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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, optimum airspeed to fly, glider
Figure 4-13. Flight computer system display.
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groundspeed, and the amount of time it will take to
reach the goal.
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 fast cruise airspeeds to enhance
performance. When lift is weak and climbs are slow,
optimum airspeed will be significantly slower than
when conditions are strong. The flight computer, sensing
the relatively slow rate of climb on a difficult day,
compensates for the weaker conditions and suggests
optimum airspeeds that are slower 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 will decline.
The glide computer can be adjusted to account for the
resulting performance degradation.
MAGNETIC COMPASS
The magnetic compass, which is the only direction-seeking
instrument in the glider, is simple in construction. It
contains two steel magnetized needles fastened to a
float around which a compass card is mounted. The
needles are parallel, with their north-seeking ends
pointed in the same direction. The compass card has
letters for cardinal headings, and each 30° interval is
represented by a number, the last zero of which is
omitted. For example, 30° would appear as a 3 and
300° would appear as 30. Between these numbers, the
card is graduated for each 5°. [Figure 4-14]
The float assembly is housed in a bowl filled with
acid-free white kerosene. The purposes of the liquid
are to dampen out excessive oscillations of the compass
card, and relieve by buoyancy part of the weight
of the float from the bearings. Jewel bearings are used
to mount the float assembly on top of a pedestal. A line
(called the lubber line) is mounted behind the glass of
the instrument that can be used for a reference line
when aligning the headings on the compass card.
Figure 4-14. A magnetic compass.
Figure 4-15. Earth magnetic force flow.
4-12
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Glider Flying Handbook(39)
