First Slope Soaring flight

Cairngorm, Scotland

August 22, 2009


On a trip to Aberdeen I had the opportunity to fly in the highlands of central Scotland, and to feel what slope soaring, or ridge soaring, is all about. As a member of the Illini Glider Club, I have made hundreds of glider flights, all of them exclusively in thermals, and those above very flat terrain, so that would be a new experience.

1stSlopeSoar_010.jpg Surrounding terrain. For scale, the runway is 1/2 mile long (GoogleMaps).

The Cairngorm Gliding Club is based on the Feshie Airstrip (XFES), practically in the center of Scotland. That Saturday I was introduced to mountain flying by Nick Norman, holder of all three diamond badges, who for a living flies 19-seat helicopters to oil rigs in the North Sea. The wind was mild from the SouthWest, enough for daylong slope soaring, but not for wave flying (that Nick used to climb to 24,000' the month before), and the clouds were scattered with rain showers, which seems to be the standard weather.

1stSlopeSoar_020.jpg The Cairngorms loom East of the airstrip, an unusual presence, coming from Illinois.

We flew in a Grob G-103A, a nice-handling two-seater; no surprises there. I wish we had one instead of the Krosno in our club. The all-wood 1974 four-seater DR400 tow (called tug in the UK) plane with 180 HP is quite efficient, and drifts down from the mountain at 120+ knots.

1stSlopeSoar_030.jpg The Club glider for the flight, a Grob G-103A Twin II Acro, G-JAPK.

clip 1/4 on YouTube VIDEO Towed up in rain along the beautiful Spey Valley (YouTube).

1stSlopeSoar_040.jpg Instrument panel has a turn coordinator for cloud flying, legal in the UK.

The first thing in the mountains is the difficulty to estimate the distance from the terrain, that is slanted on top of that. All the flying is done at an altitude that for me corresponds to "short final" (except that landing is impossible). This is very different from Illinois, where you are essentially in a landing pattern when you are below 1000' AGL. Nothing gives the scale on the slopes. There are fields of various sizes of broken rocks, some of them quite large, as big as human beings. Episodically, you would see walkers on the mountain paths, the width of which gives some indication, and I did not see a single sheep. The separation from the slope only comes from mentally integrating relative motion, so how accurate is that....

1stSlopeSoar_100.jpg To climb, you have to aim for a slope, then parallel it for as long it is upwind.

1stSlopeSoar_110.jpg Climbing close to the slope, made of rocks broken by freeze-thaw cycles.

1stSlopeSoar_120.jpg Flying a few feet above the rocks at 55 knots creates a strong impression of speed.

At one point we were circling hard in a thermal, but that thermal was drifting towards the slope faster than we could climb in it, so when to decide "this will be my last circle" when you are not sure of the horizontal distance to the slope? I gave back the controls to Nick and filmed it instead.

clip 3/4 on YouTube VIDEO In a narrow thermal drifting towards the mountain (YouTube).

In 300 thermal flights, I have had 2 inadvertent full stalls, with the ensuing loss of altitude for recovery. I am pretty sure you could encounter the same in a vortex or at the confluence of two invisible air streams in the mountains. Not a place to risk flying slow; there would be not enough elevation for the altitude loss. I was conscious of this for the whole flight.

1stSlopeSoar_050.jpg All the mountains are bald, devoid of even the smallest bushes. No drag for the wind.

1stSlopeSoar_060.jpg Very deep scars in the terrain, and enough rain to keep lakes full at the top.

1stSlopeSoar_070.jpg Valleys are pristine and stunningly beautiful; no roads; walk or soar.

1stSlopeSoar_080.jpg Slopes are wet and marked horizontally by probably sheep trails. Seen no sheep.

1stSlopeSoar_090.jpg Difficult to predict what the wind would churn up on this landscape.

When you follow the slope, you mostly look on one side at the slope, and in the corner of the eye you monitor the openness of the escape route on the other side. This happens to be a nice valley that leads directly to the airstrip, in case of total loss of wind. However, you can get caught by entering a "gulf" or a "bay", that you misjudge the dimensions of, and that may not leave you enough radius to turn within. This nearly happened to me, but Nick told me quietly: "turn now".

1stSlopeSoar_160.jpg The "escape valley" that very conveniently leads to the airstrip.

1stSlopeSoar_170.jpg The landscape of the highlands is beautiful in any direction you look.

clip 4/4 on YouTube VIDEO Escaping towards the valley from a zone of sink (YouTube).

I am not used to fly that close to clouds (and even above them), especially knowing the mass of the mountain behind them. When rain comes on top of that, it is a little uncomfortable, but as long as there is a clear path to the "escape valley" I guess it is fine. Note that in the UK, unbelievably, it is not illegal to fly gliders into clouds; the Grob had a turn coordinator as the meager instrument to allow that.

clip 2/4 on YouTube VIDEO No space at all between mountains and clouds (YouTube).

When the wind tops a ridge, it plummets down on the other side, with a lot of turbulence if the mountain top is as angular as that around Loch Einich. There would be no hope of escaping that valley if you let yourself drift too much downwind from the ridge.

1stSlopeSoar_130.jpg Loch Einich is bordered by very steep walls and seems unattainable by any means.

1stSlopeSoar_140.jpg The South ledge where lift becomes turbulent vortices down; treat it as an event horizon.

1stSlopeSoar_150.jpg It is nice not to disturb trekkers with engine noise; gliders are part of the landscape.

In the end you actually get used to slope soaring pretty fast, and the audio vario is a huge help (same as thermal soaring) to find out where to go. There must be a sweet spot where too far from the slope the wind is not enough "bent up", and too close, where the drag from the slope slows down the lift. The vario helps narrowing this down, but I have yet to see visually where it is.

1stSlopeSoar_180.jpg High enough to venture above the Spey Valley and Loch An Eilein. All the purple is blooming heather.

1stSlopeSoar_190.jpg Preparing for landing above recreational area Loch Insh (with the only landable area I have seen).

If you are ever going to Scotland, don't "fanny about" (I learned that expression there; had to use it), and check out the Cairngorm Gliding Club; you won't regret it.


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