Keep up the speed!

Flying in the Mountains

Dynamic, challenging and fast, but what is it that makes mountain flying so special?

Slope and Thermals

Gliders have two ways of staying aloft. In my country the Netherlands we use almost exclusively thermals. Warm, light air rises and by flying in the rising air your model goes skyward. The other way uses air that is forced upward by sloping terrain, such as hills, mountains or dunes. By flying upwind of the sloping terrain your model can maintain or gain altitude. We Dutchies hardly have any mountains available, just some small slopes on the coastline, but I’ve been fascinated with mountain flying since the first try. Why is that?

In the Netherlands we just have some dunes for slope flying. No mountains are present.

One of the great things about mountain flying is that both of the above mechanisms are often both present at one location. Close to the mountain you can use the slope wind, further away you can use thermals. Thermal activity is often a lot stronger and more extreme than on flat land. On a south slope the angle of the sun to the ground is better than on a flat meadow. Thermals need time and altitude to develop. At altitude thermals are normally larger, stronger and more stable than close to the ground. Starting your flight on a mountain top you will meet thermals that have been developing for hundreds of meters. The sink between the thermals can also be a lot stronger, so good nerves and faith that rising air will be ahead are sometime necessary. Having a motor in the model can decrease the stress level to more comfortable levels in these conditions.

Weather

Not just the rising air, but also other weather factors can be more extreme in the mountains. The wind at a mountain top can be a lot stronger than in the valley. The uneven terrain can cause severe turbulence. Turbulence is to be expected downwind of obstacles, but can also be present in unexpected places as vortices can travel a long way. By studying your surroundings you can predict a great deal of the turbulence, but do expect surprises. Always keep enough airspeed in your model. During the landing the model is closest to the terrain so more prone to turbulence. It’s best to keep your approach speed above that normally used on flat land.

You may be anxious to get into the air, but don’t forget to stop and smell the flowers along the way.

In many places wind and thermal activity have predictable cycles. Thermals develop later in the day than on flat land, normally only after noon. Thermal activity can generate wind in the valley, this wind has fixed patterns and blows in a predictable direction, sometimes reversing in the late afternoon or evening. Patterns that are known to locals.

If the sun shines, you do catch more UV radiation at higher altitudes, so applying enough sun block and good contrasty sunglasses are a must.

On moist days clouds often hang in the valleys. This creates beautiful sights, but also risks. During the morning the cloud base rises and clouds below may well get to eye level. If wind is blowing up the slope moisture may condense and clouds may appear out of nowhere on your flying spot. If the visibility suddenly deteriorates a very quick landing may be necessary as visibility may drop quickly to mere metres.

Beautiful but tricky conditions. Clouds may rise along the slope and reduce visibility dramatically.

Models

What models do you want to take to the mountains? A general rule: models than can take a bit of beating. An ultralight floater may be nice in the early morning or late evening, but will it handle a landing on a stone covered slope?

EPP flying wings are perfect for trying out new slopes. They are manoeuvrable and can take a rough landing. And if something does go wrong the financial damage is overseeable. For bigger models four-flap wings are favourable. Butterfly control surface deployment is a great help in difficult landing conditions. If a model does not have flaps than spoilers are very nice to have. You often have to land on downsloping terrain or in rising air, without any means for increasing drag landings can be a big challenge.

Foamies are perfect for new or small slopes.

F3B/F3F models are probably the best all around gliders for mountain flying. The have an incredible speed range, can be landed on small fields and do take a beating. I have also flown with DLGs a lot. They fly well until 5BFT wind (that is, a moderate breeze), but are more vulnerable during transport. Big scale models are a true joy to watch in a great mountain scenery, but they do need a bigger landing area that is not always available.

I always have motorized models with me when I go slope flying. On unknown slopes, in unknown conditions or in the morning (before the thermals and the wind pick up) it’s very comfortable to have the certainty that you can always get your model back to eye level. You can fly out into the valley and search for lift without nerves. Sometimes your model can get considerably lower than the starting altitude. Flying a model under eye level does take some getting used to, it’s a very different perspective than flying overhead. With heavier models it’s nice to launch your model with the motor running, decreasing the chance of a stall. Two seconds of running the motor does decrease the risks during the launch a lot.

Left: F3B/F3F models can be flown in all conditions. They are the perfect mountain flyers. | Right: Big scale models require some space for landing and are generally more vulnerable.

Left: I usually start with a two second motor run. Call me a sissy, but I think it’s safer. | Right: A DLG can be a lot fun in the mountains.

Transport

If you’re lucky you can park your car right next to the flying spot, but often a hike is involved. A large trekking packpack or a snowboard bag can be used, but you can also buy specialized model airplane backpacks that fit gliders of various sizes. If a long hike is needed to get to a flying spot than gliders up to 2.5m are the best choice. The extra weight and discomfort then stay within limits. For shorter hikes larger planes can be taken. On some mountains you need to take the ski lift. It can be a challenge to load all your stuff into the lift car in time before the doors close! Try to carry as little loose stuff as possible.

A nice hike to a flying spot can be very enjoyable, see it as part of the total experience. I find that flying on a desolate spot after a hike with beautiful views makes me feel better than flying right next to my car without the sweat.

Left: Any good sized backpack may do the trick. | Centre: Dedicated model bags may provide better protection for your models. | Right: Getting your models in and out of the ski lift is the risky part here.

Landing

Landing on a mountain slope is a lot more complicated than landing on a Dutch meadow. The terrain is rarely flat, often littered with boulders and turbulence is the norm. The landing circuit is greatly influenced by many obstacles like trees, ski lifts (and their cables!) or the mountain face. It’s key to think about the landing circuit before even starting a flight. Where is the wind coming from, where are the obstacles, what is the best piece of ground to land? You must know where and where not you can put your model on the ground before flying.

The slope of the terrain determines the way of flaring. When landing on downsloping terrain you want to come in slow, so you can ‘push’ your model to the ground at the last moment. When landing on upsloping terrain you need to have extra airspeed for a well-timed extra strong flare. In turbulence you will need some extra speed to have more pressure on the aerodynamic controls and to prevent stalling in a gust. If an approach is not working out well, retract your flaps or spoilers and continue flying. Keep trying until you get it right!

The downside of the difficult landing conditions is an increased risk of damage. There is always a chance that a fuselage will break or a wing will be dented. So make sure you take some repair tools on your mountain trip.

Left: In the mountains the risk of damage is undoubtedly greater than at home. | Right: A well deserved treat after a day of flying.

Beautiful Experience

Flying gliders in the mountains comes with many challenges. Everything is more extreme than flying on flat land. Flying spots are harder to reach, the slopes are big and steep, rising air is more violent, landings are challenging. But then the rewards! Your model is moving through the most beautiful panoramas and can cover serious distances. You can explore the performance envelope of your glider to the max. This makes mountain flying very rewarding. Every time I do enjoy how my models show their full potential in the mountains. Even if I have to take a damaged model back to the car at the end of the day I still have a huge grin on my face from the preceding flight.

Enjoy!

@2022 Raymond Esveldt

Mountain flying is not just about the flying itself. It’s also about being outdoors, enjoying the views and the good company of friends.

All images by the author. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.