How To Avoid Line Burn (Because Raw Canopies Work Better)
C’mon...just how much damage can one little line really do?
When a suspension line gets out-of-place and slides across neighboring nylon, another line, or another skydiver (in a collision scenario), the damage can be catastrophic. The lines connecting your mortal coil to your nylon conveyance are, after all, thin strands of extremely strong material – and, in deployment and flight, they move very, very fast.
Line burn is, as you have no doubt extrapolated by now, caused by the generation of heat by friction. The amount of heat a fast-moving line generates is enough to literally melt the canopy – and, under certain circumstances, the line itself. Here are the questions you’ve gotta answer in order to avoid cooking your precious canopy.
1. How melt-resistant are your lines?
Both F-111 and ZP nylon melt at 417 degrees Fahrenheit. That’s a lower melting point than almost all the common suspension line materials (Dacron®, Vectran® and HMA), which melt when exposed to heat levels of 482-932 degrees. There is, however, one exception: Spectra®. Spectra®, that tender little princess, melts at just 297 degrees.
Even if they literally melt a hole in the canopy, all lines but Spectra® will likely survive the incident unscathed. If you have Spectra® lines, however, check them carefully if you discover line burn on your canopy – they are likely sufficiently damaged to require replacement.
2. Is that crease really a crease?
Most modern sport canopies used to be made of F-111 nylon. These days, for lots of reasons--from performance to fading mitigation--they’re generally constructed of ZP (zero-porosity) fabric.
The behavior of these two materials under stress varies widely. When an F-111 canopy suffers line burn, the damage tends to be localized – often, sufficiently contained to be landable. ZP fabric is not so forgiving: high-speed line burns tend to cause major structural disintegrity. In addition to that, burn damage to ZP fabric can be difficult to identify, often appearing as a simple crease in the fabric – though testing to that crease finds it to have been massively reduced in tensile strength. (For this reason, Performance Designs doesn’t use zero-P fabric in their reserve canopies.)
3. Are you packing for a smacking?
According to the United States Parachute Association, incorrect packing is the most common source of line burn. The other cause, of course, is canopy collision – but that is a subject for another article entirely. To reduce your risk: Don’t throw your canopy in the bag. Take a moment to mindfully arrange the lines towards the center of the pack job, making sure that rogue lines aren’t nestled deep in the fabric where they could cause burn.
- Mind your slider. Keep the slider flush against the slider stops and tucked between the line groups. Not only will this help to mitigate opening shock, it will help to manage the lines as the canopy deploys and keep them from unnecessary intimacy from the neighboring fabric.
- Clear your stabilizers. The stabilizers (the “ears” of fabric that come down slightly on each lateral side of the canopy) have a tendency to tuck themselves in towards the lines when you’re pro-packing. Make sure they’re clear.
4. Have you already been burned?
- Look for melting and discoloration. Line-burn damage looks very different than puncture damage (or any other clean cut or rip).
- Check your lines. If you notice burn damage on your canopy, it means that the nylon most certainly came into contact with your lines. To check lines for burn damage, use your hands more than your eyes. While seared lines often show signs of melting at the burn point, the easiest way to determine damage is by feel: an undamaged line will feel smooth if you pinch it and slide your fingers down, while burned (or otherwise damaged) lines will feel bumpy and rough.
- Get help. If you notice evidence of line burn – or what you suspect to be line burn – on your canopy or lines, take the damage to your rigger for inspection as soon as possible. Don’t freak out! In many cases, the damage can be repaired simply and economically, with replacement suspension lines and patching.
- Don’t be a dick. If you notice any damage on a rental (or student) rig, don’t hesitate to point it out to your coach or the rental office, whether or not you believe the damage happened “on your watch.” You’d want the same treatment--and you don’t want to be burning your fellow skydivers. Right?
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Good points Annette,
Bill Booth preaches that packing ram-air canopies is basically "packing the lines." Once lines are straight, the canopy is going to open.
Back in my glory days I cutaway a bunch of "holy" tandem mains made of F-111 fabric .... back when F-111 was fashionable for mains. Holes in bottom skins did not phase me, but holes in top skins always meant pulling the cutaway handle.
I have landed two or three tandem mains split from nose to tail on the bottom skin. No big deal, they flew almost normally and flared fine.
OTOH holes in top skins are scary. My first experience blew a hole big enough to drive a van through the left side and a hole through the right side big enough to drive a city bus through! I glanced at that for a split second, then reached for my cutaway handle.
The second "holy" top skin was on the top, Center tail and only a foot long, so I did a control check. It turned fine, but folded in half (horseshoe) when I flared ........ reached for the cutaway handle.
Yes you have to watch Spectra lines for temperature related friction damage! I have seen someone with Spectra lines land safely after kicking out of severe line twists. Then their buddy walked up yanked on one of the lines and it broke. The jumper got pissed at his friend for breaking his line but then he realized his friend was actually helping and might have save him from it breaking on him in the air. If you have Spectra lines always check them for damage after having line twists.
For the metric system users...
Both F-111 and ZP nylon melt at 417 Â°F (214 Â°C).
DacronÂ®, VectranÂ® and HMA melts at 482-932 Â°F (250-500 Â°C).
SpectraÂ® melts at 297 Â°F (147 Â°C).
Good to know! I had no idea about how "low" was the melting point of my lines!! Thanks!!
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