Magazine: Vol Libre
Author: Michel Ferrer
Pictures: Michel Ferrer
Translation from French: Christiane "CC" Moisan (and special thanks to Mario Mohl who helped with some technical terms)
(See below scans of the article)
Light Material for Kleenex Paragliders?
Vol Libre has met a few manufacturers or shops working with the new light-weight materials. Their viewpoint and advice on the solidity, aging and the care to be given.
Lightweight paragliders have advantages on their ease of use, increased smoothness and reopening rapidity. Being the new fad, one can see them in many manufacturers’ line of products.
Before buying, one must ask its intended use and polyvalence. What does one want to do exactly ? What type of terrain will we be using them? Can one expect the same longevity than on the “classic” paraglider ? These questions are interesting as one is tempted to bring a wing on their next trip on very aggressive terrain while others look for more stable sites without any restrictions or extensive travels.
A specialist like Nervures has been working for many years on this type of wing. He insists on the necessity of an adapted conception using many types of fabrics. The lightweights, type Skytex 27, are used only on parts less exposed, in particular the areas which are protected against abrasion. A complete “lightweight” is not done, except for the occasional prototypes X-Alps, destined to not last long. So, let us take into consideration the work of the “specialist” which knows these types of material, and do be careful on the “lightweight versions” of existing wings or products being marketed too soon.
Porcher Skytex 27
Light wings appear to be on an up rise due to a remarkable technique, the Porcher Skytex 27. It was developed in collaboration with Nervures, which has flown many prototypes, with different versions of this material. After result analysis, the chosen version became a Nervures exclusivity. It was proposed to other manufacturers at the 2006 “Coupe Icare”. Ozone adopted it for the Ultralite. The performances, with new material, are comparable with the classic type of material. Many manufacturers (Airwave, Gin, Swing, UP, U-Turn, Windtech . . .) are introducing it in their lines now.
What to expect from this material?
We asked David Dagault (Ozone), Alexandre Paux (MCC/Sky Paragliders, Xavier Demoury (Nervures), which all have many years of experience, what they thought of lightweight materials, the potential of such a material and usual questions such as longevity, porosity, influence in the choice of colors.
For fine and lightweight materials, if we recap their assessment: one must be conscientious and careful on the type of terrain you wish to use.
David Dagault (Ozone)
What do you think of lightweight materials?
One must be realistic: with a softer fabric and elastic support, one cannot hope to have the same durability. We cannot ask for too much ! More than ever, you will have to take precautions as not storing the wing when humid, be conscientious, avoid too many brushes with the ground. If I evaluate the potential of a classic wing to be 500 to 600 hours, we can hope for approximately half with lightweight materials. But 300 hours, is still enormous to the normal pilot. It is for this reason that we are not too worried about the Ultralite. It was conceived with a good longevity margin and adapted materials: supporting walls in 40 g/m2 hard-finish and leading edge in 36 g/m2.
What is the importance of colors versus durability?
We have conducted many tests when we were using Gelvenor. We then could see that dark colors conserved better their tints, some much better than others, but we could not establish any links to the preservation of quality of the material.
Alexandre Paux (MCC-Aviation/Sky paragliders)
I have been proposing, for a little more than a year now, a mountain wing, the MCC Borea H2, which I strongly don’t recommend for a mixed use. At 300 flights, it will be very tired and my customers are told that. Aging will be different depending on terrain used: if grassy and not very aggressive, it will do. But on pebbles and rocks like in the South Alps, it will rapidly wear.
What materials do you use?
A 36 g/m2 material for the leading edge, and Contender 30 g/m2 (Holland) for the extrados and intrados. I did not opt for the Skytex27 because the Contender was more stiff, gave more dynamism and “nervousness”. The Skytex, more soft, would have given a more dampened wing. I also thought the Contender more “crispy” and agreeable to the touch. We call this the “hand” of a fabric. These are all parts of little things to which a customer is sensitive to.
And for the rest of the line?
The constraints are located at the leading edge. They decrease rapidly 50cm after. I use 45 g/m2 for leading edges and 40 g/m2 for the rest of the extrados. I find that 40 m/g2 is almost as good as 45 g/m2. Has lower warp count, but the same weft count and it is the direction (the wingspan) where efforts are done. I use “deperlant” for extrados because I think the fabric should have good waterproof qualities and often also on the intrados, because it simplifies the orders. I like the fabrics to have “nerves” as it helps to the pleasure of piloting. I do not want too elastic fabrics because the reinforcement plaits on the leading and trailing edges do not deform. They make creases.
The actual fabrics are satisfactory?
A vast majority of wings are replaced because the pilot wants to change it, not because tit is worn. Yes, I think we have good fabrics but mostly well adapted for each use.
This is the most talked about question but finally causes the less problems . . .I can fly without a care with a wing with low porosity values compared to new fabrics, as long, of course, to have an adapted conception.
A center and trim that accept aging (note: Alexandre Paux centers at approximately 30% of wing chord). Please note that the new EN norm helps a lot. Like DHV doesn’t accept any aggressiveness when wing is pitching, we sometime had to trim the wing too near its parachutal point which in turn brought aging problems. With EN which guides us better on how we must do, we can be more precise and trim nearer the optimum point with wings which will keep a better glide when aging.
I think a darker color protects better because dark colors filter light much better. For some new fabrics, it would be advantageous for light colors which have better tear values if not put through too much aggressive situations. But as far as I am concerned, there is a clear advantage in life-span for dark colored wings.
Xavier Demoury (Nervures)
We are in a very good position to talk about light fabrics because we participated in its evolution. The Skytex27, for example, did not arrive by magic. We took the time to have prototypes age with different versions of the fabric, a very long process. It is a new product but, for the moment, we are satisfied. All depends, of course, on use. There is a need for a completely readapted conception, use this material only in zones unsolicited and mostly where efforts are well distributed. We have classic fabric of 45 g/m2 on the leading edge, 40 g/m2 in intrados, at the rear of extrados and on non supporting walls. Everything was thought out for its evolutions to be synchronized, without aging differences between one part of the wing versus another. Please don’t be mistaken into thinking that a complete wing with all light fabric is possible to conceive!
What are its use limitations?
Being very conscientious. And there is one element on which lightweight fabrics cannot be compared with classic fabrics, aggressions, tears, perforations, because there is less matter for resistance. It is clear that if we let a light wing fall into a thorn bush or barbed wires, we will not have the same damages as with a classic fabric wing! But the necessity to be very careful is worthwhile. The piloting pleasure of a light fabric wing is really a plus.
It must be part of the global concept. If some designers have had more problems than others, is only because their priorities, when designing, were different. We all are using the same fabrics. The porosity can be well anticipated. I center more to the front (25%) and I prefer more rustic and tolerant parameters versus the search for performance which will demand absolute form containment when aging.
Importance of colors?
Certain colors degrade more than others, but we were not able to establish direct relations on the quality of the fabric. Be careful of colors with more chemical pigmentations, like fluorescent, that can attack the fabric and degrade. Other than that, whether dark or pale colors, it does not mean much because in any case there are some colors which require more or less fixation, baths, temperature or pigments. White for example requires a lot of pigments to start off as ecru into then becoming white (natural color to white). The less we demand on the fabric, the better. So ideally ecru would be the best, with no dyes.
A neutral opinion (RIP’AIR)
The Rip’Air workshop in Annecy, controls over 3000 wings per year. It ensures officially the service-control of 80% of wing models destined for the French market. Pilots send in different makes of wings for controls. Bertrand Maddalena is a fervent partisan to lightweight wings. Implicated in the elaboration of many products, advisor for many makes of wings, there is no better advice but his when it comes to talks about longevity of light products.
What do you think of Skywalk fabric?
To begin with, please note that the fabric coating is metal, aluminum and not just a simple coloration. It is a thin aluminum coating, which is glued to the surface of the wing. It is not glued on all its surface like Mylar is, but more specifically glued in a multitude of small points, to preserve the subtleness of the fabric. I do not know well this product from Germany. The Sofileta manufacturer had tested a similar product with Aerodyne, with good results. For me, it is returning to the Mylar idea but without all its inconveniences (when cut or becoming porous). Nonetheless, the risk with this kind of material is that we could eventually see similar problems as with Mylar. When aging, we could see a risk increase for tears, because, even though the gluing technology, fibers are more blocked by the coating compared to a normal fabric therefore probably working less together. We have the same kind of problems with the “hard finish” of walls which more often than not are good for tears because of the more rigid fibers interact more individually. This is why most brands avoid “hard finish” which have seen walls exploding when wing falls too abruptly on the leading edge (1).
Do darker pigments contribute to protecting the fabric?
For me, there is no link. It could be possible, sometimes not. Nothing has been proven yet. I would have a tendency to think to the contrary. I would like less pigments and less chemical fixes ! I think that a fabric just simply washed, no tints, would probably be the best. As an example, in 93-94, Carrington had given for Nova, Sphinx models, and certain competition prototypes, a very pale fabric, not a lot pigmented, so as to avoid any fiber aggression. This product would discolor rapidly but had an astonishing capacity to hold in time. Today I try to convey this message to pros. Do not rely on conservation of color to judge the state of a wing.
You rely on established porosity measures to control a wing ?
Yes, I have no choice because it is the only way that I can perform without taking it apart or destroy the wing itself. It is not this value alone that can induce dangerous reactions but everything else that goes with it and that we don’t see like manufacturing deformations, the loss of the original profile, seam weakness. I have therefore base values for porosity for which if undervalued, will have an unfit airworthiness by me.
Can you cite some of them?
The JDC porosity meter works with light pressure. It measure the time for 1 liter of air to go through. The value of a new material is 500 to 600 seconds. To give you a reference value, at 20 seconds, I state “Be careful, at risk of inapt behavior”, at 10 seconds, I discharge the wing as not airworthy. For a comp glider, 50 seconds is the base limit as they need more fine trim. For fabrics like Gelvenor, which usually have better porosity values, a discharge a wing at 80 seconds. The wing is not porous but I know by experience that at that level, for this type of fabric, deformations are permanent as it has gone beyond the elasticity limit. This means that we cannot base ourselves solely on porosity measurements and that all fabrics have their advantages and disadvantages. Certain fabrics are optimized for certain aspects, terrains or specific climates.
We find differences in wing size ?
The size of a problem, of a crease, of a defect will always be the same. So yes, they are proportionally more distinct on smaller wings. Furthermore, the flows are better on larger wings. They will go slower for stall on older wings. On the other hand, 100 anchor points are better distributed on small wings versus a large, so everything balances off between small and larger sizes.
The durability potential of a wing
The aging process begins immediately, the minute we fly it as the coating will start the softening process. But don’t panic this is not serious ! Afterwards, all depends on the pilot. We see some pilots not careful at all destroy their wings in 50 hours, storing it humid for example. But otherwise, if careful and in normal conditions, we can currently go to 350 to 400 hours easily. At 100 hours, the fabric will have sensibly changed when touching it. At 200 – 250 hours, it will be real soft but with no behavior differences.
At 300 hours we can see little defects like the wing being more heavy during inflation, a little less speed. But generally, nothing unreasonable. Concerning brands, we could see notable differences some years back but not as much anymore. Manufacturers give themselves a good margin. Aging is coherent between all brands, so again, everything depends on the pilot!
What do you think of Skytex 27?
I think we need to clarify our expectations towards such a fabric. For all light fabrics, I have a good comparative image: that of brake shoes on cars. They can be more or less thick but new, their performance is the same. If brake shoe is less thick originally, they will nevertheless wear much sooner” For light fabrics, it’s the same. Original performances are excellent, but one cannot expect the same thing with time. Its logical. A thinner and softer support, is a coating that can move and crack faster. As for the thread, 22 decitex instead of 33, means that 1/3 less of thread volume even though there is the same amount. So, it’s not possible that the fabric be as resistant.
But everyone wants one?
Yes, and with this new tendency of mountain wings having a small surface, with the weight and more important internal pressures, they will age even faster! Globally, there is an important message to pass along to pilots: what do you want to do with that wing? Sites? Mountains? Travelling? Polyvalence? For me, manufacturers who propose 2 versions like Nervures, or those that have equivalent wings with a combination of different fabrics, for different use: Ozone (Ultralite, Geo 2), Dudek (Airlight, Boheme, Nemo) or MCC/Sky Paragliders (Borea H2, Cima, Borea). And then, it’s up to the pilot to choose knowingly, with the kind of use it will be intended for. With that said, I still am a partisan to lightweight fabrics. The lighter a wing, the more pleasant in flight, take-off, everywhere! In flight, compared to an equivalent model, it is always more pleasant, softer, nicer . . . When we have experienced a light wing, we have no inclination to return to the past !