Thursday, December 6, 2018

What you need to know about single-surface wings

Single-surface wings are incredible. They weigh nearly nothing, fit in to your hand luggage, and yet are still real paragliders, capable of soaring and even cross-country flights. Understandably, many pilots are considering buying one. This post exists to help you make that decision.

All wings are compromises. Traditionally the compromise has been between performance and passive safety as measured by certification. Single-surface (SS) wings are equally compromises, trading some disadvantages for other advantages over classical double-surface (DS) wings. Let's go through these.

Weight. SS wings are much lighter - but not half the weight, as you might have expected. There's no under-surface, but there is still a lot of fabric structure, more line, and the same risers as a DS wing. Consequently, you typically save about 40% of weight - significant, but not 50% - compared to a DS wing.

When considering weight, you need to consider the total weight of your gear, which includes your harness, reserve, helmet, flight clothing, and food. Dropping the wing weight from a 2.2kg DS to a 1.2kg SS sounds like at 45% saving, but is much less interesting if your total flying gear weight drops from 5.4kg to 4.5kg - that's just 17%.

Pack volume. Fabric is not heavy (typically 27g/m^2 for a lightweight cloth) but it does take volume. SS wings have much less fabric, and you can squeeze the air out of both ends, so they pack much smaller. You can pack them into 4-6 litres of space (that's a tiny backpack), easily half the volume required for a DS wing. When they're this small, there's no excuse for not having the wing with you on every trip.

Price. The cost of building a paraglider is the composition of many things. Fabric is expensive (which SS wings have less of), but so is line and construction complexity (which SS wings have the same or more of). Overall, like weight, expect an SS wing to be cheaper than a DS wing, but not by as much as you might initially expect.

Fragility. SS wings are built to be light, and feel very fragile in your hands. Yet, they still pass the same 8G load tests as normal wings. Made of light materials, you need to be more careful not to snag lines or fabric on rocks or bushes, but here they are no different to their DS cousins.

Inflation. SS wings love to fly. Like, they just wanna be up there above your head all the time, even in the lightest zephyr. This is fantastic in zero or light winds (and even backwinds) but becomes a problem in stronger winds. Specifically, DS wings are easy to pin down on the ground using the brakes or D-risers. SS wings are always trying to leap up into the air. Great if you're looking to fly from a tight spot, but if you're launching in wind you're gonna be fighting the wing all the time until you get off. Similarly, for landing in wind this is a problem: the only way to "kill" the wing can be to run downwind past it, gathering the wing up as you go. Doable on a solo wing but almost impossible on a tandem.

Launch. They're immediately above your head and inflated, but they're not lifting you yet. You still have to run, The runway needed to take off is perhaps slightly longer than a DS wing.

Calm-air glide. Here, they're pretty OK. They don't glide as well as DS wings, but modern SS wings get a comfortable 7:1 or so in still air.

Speed. First-generation SS wings were very slow (e.g. 26km/h, with no accelerator). Modern SS wings claim trim speeds closer to DS wings and have speed systems offering a few extra km/h. However, if you're considering a SS wing you should measure the trim and accelerated speeds yourself.

Turbulence. This is where the compromise happens. Many things are different.

Firstly, SS wings move around a lot. They don't contain the mass of air that DS wings do. The air in a DS wing easily weighs a few kilograms, SS wings have no air in them. SS wings move initially very quickly, and then stop. This makes the glider feel very nervous: they jump around, feeling like they're gonna dive too far, but then they just stop. This takes some getting used to. They can be more stressful to fly than CCC competition wings.

These damped responses make SS wings great wings to throw around: you can wingover and spiral as much as you want, but it takes perfect timing to get large-amplitude movements, and as soon as you stop, the wing immediately loses all energy and resumes normal straight flight.

Secondly, SS wings lose all performance in turbulence, period. Rough air is where glider performance differences are most evident, and here SS wings are the worst of the bunch. Once it gets even a little bit bumpy, SS wings perform significantly worse than a school EN A wing, At times, it can feel like you're descending vertically with no forward speed - and there's nothing you can do about it.

This is really important for your flight planning. If you launch a SS wing, you need to have a landing field within a 2-3:1 glide angle, unless you're very sure of the weather conditions.

Sink rate. SS gliders have higher sink rates (especially in thermals which are by their nature turbulent) and have less efficient turns, even in smooth dynamic lift. You get more feedback from the wing's nervousness, which compensates to a certain extent, but you're still going to climb less well than a school wing. Don't expect to be top of the stack, and you'll almost definitely be the first to sink out and land.

Landing. Older SS wings have very poor flares. You need to pull on the brakes fractions of a second before you touch down, and even then you get a hard and fast landing. Modern SS wings claim much better flare characteristics, but you should test the wing yourself before buying it.

In conclusion, SS wings are awesome. If you want a wing that you can take with you everywhere to fly in good conditions, then get one. They're not without compromise though. The range of conditions in which SS wings are safe and fun to fly is significantly smaller than the conditions for a lightweight DS wing. An SS wing is not a replacement for a DS wing, it is a complement to it.

Sunday, January 9, 2011

Bessans Cross Country Ski Marathon

Today I returned to Bessans, deep at the end of the Maurienne Valley for a second crack at an cross country ski marathon. Last year conditions were difficult with several centimetres of fresh snow and temperatures the cold side of minus ten. I struggled round in about three and an half hours - slower than my normal running pace, but satisfied to have completed my first cross country ski race.

This year conditions were completely different. After two huge snowfalls before Christmas the weather in the Northern French Alps has been sunny but cold. Until this week when it changed for the worse: SW'ly winds brought warm, humid air and wind and rain to most resorts. Saturday was as warm as a spring day and the snowpack at all levels has suffered catastrophically. There simply isn't much snow, and what there is below 1800m has been rotted by the rain.

But Bessans is special. Deep in the mountains and surrounded by the glaciers of the Vanoise National Park, it is legendarily cold - as I had discovered in 2009. This year it is one of the few cross country ski resorts in the area that still has reasonable snow cover. Conditions today were warm and the pistes were in fantastic condition. Instead of hacking through fresh snow, it was pure glide on perfect pistes - a potentially record day.

The event is a mass start with both the half- and full-marathon skiers starting side by side. In total well over a thousand people were chomping at the bit at the line and when the gun went they launched themselves forward in a mad folly. Skis were trodden on, there were falls and crashes, and and at least one marathoner's race ended early with a broken pole in the first four hundred metres. I saw him unhappily skiing back to the start, staying to the side of the piste to avoid the swarming mass of skiers.

After the excitement of the start, normally the pace cools off a bit and people settle into a more relaxed marathon rhythm. Not this time. The glide was fantastic and people were enjoying it, hungry to break their own personal records. With so many around it was nigh on impossible to overtake and so I settled into a comfortable pace, pacing myself and knowing that I'd still be fresh for the second half.

For the first 15km the course winds left and right, making a wobbly loop through the fields up the valley from the village. Glancing at my GPS, the first 10km takes only 36 minutes, not bad given the crowds. From there, we descend gently and consistently next to the river. It's a good consistent gradient giving a good cruising speed of over 20km/h. I sneak around one group of skiers and squeeze through another, enjoying the descent and keen to make time. After crossing the river down the valley, we make a U-turn and head back towards the village. Here comes the only extended climb of the course, a perfectly wide and steady slope. The snow is good, I change down two gears, and keep my technique for the climb, occasionally changing stride to give alternative sides of my body a rest.

Cresting the top, I grab a warm sugary tea from an aid station without breaking pace. It's a flat run to the village from here, and the half-marathoners break off left for their finish. I'm in the marathon and I have a second lap to do.

With half the number of skiers and everyone slowly spreading out there's suddenly much, much more space. I'm still fresh and I know the terrain from the first lap. I step up my effort and focus on the skier twenty metres in front of me, hauling in him. Once I'm past him I focus on the next one and haul him in too. And then the next one. The glide is good and despite one wobbly moment while wolfing down a carbohydrate gel, my technique is holding together. This is the best part of the race.

With just 10km to go I glance down at my GPS watch - I've been only going 1h50m. With a quick mental calculation I realise that a sub-2h30m time is possible. Not wanting to waste this opportunity I step up my pace. Once again I'm on the cruising downhill section by the river and I push harder, tucking in behind a group of five skiers. I'm skiing into the increasing wind but that means that the wind will be with me for the long climb. Rounding the corner after the river I again gear down, not wanting to blow up three kilometres before the finish. It works. I crest the top for the second and final time, having gained a few more places on the way up.

On the flat I step up the speed again. The skis are still working well and the finish is in sight. I'll be comfortably under 2h30m, but can I gain any more time? Pushing on and counting down 800m... to go. 600m... At 400m I start my sprint - a somewhat wobbly proposition given my "English" technique - and cross the line at full pelt and 2h23m on the clock, over one hour faster than last year! Yes!

Thanks so much to Sylvain Dhonneur for organising a brilliant weekend and waxing my skis to perfection. This was great training and a real confidence boost for my big cross country ski challenge this year: the 76km Transjurassienne Ultramarathon on Sunday, 13th February. Let's hope there's some snow!

Friday, June 18, 2010

4 days, 24 hours of flying, 580 kilometres XC and 3 kilos of cheese

The brief was simple: take off early, fly your socks off as far as you dared and then fly back again to land back at HQ. The Cat's Cradle Trophy is a new pure XC competition organised by Dezair Paragliding in Marlens, Annecy. I joined thirty French pilots and one New Zealander for what turned out to be one of the best XC weeks on record.

Pure cross country competitions have been gaining popularity with events like the XC Open and the Czech-organised XCamp. French and PWC Champion Patrick Bérod brought the format to his home site of Méruz at the south end of the Aravis mountains near Annecy in the French Alps in April. I signed up partly for a much-needed break from the day job and partly to get first-hand experience of the XC comp format.

The organisers promised less follow-the-leader gaggle flying, less mindless bar pushing and instead more flexibility, more decision making, and the opportunity to make the most of every day - in contrast to the hanging around and three-hour stress-fest of a traditional comp. I was skeptical. I had concerns about safety (XC comps have a much worse safety record than traditional comps), logistics (how do you organise retrieves when pilots scatter themselves to the four corners of the map?) and fairness (surely the local pilots would have a huge advantage?). As it turned out, I would be wrong on almost all counts.

The first day dawned with exceptionally clear skies and an excellent forecast. The deep blue was pure: an Icelandic volcano had scattered engine-eating ash into the upper atmosphere and there was not a single jet trail in the sky. Kiwi Glen Stevens had braved 36 hours of surface transport to get to the comp from London. With the magical sensation that the skies would be ours and uniquely ours the atmosphere on launch was palatable. We all knew the day would be special and it did not disappoint.

From the start the atmosphere amongst the competitors was positive. We all realised that the battle would be fought in the air but by sharing information and route ideas we would all benefit. The task was set informally by the pilots: blast down the East faces of the Bauges mountains, do the huge transition into the Chartreuse, bar down to Grenoble to the south, tag a turnpoint somewhere near the Fort St Eynard and then race back north. Big transition back into the Bauges, and then keep going: tag Annecy and then cruise into goal on the valley winds just before the window closed at 17h30. Having launched ten minutes after the first pilot (it was effectively a ground start from a one glider launch) it took me 10km to catch him but conditions were fantastic and once away from launch I made only sixty turns in the first 80km to Grenoble, spending the rest of the time on half bar. I lead out, falling into a natural rhythm with the thermals and the clouds, until about 160km into the task. If it was good I stayed, but as soon as the lift dropped below 2m/s on the 20s averager I put on the bar and glided to the next source. Finally, bizarrely, it was at one of the most reliable thermals in Annecy (the rocks above Bluffy) that I finally fell out of cycle and was caught by Nicola di Bernardo (Mac Magus) and Sylvain Dhonneur (Aircross Usport) who had been chasing hard. After six hours of racing we fumbled our way up to base and headed in different directions to maximise our distances as the final minutes ticked away and goal beckoned. As it was we all made different decisions. Nicola claimed the longest flight but was 130 metres short of the line as goal closed. Similarly for Sylvain. Not getting to goal in time was costly. I'd blasted in with two minutes to spare to take my first 1000-point task win in an FAI Cat 2 competition. Day 1: 180km and 6.5 hours of flying.

Day two was very different. Cloudy. Over-development later. Pilots were tired from destroying their personal bests the day before. An earlier land-by time was set. Despite the tricky conditions this would prove to be the defining task of the competition.

With the forecast of big clouds in the mountains I'd planned a route that took me to the edge of the flying area during the strongest part of the day. The goal was to head towards the flats, clock up the kilometres on the lower ridges away from the main massifs, and then cruise back into Marlens on the valley winds before land-by time. It wasn't easy and I would have bombed out early on had I not been working low slopes with the eventual female winner, Christine Metais (Gin Boomerang 6 X-Alps). But it worked. In a dance of patience and planning I flew from sunny spot to sunny spot, occasionally relying on the magical lift-sniffing abilities of my Axis Mercury 08, and sometimes counting only on its raw speed and stability when jumping from mountain to mountain. Christine doubled back at the Montagne de Banges but I continued. The game was sunshine and shadow. Working large-scale weak lift I got rained on and hailed on, but it was only light. I flew into goal with just over five hours on the clock and a slow 105km on the counter. An insignificant distance compared to the previous day but hard-fought and enough to hand me my second 1000-point task win. Day two: 105km, 5.5 hours.

For day three the excitement was manifest. Almost the entire field (including me) had broken their personal best on day one, and Wednesday was looking even better. It was. The game was kilometres and everyone (except local XC hound Betrand Bellet (Gradient Avax XC2)) opted to follow the same flight as the first day but to extend it further north. I was once again a bit late to launch and it took me 80km to catch up with the ten-minute first launch advantage of task leader Maxime Pinot (Aircross U4) at Grenoble at the extreme south end of the defined flying area. The flying was fast - not dumb balls-out fast but intelligent fast - using the best lift, gliding at speed to fly. My impatience was on my side as a left Mont Granier below cloudbase for the big transition into the Bauges. This proved to be the decisive moment in the flight as I led out alone but in cycle, tagging the summit of Sur Cou at the extreme north end of the flying area before relying on raw bar speed to get me back to HQ with ten minutes to spare. I could have flown further. As it was, I ticked off the longest flight of the day with 211km in 7.5 hours, another personal best and a tidy average speed of almost 30km/h for a XC flight flown predominately alone. That day, four pilots flew over 200km circuits despite having a land-by time that still left 1.5 hours - 45km - of flying time. As you can probably imagine, the atmosphere in goal was electric. Almost everyone made it back in time having broken - no, destroyed - their personal best. Those who didn't make it in time landed in goal later, with fewer points but with even wider smiles. There was a barbecue at the HQ at the Auberge des Aravis and you can imagine as well as well as I the atmosphere amongst thirty pilots who had each just flown the best flight of their lives so far. For the third day in three, I won with 1000 points and the French were beginning to get annoyed.

The Meet Director Patrick Bérod announced that Thursday would be the last day. The accumulation of twenty hours flying in the best conditions that the French Alps have to offer was beginning to show in the eyes of the competitors. Of course, it's never easy. The beloved French President Sarko was in the area and this meant that there was an air exclusion zone around our normal playground of the Bauges until 13h30. We headed further away to take off - the ski resort of les Saises with it's south-facing slopes at 2000m - but it was still a game to make the most of the day.

Flush from three days of success, I got it horribly wrong. In my mind the goal was simple: don't take any risks, fly well enough to score 600 points which given my 400-point lead over second place Julien Senzier would be sufficient to secure the competition win. Even with this, we discussed tactics beforehand, freely sharing our information. But this day would not be mine. In the air, sensing a weakening of conditions, I took the conservative option of flying in the Bornes and Aravis mountains with a guaranteed return to goal in the Annecy valley. I got trapped under an inversion. Twice. On a weak day that would also be worth 1000 points like the others, in a four hour task I spent two hours scratching, going nowhere. I limped into goal, a few km under the belt but doubtful whether it would be enough.

While I had been stuck surviving, Kiwi Glen had been blasting up and down the East faces of the Bauges as fast as his Niviuk Peak would take him. Not bad for a non-local pilot who'd just learned the entire area in three days flat. While I'd done a mere 80km in four hours he'd clocked up 120km in the same amount of time but had been agonisingly a couple of kilometres short of goal when the time ran out. Nicola di Bernardo had got it right. He'd flown at speed-to-fly and blasted into goal a little early due to confusion about the land-by time. Having won three days in succession, was I about to lose it all?

On that final day I was 18th out of thirty. Everybody else was celebrating finally beating me. I was gutted that I'd fallen short, failing at the last hurdle. In those tense few hours before the final results came out I was not a good person to be around. My mood had changed from loving the flying and the atmosphere to playing zero-sum games of your win is my loss. It was not a proud moment.

Friday dawned cloudy and inverted. There would be no task. Despite my errors the previous day I had kept my first place albeit giving away two hundred points to second-placed Julien. I topped off the week by landing on the spot in the local stadium in Ugine to thank the local commune for letting us use the launch and adding a kilo of mature Tomme cheese to my pile of delicious Reblochons from three task wins and my first FAI Cat 2 win.

So, how were the logistics? Pretty good. The retrieve was organised using a minibus in each area. I got back to goal each day in time so didn't get to test out the retrieve system myself, but no-one was late back and everybody was happy. Safety? There was one reserve deployment with no injury, which given the 1000 hours of flying in strong Alpine conditions accumulated by the pilots was about par for the course. The emphasis on personal decision making meant that each pilot made his/her own individual decision to fly or land rather than being told what to do. Fairness? Well, the jury's still out on this one. I knew the area well and did well, but Kiwi Glen arrived with no local knowledge and nearly won the last day. As a non-local pilot you're unlikely to win but you'll certainly walk away having learned a fantastic amount.

Rumours are that they'll be another Cat's Cradle at St Jean de Montclar (site of the 2009 British Open) towards the end of the summer, and maybe a wider series to follow. See you there?

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