Circling in Thermal Lift
Thermal lift is the most common in soaring and is formed when solar radiation heats the ground which then heats the surrounding air. Rising like a hot air balloon, the warm air forms thermals, a source of surprisingly strong lift. Just how strong? An average day will loft a 1,000 pound sailplane up to cloud base at 300-600 feet per minute. A really good day provides over a 1,000 feet per minute lift. That would be like hiking mount Everest in under half an hour... Eat your heart out, Sir Edmund Hillary!
Thermals can often be spotted by their cap of cumulus cloud formed when moist, rising air condenses. The base of the cumulus cloud capping a strong thermal is a thrill to fly under. Pushed up by the rapidly rising air, the cloud's center is often several hundred feet higher than its edges, creating an inverted bowl. On a hot day, gently circling in the cool air under this dark, wispy bowl is one of flying's greatest thrills; and one enjoyed only by soaring pilots.
Ridge lift is completely different. Formed when the wind is at right angles to a ridge line, ridge lift can extend for hundreds of miles along a mountain range. Sailplane pilots have flown over a thousand miles in ridge lift.
Flying the ridge, an experienced pilot can cruise just above the ridge line at well over 100 miles per hour for many miles. But he had better be sure his belts are tight, it's a bumpy ride. Climbing to a lofty 500 feet above the ridge smoothes things out considerably, but cuts cruising speed down to 60 miles per hour or so.
Soaring in mountain waves is for many soaring pilots the epitome of the soaring experience. Under certain atmospheric conditions, huge standing waves of rising and falling air can form on the leeward side of a mountain, just as the water ripples downstream of a rock.
Once in the wave, flying it is easy. Point the ship's nose into the wind and enjoy the elevator ride up at sometimes 1,500 feet per minute while staying over the same point on the ground far below. Since the wave's airflow is laminar, it is incredibly smooth, and sometimes a ship can be flown for literally minutes without touching the controls. Mountain waves can extend upwards to ten times the height of the mountain creating the wave. The world's sailplane altitude record, 49,009 feet, was set in 1986 by Robert Harris in a California mountain wave flying a medium performance Grob sailplane. Even at Sugarbush, where our highest mountain is under 4,500 feet, pilots reach 20,000 feet every year and the local record is said to be over 31,000 feet.