rack one`s brains
to try hard to think of something or remember something
I have been racking my brains all day trying to remember the man's name.
Rules to play Hang Gliding
Soaring flight and cross
A glider in flight is continuously descending. To achieve an extended flight, the pilot must seek air currents rising faster than the sink rate of the glider. Selecting the sources of rising air currents is the skill that has to be mastered if the pilot wants to achieve flying long distances, known as cross country (XC). Rising air masses derive from the following sources.