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possibility. Caution is needed if penetrating upwind at
high speed. The transition into the downwind side of
the rotor can be as abrupt as on the upwind side, so
speed should be reduced at the first hint of turbulence.
In any case, expect to lose surprising amounts of altitude
while penetrating upwind through the sinking side
of the next upwind wave. [Figure 10-28]
If a quick descent is needed or desired, the sink downwind
of the wave crest can be used. Sink can easily be
twice as strong as lift encountered upwind of the crest.
Eventual descent into downwind rotor is also likely.
Sometimes the space between a rotor cloud and overlying
lenticulars is inadequate and a transition downwind
cannot be accomplished safely. In this case, a
crosswind detour may be possible if the wave is produced
by a relatively short ridge or mountain range. If
clouds negate a downwind or crosswind departure
from the wave, a descent on the upwind side of the
wave crest will be needed. Spoilers or dive brakes may
be used to descend through the updraft, followed by a
transition under the rotor cloud and through the rotor.
Adescent can be achieved by moving upwind of a very
strong wave lift if spoilers or dive brakes alone do not
allow a quick enough descent. A trip back through the
rotor is at best unpleasant. At worst it can be dangerous
if the transition back into the rotor is done with too
much speed. In addition, strong wave lift and lift on
the upwind side of the rotor may make it difficult to
stay out of the rotor cloud. This wave descent requires
Band of Wave Lift
Lift Weakens -
Turn Back
Into Wind
Downwind
Turn Leads to
Strong Sink
or Rotor
Figure 10-26. Proper crabbing to stay in lift and effects of
upwind turn (correct) or downwind turn (incorrect).
Weak
Wind
S - Turns with
Slight Drift to
Stay in Weak Lift
Upwind Leg
with a 360°
Turn
Series of
Circles with an
Upwind Leg
Figure 10-27.Techniques for working lift near the top of the wave in weak winds.
Primary
Wave
Secondary
Wave
Tertiary
Wave
Figure 10-28. Possible flight path while transitioning from
the tertiary into the secondary and then into the primary.
10-18
a good deal of caution and emphasizes the importance
of an exit strategy before climbing too high in the
wave, keeping in mind that conditions and clouds can
rapidly evolve during the climb.
Some of the dangers and precautions associated with
wave soaring have already been mentioned. Those and
others are summarized below.
• If any signs of hypoxia appear, check the oxygen
system and immediately begin a descent to lower
altitudes below which oxygen is not needed. Do
not delay!
• Eventually, regardless of how warmly you are
dressed, it will become cold at altitude. Descend
well before it becomes uncomfortably cold.
• Rotor turbulence can be severe or extreme.
Caution is needed on tow and when transitioning
from smooth wave flow (lift or sink) to rotor.
Rotors near the landing area can cause strong
shifting surface winds—20 or 30 knot. Wind
shifts up to 180° sometimes occur in less than a
minute at the surface under rotors.
• Warm, moist exhaled air can cause frost on the
canopy, restricting vision. Opening air vents may
alleviate the problem or prolong frost formation.
Clear-vision panels may also be installed. If
frosting cannot be controlled, descend before
frost becomes a hazard.
• In “wet” waves, those associated with a great
deal of cloud, beware of the gaps closing beneath
the glider. If trapped above cloud, a benign spiral
mode is an option, but only if this mode has been
previously explored and found stable for your
glider.
• Know the time of actual sunset. At legal sunset,
bright sunshine is still found at 25,000 feet while
the ground below is already quite dark. Even at
an average 1,000 fpm descent it takes 20 minutes
to lose 20,000 feet.
SOARING CONVERGENCE ZONES
Convergence zones are most easily spotted when
cumulus clouds are present. They appear as a single
straight or curved cloud street, sometimes well defined
and sometimes not, for instance when a wind field as
in Figure 9-30(B) causes the convergence. The edge of
a field of cumulus can mark convergence between a
mesoscale air mass that is relatively moist and/or
unstable from one that is much drier and/or more stable.
Often the cumulus along convergence lines have a
base lower on one side than the other, similar to Figure
　
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