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Wave is formed when a steady wind blows roughly perpendicular to a line of hills. The wind rides up the hills and carries on high beyond the tops until is is deflected downwards by a more stable layer of air at a higher altitude. The downward wave then bounces off a lower layer of air or follows further hills downwind. This can continue several times carrying on to great heights. |
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Royal Deeside is famous for regular wave soaring - the U.K. height gain record was achieved there - about 38,000 feet. Wave is often revealed by smooth lenticular (lens shaped) clouds, often forming in a long bar along the wave crest. |
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One day early in training there was little lift at low levels so it looked like we'd do a slow glide back to base. There was no apparent thermal activity due to the cloud, and there was insufficient wind for any significant ridge lift. But other pilots had confirmed the signs of higher wave lift. So we took an aerotow up to 3000 feet (the usual height is 2000 feet) to try and find it.
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We could see signs of the distinctive lenticular (lens shaped) clouds that often betray the presence of wave. We soon moved in on a likely wave-front, bucking around in some wild turbulence. A couple of times we lost the area of lift. As we sought some more, we often skimmed quickly along the edges of the clouds, and had to turn steeply on a couple of occasions to avoid entering deeper cloud. |
Cloud is best avoided as it can quickly cause dangerous disorientation and result in a complete loss of control. It also hides other aircraft in the area, increasing the risk of a collision.
At times we were a few thousand feet above the main cloud-base, looking down through gaps, with more broken cloud higher up and a few signs of the lenticular shapes often associated with wave lift. It was an amazing experience to weave silently among the fluffy clouds without any reference horizon. It was also hard work to keep sight of the airfield or even remember in what direction it lay. It is always wise to know exactly where the airfield is in case you need to return quickly and not enter cloud in the process. This flight was a good demonstration of the need always to maintain a good lookout.
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We soared up to a about 7,000 feet - 7,500 above sea level as the airfield is around 500 feet in the foothills of the Highlands. I could feel the air was thinner. Beyond 10,000 feet it is very wise to start using oxygen. All the Deeside club gliders have oxygen on board for high altitude soaring. It was also much colder than on the ground: the air cools by about 2-3 degrees Celsius for every 1,000 feet of height. So the outside temperature had dropped around 20 degrees in the few minutes since we had left the ground. |
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Another phenomenon to look out for associated with wave lift is rotor: Below the crest of a wave the air can rotate in a turbulent ragged manner. Unlike smooth lenticular wave clouds you may see torn & twisted clouds: perhaps visibly rotating. Rotor can create a wild ride - lower down rotor can cause severe turbulence and even dangerous wind shear.
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Meanwhile, while riding high in smooth wave, I was once again amazed how much lift you can get 'for free' in the right conditions. You can stay up all day. While we were floating up and down close to the airfield some of the experts were flying 300km circuits via Perth - others in the clubhouse were even considering one-way trips to places as far away as Mull. An hour and five minutes after takeoff we were back on the ground. It had seemed like much less. |
It was almost twenty flights later that I encountered wave again:
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After climbing out and settling down we were at the level of the lowest cloud - long dark wispy shapes which the instructor informed me indicated wave lift. The clouds were bars that indicated the wave front. I flew along the edge and we started to climb. The lift was intermittent so I had to turn around and fly back along the edge where the lift was greatest. With one wing almost into the cloud the lift was at its strongest. Turning around once more to traverse the area of best lift once again, a couple of hundred feet higher I could see the way the cloud curled over into wispy tendrils showing how the air was rolling. |
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We were approaching Ballater climbing past 3500 feet and the sun was sinking in the west illuminating the many layers and clusters of clouds all around, with signs of a deep red sunset to come. The sky was a crazy mix of different colours and shadows. To the south (left) I could see a large mountain peak with the heathery slopes brilliantly lit in a band of golden sunshine. We reached 3900 before losing the lift again.
In search of better lift I weaved through a set of fatter puffier clouds until another long wispy bar came into view about half a mile away. I put the nose down and accelerated to 60 knots to get there quicker and lose less height in the process. About half-way I encountered some unexpected lift, but kept going to the cloud bar which promised more. However, despite skirting up and down the bar there was only sink.
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I turned us around and flew back across the area of lift, which was now weaker, and returned back to the original area. I encountered pockets of deep sink on the wrong side of the wave as I moved in and then re-established the glider in rising air. Weaving in and out of the soft wispy clouds gave a real sense of motion and the panorama of the Highlands in the gloaming sweeping far into the distance was a real spectacle. This was surely flying at its best. |
Wave lift tends to dip to lower altitudes in the same spots around the local scenery, e.g. at Deeside it can often be found above an offset crossroads near Loch Kinord in the lee of Morven.When flying in wave, fly into wind and monitor ground features to determine progress into wind or with wind. The wave is normally stationary. Unless you are flying into wave at the exact windspeed you will move in and out of the area(s) of greatest lift. If losing lift and making progress into wind, decrease speed to drift back into the area of greater lift. If already flying slow, circle instead. Be careful you do not drift downwind of the airfield. If losing lift and drifting downwind, increase speed to get back into the area of greater lift. Be careful you do not drift downwind of the airfield. Remember that wave is usually aligned with terrain (the line of hills) rather than the wind. If you are tracking at right-angles to the wave, e.g. to stay in lift while crossing country, remember to allow for the wave alignment by making appropriate progress into wind or with the wind.
Sometimes the whole wave can be seen due to smoke or dust in the air: click here for a view in Colorado
