during the early part of inflation, kept there by the same forces that would smack the canopy open with bottom-skin inflation.

The slider is finally pushed down when the wing pressurizes and spreads the lines forcefully apart. By that time, descent has slowed to the point where the forces on the jumper are no longer dangerous.

A slider can’t do any of that if the packer doesn’t set it up for success.  It must be placed correctly.

Here’s how to help your slider help you:

  • Snuggle the slider grommets right up against the slider stops (and make sure it stays that way throughout the pack job)
  • Conscientiously quarter the slider, drawing folds between each of the four line groups. This ensures that the slider is evenly and centrally placed, which allows it to present correctly to the relative wind.

Line Stows

Bottom-skin spreading isn’t the only thing that can make you see stars on deployment. Incorrect line stows can “dump,” resulting in the serious discomfort of a “canopy-first” opening.

Line dump (sometimes called “line strip”) occurs when the line stows release prematurely. In this situation, the canopy inflates while there is still significant slack in the lines; when the lines catch up to the canopy, the force rings the jumper like a bell.

When you pack your parachute, keep in mind that your deployment bag (“d-bag,” without any of the funny connotations) is designed for one purpose: to keep the canopy hidden from the wind until the point in deployment upon which it should be presented. To that end, it’s your responsibility to manage the stresses on the system by closing the bag and stowing your lines conscientiously.

Here’s how to properly mind your lines:

  • Wrap your rubber bands securely. It should take roughly 8 to 12 pounds of pressure to pull your lines loose of your rubber band stows. If you’ve gotten lazy (or your fingers have gotten boogie-itis), you’re putting yourself at risk.
  • Keep your bights (the loops of line on the outside of each rubber band stow) an average of two inches long. This may be longer than you’re used to, but it ensures that approximately 25 percent of the side-to-side length of the stowed line sits outside the bight, minimizing its ability to “dump.”
  • Equalize the length of each stow. The edges of the bights on each side should sit in a tidy line.
  • If you have a stowless bag, think “even.” Though packing practices for stowless (rubber-band-free) deployment bags are very different, the principles are the same: fold the lines neatly and evenly, then close the bag with 8-12 pounds of pressure, equal on each side.

    Another note: if you consistently experienced harder-than-you'd-like openings, even when you pack correctly and mindfully, look into the material your skydiving lines are made of. Some are distinctly "springier" than others.

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    Your Citation
    O'Neil, Annette. "Do You Make These 6 Mistakes When You Pack?" ThoughtCo, Feb. 5, 2016, O'Neil, Annette. (2016, February 5). Do You Make These 6 Mistakes When You Pack? Retrieved from O'Neil, Annette. "Do You Make These 6 Mistakes When You Pack?" ThoughtCo. (accessed November 17, 2017).