Make a first tandem flight in Annecy Whether you fly autonomously or not, the paraglider's intrinsic behaviour is always the same: it moves forward while descending gently. How could it be otherwise, given that the paraglider has no engine whatsoever. However, the magic of free flight lies in the wing's ability to climb and regain altitude in certain aerological conditions. But how is this possible without a motor?
The different techniques for gaining altitude with a paraglider
First of all, you need to understand how a paraglider flies. Once airborne, the paraglider flies at a fixed speed of around 30-35 km/h, or even a little more for two-seaters, and gradually loses altitude. This loss of altitude is directly linked to the glide ratio of the wing, which is linked to its drag in the atmosphere. The more resistance the wing offers to the air, the more its glide ratio is degraded. In stable flight with no control input, the glide ratio of a classic paraglider is around 8. This means that when the glider moves forward 8 metres it loses 1 metre in height. By deduction, if you take off from Planfait with a difference in altitude of around 400 metres under your feet, you can advance 400 x 8 = 3200 metres. This is, of course, a theoretical calculation, as it doesn't take into account the aerology and thermal conditions of the day. And it is thanks to these 2 factors that a pilot manages to stay in the air for a long time and to gain altitude in a paraglider in the manner of birds.
Take to the skies thanks to thermal bubbles and updrafts
The use of thermal bubbles, often called thermal currents, has revolutionised paragliding. At first, paragliders were just used to fly along the slope and down a mountain, but flying in thermals made it possible to slow down the descent and then reverse the trend by regaining altitude.
Thermal bubbles form when the sun heats the ground. The hotter the sun, the hotter the ground. When the layer at ground level reaches a temperature significantly higher than the ambient air, the layer falls away and forms a thermal bubble. This bubble, which is warmer than the surrounding air and therefore less dense, will naturally rise until it reaches an atmospheric layer of the same density. This upper limit is called the ceiling. The ceiling is totally variable, depending on the season, the day and the time of day. It depends on many factors, such as the inclination of the sun's rays in relation to the ground, and therefore the season and time of day, the orientation of the ground in relation to the sun's rays (cliffs, for example, heat up very quickly), the air temperature at different altitudes, but also atmospheric pressure, cyclones and anticyclones. Some days the thermal conditions will be generous, with numerous large-diameter bubbles rising very high, while on other days the conditions will be unfavourable, with ultra-stable air conditions that will make it impossible to climb. So you'll need to choose your flying days wisely if you hope to gain altitude by paragliding. Sites such as Paragliding weather provide excellent forecasts for preparing your flight.
How do you identify a thermal bubble?
Before you can hope to gain altitude by paragliding, you need to start by identify a thermal bubble. In the middle of nowhere, this search is quite tricky. The good days thermal bubbles are marked by cumulus clouds at the topThe peak indicates the maximum ceiling that can be reached. But most of the time, these thermal bubbles are invisible. We then speak of blue thermal. To spot them, you need to rely on observation and feel. A good indicator is to observe birds of prey, which are real masters at this game. When you see a bird circling and gaining altitude, all you have to do is head for that area to do the same. If there are no clues, you'll have to rely on your own senses. When you enter a relatively powerful thermal bubble, you feel yourself being drawn upwards and you see yourself rising in relation to the surrounding terrain. But in light conditions it's much trickier. The use of a quality variometer is therefore essential.
How can it be used to gain maximum height?
Once you've found the bubble, you need to exploit it, because if you fly in a straight line, you'll get out of it very quickly. Just as birds circle in the sky in summer, paragliders work in the same way. You make a turn inside the thermal bubble to stay there as long as possible.
The ascent speed is calculated as follows: ascent speed of the thermal bubble in relation to the ambient air minus descent speed of the glider in relation to the ambient air and therefore in relation to the inside of the thermal bubble. For a thermal bubble rising at a speed of 3 m/s and with the glider constantly losing 0.5 m/s, we end up climbing at +2.5 m/s.
The trick is to stay inside the bubble while turning as flat as possible.
In the mountains, it's easier to find thermals because the slopes and cliffs facing the sun always heat up intensely. All you have to do is ride along or over the cliffs to take advantage of a large thermal zone rising upwards. In the Alps and Pyrenees, it's often unnecessary to roll up the cliffs. Instead, it's better to fly long distances back and forth to gain altitude in your paraglider until you reach the summit, then roll up the main thermal and refuel before transiting.
Of course thermal flying requires technique and experience. Don't hesitate to follow a thermal internship in school to learn how to use thermals effectively and fly safely in the mountains.
Climbing back up by exploiting dynamic lift in the mountains
The other method for climbing and gaining altitude by paraglider is to exploit the wind and the shape of the terrain. It will not have escaped you that on the Dune du Pyla, for example, it is possible to gain height even though neither the water nor the sand are conducive to the formation of thermal bubbles. It's actually a question of the aerodynamic principle of air flow over a terrain that is an obstacle to the flow. The air flow accelerates at the top of the slope, close to the relief. Depending on the wind speed and the shape and height of the relief, this dynamic current can be more or less significant. This phenomenon does not exist on the plains but is very interesting in the mountains. All you need to do is lean against a well-fed windward slope to gradually climb to the summit. But be careful not to go behind the ridge at the summit and stay upwind to avoid getting caught in the rollers.
In addition to the dynamic lift provided by the weather wind, you can also benefit from slope breezes created on sunny faces. These warm air currents flow along and up the slope to the summit, where they form thermal bubbles that break away from the mountain to form a true thermal. These slope breezes can oppose the weather wind. So you need to be able to understand the aerology in which you are evolving to position yourself correctly and avoid finding yourself downwind or in a roll of some kind on the ridge.
How high can you go paragliding?
As long as the thermal bubble rises, the paraglider rises with it. The theoretical limit is therefore the altitude of the day's ceiling. On certain days of the year, it is possible to fly over Mont Blanc and reach 5,000 metres in France. Be careful, however, to respect the legislation and the airspace. As a reminder, in the Alps and the Pyrenees it is possible to exceed FL 115 (3450m) as long as you remain below 900m above ground level (LTA "E" airspace). In practice, it is therefore possible to climb to an altitude of 5709 metres above Mont Blanc. Airspace is then shared with commercial IFR instrument flights.
The altitude record in thermals is currently held by Antoine Girard at 8407 metres above Broad Peak in the Karakoram.
