Pitot-Static Instruments Impact and Static Pressure Lines Airspeed Indicator There are two major divisions in the pitot-static system:  entering. Increasing the airspeed of the glider causes the  force exerted by the oncoming air to rise. More air is able to  push its way into the diaphragm and the pressure within the  diaphragm increases. The pressure inside the diaphragm to  oncoming airflow increases as airspeed increases. The static pressure (pressure of the still air) is taken from  the static line that is attached to a port, or ports, mounted  flush with the side of the fuselage or tube mounted on the  vertical stabilizer.  [Figure 4-3]  Gliders using a fuselage flush  mounted static source have two vents, one on each side of the  fuselage. This compensates for variation of static pressure  due to changes in glider attitude and air turbulence. The impact air pressure (air striking the glider because  of its forward motion) is taken from the pitot tube, which  is mounted on either the nose or the vertical stabilizer.  [Figure 4-1]  Pitot tubes are aligned with the relative wind.  These locations minimize air disturbance or turbulence during  glider flight through the air. The openings of both the pitot tube and the static port(s)  should be checked during the preflight inspection to ensure  they are free from obstructions. Clogged, or partially clogged,  openings should be cleaned by a certificated mechanic.  Blowing into these openings is not recommended, because  this could damage flight instruments. The airspeed indicator  displays the indicated airspeed  (IAS) of the glider  through the air.  [Figure 4-4]  Some  airspeed indicator dials  provide color-coded arcs that depict  permissible airspeed  ranges for different phases of flight. The  When a glider is in flight, the oncoming air tries to flow into  the open end of the pitot tube.  [Figure 4-2]  Connecting a  diaphragm to the back end of the pitot tube means that the air  flowing in has nowhere to go. The pressure in the diaphragm rises until it is high enough to prevent any further air from  1. Impact air pressure due to forward motion (flight)  captured in the pitot tube transferred to instruments  by way of air pressure lines or tubing. 2.  Static or free air pressure sensed at static air ports  designed to be free of motion induced pressure  variations. This reference pressure is necessary  because the free pressure of the atmosphere decreases  as altitude increases and changes due to the current  weather (barometric) pressure variations. This static  or free air pressure is transferred to instruments by  way of the static pressure lines or tubing.  Static port Pitot tube Pitot tube Static port Figure 4-3.  Static ports mounted flush with the side of the fuselage  or tube mounted on the vertical stabilizer. Figure 4-1.  A pitot tube is often mounted in the glider’s nose or  the vertical fin, the open end of which is exposed directly to the  oncoming airflow. Figure 4-2.  Pressure inside the capsule increases as airspeed increases. Figure 4-4.  Airspeed indicator. Speed: 0 knots No oncoming airflow Diaphragm pressure: 1013 mb sea level atmosphere Speed: 30 knots +2 mb due to oncoming airflow Speed: 60 knots +6 mb due to oncoming airflow Pitot tube Diaphragm Pitot tube Pitot tube Static port 4-2