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Geeks on Hot Wings( Advance/Sigma 4 , Nova/Argon , Ozone/Proton )
By Mike Steed (E-mail) with second opinions by Steve Roti (E-mail)
Join the geek major and geek minor as we over-analyze DHV 2-3 wings. Why should you care about DHV 2-3 wings? Chances are, you’re among the 80% of pilots who won’t buy one, or the 10% of pilots who shouldn’t have. Today’s DHV 2 wings can outfly yesterday’s 2-3 wings, and even the 1-2 wings are catching up to my old Energy, may it rest in peace. But guess what – the 2-3 wings are getting better too, and they’ll continue to have a performance advantage. Even if you’ll never fly a DHV 2-3 wing, you may want to see how they’re being built, because the same technology tends to appear in the more popular models a year or two later.
First, in the spirit of late-night television, here’s my top-ten list of reasons to buy a DHV 2-3 wing:
10. I need more distance to get a record.
9. My flying days are very limited and I don’t mind "cheating" to get a few extra minutes in the air.
8. I fly in competitions.
7. It’s safer than an unrated or "comp" wing.
6. I don’t mind paying more for a wing.
5. I don’t care that it will have little or no resale value.
4. I never fly in third-world countries and there’s always a friend or cell phone to summon help.
3. It won’t spoil my day if my wing wads up in midair; I can handle it.
2. In case I’m wrong about 3, my medical and disability insurance is excellent.
1. I have plenty of life insurance coverage.
Kidding aside, this is not a bad list to consider. Reasons 10 through 7 are optional, but the others all deserve an honest answer. Most of your safety is determined by your judgement and the risks you are willing to take, plus your ability to keep a cool head when you get a surprise. But higher-performance wings do demand more skill and attention, so if all else is held equal, these wings are not as safe to fly.
In the last two years a "serial class" was created in paraglider racing, which is limited to wings certified DHV 2-3 or better. This has put more emphasis on racing in this category, and the newer wings are designed to fly heavy and fast. This does not necessarily make them better at scratching in light conditions. If low sink rate is what you want, you can probably do better by flying in the low end of the weight range on a more stable wing, like an Apco Allegra or even an Edel Atlas. What you get with the performance wings is the ability to cover more distance with the same sink. This is useful when searching for thermals, jumping from ridge to ridge, or just penetrating back to where you started after drifting downwind with a weak thermal.
To keep the DHV 2-3 wings all straight, it helps to have a background in science: Ozone Proton, Nova Argon, Freex Oxygen, Firebird Rocket, and others. Most are capable of fully-loaded speeds above 50 km/hr. [Even intermediate wings are starting to make such claims: Firebird Matrix (52), Pro-Design Effect (51), Flight Design SX (50), and Nova Phelix (50). We’re guessing the DHV 2-3 wings tend to have better glide slopes at these speeds.] One of the big design challenges is to recover safely from a collapse at this kind of speed – accelerated asymmetric collapse tends to be the worst score in DHV testing, and is sometimes the only reason a wing is rated 2-3. Paratech P70, Gin Bonanza and Edel Response are in this "low 2-3" group, along with the Sigma 4 tested. Others test without the speed bar or limit its travel for better DHV scores. Trim systems have largely disappeared from DHV-rated wings; their benefits don’t justify testing at both extremes of trim adjustment and the consequent worst-of-both rating.
For this article I obtained The Advance Sigma 4, Nova Argon, and Ozone Proton. Steve Roti and I flew them all, and I collected dimensions for the comparisons below. As you’ll see, these are not quite birds of a feather – the latter two are pretty much designed to race, while The Sigma 4 is more of a "kinder/gentler" performance wing. Advance took the unusual step of getting DHV listings both with and without speedbar, and the Sigma 4 is officially rated DHV 2 without speedbar. We wanted to compare it to other low-end 2-3’s like the Paratech P70 or high-end 2’s like the Apco Bagheera, but neither of those found its way to my front porch. At the other extreme, Nova took the unusual step of getting DHV ratings with both standard and skinny lines – the Argon is rated DHV 2-3 with either set of lines, qualifying the Argon to race in the serial class with the faster/less durable unsheathed lines.
The Proton would fit neatly under the Argon, while the Sigma 4 overlaps both.
The Sigma 4 and Argon have a remarkably similar flat shape. The leading edge is swept back, the wingtip is wide (70 or 71 cm) and squared-off at the rear. The wide wingtip allows a brake line to attach at or near the tip with minimal risk of tip stalls. (The Sigma 4 has even less risk; see the photo showing how the brake line runs through loops, causing the tip to gather more than pull down.) The Proton has a shape much closer to the theoretically ideal lifting shape – elliptical, less swept back, tapered to relatively narrow 44 cm tips. The brake lines stop short of the tip, the last one being attached where the wing is 97 cm wide. We judged the Proton to be slightly easier to turn than the others; more about handling below.
All of these wings come overhead easily, but there the differences become apparent. The Sigma 4 will kite comfortably overhead, or launch immediately. The Argon feels identical up to the point of being overhead and will stop there without brakes, but you soon discover the wing is thinner, has less lift at this speed, and is easily smacked down by turbulence. The trick is to accelerate immediately and get yourself to a speed where the wing is more comfortable. The Proton comes up much faster than the others, in part because the lines are a bit shorter, but also because the trim seems to be faster. This quickness is found in all aspects of its flight behavior. During launch, the Proton needs a pop of the brakes to decelerate it overhead, then run and launch like the others.
These days, high-performance wings include internal rib structures that permit fewer attachment points, and therefore less line drag. In order to discuss these structures, we’ll need some naming conventions. I’ll propose naming the structures by the shape of the cells between attachment points, as shown in the illustration. The cell shapes correspond to the letter shapes: 3-sided cells are either "V" or A" depending on orientation. Four-sided cells are "0" and are not necessarily rectangular.
The Plain 0 structure will always be the choice for low weight, simplicity, and low cost. This is the structure used on alpine descent wings, plus most beginner and many intermediate wings. The additional lines add little weight and expense, but there is a drag penalty.
The 00 structure works if the cells are relatively tall and narrow, but the unsupported rib in the middle tends to bulge toward the topside. This structure is found on some older performance wings. Virtually all wings use 00 or 000 structures at the D lines -- the rear of a wing isn’t thick enough to fit good diagonal ribs, loading is low, and the shape of the wing is not as critical.
The VAAV structure appeared briefly as manufacturers first brought out ribbed designs. It improves on the shape of the 00 structure, but weighs more, and has one big disadvantage: triangular cells are relatively rigid when inflated, and this wing consists entirely of triangular cells. Any slight defect in design or manufacturing causes the wing to buckle somewhere, and the resulting bulge is unsightly if not inefficient. It’s also been suggested that these wings were more difficult to reinflate after a collapse.
The Sigma 4 improves on the VAAV by using the similar 0AA0 structure. The short fourth wall gives the wing just enough flexibility to avoid unsightly bulges. They also place ribs (straps, really) only at the line attachment points, saving weight for the considerable amount of reinforcing and other features in various other parts of the wing. No stitching is visible on the Sigma 4’s topside, unlike the others tested.
But to really minimize parasitic drag, you need structures that can space the lines even further apart. Here the structures begin to approach the limits of what is possible with a tension-only structure.
The VA0AV structure is probably the most popular for performance wings today. It limits the attachment points to every third cell, and cell counts are identical top and bottom. Where the diagonal ribs end (typically at the C lines) there is no sudden doubling or tripling of the cell width. The Proton uses this structure.
The "non-A" structures consist entirely of V and 0 cells. Cell counts are higher on the topside, where the wing shape is most critical. The front portion of the top surface sees the greatest lifting forces, so frequent ribs help to minimize bulging of this area. Stitching is visible on the top of the wing; typically the ribs are single-sewn to the top. On the V00V structure -- used on the Argon -- it is worth mentioning that the unsupported center rib does not bulge toward the topside like on the 00 design – this is because pressure forces on the smaller top surface are approximately balanced by forces on the larger underside area.
The "compound" structures (0:…) insert a single 0 cell between segments of one of the other structures. This spreads the attachment lines even further apart, at the expense of a short cascade for the extra cell. The overall line usage can be less than on the simple structures, but the additional cascade increases the chance of line tangles. Literature for the Ozone Octane shows the 0:VA0AV structure, but the 0:V00V structure hasn’t appeared yet.
These structures have evolved about as far as they’re going to, given the current design assumptions. But change one assumption and there are some new possibilities. Specifically, why must all the seams be parallel? What if the cell structures could taper in and out in more organic shapes? This adds complexity to an already-complex sewing job. It also makes the V0 and V00 structures practical, and the compound structures become more attractive if the added cell can change width toward the rear of the wing.
Back On Track
Whew, we’re back. All that so we can say the Proton has a VA0AV rib structure, The Sigma 4 has an 0AA0 structure, and the Argon has a V00V structure. The Sigma 4 has the most attachment points. The Argon’s diagonal ribs extend all the way to the trailing edge of the wing, adding some weight but also marginally improving wing shape and eliminating bumps at sudden transitions. The Argon’s additional topside panels serve to reduce the rib angles, and the design takes advantage of this difference: the wing is unusually flat (low arch) in flight. In the table you’ll see that the Argon’s similar flat span becomes the largest projected span in the group, and the weight range is consequently higher. The "span ratio" measure in the table is a good way to compare the arch shape of wings, where 0.8 is typical for a paraglider and 0.9 would be extremely flat.
The other way to flatten a wing is to make the lines very long, so the pilot hangs far below the wing rather than between the tips. The tradeoff is increased line drag, but this is not such a big factor with reduced line counts. All of the wings in this group have relatively long lines.
So a flat wing is good for efficiency, which relates mostly to straight glide. But what about turning? Beginner wings tend to have an advantage in turning simply because of their compactness. Within a performance category, the sense of control changes with line length and wing shape: If you’re hung high directly between the wingtips, every wing twitch will be felt immediately. With long lines and a relatively flat wing, you get more of a limousine ride – you’re more distant from the bumps, and changes are not as dramatic. This is good and bad – good because you’ll have time to react to problems, but bad because you may not realize immediately that there is a problem. For a given wing, the "feel" is likely to improve toward the heavy end of the weight range, because the wing reacts more quickly at speed.
The Argon has excellent proportional brake force through a long travel, partly because only one brake line engages at first. By the time all the brake lines engage (as you might prefer for active flying) you are flying at less than minimum sink. The Argon flies willingly in this range, but remember you need to ease off the brakes when you can. The Proton turned slightly better than the others in this group, perhaps because of its fast trim. It also engages a single brake line to begin, but through a shorter range, and the lines are probably all engaged at minimum sink. The Sigma 4 uses all brake lines about equally and still has good brake travel, perhaps assisted by the eye-and-loop attachment at the wingtip. In Steve’s opinion, in thermal conditions the Sigma 4 provides the best feedback to the pilot of the three gliders reviewed.
All three wings have 3:1 speed pulley systems – I prefer these to the 2:1 systems in spite of the long travel because they work more smoothly. We weren’t able to compare speed directly, but all of these wings can go fast when you get on the bar. The Sigma 4 has an aggressive speed system that pays a stiff price in glide angle to get maximum speed. Steve also discovered you shouldn’t stomp on the bar immediately after launch as this can cause a frontal collapse. By contrast, the Argon speed bar should be used liberally, since best glide appears to happen with no brake and a significant amount of speed bar. At half speed bar you can listen for thermals on the vario, and your climb rate won’t change much when you slow down! The Proton’s speed system performance is reasonably good as well; it has the longest travel of the three, too long even for my long legs were it not for the nice two-step speed bar Ozone supplies with the wing.
Advance does not recommend a B-line stall for the Sigma 4, in part because the descent rate is not much better than big ears. This is apparently a downside of a relatively stiff wing. The other wings claim B-line stalls are OK with the usual disclaimers. We didn’t try these stalls, but I expect you’d need tremendous strength to pull B-lines on the Argon since most of the pilot and harness weight hang on the B riser. The Proton, with an additional riser and wingtips attached to the C riser, should be easier, but the manual warns of requiring strength. [Late addition: The Argon is actually easy to pull into a B stall -- so easy that I pulled too far on my first attempt and put the wing into a front horseshoe. I can't recommend this as a routine descent technique!] All manufacturers mention the use of steep spiral dives as the most extreme descent technique, with appropriate cautions about the hazards involved.
I’d rather let someone else be the crash test dummy, so these wings have already been tested for safety. While several groups do safety testing, DHV has probably the most comprehensive testing program. When you’re considering a new wing, get the whole safety report, not just the rating. There’s a big difference between a DHV 2 wing with eight 2’s in the report and another with just one 2; the former is more like a 2-3 wing, and the latter is nearly a 1-2 wing. Also, compare weight ranges. The manufacturer can set these numbers somewhat arbitrarily, and they may be skewed toward passing the DHV test more easily. Be suspicious of unusually narrow weight ranges, or ranges that call for an unusually large wing. Among the tested wings, there are two where the weights listed by DHV don’t match the manufacturer’s current recommendations. I would go with the manufacturer’s range (especially if there has been lots of flying experience since the test was done) but be cautious about the unrated end of the range.
Another measure of safety is the shape of the wing. Longer, skinny wings will be more "twitchy" and prone to collapses than shorter, fatter wings. For this measure I would look at two lines in the table: the flat aspect ratio and the wing thickness. The flat aspect ratio is better than the projected measure because it tells you how long and flexible the fabric is and therefore how prone to get wiggly or tie in knots. The wing thickness relates to speed and rigidity. A thick wing flies better at low speed for launching, maneuvering, and landing, plus the larger cross-section increases the rigidity due to internal pressurization.
Finally, there is one downside to a low-arch profile: a large collapse leaves the pilot under a sloping wing. This collapsed wing will turn more before recovering, and pilot inputs to prevent the turn may be more likely to cause a stall. In the DHV’s asymmetric collapse test, where the wing is allowed to recover from a large collapse without pilot input, the Argon turned more than 360 degrees. The other two wings we tested are listed as turning between 180 and 360 degrees.
So how did we like them? Steve flew lots of hours on the Sigma 4 and we both liked the feel in thermals. We don’t like the speed system, but many pilots rarely use a speed system. Steve didn’t get much time on the Argon; I liked its behavior in mild thermals. We reviewed the Proton last, in June thermal conditions, so it certainly got the roughest conditions for testing, plus the only significant cross-country flight. Steve liked the turning quickness of the Proton. The Proton reinflated quickly and cleanly after the unavoidable tip collapses or frontals you get when wandering in and out of strong thermals. The silicon-impregnated fabric was initially a dust magnet, but that seems to have abated with time. I’d call the Proton a good choice for the experienced pilot who likes its combination of extreme quickness and well-rounded behavior. Go with the Sigma 4 if you’d trade a little of that quickness for a more forgiving and secure ride. I don’t think we tested the Argon enough to compare it accurately with the others; I’m guessing it will prove itself on the competition circuit this year (as the Proton did last year) with a combination of speed and efficiency. I’m less certain about its behavior in big air, so I’ve ordered one to continue testing… ;^)