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glider sees you and is giving way in plenty of time.
In general, gliders approaching head-on are difficult to
see; therefore, extra vigilance is needed to avoid collisions
while slope soaring.
If the wind is at an angle to the ridge, bowls or spurs
extending from the main ridge can create better lift on
the upwind side and sink on the downwind side. If at or
near the height of the ridge, it may be necessary to
detour around the spur to avoid the sink, then drift back
into the bowl to take advantage of the better lift. After
passing such a spur, do not make abrupt turns toward
the ridge (Rule #1), and as always, consider what the
general flow of traffic is doing. If soaring hundreds of
feet above a spur, it may be possible to fly over it and
1 2
3 4
Figure 10-15. Ridge rules.
10-11
increase speed in any sink. This requires caution, since
a thermal in the upwind bowl, or even an imperceptible
increase in the wind, can cause greater than anticipated
sink on the downwind side. Always have an escape
route or, if in any doubt, detour around. [Figure 10-16]
It is not uncommon for thermals to exist with slope lift.
Indeed, slope soaring can often be used as a “save”
when thermals have temporarily shut down. Working
thermals from slope lift requires special techniques.
When a thermal is encountered along the ridge, a series
of S-turns can be made into the wind. Drift back to the
thermal after each turn if needed and, of course, never
continue the turn to the point that the glider is turning
toward the ridge. Speed is also important, since it is
easy to encounter strong sink on the sides of the thermal.
It is very likely that staying in thermal lift through
the entire S-turn is not possible. The maneuver takes
practice, but when done properly, a rapid climb in the
thermal can be made well above the ridge crest, where
thermalling turns can begin. Even when well above the
ridge, caution is needed to ensure the climb is not too
slow as to drift into the lee-side sink. Before trying Sturns
make sure it will not interfere with other traffic
along the ridge. [Figure 10-17]
A second technique for catching thermals when slope
soaring is to head upwind away from the ridge. This
works best when Cu mark potential thermals and aide
timing. If no thermal is found, the pilot should cut the
search short while still high enough to dash back downwind
to the safety of the slope lift. [Figure 10-18]
As a final note, caution is also needed to avoid obstructions
when slope soaring. These primarily include
wires, cables, and power lines, all of which are very
difficult to see. Aeronautical charts show high-tension
towers that, of course, have many wires between them.
Soaring pilots familiar with the area should be able to
provide useful information on any problems with the
local ridge.
Sink
Lift
Figure 10-16. Avoid sink on the downwind side of spurs by
detouring around them.
Figure 10-17. One technique for catching a thermal from
ridge lift.
Figure 10-18. Catching a thermal by flying upwind away from
the slope lift.
10-12
WAVE SOARING
Almost all high-altitude flights are made using mountain
lee waves. As covered in Chapter 9—Soaring
Weather, lee wave systems can contain tremendous turbulence
in the rotor, while the wave flow itself is usually
unbelievably smooth. In more recent years, the use
of lee waves for cross-country soaring has lead to
flights exceeding 1,500 miles, with average speeds
over 100 mph. [Figure 10-19]
PREFLIGHT PREPARATION
The amount of preflight preparation depends on the
height potential of the wave itself. Let us assume that
the pilot is planning a flight above 18,000 feet MSL
during the winter. (Pilots planning wave flights to
much lower altitudes can reduce the list of preparation
items accordingly.)
For flights above 14,000 feet MSL, the CFRs state that
required crewmembers must use supplemental oxygen.
Pilots must be aware of their own physiology; however,
it may be wise to use oxygen at altitudes well
below 14,000 feet MSL. In addition, signs of hypoxia
should be known. The U.S. Air Force in cooperation
with the FAA provides a one-day, high-altitude orientation
and chamber ride for civilian pilots. The experience
is invaluable for any pilot contemplating high
altitude soaring and is even required by many clubs
and operations as a prerequisite. Before any wave
flight, it is important to be thoroughly familiar with the
specific oxygen system that will be used, as well as its
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Glider Flying Handbook(142)
