Wind revisited
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Wind by itself is not that dangerous in aviation, as long as it is within the limits of what the pilot and aircraft are able to handle. The main danger lies in the wind strength exceeding the aircraft's flight envelope, which unfortunately happens rather soon for a paraglider. A 30 km/h headwind may seem just a minor nuisance for a sailplane pilot cruising at 150 km/h, but the same wind is likely to be a major challenge for a paragliding pilot. In turbulent and windy conditions, a paraglider seems more like a leaf in the wind than an actual aircraft. It has (very) little margin when the wind raises its voice. If you like flying in strong wind, you are probably better of piloting a sailplane instead. Having done both, I can assure you that flying in (moderate) mistral conditions is a lot more fun with a sailplane than a paraglider. Battling your way through the air on a (nearly) blown out day is almost certain to result in some interesting flying experiences. By frequently flying in these kind of conditions however, you are likely to increase your piloting skills and get more or less used to the challenging circumstances. Still, flying a sailplane in this case remains far more relaxed and less risky. Skills come at a cost, paid in time and effort. Paid in pain when making a mistake or overloading the learning curve.

A strong wind at altitude could be a great help for flying long distances, or a just nuisance that blocks the hoped for progress over ground. Closer to the earth however, such a wind can be deadly dangerous. It is not so much the wind strength that causes problems here, but the turbulence created by obstacles. Undisturbed wind flows in a clean and predictable manner, which makes it easily manageable. Even when strong, even with a paraglider. Soaring at the coastal dunes for example, can be safely done in wind speeds that could cause severe trouble in the mountains. There is a large and unobstructed space in front of the beach, ensuring that the wind is mostly laminar. Others like to profit from this wind as well, quite understandable since it is free, but unfortunately disturb the laminar flow in the process. The resulting turbulence can be felt when flying through the wake of a fellow pilot's wing for example, or when flying in the lee of a far away wind farm. The latter doesn't create the same bumpy air as the former, but it isn't just as smooth anymore and feels less pleasant than before. All obstacles affect the wind's flow, resulting in turbulence and occasionally lift. The stronger the wind and the larger the object, the stronger the turbulence. The stronger the turbulence, the more difficult to manage. Up till the point where turbulence takes over and (frequently) folds your wing mid air, leaving you with little to no control to sort it out. But as with most of the piloting, difficult situations are often the most interesting ones as well. Undisturbed airflow is a bit boring after a while, isn't it? So, let's have a look at some of those interesting situations.

Venturis

Wind can only be stopped from blowing by eliminating the pressure differences that created it in the first place. And that is precisely what the winds are doing. Its direction and velocity can (temporarily) be changed however, either by man made obstacles or natural ones. A wall does not stop the wind from blowing for example, but simply diverts it elsewhere. The wall shields you from the wind of course, but this also means there will be a stronger wind near the edges of the wall. When a valley narrows, its wind has less space to pass through then before. In order to maintain the same flow (conservation of mass and energy), the valley wind has no other option here than to accelerate,. Its similar to squeezing the end of a garden hose, in order to spray the far end of the garden without having to walk over there.

Assuming you try to avoid or pass a venturi by flying away from it an not into it, the accelerating wind will decrease ground speed. It will also increase sink, similar to the accelerated air flow over a wing creating part of the lift. Venturis suck, in a big way. The usual advice is to stay away from them. This is a sound, but unfortunately also a rather unrealistic option if you happen to fly cross-country in the Alps. The existence of mountains implies venturis, of all sizes. The two go together like lift and sink and you are bound to run into a venturi sooner or later. So, let's have a look on how to deal with them.

The more or less satisfying progress during the initial part of the transition, often lure pilots into flying straight across a venturi. Despite such a promising start, the wind a little further may already be strong enough to stop any progress whatsoever or even make you fly backwards. The stronger the wind in front and the more narrow the venturi, the bigger the risk thereof. At the same time, the increasing sink makes you descend faster than usual. Since venturis tend to narrow towards the bottom, the already strong wind increases as you descend and slows your forward progress even further. Once a venturi grips you, it seldom lets go. In addition to this, venturis such as a gorge or a mountain pass, often happen to be the most efficient way to access a plateau or another (part of the) valley. Being already a dangerous place from a windy perspective, you also risk to encounter other complicating issues such as busy roads, raging torrents, and power lines, as the venturi swallows you and 'landing' becomes imminent.

Cousson - Beynes transition.Even though it is a detour, you are likely to loose less altitude and make more progress by passing in front of a venturi. The image shows the regular breezes near the Cousson and Beynes mountains. There is a narrowing valley in between these mountains, with a substantial breeze arriving from the plain to the south-west (the root of the blue arrows). Near Cousson this main breeze splits into a northern branch heading for Digne and an eastern branch heading for Barrême. Part of the latter breeze bends north again behind the east side of Cousson and will rejoin the earlier separated breeze from Digne somewhere between Cousson and the Bléone valley. The exact location of this rendez-vous depends on the wind that day and is an interesting puzzle to solve, especially on a blue thermal day.

The main branch of the breeze heading east to Barrême, forces its way through the clue de Chabrières, a narrow gorge that has been carved out by the l'Asse river over millions of years (even though it didn't have a name for most of this time). Nature works marvels, albeit a bit slow in comparison with human standards. When humans arrived in the region and started shaping and naming it, nature somehow seemed behind schedule. Or maybe humans were just to far ahead. When people felt the need to drive a car(t) through the gorge, nature had not yet created enough space to do so. Humane nature has far less patience and especially less time than nature itself, so a narrow corridor has been blasted out of the rocks for a road. Nature could have done it for free in another few million years or so, but that simply took too much time according to human standards. Occasionally I wonder where all that time has gone that humans have saved by now. It probably got lost in increased efficiency and productivity, or crunched by mediocrity and haste.

A large part of the breeze in the kilometres wide valley between Cousson and Beynes is squeezed through this ten to twenty metres narrow gap. Having only a fraction of the space here, the wind is a lot stronger than in the wide valley in front. As a general rule, the further you stay away from these kind of places, the better. Path B in the image is likely to work better than path A, assuming the regular breezes are as sketched. This doesn't seem logical at first sight, since path B is longer than path A. It also involves flying straight into the (strong) breeze during the initial part of the transition, apparently not getting that much nearer to the other side of the valley. These two worries are mainly psychological and precisely the reason why I see the majority of pilots trying the direct transition via path A. All works well in the beginning, but the strong wind and accompanying sink during the later part of the transition, is likely to result in landing out. Once you sink into the lee of the hills in front, the game is over. Path B is longer, but it avoids the venturi with a large margin. This also means it avoids most of the excessive sink and gives us more ground speed overall, even though we have been flying straight into the breeze most of the time. In addition to that, the hills in front of Cousson will provide us with (small) thermals during the initial part of the transition. These hills are well exposed to the sun and breeze, and have a good thermal surface. As a final bonus, there is likely to be a convergence near the col to Digne as well.

The most important advantage of path B however, is that it allows good piloting. We have margin, an escape in case we were wrong about our assumptions and possibilities. If we encounter stronger than expected sink or wind on our chosen flightpath, there are numerous fields to land safely or we can quickly return to Cousson with the wind in the back (instead of fighting our way back into head wind compared to path A). If we insist on the chosen path, despite being low, we can shorten our transition by aiming for the low hill that leads to Beynes village (path B'). This hill causes much problems for the pilots that are low on path A, but allows us to connect to Beynes mountain. It requires a bit of (hard) work, but certainly less work compared to hiking up to its summit for a relaunch. I have done both several times, so I think my conclusion is a valid one. I have to admit though that the view up to the village of Beynes may be a bit discouraging at the start. The trees below the hill and the power lines crossing the slope in order to feed the village, do not ease this discomfort. Landing out can be a delicate affair if you forgot to keep an adequate safety margin. All these troubles are soon forgotten however, upon climbing out and looking down on the village. I often top land for a pick-nick on Beynes mountain, just to enjoy the view and feeling a little longer. Be aware though that the most logical spot to do so, is in the lee of the south breeze. The approach can be a bit bumpy and requires adaptive piloting in order to avoid having a similar landing.

Path A on the other hand, has no real (safe) options when running out of altitude during (the later part of) the transition. The most important drawback of path A is that you risk being sucked into the venturi or blown over the hills on either side. Even if the breeze doesn't seem that strong in the valley, it could be too strong near the venturi. You could land in the valley when failing the transition, but this is likely to a more turbulent affair compared to landing out on path B. If you want to try your luck, you could fly with the breeze to the northern side of clue the Chabrières. If you are not blown over the back here, you could soar your way up again and fly to Cousson for another try. The latter requires considerably more effort compared to path B, since the breeze is working against us here. If you insist on trying to make the transition on the other hand, despite being (too) low, there is even harder work ahead. You may be tempted to 'jump soar' your way west for example, via the hills on the southern side of the valley (path A'). By gaining altitude on the windward side of a hill and flying around the lee side of the next one, and repeating this a few times, you could hope to hop to the windward side of Beynes mountain. Unfortunately, you will be in the lee of the latter during the whole risky effort. The breeze from the plain to the south-west is stronger than the breeze heading for the clue de Chabrières, which is but offspring of the former. It is a messy solution that is unlikely to work. It carries a significant risk that could have been avoided by taking path B or B'.

To illustrate the above, one day I did the Cousson to Beynes transition with eight other pilots. I nice opportunity to test my opinion, since I am usually alone in this spot and can't verify whether I am talking nonsense or not. We all had been searching for transition altitude near Cousson for a while, without finding a comfortable amount. After finally finding a decent thermal to the south-east of Cousson, the other pilots drifted with it and and took a path even closer to Clue the Chabrières than path A. All of them had (far) better performing (competition) wings than me, and all but one made it across. Some of them tried to correct their mistake by following path A', but to no avail. Showing once more that flying a performing wing is no guarantee for performance. Oscar, who had caught up with me after making a small detour at the start of the flight, confirmed my opinion. He knows his skies and seldom makes a mistake. He found a thermal north-west of Cousson, precisely in the spot were there had been none during my half hour search earlier on, and joined me on path B. As he passed me 500 metres overhead, he showed that the success rate of path B was not just a statistical coincidence. He also showed that intelligent flying with a performing wing is an unbeatable combination. As he disappeared behind Beynes at cloud base, I started working my way up from below the village of Beynes and made it back long after he had landed for his beer.

Path A could work better than path B however, when you have a considerable altitude at the start of the transition. That means, an altitude where you are no longer bothered by the venturi. Unfortunately, this occasion is rarer than hoped for. My guess is that this occurs in one out of twenty flights or so. A figure that is slightly skewed to the negative side, since I am flying on all days that are flyable and not just the good days. On a good thermal day, the Cousson - Beynes transition isn't that interesting at all. Another exception could be north wind, which weakens or even cancels the southern breeze and shortens the transition time by giving wind in the back (all transitions mentioned here are north to south, the reverse requires an another chapter that I leave as an exercise to the reader).

There are more options of course, but I merely hoped to show you how to adequately analyse interesting situations. Sometimes a sailplane tricks comes in handy, such as venturi soaring. Since the air is not capped (not at this altitude at least), a venturi not only creates horizontal acceleration, but also a (much smaller) vertical one. The resistance created by the venturi partly deviates the wind upwards. The result is a vertical compression zone, just like the ones we use when soaring a mountain or a dune. Except that the mountain is invisible here, since it consist of nothing more but compressed air. These kind of soaring zones can be comfortably exploited with a sailplane, but the wind often too strong for paragliders and the vertical lift component is too shallow considering their glide ratio. There might be lift, but a paraglider will simply be pushed back by the wind rather than upwards. Under which conditions exactly venturis may be exploited with a paraglider, remains unclear to me. It seems that the wind needs to be relatively calm and the venturi narrow, so that there is a enough compression to build a 'wind wall', but not too much acceleration to blow us away. The lift zone will normally be slightly in front of and above the venturi, but is not guaranteed to be there. If not, you find yourself on the verge of being sucked into a gigantic vacuum cleaner with little to no means of escape. So, don't try to solve this kind of puzzles unless you are very certain about what you are doing and have adequate margin to get out of there safely in case you are wrong.

I have used the above trick to do a direct transition once, straight from the summit on one side of the clue de Chabrières to the other. There was a strong northern wind that day and a calmer southern breeze than usual. Starting at about 2000 m altitude at the northern summit of the venturi, I lost quite a bit of altitude in the initial part of the transition. Arriving over the centre of the venturi, having a wonderful view that few paragliding must have had, I gained a few hundred metres. This allowed me to pass the summit on the southern side of the venturi by an adequate margin and even to make it against the breeze to the windward side of Beynes mountain. I encountered an apparently similar situation in clue de Taulanne half an hour later. There were no cumulus clouds to be seen in the area, all blown to smithereens by a breeze that was slightly below trim speed. But right above the centre of clue the Taulanne, there was a single puffy cloud. Thrilled by this observation, I wondered whether I could repeat the venturi soaring experiment here. The considerably stronger breeze however, made me decide to give it a miss. I risked ending up in the lee behind clue de Taulanne in case I was wrong, or getting wacked by the turbulence just in front (it is not exactly a smooth venturi). While I was working hard to make the last miles home via the lee of Aup in timid thermal conditions and a breeze that occasionally exceeded trim speed, I wondered whether Taulanne would have been the better and especially the safer choice. It would have been nice to have other pilots nearby to prove me wrong. I suddenly realised I hadn't seen any other paragliders in the air, reminding me that is was probably one of those day that I shouldn't be flying. Not with a paraglider at least. One of those flying days that make others consider me crazy. I am not crazy, I am just devoted. Or is that the same?

The fundamental problem of understanding wind or thermals, is that you can't observe them in a direct manner. You can't see exactly how the air is behaving in places such as clue de Chabrières or clue de Taulanne. Clouds may give occasional hints, but the air by itself remains invisible and leaves you guessing about its precise behaviour. You never know for certain which way the wind blows in a certain spot, unless you happen to be there. The resulting knowledge could arrive too late to keep you out of trouble. However, there is a lot to learn from the flow of stuff that is visible. I have spent days on end observing precipitation, fog, ice and snow sculptures, streams and rivers, lakes, or anything else that got my fancy and seemed connected to natural flow in general. And not just flow. I am observing everything, all the time. Wondering what is happening or has happened, but especially why and how. And often whether I would be able to find or even predict similar behaviour in the air. Sometimes I feel like a little boy that, filled with curiosity about the big new world he is discovering, drives his parents mad by asking questions all the time. All the time trying to understand the world around me. A world which seems so simple, but complicated at the same time. Sometimes my understanding of quantum and particle physics is a lot better, compared to my understanding of how intricately nature works. Especially when looking at the whole system or the tiny details. And in order not to confuse you, quantum and particle physics are beyond my brain.

Despite air and water being very different substances, there are similarities that help me better understand the wind's behaviour. The flow of a stream will never be exactly duplicated in the air of course, but there are some general characteristics that facilitate understanding. For example, disturbances in the water caused by branches, rocks or variations in the depth or width of a stream, tell me how air is likely to behave when encountering hills, rocky outcrops, trees or venturis.

Water flow in a venturiThe two water venturis on the left reveals several interesting characteristics. The most important one, acceleration, cannot be seen. It can only be felt by getting your fingers wet. Something the internet is not yet (2011) capable of. There are plenty of other interesting things to notice though. First of all, the stones in the water send ripples upstream. The water actually 'knows' that there is an obstacle downstream, even though it hasn't arrived there yet! This implies that an obstacle in the wind can be felt in the air before you get there. I use this characteristic to judge a mountain before getting (too) close. Especially when I suspect it to be a nasty spot. A lee slope will communicate different signals than a windward slope. If you are not (yet) able to identify these signals, a look at water patterns might help you. Depending on what I feel in the air during a transition, I either insist on my original plan or switch to an alternative one. When sensing 'bubbling' air in front of a mountain, I will continue to fly towards it. Sensing increasingly turbulent air, accompanied by sink without encountering the complementary rising air now and then, will normally make me choose a different destination in order to avoid a nasty lee side. If I am just running into strong sink (without the turbulence), then I am likely to insist on the chosen path, knowing that there must be rising air nearby as well.

You can also see interference originating from the two sides of the water venturi (click on the image for a more detailed look). The waves sent upstream by a wind venturi cause a similar pattern of lift and sink, but at a different angle. The latter has probably to do with wind being less dense than water. Wind has less inertia than water and is thus easier deflected, which causes the effects to occur more upstream/upwind in comparison with water. I am unable to see the lift waves created by a wind venturi, but it seems they extend more or less as half circles in front thereof. Like the ripples you see moving up a lake when throwing in a stone near the banks. I could be completely wrong about these wind waves, meaning I have a wrong model, but at least it explains to me in a nice way why sometimes I find lift during a transition. Lift that shouldn't normally be there and often is too small and unreliable to exploit efficiently. It seems to come and go as I try to centre it. But of course that is exactly what I should not be doing, since I should simply follow the wave line. When I find a good line, I encounter less sink and it helps me in getting across with less altitude loss than one would expect at first sight.

I have been more lucky exploiting these kind of waves when piloting sailplanes. It confirms that passing with a large margin in front of a venturi is likely to be superior to flying straight across. Upon starting a transition, I align the sailplane more or less into the wind. Roughly at a 60 degrees angle from the venturi. As soon as I encounter lift, I try to align my flight path with the wave. This is usually at a similar angle, but I need to adapt it while trying to follow the wave's curve further down the transition. This alignment often involves just as much luck, as piloting skills. It is all rather vague and intuitive. If I happen to lose a wave, I will fly straight upwind again in order to find the next wave. The aim of flying straight, rather than trying to find the lost wave again, is that lingering in the sinking air around the lost wave (without quickly finding it), is likely to cause more altitude loss than looking for the next wave. The latter will be more easily distinguished than the former, due to the larger sink/lift variations during the search.

So far, we have seen single wind issues only. These are the most frequent and easy to understand situations. When different winds meet however, much more interesting thing are bound to happen such as convergence or wind shear.

Convergence

Enclosed by mountains on both sides, two opposing valley breezes that meet have no other way to go than up. This could result in convergence, if we are lucky, or just a big turbulent mess of course when not. The Thorame valley, ten kilometres north of Saint-André, has a convenient convergence that allows you to cross a valley that is often too wide for a regular crossing. It is often overlooked by pilots coming back from Dormillouse. It is a bit of a pity to end this classic flight by landing out, seeing nearby Saint-André sink behind Cordeil. Especially when when realising that there is often lift nearby that could have prevented this sad ending. Finding this convergence has always been a delight, especially when getting back from a long flight at the end of the day. It usually gives me just that little extra height I need in order to connect with Cordeil, or more. It enhances my chances of flying the last kilometres home, which tends to be less tiresome than the three hour hike that awaits me when landing out. And for those who consider hitch hiking as an alternative, there is not an awful lot of traffic on the quiet country road to Saint-André when the evening falls.

Convergence in Thorame valley.The breezes normally flow north in both the Issole (left) and Verdon valley (right), heading towards the bigger mountains to the north. Having chosen separate ways at Saint-André, the Thorame valley reconnects these two and their corresponding breezes. The resulting convergence is often indicated by a (tiny) cloud somewhere in the middle of the valley, with the exact place mainly depending on the wind that day. For example, a west wind is likely to move this meeting point to the east. A significantly strong west wind could even push the Issole breeze all the way to Chaudeirolles, the rocks terminating the eastern side of the valley. In this case, looking for the confluence is a waste of time and you are better off flying directly to Chaudeirolles instead. The strong tailwind will get you there fast and drop you right in the lift zone. From there, you could try to get on to Saint-André through the Verdon valley. It is a more challenging way than via Cordeil, but a nice change from the beaten track. And for a good reason, landing out is a delicate affair here. It is a narrow valley, full of trees and few spots to land. Some of these might seem ideal for landing out, until you are low enough to discover the power lines that make it close to impossible (or at least very risky). There is a large field at the end of the valley for example, but it often houses bulls. The long stretch of grass just before Thorame Gare is perfect for landing, but occasionally sees sheep (and the patous that come with it...). Look for them when you still have other landing possibilities. And there is more... So, it probably shouldn't come as a surprise that very few pilots are flying here. The pilots that do, are able to tell me all the difficulties and all the (few) landing spots.

When heading south to Cordeil, looking for the Thorame valley convergence usually makes more sense than looking for altitude on Côte-Longue (though I am unlikely to give the latter a miss when I do find it). Especially at the end of the day, when thermal activity dies down. You risk wasting time searching for something that isn't there (anymore), while the convergence is still working. Even if you do find a comfortable transition altitude on Côte-Longue, say 2700 m or so, you risk losing quite a bit of that during the later part of the transition. The less comfortable altitude of 1600 m on the other hand, could be enough to make it when you exploit the convergence. As usual, altitude is a meagre substitute for understanding. Luckily for me, understanding came within a few transitions here.

If you are unsure about the wind direction or the location of the Thorame convergence, than have a look at the lake towards the east end of the valley. And have a look at determining wind direction if you don't know how. When transiting low from Cordeil to Chamatte at the end of the morning for example, a quick look at the lake should give you the breeze direction at the foot of Chamatte. It could mean the difference between landing out (arriving low on the lee side Chamatte) or flying on (arriving low on the windward side).

Cumulus congestus caused by convergence.Flying near the la Blanche mountain range, you can see an isolated peak on the other side of the valley. It has a big antenna tower on top and is called Blayeul. It is roughly ten kilometres away and seems out of reach for paragliders flying on la Blanche. Sail planes however, have a much better glide ratio and do the transition with ease. One day, it finally dawned on me that the cloud I had frequently seen somewhere in the valley, could be be caused by convergence from the opposing breezes from Digne (south) and Seyne (north). This realisation made the transition a lot easier. Be aware though that on a unstable day this is the most likely place to overdevelop quickly, as you can see in the image. Be on you guard when thunderstorms are forecasted. The convergence could be impressive, but negotiable, when passing it on your way to Dormillouse. However, it could block your return south to St.-André a little later. Flying a convergence for miles is magic. Flying a cumulus congestus much less so, let alone a cumulonimbus.

Blayeul looks a bit isolated, due to it relatively large size compared to the mountains surrounding it. That is why I neglected it in the beginning (I was wrong about that, Blayeul is a good source of thermal activity all around). Isolated mountains in the middle of a valley breeze tend to be unproductive spots for soaring, or thermalling if the valley breeze is strong. The wind tends to go around them, rather than up and over. This characteristic does not make them useless though, on the contrary. There could be convergence behind these kind of mountains. In the spot where you would normally expect lee side turbulence trouble.

Le Môle convergence.Le Môle sits in the middle of a valley that expands into a large plain in front of it. There are some impressive mountains at the end of the valley behind le Môle (the Mont Blanc massif being one of them), creating a strong valley breeze arriving from the plaine. Le Môle splits this breeze into branches passing via the southern side (left in the image) and the northern side (right). These two breezes meet again behind the mountain, similar to the earlier Thorame example. The principle should be clear by now, so I leave it up to you to draw the breeze arrows in the image. If all works out well, the rejoining breezes create a convergence in what (at first sight) appears to be a turbulent lee side. And maybe it is. Before getting there, the convergence hypothesis should have been confirmed. For example, is the cloud over the presumed convergence spot caused by the latter, or is it caused by a thermal blown over from the windward side? The puzzle here is more challenging than the one in Thorame valley. If you get it wrong there, you simply land out. If you get it wrong here, you risk ending up in a turbulent sink area with very few places to land safely. And did you notice those impressive power lines? Excellent! But did you also notice the smaller ones, at the bottom of the valley behind le Môle? Close to where you planned to land in case you hypothesis turned out to be wrong.

There are even more interesting, and certainly more challenging examples than the ones above. One of my favourite puzzles involves a spot with three to four different wind directions, their precise number depending on the weather conditions that day. It is a pleasure to puzzle over this convergence and get it right. I have never gotten it wrong so far, but nature has lots of time and patience to prove me wrong one day. In order to be ready for that day, I always count on being wrong. I could write a few pages about this convergence spot, but there are other interesting windy issues that I would like to talk about as well. For example, when conflicting wind do not cooperate.

Wind shear

Convergence implies conflicting wind directions. But conflicting wind directions do not necessarily imply convergence. Two volumes of air having different characteristics do not mix for example, or at least not that easily. Which is great news, since that is why thermals rise instead of just mixing with the colder air around them. If warm air would easily mix with colder air, we would have a single large air mass that would slowly and evenly heat up during the day, rather than lots of small one that climb skywards. Any (tiny) pocket of warm air would be absorbed by the surrounding colder air, long before it could become a thermal. Fortunately for us free flyers, different airs do not mix easily. This characteristic has a drawback however. Winds with different air characteristics won't mix that well either. A cold wind for example, dives under a relatively warmer wind, creating wind shear instead of convergence. You can't see this wind shear, but somewhere in the air there is a boundary layer where the winds flow in different directions. Not a very comforting thought for those who rely on a clean and steady airflow to keep their wing inflated.

Saint-André-les-Alpes is known for its excellent flying, as well as its tricky landing conditions. It seems as if someone, in order to compensate for the excellent flying conditions (or just in order to keep the pilots alert), had the bright idea to locate the landing zone right in the middle of three often conflicting wind directions. Depending on the conditions, the wind could come from the lake (south), from col des Robines (north-west), or from la Mure (east). It is not so much the varying directions that pose problems here, but their rapid changes and their rather vague meeting point. There are various wind socks all over the landing field, frequently pointing to different directions at the same instant. This mostly happens in the afternoon, when thermal activity is at it highest and the wind on the landing field randomly seems to change in direction and strength. Unfortunately, the probability of such an abrupt change seems inversely related to your distance from the ground. The wind direction seems a sort of stable as you lose your surplus altitude, but the closer you are to landing, the more likely the wind direction is about to change suddenly. Often including a change in strength as well.

If you can't stand the heat, stay out of the kitchen. Landing in nearby la Mure is far more pleasant under these circumstances. Half an hour hiking back to Saint-André is a small price to pay for a sane and safe landing. And there are more options to keep your flying sane. So, don't become focussed on the regular landing field when the conditions risk to overwhelm you. With a very strong north wind for example, landing in Méouilles is likely to be safer than stepping full on bar close to the ground in order to make it. Remember that the water from the Verdon river is colder than that of the lake, so it tends to sink when arriving at the lake. If you land in the Verdon, your glider risks to be drawn to the bottom of the lake, and you with it. If you have been lucky enough to make it across the Verdon at low altitude, then remember that those trees at the southern end of the landing field have seen their fair share of pilots (hangliding pilots included). Sinking into their lee, with the rapid flowing Verdon river below you, is an unpleasant experience. Hiking back to Saint-André from Méouilles only takes about half an hour and there is lots of space to land. The latter is no coincidence, since it is the pente-école of the local school. If beginners can practice there safely, you shouldn't have a problem with it. One pilot even managed to safely land in Méouilles on her reserve parachute once. You might not think this a special event, but this was after she was forced to throw the reserve over the regular landing field. A one kilometre cross-country flight on a reserve parachute, thermalling up from fifty metres above the ground when the reserve opened, should be an impressive illustration on whether you are really ready to deal with the landing conditions that may await you. Or whether you are just counting on luck to land you safely.

The uncertain breeze direction upon landing is a problem in Saint-André-les-Alpes, but mostly manageable (for paragliding that is, it is a different story for hang gliding). The landing field is enormous and offers enough margin to safely escape from an approach gone wrong. If you count on an eventual wind change at the last moment, reacting timely and wisely if it does happen indeed, then the landing may be less enjoyable than usual, but manageable. There are plenty of (big) windsocks in the vicinity that allow you to actually see the problem before it hits you, and thus deal with this horizontal wind shear. Vertical wind shear however, is much harder to notice. Even if you do notice that the wind direction near the ground is different from the one your flying in higher up, it is hard to see where the two will meet. This turbulent meeting point may be a couple of hundred metres above ground, or just a few dozen metres. If you are lucky, pilots flying below you might indicate where this layer is by showing collapses, frontal stalls or any other entertaining events. Seeing their wings thrashed, hopefully followed by a timely recovery, is unlikely to boost your confidence when coming in for a landing. Seeing the altitude of the wind shear and its effects on other wings however, somehow make it all more manageable. More manageable at least compared to a complete wind shear surprise out of the blue, thirty metres above ground.

When I perceive wind shear, I usually cut trough the presumed turbulent layer by spiral diving for a few hundred metres. Since the wing has a higher load during the spiral, it is more solid than in stationary flight and thereby more likely to avoid the nasty events that could occur. When these do occur however, I am likely to be in a more vulnerable position. So far, this hasn't happened yet. Another drawback of this method is misjudging the presumed wind shear altitude, exiting the spiral too early. The worst case scenario being an exit just before or in the wind shear itself. Compared to stationary flight, the wing is in a more vulnerable state upon exiting the spiral dive. Exactly the opposite of what we are trying to achieve. It could cause far more interesting results than simply flying through the wind shear in a normal manner. Been there, done that.

If you haven't found the wind shear while descending, then stop doing risky things when having less than 200 m to spare. Any lower than that and your reserve may not deploy in time when needed. Especially when in a spiral dive or similar rapid descend manoeuvre. Get ready for the wind shear to happen and concentrate on piloting the wing in case it does. Do not fall into the trap that there is no wind shear, until you have landed safely. The wind shear could happen to be as low as 20 to 30 metres above ground. At this altitude, a collapse or frontal stall is already a challenge. Not being prepared for them, makes matters worse. Having one during a wing-over or similar manoeuvre in order to descend the last dozens of metres or so, could make it more than that. Whatever happens to the wind, do not change direction close to (a few to ten metres) the earth. Compared to flying straight, you will loose altitude far more rapidly during a turn. Combined with the wind gradient and the dynamics resulting from the turn, your landing could be more shocking than your legs, back, or airbag tolerate. Landing with a cross or even tail wind on the other hand, does not pose that much problems with a good flare.

I realise that Saint-André-les-Alpes has gotten a bit of overexposure here, but pilots are likely to be more familiar with this spot than the other ones I am flying. Hopefully this will facilitate their understanding of wind shear, before going to other (unknown, more challenging) places. To correct this imbalance a bit, let's have a look at another interesting case of wind shear that I encountered in the Maurienne valley one day. The Lombarde (Italian wind) comes over the col du Mont Cenis from the east, while the regular breeze is heading up the valley from the west. Arriving from the south one day on one of my Tour des Alpes and noticing a west wind during the valley transition, I picked the west face of a ridge on the other side. Unfortunately, just before I got there, the breeze suddenly switched to east. Apparently, the Lombarde wind was colder and ruled in the lower altitudes, while the relatively warmer west wind, dominated in the higher altitudes. The way to the east had been blocked near Galibier, so I was aware that the Lombarde was very strong. Despite this knowledge, I was surprised by the Lombarde descending so far down into the Maurienne valley. I still managed to squeeze myself to an east slope at the last moment, but it was not well exposed to the Lombarde. My misjudgement made me realise I was getting tired. Strong winds and turbulence/convergence had made it a challenging flight, especially over Écrins. So, rather than fighting the Lombarde, I let it carry me a few kilometres west. To a gentle grassy slope I had seen from far, which seemed to be a good bivouac spot. It turned out to be an excellent one, with water and foot within arms reach. Refreshed and rested the next day, but lacking decent altitude, I fought my way west against the regular breeze. Which is just as strong as the Lombarde, but somehow more logical and thus more manageable.

Lee sides

A slope and wind make a perfect combination when the two match well. The perfect match being a moderate laminar breeze perpendicular to a clean slope, i.e. a slope with no obstacles or other irregularities. Unfortunately, or rather interestingly, this seldom is the case in the mountains. You'd better analyse a slope and the conditions well before committing yourself. In the same manner that you analyse where and how the next thermal might be. Most of the time, the situation is evident and does not consume much brain capacity. But if you fly on automatic pilot here, you are bound to end up in an unpleasant surprise one day. Today could be the day on which a slope that has served well for the last hundred flights or so, 'suddenly' turns out to be a nasty lee side. There are places in the Alps were just a minor change in the local weather could tip a slope from being windward to lee, and vice versa.

Understanding wind is an essential cross-country skill for staying out of trouble, wind direction being the most important one. Because of their importance, two seperate articles have been dedicated to determining wind direction and lee sides

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2011-08-09