Regarding the high-tech kite and paraglider fabrics, UV degradation, and other risks.

On Apr 4, 2013, at 4:38 AM, magnus@*****.*** wrote:
Hi! This is not so much a repair inquiry, but more like a question spurred out of curiosity. I'm a paraglider, and in our community it's a well known fact that the canopy is very sensitive to all sorts of things, such as unnecessary exposure to sunlight, crease, water (especially salty water), and dragging it along the ground. 

There are a LOT of theories on how to best store and pack your glider to keep it in good condition. Some of the newer gliders force you to pack the glider accordion-style, which some people say is bad due to the extra crease. Hell, some people even try to convince me to use a different packing method when storing my glider for the winter, compared to when its being packed for hiking or to be used within the next few days. 

I am not a kite surfer, but I sometimes fly in the same area. It always amaze me how the kites apparently have no problem dealing with salty water, and (from the looks of it) a lot more wear and tear. I also hardly ever see the kite surfers store their kites in UV-bags in-between flights. We paragliders always do that, to minimize UV-exposure when the glider is on the ground. 

My question to you guys is how does the fabric in a paraglider differ from a kite, and why is so much more sensitive to these things? Would it be possible to create a paraglider with the same material, without losing to much of its performance etc? I'm not entirely sure you are the correct people to ask this question, but with your unique view on both kites and paragliders, i thought I'd ask anyway! 

Thanks in advance, Best regards Magnus

In response to this we wrote:
On Apr 4, 2013, at 7:11 PM, Tim at WindFire Designs wrote:

Hi there Magnus,

This is actually a great question, and one that we have given quite a bit of thought to over the years.  We have repaired literally thousands of wings now, from everyone using soft wings in all kinds of sports.  Also, as I am personally a materials freak, and a collector of forensics knowledge via all the different types of damage we see, I have formed a rather large data set about everything you mention here.

I agree that paragliders fall under special scrutiny, but I don't agree that it's totally warranted in every area, and every case. Like any industry with enthusiasts, there are a lot of rumors and practices that may or may not have any basis in real data. That said, here is what we see as demonstrable fact.

The factors that kill paraglider cloth are not much of a mystery, and they are exactly the same as those which kill the fibers used in kitesurfing kites.  They are UV, and direct abrasion.  Creasing repetitively in the same place isn't great either, but it's mostly a secondary factor that actually relates back to UV in a way that I'll explain later.  

Direct abrasion, where focused point pressure is dragged across a set of fibers will be hard to avoid suffering damage from as a result.  However, free floating sand, that is not trapped between the cloth and another surface that's able to apply pressure against it, will not cause any appreciable problem for the fibers.  So as long as the sand is just a small amount, and is free to fly around and eventually fall out, i wouldn't freak out over it too much.  We see a certain level of sand in almost every wing we work on, and it doesn't seem to us to be the huge enemy everyone imagines it is.

Another obvious factor in damage, is simply where the breaking load on a fiber exceeds its rating.  This is obvious, and doesn't really merit a lot of discussion.  Don't pull on the fibers with greater force than they are proven via testing to rebound from.  

There is no question that sun exposure is to blame for most of the degradation occurring over the life of any fabric wing. Actually I don't agree that water, or even salt water, plays a huge role in the breakdown of high performance fibers.  Take Dacron for instance.  It's actually just a brand name for very pure polyester.  Polyesters, woven thinly, are what the canopies of kites and paragliders are made from.  This same fiber, albeit woven differently, is regularly used inside the body as a way to fix hernias.  As one must now ask, how can water, even water with electrolytes, be a huge factor on these fibers if they are used in the body?  The answer is that water is not a real risk at all.  These fibers are incredibly noble, and are actually used in their sheet and film forms to make normal plastic bottles that store all kinds of crazy chemicals, like solvents, and acids, and all kinds of things in very toxic industries.

There are a few secondary risks to water, such as mildew, dye transfer, and the extreme forces associated with dragging a submerged wing out of a body of water.  But wet fabric in and of itself should pose no real threat.  So what about salt? Well, it's true, that salts can crystalize after the water dries, and these micro crystals can then start to break down the coatings on the fabric.  However, usually it's UV that beats all of these factors no matter how much care is taken. Wet synthetic fabrics will change dimension while wet, but this is true also with changes in humidity.  People regularly fly soft wings when there is measurable humidity in the air.  Is that a factor?  Well it certainly interacts with the cloth, we can see this as dew forms on wings late in the day.  The water is there whether it's forming droplets or not.  Personally I wouldn't give it a second thought. 

These fibers are coated both before and after the weaving process.  In their coatings they use compounds just like you smear on your skin for sun protection, such as aluminum dioxides, and titanium dioxides.  The UV gradually starts to work on these compounds, breaking them apart each time the energy collides with the substances.  The reason that repetitive creasing is bad, is because it will start to form cracks in the coatings on the fibers.  These coatings then loose their ability to protect the fibers from the sun in those cracks, and leaves the sun to hit the fibers directly.  Again, there is some secondary risk to the fiber via the hinging effect that happens when you have intact coating with a crack in it, which then focuses the bending force on one part of the fiber, but this is not as big a factor as the UV, yet again.  

The good news is, paraglider fabric is in an upper-echelon of fabrics, and rapidly adopts, and drives all the latest advancements in all the available areas of textile technologies.  It's incredible stuff, and honestly much of the paranoia is just paranoia.  I know that every paraglider wing we touch is a cut above all of the kitesurfing kites on the market.  Also, they tend to wear much more evenly over the entire wing surface than does a LEI type kite surfing kite.  They wear more evenly because a ram-air foil is simply a more force-balanced structure than an LEI with rigid pneumatic structural components.  ie., the force map on a ram-air foil is beautifully even and free of major hot spots of stress.

To answer some of your questions more directly:

Making paragliders from kite cloth would actually be a downgrade in durability on all fronts.  Paraglider cloth is both stronger, and will last longer even with its lighter weight.  Paraglider cloth also has far superior memory after being deformed on the bias, because of superior chemistry of the coatings.  

The main differences in the care taken with the two sports seems to largely be cultural.  When kitesurfing started, nearly none of the people getting into the sport were even wind sport enthusiasts.  They just wanted a hook into a power source like a boat in the sky.  They didn't care how it performed, or why it worked, and the vast majority were certainly not sailers or kite fliers.  Of course this is a generalization, and I don't want to sound jaded, but 10-15 years ago, this is what we observed.  

Kites do tend to break down fairly rapidly.  It's rare these days for us to see kites from say, 2007.  The fabrics in kites do not age as gracefully as paragliders, and because less care is taken with the wings, they simply take more abuse.  Also, they spend a lot more usage time in proximity to land, and they are under less direct and immediate control of the pilot when they are near the ground than a paraglider is, thus they suffer more damage.  The fabrics used in kites can afford to be a bit heavier, and a bit cheaper.  The coatings are not as advanced, the weight of the cloth is a bit higher per area, and in general, people just tend to accept lower end fabrics because the performance and safety can simply tolerate a bit more leeway in kitesurfing. 

In regards to folding methods, there are many ideas, and when people spend a ton of money on something, they are going to make up all kinds of rationalizations and ways to add complexity to their habits.  This gives the sport something to talk about, and gives people a way to engage with the culturally-defined knowledge base that floats from person to person. Are there bits of wisdom in all the voodoo?  Absolutely, lots!  However, does it have to be followed quite as strictly as you might be lead to believe in a discussion forum?  Almost certainly not.  

Hey, don't form hard creases, and then crease on them again and again.  Subtly changing how you pack the wing over time is not a bad idea—it doesn't take much change to combat repeated folding.  Slavishly following every fold is not a great idea.  Sailors often promote the randomization of the pack.  All sails used to be systematically stuffed randomly into their bags to combat hard folds, most still are.  This actually would be a great idea for paragliders too, if it weren't for the LE.

New stiffeners in the LE of paragliders are very like sail cloth, and are often made of just that.  The main problem with wrinkling the heavier LE reinforcement panels that form the front of each rib isn't that it will weaken the cloth in any way, it's that the folds are difficult to straighten from the mild pressure differential alone found in a ram-air foil.  Thus the folds inhibit graceful inflation on launch if there are too many wrinkles in the LE.  Also, they now have rods, or other large (.080-.125") monofilament stiffeners in some high performance wings which afford the removal of some of the suspension lines (bridle).  They will prevent much creasing up there in one dimension, but as you stated, they will cause you to fold it very much the same way each time, which isn't really ideal.  The good news is stated above, that folds probably will not beat the rate of breakdown caused by other factors in the wing's life.

We see a ton of paragliders come through our shop for repair, and the ways they are packed are all very different.  I would wager to say that the users of these wings are all seeing very much the same lifespan of the wings even though their packing is so radically different from customer to customer.  It's difficult for us to form a habit of our own with packing.  This is because we recognize that the packing method is important to the user, so we attempt to copy their style of fold when we pack the wings for their return trip.  It's not easy to do well, but we try.

Wow, I wrote more than I set out to.  I often have this conversation on the phone, but I think I'll post this to our site somewhere if that's ok with you.

I hope it helps, and please let us know if you have any other thoughts.

Best,
Tim Elverston

Repair of Dudek Nemo paraglider wing after a strike from the propeller

Hi there all,

We were feeling like shooting some photos today, so we got some great images of our careful attention to fiber alignment.  I've been meaning to shoot this for years, but only recently did my brother-in-law give me the gadget that does macro so well.  While we repair these sensitive paragliding wings we all love, we see a lot of fine details.  I have long felt that looking closely at ripped edges is a fascinating education on the forensics of fabric failure.  We can almost always tell how and where the failure started.  Sometimes you can even see oxidation on the ends of fibers which tells you they were damaged before the current failure, like rust on a dent in a car panel.

Here we see a Dudek Nemo paraglider that was hit by the propeller.  We see and repair this a lot, and we take great care that the shape is undisturbed, and the restoration is total.

Above we see the rather brutal prop strike that ripped the fabric across two cells.

This is the part that even after all the years of sewing, we still find pleasing to do.  We talk elsewhere on our site about fiber-for-fiber alignment for our fabric wing repairs, and this is what we mean here.  Every part of a rip in fabric has a unique key that you can plainly see.  If you look carefully enough, and you have the patients to pay attention, the edges can be aligned within less than 1 mm .  For us, that is still a bit of fun, and it makes for results as near to perfect as we can figure.

The grid pattern of the "ripstop cloth" in these shots is 4mm square.  The individual fibers fit into the ridge of a fingerprint.  This rip was a particularly good example of the "keying" that happens when fabric of this type fails.

These after shots are here on our studio floor at WindFire Designs.  We will try to get some shots of this wing when it's back in the sky.

The shot below shows our repair as it meets a main seam between paraglider wing cells.  This repair was done internally, so the pressure in the cell pushes against the patch in the correct direction. It also means the cosmetics of the wing are impacted very little.  It has the advantage that the edges of the patch won't be exposed to snagging on objects that might lift up the edge and start collecting debris.  Our stitching is the triple-step zigzag.  If one were to cheat here, and jump the patch over the seam, it wouldn't look nearly so nice, and it would change how the fabric acts at that seam.  We like rebuilding the seams just the way the factory does.

Two tips completely ripped away from this North Rebel

Ok, so, we love that we had before and after photos of this. We do a lot of kite repairs at this level, but often we miss having either the before or the after photos. This North Rebel inverted, and loaded up really hard. We imagine that it was like the way you eat a wedge of citrus fruit, by flipping it and pushing the guts out.

Anyway, wow! This one had both tips completely ripped away. The customer did a great job of keeping the pieces intact and because of this we were able to put this back together perfectly. The natural craziness of the graphics allowed us to really hide the repair well. Check back, we hope to get photos of this kite in flight.

If you ever do have fabric, or any piece of the bridle completely separated from a damaged kite, save every single shred. It's critical that we at least be able to copy these pieces even if they don't get re-included in the final repair.

North Rebel 11 Kite Repair by WindFire Designs

This one was rebuilt for Jose Suarez in Miami. Thanks Jose!

Enjoy your restored kite. This one was very extensive with a destroyed wing tip and the strut having completely separated from the canopy.

paraglider repair

Since we started doing kite repair we've also been getting a fair few paraglider repairs in. Now we do paraglider repair officially. Here is a pro designs wing with a lot of damage to a few cells. Most of the repairs can be completed internally. We used a very clever method to repair these right against the seams without having to disassemble the fabric. This preserves factory alignment and strength.

Extensive Leading Edge Rebuild on Best Waroo Kite

This is among the largest repairs we do on leading edges. On Best Waroos, the leading edges are always pesky to work on because of the silver-colored webbing that is merely cosmetic used over the main leading edge closure seam. Any leading edge has to be sewn back together with absolute precision if it is to hold up to the pressure and use in the sky. Here we see that this entire section of leading edge needed to be rebuilt and the beige area is all patching added internally.

Cabrinha meets the rocks

Wow, so this one was epic for lack of a better word. Nothing complicated, but it just kept going and going. Our customer said that he was in heavy surf and the kite came down and was pushed against a rock wall. There were rips everywhere. We thought this looked quite good after the sewing. Our grey and orange repairs fit right in with the colors.

cabrinha kite repair | we have this weird color

So I bought this cloth wondering if we'd ever use it. Sure enough Cabrinha makes kites in this strange yellow.


Believe it or not, there was a rip down the middle of these three lines of stitching. This is the sort of alignment that we achieve on all our repairs.

Wainman Rabbit leading edge repair and shape test

This repair runs the full length of this wide shot. Here we are just shape testing it with a new bladder. The seam blew out from the H over to the next junction. We had to rebuild both edges over that length.

Fancy repair of an Ocean Rodeo Kite

As you can see from the sketch we made after we were done, this kite was messed up. I'm always amazed at how many simultaneous points of damage some kites come in with. This went back together really well though. The repairs are barely noticeable.

Another powered paraglider repair

Recently we've been doing quite a few paraglider repairs. This one is a Dudek 27 meter. Apparently it was damaged because of the motor and prop. One cell needed to be completely rebuilt. All of our work was done internally so there was almost no change to the color of the wing.

Kite repair graphics

Nothing too exciting, but I thought this one looked nice.



On the front side you can see the graphics line up really nicely and are preserved very well.

Best HP - classic over inflation

This is a glimpse of the interior surface of the leading edge tube of a Best Waroo Pro HP. It has cuben fiber on the inside of the middle third of the leading edge. It's actually a great idea. The cuben is actually a pure spectra laminate that is simply amazing. I personally use it in many of our own kite designs. This is the main closure seam of the leading edge. It is perhaps the most important seam on the whole kite. It takes the most force and is often one of the first to fail. It's not because they are under-built. They are actually quite strong. It's just that the forces involved can be amazingly powerful, as any of you who have been lifted off the water know. This seam has signs that are classic of having been over-inflated. As you can see here the fibers have actually moved over and started to unweave. This was not evident until I opened the leading edge up. It looked like it was just a tiny section of the leading edge that was having problems, but it turned out that the seam was weak down a section about 2 feet long. Keep in mind, I think Best Waroo Pro HP stands for High Performance, not High Pressure. You still have to inflate these with care.



If you look closely in the above picture, you can see that there are fibers that are running diagonally. This is because the cuben fiber is made on a table, not on a loom. Thus they can get away with running fibers at any angle, not just 90 degrees. You can also see that the cuben fiber doesn't quite reach out all the way into the seam far enough to be structural. This I think is why this section failed.

A break from repairing kites

Every now and then we get to actually go to the beach and fly kites still. To get away from the sewing machines is a nice thing and reminds us why we got into this kite flying thing to begin with. This is a foil that I designed back in 2000, wow, can't believe that it's almost 2010. Anyway, Paul has been wanting his own foil for quite some time now. He finally built it, and this is the first, and very impressive flight.

Woah there - Settle down

Got this here today. We extensively repaired other areas but almost sent this out until we saw this great example of getting too excited when you are sewing. There's nothing wrong with doing this on a test piece of cloth while also staring out the window at whatever happens to be out there. And don't get me wrong, we are practiced at diplomacy, but every now and again we get the very accute urge to say woah there, put down the crack pipe and step away from the sewing machine. Anyway, after the small task of removing all the stitching, we just replaced this. Below is what it looked like after we redid it.

Truck Bike | The environment and our kite repair service

With the weather getting better and better for kiteboarding, we are in our busy season for our kite repair service. Here I am riding repaired kites in boxes from two days of Paul and me working around the clock. Some of these boxes have two or three kites in them too. I love this bike, it's a Worksman Frontloader Trycycle made in New York. I use it all the time to move repaired kites up to where I ship them at the end of each sewing day.

Thanks to all our great customers for making us so busy. We are trying to keep up with you, and trying to use less fuel to do so.

Tim

p.s. yes I know the tires are low on air, man this is such a pet peeve of mine that I almost photoshopped it.

F-One leading edge Repair

This nicely made F-One hit some rocks and tore up the leading edge very badly. We forgot to take before images, but as you might be able to see, our repair goes from the center of the kite's leading edge all the way out to the tip. Paul, who did this one, said it was the longest he'd had to open and close a leading edge on a single kite in a long time, probably about 12 feet. F-One likes to double stitch their leading edges closed too, and this makes them nicely strong, but also makes them more difficult to open.

If you study the image, you can see our slightly darker red patches, but around those, you can also see the interior reinforcements. Paul staggered the edges of the inner and the outer patches to step down the increase in thickness which prevents a hinge from forming at the margin of our patches. Theoretically this should increase the life of the patch by preventing the material from always bending at the edge of our stitching.

The strut was also ripped. Below you can see the rather complex area that F-One makes around their struts. They at least are smart about it, unlike the slingshot splitstrut system that is impossible to open the struts for service, these are at least made with seams that can be removed from the exterior of the strut.