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light. However, moderate to severe turbulence is usually
encountered. The nature of rotor turbulence differs
from turbulent thermal days, with sharp, chaotic horizontal
and vertical gusts along with rapid accelerations
and decelerations. At times, the rotor can become so
rough that even experienced pilots may elect to remain
on the ground. Any pilot inexperienced in flying
through rotors should obtain instruction before
attempting a tow through rotor.
When towing through a rotor, being out of position is
normal. Glider pilots must maintain position horizontally
and vertical as best they can. Pilots should also be
aware that an immediate release may be necessary at
any time if turbulence becomes too violent. Slack-producing
situations are common, due to a rapid deceleration
of the towplane. The glider pilot must react quickly
to slack if it occurs and recognize that slack is about to
occur and correct accordingly. The vertical position
should be the normal high-tow. Any tow position that is
lower than normal runs the risk of the slack line coming
back over the glider. On the other hand, care should
be taken to tow absolutely 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 level.
Full aileron and rudder deflection, held for a few seconds,
is sometimes needed.
Progress through the rotor is often indicated by noting
the trend of the variometer. General down swings are
replaced by general upswings, usually along with
increasing turbulence. The penetration into the smooth
wave lift can be quick, in a matter of few seconds,
while at other times it can be more gradual. Note any
lenticulars above—a position upwind of the clouds
helps confirm contact with the wave. If in doubt, tow a
few moments longer to be sure. Once confident about
having contacted the wave lift, make the release. If
heading more or less crosswind, the glider should
release and fly straight or with a crab angle. If flying
directly into the wind, the glider should turn a few
Slope Lift
Wave Sink
Wave Lift
Rotor Cloud
Wave Sink
Figure 10-21. If possible, tow around the rotor directly into the wave.
10-15
degrees to establish a crosswind crab angle. The goal is
to avoid drifting downwind and immediately lose the
wave. After release, the towplane should descend
and/or turn away to separate from the glider. Possible
non-standard procedures need to be briefed with the
towpilot before takeoff. [Figures 10-22 and 10-23]
FLYING IN THE WAVE
Once the wave has been contacted, the best techniques
for utilizing the lift depends on the extent of the lift
(especially in the direction along the ridge or mountain
range producing the wave) and the strength of the wind.
The lift may initially be weak. In such circumstances,
be patient and stay with the initial slow climb. Patience
is usually rewarded with better lift as the climb continues.
At other times, the variometer may be pegged at
1,000 fpm directly after release from tow.
If the wind is strong enough (40 knots or more), find
the strongest portion of the wave and point into the
wind, and adjust speed so that the glider remains in the
strong lift. The best lift will be found along the upwind
side of the rotor cloud or just upwind of any lenticulars.
In the best-case scenario, the required speed will
be close to the glider’s minimum sink speed. In quite
strong winds, it may be necessary to fly faster than
minimum sink to maintain position in the best lift.
Under those conditions, flying slower will allow the
glider to drift downwind (fly backwards over the
ground!) and into the down side of the wave. This can
be a costly mistake since it will be difficult to penetrate
Variometer
Indications
Wave-
Steady Lift
Upwind
Side
Downwind
Side
Rotor
Foehn Cloud
Release
Smooth
Wave
Tow Path
Turbulent
Rotor
Figure 10-22.Variometer indications during the penetration into the wave.
Wave Lift
Rotor Cloud
Strong
Wind
Moderate
Wind
Figure 10-23. Possible release and separation on a wave tow.
10-16
back into the strong headwind. When the lift is strong,
it is easy to drift downwind while climbing into
stronger winds aloft, so it pays to be attentive to the
position relative to rotor clouds or lenticulars. If no
clouds exist, special attention is needed to judge wind
drift by finding nearby ground references. It may be
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Glider Flying Handbook(145)
