When is an old paraglider wing too old?
When is an old paraglider wing too old such that it should be retired?
Ultimately this appears to be the rule: If you think you wing is old and crappy, probably it is.
If you have any doubt, you should have it inspected, listen to the results, then perhaps put it through its paces in a maneuvers clinic such as that offered by Chris Santacroce at Superfly Inc. outside Salt Lake City. That way you and he can get a good idea about whether the wing is performing as it should.
The problem with older or suspect wings is that you might not know whether the wing will behave correctly, as in reinflating from a frontal collapse, until that kind of thing occurs. Or you might have a frontal or horseshoe collapse with successful recovery, only to learn later that won’t recover from some other type of maneuver. And then the issue is whether you are completely ready in terms of both ability and equipment for the potentially resulting emergency. See reserve-toss post. Having the wing inspected is cheap insurance. Even replacing the wing is cheaper than other possible downside outcomes.
We have a few objective measures that can factor into whether a wing should be retired. The objective measures can be combined with your own subjective impressions and the subjective impressions of a qualified instructor or shop.
The porosity test
The porosity test is a way to understand the condition of the wing’s material–it’s an objective measument. Wing material comes in various varieties, with various weaves and coatings. Over time, these weaves and coatings degrade, becoming more and more porous. Thus the wing becomes less and less like the manufacturer intended it. In the practical world, at some point the wing’s ability to fly or to behave correctly will be compromised. This is especially true under atypical conditions.
Porosity testing, shown in the video below, is performed with a simple device in which a weighted chamber sucks air through the material of your wing. Generally this is tested on the top surface, because that surface is most subject to the adverse effects of being placed on the ground repeatedly. But other surfaces also are tested to get a general assessment. In the event of localized low porosity readings, sometimes a couple of panels might be replaced to give the wing some additional lifespan. But sometimes the entirety of the wing is showing low porosity overall, objectively pointing toward wing retirement.
The wing below is very porous. Generally the falling weight should fall over the course of minutes, not a few seconds like this one.
The tear test
The tear test is a way to prognosticate whether the wing material might rip, particularly in high-stress conditions. The device is relatively simple, consisting of a pin that goes through your wing’s material. The pin is attached to a guaged-spring device that looks something like an air-pressure gauge. The pin is stuck through the material of the wing, then the handle is pulled to see what the reading is on the gauge when the material starts ripping. No, the shop will not create a large rip in the material; the wing tear test will rip perhaps a thread or two. This generally is done in a couple spots on the wing. A low reading suggests that the wing could rip in high-stress conditions.
The wing below has low tear strength.
Riser condition and length
Riser length is checked by holding the carabiner end of the risers in one hand, and determining whether the maillons’ placement matches up. Generally the risers should be the same length, showing no signs of stretch, which could adversely affect performance.
Line condition and length
Lines should be checked for points of wear. Sheathing that has worn away from lines suggests that they should be replaced.
Lines should be appropriate length. Improper lengths suggesting stretching or shrinking will adversely affect the wing performance.
A final thought
Just because you can fly your wing that you think is getting old doesn’t mean you should fly that wing. I’ve found that you can fly wings that have the porosity of a T-shirt, but that does’t mean it’s a good idea. See reserve-toss post. Manufacturers generally have a lifespan identified–like 300 hours or so. That probably is a good guide. If you have a tendency of buying used wings rather than new, you ight inquire as to the number of hours on the wing already (seems like on eBay they all say “20 hours”), consider an inspection that will give you objective meansurements, and consider a manuvers clinic that will demonstrate the wing’s abilities–and yours.