As we all know, paragliders glide steadily and progressively downwards. To maintain or, even better, gain altitude there has to be an updraft or ascending air current as discussed in a previous section. For flight within thermals we can use the term "thermal soaring" or "thermaling". Winds also provide another opportunity to stay aloft as we shall see below. We call such a practice "ridge soaring" and it is a result of "orographic lift". The combination of "thermal lift" and "orographic lift" is called "convergence lift".
Two pilots glide in different conditions. [Demonstrated in the upper drawing gaining height due to thermal]
When wind blows on to a mountain slope, it is forced to
follow the mountain's contour towards the peak. An ascending air
current, called "orographic lift", is produced. We can fly up
alongside the slope and benefit from this lift. Flying in this lift is
called ridge soaring or slope soaring.
The height reached once above the peak will not be that great since the wind flow will resume its horizontal course again once the obstacle of the slope has been passed. Rounded hills and other shapes which do not block the airflow are not very suitable for ridge soaring. Often hills with bowls and ravines are the most appropriate for slope soaring, especially if they help channel updrafts. Ridge soaring allows student pilots to get their first long duration flights. This result often occurs when the wind is stable but may present danger if there is thermal activity because of turbulence.
On days that present a lot of thermal activity all pilots should gain height and stay well above the slope. Student pilots should not fly under such conditions. The feeling of safety near the slope can bring trouble to the pilot. Remember that no one gets injured in the air but on contact with the ground.
Ridge Soaring in Practice:
1. Right of way rules must be strictly adhered to, especially
if there are a lot of paragliders in the same vicinity.
2. Figure 8's should be performed into the wind and you must not be tempted to head toward the ridge. Always make your turns heading away from the ridge.
3. Make turns whenever you are in ascending air so that no altitude is lost. 4. Pull gently on the brakes and avoid maximum airspeeds. Reserve some speed and use it when needed.
5. When flying low and close, always shift your weight away from the hill. This way, if you have a one side collapse you will be less likely to turn into the hill as you are ready to correct before a problem develops. Note that too much weight shifting away from the hill will require extra hill-side braking that is detrimental to the wing's performance. Determine your own safety and performance compromise.
6. Do not fly straight ahead when descending air currents are ahead. Bear in mind rotor turbulence produced by trees, rocks and other wings and alter your flight path to avoid undesirable air.
7. Do not attempt to fly in windspeeds of over two thirds (2/3) of your canopy's maximum speed. On many occasions there will be an upward deflected ridge current combined with thermals, which are released on the mountain slope or drift into the mountain. In such a case we may decide to fly in stronger wind because thermals add to the wind felt at launch, but not the true horizontal speed. The windspeed should be measured on the hillside itself at launch and should not fluctuate beyond the range of 15 km/h (9mph) minimum to 30 km/h (18 mph) maximum.
8. The further away we are from the hill the more the windspeed and lift will diminish.
9. Keep in mind that when the wind crosses from perpendicular to the slope, less lift is produced. If it is blowing parallel to the hill, no updraft is produced. In a tail wind sink and dangerous rotor are usually present.
10. Wind tends to accelerate through gaps and close to the slope. There is increased wind due to the "venturi effect" combined with anabatic flow.
11. You should not fly into ravines, because wind tends to be come stronger and turbulent there.
12. Wind speed and direction can change as you go out to land due to the deflecting effect of the mountain lower down to or the release of thermals.
13. You should check your ground speed at regular intervals. One sign that the wind is increasing is a general increase in lift beyond what it was before at a given area of the ridge.
14. You may encounter thermals which change the flow when flying near the ridge on an unstable day.