Just how can a sailplane fly without an engine?
Sailplanes are very efficient aerodynamically. In still air, a well designed sailplane will only descend at a rate 125 to 150 feet per minute. If the air in which the sailplane is flying is rising at exactly the sailplane’s natural descent rate, the sailplane will remain at the same altitude. If the surrounding air is rising faster than the sailplane’s natural descent rate, the sailplane will actually gain altitude.
