Tension Knots

Q:

 

What are tension knots, and how can I avoid them?

A:

Sloppy line bights such as these can lead to tension knots forming during deployment.
This twisted brake line illustrates how tension knots can form.

A tension knot occurs when two or more of a canopy’s lines tangle during deployment and then lock together when tension is applied (i.e., when the canopy starts to inflate and the lines are placed under a load). A tension knot most frequently involves a brake line. Because a brake line is free at the riser end, it is easy for it to twist up (particularly if the jumper is not in the habit of stowing his toggles back on the risers after landing). Jumpers need to periodically untwist their brake lines so that the twists don’t become so severe that they cause the lines to loop and wrap around nearby suspension lines during deployment.

 

John LeBlanc, vice president of Performance Designs, offered these additional observations and some advice about tension knots gleaned from his more than 30 years in the parachute business:

  • Use the same type and size stow bands. This helps to keep the tension on each line bight (the loop of line after each stow band) equal so that the lines unstow in an orderly fashion. A loose stow can lead to a premature release of the entire bight of suspension line during deployment. This out-of-sequence unstowing leaves a lot of slack in the lines and provides the lines more opportunity to wrap around each other and lock into a tension knot once they are pulled tight during canopy inflation.
  • Old and fuzzy suspension lines have a greater chance of knotting than new, smooth lines.
  • Pack by keeping even tension on the canopy, as well as the line stows. Sloppy and uneven cascade lines are actually caused by uneven tension throughout the canopy surfaces during packing, so sort out the sloppy lines by packing the canopy neatly. Trying to stuff loose lines up under the tail of the canopy or milking the loose lines down to the risers will lead to large loops of loose suspension line and a greater chance of experiencing a tension knot.

Tension knots have been around as long as there have been parachutes. Careful packing and regular maintenance are the keys to ensuring that you don’t end up with a malfunction due to a tangled mess of lines.

—Jim Crouch | D-16979
USPA Director of Safety & Training

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Dennis Luque
Sat, 02/21/2015 - 13:40

i have seen some packer to flake the tail out side and i have seen other to flake it inside the parachute. what it depends? what's the effect?

Thank you!

Post new comment

Please provide your full name. We will not post responses from anonymous sources.
The content of this field is kept private and will not be shown publicly.
Type the characters you see in this picture. (verify using audio)
Type the characters you see in the picture above; if you can't read them, submit the form and a new image will be generated. Not case sensitive.