The history of ridge soaring goes back over 100 years, as early glider pilots discovered they could prolong their flights by remaining upwind of the hills they launched from. Ridge or slope lift is the easiest form of lift to understand and visualize. As moving air encounters rising terrain, it is deflected upward, resulting in a region of updrafts on the upwind side of a ridge or slope. The only conditions required for ridge soaring are rising terrain, and strong enough winds. ![[GFH ridge soaring.png]] ## Terrain ### Ridge Length Singular rising terrain features (ie isolated hill or mountain) tend to have wind flow more around, rather than up the slope. Ridges around a mile long may have lift, but it will be concentrated over a relatively small area. The ideal length for ridge soaring is at least a few miles. ### Ridge Height At a maximum, glider pilots may be able to find lift 2-3 times the height of the ridge, but this cannot be guaranteed. Low ridges of only a few hundred feet may provide lift, but leave insufficient altitude for safe maneuvering or a safe landing in the valley below. Generally, 500-1000ft above the surrounding terrain is a minimum for safe, practical ridge soaring. ### Ridge Slope Very shallow slopes do not produce enough vertical deflection for useable lift, while very steep slopes produce hazards like turbulent eddies near the surface. The ideal slope is approximately 1:4. ### Ridge Profile The ideal ridge is uniform in height and slope throughout its length. Any irregularities such as individual peaks, spurs, bowls, etc will introduce three-dimensional effects and produce adjacent areas of concentrated lift and sink. ![[GFH slope irregular.png]] ![[GFH slope profiles.png]] ## Weather ### Winds Wind speed should be at least 10-15kts, from a direction within 30°-45° of perpendicular to the ridge line. The presence of vertical shear may concentrate lift only at higher altitudes, close to the ridge top. ### Additional Considerations Stable air usually produces a smooth ride along the ridge, while instability encourages [[Thermal Formation]] and a turbulent (or even hazardous) ride. Sufficient moisture results in upslope fog or cloud development. Terrain features upwind of the soaring ridge may produce undesired effects, such as turbulence or [[Wave Formation]].