to wave lift without the rotor. At times, the glider pilot may not realize wave has been encountered until finding lift steadily
increasing as the glider climbs. Climbing in slope lift and then turning downwind to encounter possible lee waves produced
downwind of the ridge should generally not occur. Even with a tailwind, the lee-side sink can put the glider on the ground
before contact with the wave.
Another possibility involves a tow into the upside of the rotor and a climb using the rotor to reach the wave. The technique
relies on finding the rising part of the rotor. Since rotor lift usually remains stationary over the ground, this may involve
flying a “figure-8” in the rotor lift to avoid flying downwind. The pilot can also fly several circles with an occasional
straight leg or fly straight into the wind for several seconds until the lift diminishes followed by circling to reposition
within the lift. Which choice works best depends on the size of the lift and the strength of the wind. Since the rotor may
contain regions of rapidly changing and turbulent lift and sink, staying in it as well as simple airspeed and bank control may
prove difficult. Inexperienced pilots should avoid using a tow to the upside of a rotor to reach the wave.
Towing into the wave occurs by towing ahead of the rotor or through the rotor. Complete avoidance of the rotor by
towing around it will generally increase the time on tow, but the reduced turbulence increases the tow pilot’s willingness
to perform future wave tows. [Figure 10-31] If the launch site sits near one end of the wave-producing ridge or mountain
range, a tow around the rotor and then directly into the wave lift becomes more feasible.
Wind
Slope lift
Wave sink
Wave lift
Rotor cloud
Wave sink
Ridge crest
Figure 10-31. A tow around the rotor directly into the wave avoids turbulence.
Often, a tow directly through the rotor provides the only route to the wave. The tow will usually encounter moderate to
severe rotor turbulence. The nature of rotor turbulence differs from a turbulent thermal. The rotor subjects the aircraft to
sharp, chaotic horizontal and vertical gusts along with rapid accelerations and decelerations. At times, the rotor can become
so rough that even experienced pilots will elect to remain on the ground. Any pilot without experience flying through rotors
should obtain instruction before attempting a tow through a rotor.
During a tow through a rotor, the glider often gets out of position, and the glider pilot should attempt to maintain position
horizontally and vertically. Turbulence too violent to handle may require an immediate release. Slack-producing situations
occur commonly due to a rapid deceleration of the towplane. The glider pilot should recognize the onset of slack line and
correct accordingly. The glider pilot should maintain the high-tow position because any tow position lower than normal
runs the risk of the slack line coming back over the glider. On the other hand, the glider should fly no higher than normal to
avoid a forced release should the towplane suddenly drop. Gusts may also cause an excessive bank of the glider, and it may
take a moment to roll back to a level attitude. The pilot may need to use full aileron and rudder deflection for a few seconds.
The trend of the variometer often indicates the progress through the rotor. General downswings get replaced by general
upswings, usually along with increasing turbulence. The penetration into the smooth wave lift can occur in a matter of
seconds or it can occur gradually. The glider pilot should note any lenticulars above as a position upwind of the clouds
helps confirm contact with the wave. If in doubt, the tow may continue for a few moments longer to confirm wave contact.
Once confident of the wave lift, the glider pilot makes the release. If on a crosswind heading, the glider should release
and fly straight or with a crab angle. If flying directly into the wind, the glider should turn a few degrees to establish
a crosswind crab angle. The pilot should avoid drifting downwind and immediately losing the wave. After release, the
towplane should descend and/or turn away and create separation from the glider. The glider and tow pilot should brief any
nonstandard release procedures before takeoff. [Figure 10-32 and Figure 10-33]
knotswinter
50 60 70 80 90 100
knots SALTO
knotswinter
50 60 70 80 90 100
knots SALTO
knotswinter
50 60 70 80 90 100
knots SALTO
Downwind sideUpwind sideWave steady lift
Smooth wave
Towpath
Wind
Variometer indications
Foehn cloud
Turbulent
rotor
Rotor
Release
Figure 10-32. Variometer indications during the penetration into the wave.
Wave lift
Rotor cloud
Strong wind
Moderate wind
Figure 10-33. Possible release and separation on a wave tow.
Flying in the Wave
After wave contact, the best technique for utilizing the lift depends on the extent of the lift and the strength of the wind.
In weak lift, the pilot should stay with the initial slow climb as better lift should develop as the climb continues. At other
times, the variometer may peg at 1,000 fpm directly after release from tow.
In strong winds (40 knots or more), the pilot should find the strongest portion of the wave, point into the wind, and adjust
speed so that the glider remains in the strong lift. The best lift usually occurs along the upwind side of the rotor cloud or
just upwind of any lenticulars. In the best-case scenario, the required speed matches the
glider’s minimum sink speed. In quite strong winds, the pilot flies faster than minimum sink to maintain position in the
best lift. Under those conditions, flying slower would allow the glider to drift downwind (fly backward over the ground)
and into the downside of the wave. Once on the downside, getting back to the frontside requires penetrating a strong
headwind. With strong lift, stronger winds aloft might push the glider downwind, so the pilot should monitor the position
relative to rotor clouds or lenticulars. If no clouds exist, the pilot can use nearby ground references and increase speed with
altitude as needed to maintain position in the best lift. In a wind not strong enough for the glider to remain stationary over
the ground, the glider slowly moves upwind out of the best lift. If this occurs, the pilot should turn slightly from a direct
upwind heading, drift slowly downwind into better lift, and turn back into the wind before drifting too far. [Figure 10-34]
Strong wind
Glider speed less
than windspeed
Glider speed
equals windspeed
Glider speed greater
than windspeed
Wave lift
Wave crest
Wave sink
Figure 10-34. Managing wave position with speed.
Often, the wave lift moves over the ground since small changes in windspeed or stability can alter the wavelength of the
lee wave within a few minutes. If lift begins to decrease while climbing in the wave, one of these things has occurred: the
glider approached the top of the wave, the glider moved out of the best lift, or the wavelength of the lee wave has changed.
In any case, the pilot can explore the area for better lift by searching upwind first. Searching upwind allows the pilot to
drift downwind back into the rising part of the wave if not finding better lift upwind. Searching downwind first can make
it difficult or impossible to contact the lift again if encountering sink on the downwind side of the wave. In addition, the
pilot might exceed the glider’s maneuvering speed or redline for rough air as gliding from the downwind to upwind could
put the glider back in the rotor. [Figure 10-35]
Wind
Search upwind first
Turbulent rotor
Figure 10-35. Search upwind first to avoid sink behind the wave crest or the rotor.
In moderate winds (20 to 40 knots) and if the wave extends along the ridge or mountain range for a few miles, the pilot
can fly back and forth along the wave lift while crabbing into the wind. The pilot can use the rotor cloud or lenticular as a
reference. All turns should occur into the wind to avoid moving to the downside of the wave or back into the rotor. When
making an upwind turn to change course 180°, the pilot changes heading less than 180°, with the reduction in turn based on
the strength of the wind. The pilot notes the crab angle needed to stay in lift on the first leg and can use that same amount
of into-the-wind crab angle initially after completing the next upwind turn. With no cloud, ground references allow the
pilot to establish and maintain the proper crab angle. While climbing higher into sufficiently strong winds, the pilot may
transition from crabbing back and forth to a stationary upwind heading. [Figure 10-36]
Band of wave lift
Lift weakens—Turn back into wind
Downwind turn leads to strong sink or rotor
Wind
Figure 10-36. Crabbing and turns in a wave
Weaker winds (15 to 20 knots) may call for different techniques. Lee waves from smaller ridges can form in relatively
weak winds of approximately 15 knots, and wave lift from larger mountains rapidly decreases when climbing to a height
where winds aloft diminish. In a small area that still provides lift near the wave top, the pilot can fly shorter figure 8
patterns to reach the maximum altitude. The pilot can also fly an oval-shaped pattern straight into the wind in lift and fly a
quick 360° turn to reposition and as it diminishes. If a consistent climb is not possible, the pilot can fly a series of circles
with an occasional leg into the wind to avoid drifting too far downwind. In a sufficiently large lift area, the pilot can use a
technique like that used in moderate winds. [Figure 10-37]
Weak Wind
S-turns with slight drift to stay in weak lift
Series of circles with an upwind leg
Upwind leg with a 360° turn
Figure 10-37. Techniques for working lift near the top of the wave in weak winds.
The discussion thus far assumed a climb in the primary wave. The pilot can also climb using any secondary or tertiary lee
wave and then penetrate the next wave upwind. The success of this strategy 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 could occur. Pilots should exercise caution 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 the pilot
should reduce speed at the first hint of turbulence. In any case, the glider could lose a significant amount of altitude while
penetrating upwind through the sinking side of the next upwind wave. [Figure 10-38]
Primary
wave
Secondary
wave
T ertiary
wave
Wind
Figure 10-38. Possible flightpath while transitioning from the tertiary into the secondary and then into the primary.
The sink downwind of the wave crest can assist a pilot who decides to make a quick descent as sink can easily attain twice
the strength of the lift encountered on the upwind side of the wave crest. Eventual descent into downwind rotor might also
occur. An inadequate space between a rotor cloud and overlying lenticulars can prevent a safe downwind transition that
might then occur with reduced visibility. In this case, the pilot can make a crosswind detour if a short ridge or mountain
range produces the wave. If clouds negate a downwind or crosswind departure from the wave, a descent on the upwind side
of the wave crest can occur. Spoilers or dive brakes may be used to descend through the updraft, followed by a transition
under the rotor cloud and through the rotor. The pilot should control speed during flight through the rotor. In addition, lift
on the upwind side of the rotor may make it difficult to stay out of the rotor cloud. This type of descent requires caution and
emphasizes the importance of an exit strategy before climbing too high in the wave. Pilots should remember that conditions
and clouds can evolve rapidly during the climb.
Some of the dangers and precautions associated with wave soaring include:
• Symptoms of hypoxia—check the oxygen system, and immediately begin a descent to lower altitudes that do not
require supplemental oxygen. Do not delay!
• Extreme cold—descend before becoming uncomfortably cold.
• Severe or extreme rotor turbulence—exercise caution 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 of 20 or 30 knots. Wind shifts
up to 180° sometimes occur in less than a minute at the surface under rotors.
• Restricted vision—warm, moist exhaled air may cause frost formation on the canopy and restrict vision. Opening
air vents may alleviate the problem or delay frost formation. The pilot can use heated panels or descend before frost
becomes a hazard.
• Entrapment above clouds—wet waves associated with a great deal of cloud formation may close gaps beneath the
glider and the pilot should descend in visual conditions before becoming trapped. If trapped above clouds, the pilot
could attempt a benign spiral through the cloud as an emergency maneuver only if previously explored and stable
for the glider in visual conditions.
• Inadvertent night flight—at sunset, bright sunshine still exists at 25,000 feet while the ground below gets quite dark.
Know the time of actual sunset. Even at an average 1,000 fpm descent, it takes 20 minutes to lose 20,000 feet.
Caution: Flights under a rotor cloud can encounter high sink rates and pilots should approach those areas with caution.
Soaring Convergence Zones
Pilots can most easily spot a convergence zone in the presence of cumulus clouds. They may appear as a single well-
defined straight or curved cloud street. The edge of a field of cumulus can mark convergence between a relatively moist
or unstable mesoscale air mass from a drier or more stable one. Often, the cumulus along convergence lines have a base
lower on one side.
With no cloud present, pilots can sometimes spot a convergence zone by a difference in visibility across it, which may be
subtle or distinct. Even without any clues in the sky, conditions on the ground can indicate a convergence zone. Pilots can
look for wind differences on lakes a few miles apart. A lake showing a wind direction different from the ambient flow for
the day may indicate conditions that can create a convergence zone. Wind direction shown by blowing smoke can also
indicate convergent conditions. A few dust devils, or a short line of them, may indicate the presence of ordinary thermals
versus those triggered by convergence. Spotting these subtle clues takes practice and good observational skills and explains
why a few pilots can continue soaring while other cannot.
The best soaring technique for this type of lift depends on the nature of the convergence zone itself. For instance, curtain
clouds mark a well-defined, sea-breeze front, and the pilot can fly straight along the line in steady lift. A weaker convergence
line often produces more lift than sink. An even weaker convergence line may simply serve as the focus for more frequent
thermals, and the pilot can use normal thermalling techniques such as flying slower in lift and faster in sink along the
convergence line. Some combination of straight legs along the line with an occasional stop to thermal might provide
sufficient lift to stay aloft.
Convergence zone lift can at times become turbulent, especially if air mixes from different sources, such as along a sea-
breeze front. The general roughness could indicate a convergence line. When narrow, rough, and strong thermals exist
within the convergence line, the pilot can work these areas like any other difficult thermals by using steeper bank angles
and more speed for maneuverability.
Combined Sources of Updrafts
Lift sources categorize into four types: thermal, slope, wave, and convergence. Often, more than one type of lift exists
at the same time, such as thermals with slope lift, thermals leading to an existing wave, convergence zones enhancing
thermals, thermal waves, and wave and slope lift. In mountainous terrain, all four lift types may exist on a single day. The
glider pilot needs to remain mentally nimble to take advantage of various types and locations of rising air during the flight.
Rising air might not always come from these four lift categories. Sources of lift that do not fit one of the four lift types
discussed probably exist. For instance, a few reports suggest pilots soared in travelling waves from an unknown source. At
some soaring sites, debate exists over the classification of the type of lift. This should not create a problem if the pilot can
work the lift as needed, get safely back on the ground, and ponder the source of lift after the flight.
Chapter Summary
Pilots should understand the source of lift they intend to use for a given flight. They should also understand how to
maximize that potential lift and avoid spending extra time in sink. Learning to take full advantage of each kind of lift takes
patience and experience. In the interest of safety, pilots should follow certain rules that apply to different soaring regimes.
These include positioning the glider so the pilot can see other gliders in a thermal, yielding the right-of-way as needed
when approaching another glider during ridge soaring, avoiding downwind turns that could bring the glider in contact with
ridge terrain, respecting the potential for rotor turbulence, and knowing how to control the glider if encountering extreme
turbulence during wave soaring. Since flying a glider involves dynamic conditions, a pilot should always have a place to
land in mind should a landing become necessary.