Slip.  A descent with one wing lowered and the glider’s  longitudinal axis at an angle to the flightpath. A slip is  used to steepen the approach path without increasing the  airspeed, or to make the glider move sideways through the  air, counteracting the drift resulting from a crosswind. Pressure altitude.  The height above the standard pressure  level of 29.92 "Hg. It is obtained by setting 29.92 in the  barometric pressure window and reading the altimeter. Radiant energy.  Energy due to any form of electromagnetic  radiation (e.g., from the sun). Radius of turn.  The horizontal distance an aircraft uses to  complete a turn. Speed to fly.  Optimum speed through the (sinking or rising)  air mass to achieve either the furthest glide or fastest average  cross-country speed depending on the objectives during a  flight. Spin.  An aggravated stall that results in the glider descending  in a helical, or corkscrew, path. Rate of turn.  The amount of time it takes for a glider to turn  a specified number of degrees. Relative wind.  The airflow caused by the motion of the  aircraft through the air. Relative wind, also called relative  airflow, is opposite and parallel to the direction of flight. Spoilers.  Devices on the tops of wings to disturb (spoil) part  of the airflow over the wing. The resulting decrease in lift  creates a higher sink rate and allows for a steeper approach. Squall line.  A line of thunderstorms often located along  or ahead of a vigorous cold front. Squall lines may contain  severe thunderstorms. The term is also used to describe a  line of heavy precipitation with an abrupt wind shift but  no thunderstorms, as sometimes occurs in association with  fronts. Rotor.  A turbulent circulation under mountain-wave crests,  to the lee side and parallel to the mountains creating the wave.  Glider pilots use the term rotor to describe any low-level  turbulent flow associated with mountain waves. Rotor streaming.  A phenomenon that occurs when the air  flow at mountain levels may be sufficient for wave formation,  but begins to decrease with altitude above the mountain. In  this case, the air downstream of the mountain breaks up and  becomes turbulent, similar to rotor, with no lee waves above. Stabilator.  A one-piece horizontal stabilizer used in lieu of  an elevator. Stability.  The glider’s ability to maintain a uniform flight  condition and return to that condition after being disturbed. Rudder.  Attached to the back of the vertical stabilizer, the  rudder controls movement about the vertical axis. Stall.  Condition that occurs when the critical angle of attack  is reached and exceeded. Airflow begins to separate from the  top of the wing, leading to a loss of lift. A stall can occur at  any pitch attitude or airspeed. Sailplane.  A glider used for traveling long distances and  remaining aloft for extended periods of time. Saturated Adiabatic Lapse Rate (SALR).  The rate of  temperature decrease with height of saturated air. Unlike the  dry adiabatic lapse rate (DALR), the SALR is not a constant  numerical value but varies with temperature.  Standard atmosphere.  A theoretical vertical distribution  of pressure, temperature and density agreed upon by  international convention. It is the standard used, for instance,  for aircraft performance calculations. At sea level, the  standard atmosphere consists of a barometric pressure of  29.92 inches of mercury ("Hg) or 1013.2 millibars, and a  temperature of 15 °C (59 °F). Pressure and temperature  normally decrease as altitude increases. The standard lapse  rate in the lower atmosphere for each 1,000 feet of altitude  is approximately 1 "Hg. and 2 °C (3.5 °F). For example, the  standard pressure and temperature at 3,000 feet mean sea  level (MSL) is 26.92 "Hg. (29.92 – 3) and 9 °C (15 °C – 6 °C). Self-launching glider.  A glider equipped with an engine,  allowing it to be launched under its own power. When the  engine is shut down, a self-launching glider displays the same  characteristics as a non-powered glider. Side slip.  A slip in which the glider’s longitudinal axis  remains parallel to the original flightpath but in which the  flightpath changes direction according to the steepness of  the bank. S R G-5