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valve. Pitot pressure pushes minute quantities of air through the valve and into the reference chamber tubing. The effect is to remove the glider’s sink rate at various airspeeds from the variometer indication (polar sink rate). [Figure 4-28] 

Computerized (electronic) Netto variometers employ a di ffe rent method to remove the glider performance polar sink rate from the variometer indication. In this type of system, sensors for both pitot pressure and static pressure provide airspeed information to the computer. The sink rate of the glider at every airspeed is stored in the computer memory. At any given airspeed, the sink rate of the glider is mathematically removed, and the variometer displays the rate of ascent or descent of the air mass itself. 

## Electronic Flight Computers 

Electronic flight computers are found in the cockpits of gliders that are flown in competition and cross-country soaring. Since nonpowered gliders lack a generator or alternator, electrical components, such as the flight computer and very high frequency (VHF) transceiver, draw power from the glider battery or batteries. The battery is usually a 12- or 14-volt sealed battery. Solar cells are sometimes arrayed behind the pilot, or on top of the instrument panel cover, to supply additional power to the electrical system during flight in sunny conditions. 

The primary components of most flight computer systems are an electric variometer, a coupled GPS receiver, and a microprocessor. The variometer measures rate of climb and descent. The GPS provides position information. The microprocessor interprets altitude, speed, and position information. The microprocessor output aids the pilot in cross-country decision-making. Shown in Figure 4-29  is a high end glider flight computer. 

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The GPS-coupled flight computer can provide the following information: 

• Where you are 

• Where you have been 

• Distance to planned destination 

• How fast you are going there 

• How high you need to be to glide there 

• How fast you are climbing or descending 

• The optimum airspeed to fly to the next area of anticipated lift 

• The optimum airspeed to fly to a location on the ground, such as the finish line in a race or the airport of intended landing at the end of a cross-country flight 

The primary benefits of the flight computer can easily be divided into two areas: navigation assistance and performance (speed) enhancement. 

Fundamental to the use of the flight computer is the concept of waypoint. A waypoint is simply a point in space. The three coordinates of the point are latitude, longitude, and altitude. Glider races and cross-country glider flights frequently involve flight around a series of waypoints called turnpoints. The course may be an out-and-return course, a triangle, a quadrilateral or other type of polygon, or a series of waypoints laid out more or less in a straight line. The glider pilot must navigate from point to point, using available lift sources to climb periodically so that flight can continue to the intended goal. The GPS-enabled flight computer aids in navigation and in summarizing how the flight is going. When strong lift is encountered, and if the pilot believes it is likely that the strong lift source may be worth returning to after rounding a turnpoint, the flight computer can mark the location of the 

