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.
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 thermal. Then, the glider pilot can round a nearby turnpoint and use the flight computer to guide the return to the marked thermal in the hopes of making a rapid climb and heading out on course toward the next turnpoint.
During the climb portion of the flight, the flight computer’s variometer constantly updates the achieved rate of climb. During cruise, the GPS-coupled flight computer aids in navigating accurately to the next turnpoint. The flight computer also suggests the optimum cruise airspeed for the glider to fly, based on the expected rate of climb in the next thermal. During final glide to a goal, the flight computer can display glider altitude, altitude required to reach the goal, distance to the goal, the strength of the headwind or tailwind component, and optimum airspeed to fly.
Most flight computers incorporate an electronic audiovisual variometer. The rate of climb or descent can be viewed on the computer’s visual display. The variometer also provides audible rate of climb information through a small loudspeaker. The loudspeaker allows the pilot to hear how fast the glider is climbing or descending. Because this information is received through hearing, the pilot’s vision can be constantly directed outside the glider to enhance safety of flight and cross-country performance.
Flight computers also provide information to help the pilot select and fly the optimum airspeed for the weather conditions being encountered. When lift is strong and climbs are fast, higher airspeeds around the course are possible. The flight computer detects the rapid climbs and suggests very high cruise airspeeds to enhance performance. When lift is weak and climbs are slow, optimum airspeed is significantly lower than when conditions are strong. The flight computer, sensing the relatively low rate of climb on a difficult day, compensates for the weaker conditions, and suggests optimum airspeeds that are lower than they would be if conditions were strong. The flight computer relieves the pilot of the chore of making numerous speed-to-fly calculations during cross-country flight. This freedom allows the pilot to look for other air traffic, look for sources of lift, watch the weather ahead, and plot a strategy for the remaining portion of the flight.
The presence of water ballast alters the performance characteristics of the glider. In racing, the ability to make faster glides without excess altitude penalty is very valuable. The additional weight of water in the glider’s ballast tanks allows flatter glides at high airspeeds. The water ballast glider possesses the strongest advantage when lift conditions are strong and rapid climbs are achievable. The flight computer compensates for the amount of water ballast carried, adjusting speed-to-fly computations according to the weight and performance of the glider. Some flight computers require the pilot to enter data regarding the ballast condition of the glider. Other flight computers automatically compensate for the effect of water ballast by constantly measuring the performance of the glider and deducting the operating weight of the glider from these measurements. If the wings of the glider become contaminated with bugs, glider performance declines. The glide computer can be adjusted to account for the resulting performance degradation.