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necessary to increase speed with altitude to maintain
position in the best lift. Often the wind is strong, but
not quite strong enough for the glider to remain stationary
over the ground, so that the glider slowly moves
upwind out of the best lift. If this occurs, turn slightly
from a direct upwind heading, drift slowly downwind
into better lift, and turn back into the wind before drifting
too far. [Figure 10-24]
Oftentimes, the wave lift is not perfectly stationary
over the ground since small changes in wind speed
and/or stability can alter the wavelength of the lee wave
within minutes. If lift begins to decrease while climbing
in the wave, one of these things has occurred: the
glider is nearing the top of the wave, the glider has
moved out of the best lift, or the wavelength of the lee
wave has changed. In any case, it is time to explore the
area for better lift, and it is best to search upwind first.
Searching upwind first allows the pilot to drift downwind
back into the up part of the wave if he or she is
wrong. Searching downwind first can make it difficult
or impossible to contact the lift again if sink on the
downside of the wave is encountered. In addition, caution
is needed to avoid exceeding the glider’s maneuvering
speed or rough-air redline, since a penetration
from the down side of the wave may put the glider back
in the rotor. [Figure 10-25]
If the winds are moderate (20 to 40 knots), and the
wave extends along the ridge or mountain range for a
few miles, it is best to fly back and forth along the wave
lift while crabbing into the wind. This technique is similar
to slope soaring, using the rotor cloud or lenticular
as a reference. All turns should be into the wind to
avoid ending up on the down side of the wave or back
into the rotor. Once again, it is easy to drift downwind
into sink while climbing higher and searching for better
lift should be done upwind first. When making an
upwind turn to change course 180°, remember that the
heading change will be less, depending on the strength
of the wind. Note the crab angle needed to stay in lift
on the first leg, and assume that same crab angle after
completing the upwind turn. This will prevent the
glider from drifting too far downwind upon completing
the upwind turn. With no cloud, ground references
are used to maintain the proper crab angle, and avoid
drifting downwind out of the lift. While climbing
higher into stronger winds, it may become possible to
transition from crabbing back and forth to a stationary
upwind heading. [Figure 10-26]
Weaker winds (15 to 20 knots) sometimes require different
techniques. Lee waves from smaller ridges can
form in relatively weak winds, on the order of only 15
knots. Wave lift from larger mountains will rapidly
decrease when climbing to a height where winds aloft
diminish. As long as the lift area is big enough, use a
technique similar to that used in moderate winds. Near
the wave top, there sometimes remains only a small
area that still provides lift. In order to attain the maximum
height; fly shorter “figure-8” patterns within the
remaining lift. If the area of lift is so small that consistent
climb is not possible, a series of circles can be
flown with an occasional leg into the wind to avoid
drifting too far downwind. Another possibility is an
oval-shaped pattern—fly straight into the wind in lift,
and as it diminishes, fly a quick 360° turn to reposi-
Wave Lift
Wave Crest
Wave Sink
Strong
Wind
Glider Speed
Equals
Wind Speed
Glider Speed
Greater Than
Wind Speed Glider Speed
Less Than
Wind Speed
Figure 10-24. Catching a thermal by flying upwind away from
the slope lift.
Search Upwind
First
Turbulent
Rotor
Figure 10-25. Search upwind first to avoid sink behind the
wave crest or the rotor.
10-17
tion. These last two techniques do not work as well in
moderate winds, and not at all in strong winds since it
is too easy to end up downwind of the lift and into
heavy sink. [Figure 10-27]
In the discussion thus far, we have assumed a climb in
the primary wave. It is also possible to climb in the secondary
or tertiary lee wave (if they exist on a given
day) and then penetrate into the next wave upwind. The
success of this depends on wind strength, clouds, the
intensity of sink downwind of wave crests, and the performance
of the glider. Depending on the height
attained in the secondary or tertiary lee wave, a trip
through the rotor of the next wave upwind is a distinct
　
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本文鏈接地址：Glider Flying Handbook(146)