Common Errors
Common errors when boxing the wake include:
• Performing an excessively large rectangle around the wake or too small a rectangle that enters the wake. Note that
Figure 7-16 has exaggerated positions and is not to scale.
• Improper control coordination and procedure.
• Abrupt or rapid changes of position.
• Allowing or developing unnecessary slack during position changes.
Aerotow Release
When the aerotow reaches release position, the glider pilot should clear the entire area for other aircraft. Scanning should
include to the right, which is the direction the glider will turn after release. Scanning should also include to the left, the
direction the towplane turns after release. A normal release occurs with the tow line under tension since hook-type towing
attachments may need that force to make the hook swing open. When ready to release, … but the glider pilot should
visually confirm the tow line release prior to beginning a 90° right turn. [Figure 7-16A]
Glider release.
Pilot clears right and
then turns right 90°.
Glider continues away, tow
pilot clears left, and turns left.
Figure 7-16. Aerotow release.
Figure 7-16B shows how this 90° change of heading achieves safe separation between towplane and glider in minimum
time. After confirming glider release and seeing the glider turn right 90° away from the towplane, the tow pilot turns left,
descending away from the release point.
Shown in Figure 7-16C, once clear of the glider and other aircraft, the tow pilot continues a descent toward the airport for
landing. The tow pilot should continue to observe the glider as the glider pilot may start thermaling procedures and lose
sight of the towing aircraft.
Common Errors
Common errors in aerotow release include:
• Lack of normal tension on tow line or slack in tow line.
• Failure to clear the area prior to release.
• Failure to visually confirm seeing the released tow line falling away prior to turning away from the towplane.
• Failure to make a 90° right turn after release.
• Release near other aircraft.
• Glider pilot or tow pilot losing sight of the other’s aircraft.
Proper release procedures ensure proper aircraft separation in case the pilots lose sight of each other’s aircraft. In any case,
the tow pilot should exit the immediate area of the glider release. If the glider releases in a thermal or other lift, the glider
normally remains in that lift to gain altitude, whereas the tow pilot can use power to return to the airport. However, both
the tow pilot and glider pilot should maintain awareness of other gliders near areas of lift.
Ground Launch Takeoff Procedures
Ground launch uses a center of gravity (CG) tow hook that has an automatic back release feature. This protects the glider
if the pilot cannot release the tow line during the launch. Since the failure of the tow release could cause the glider to be
pulled toward the ground as it flies over the launching vehicle or winch, the pilot and ground crew should test the tow
release feature prior to every flight. [Figure 7-17]
Automatic back release—
check before every launch.
Tow ring
Figure 7-17. Testing the tow hook.
CG Hooks
Since attachment of a ground-launch tow line to a nose hook would pull the glider into the ground and overload the
horizontal stabilizer and elevator, some training and high-performance gliders use a tow hook located near the CG. A CG
hook gives the glider pilot control, free from any undue down moment during a ground tow. A CG hook uses a location
either ahead of the landing gear, in the landing gear well, or on a bracket that attaches outside on the fuselage. If a glider
only has a CG hook, and the CG hook does not have sufficient movement to fully release from an aerotow line under
pressure, no aerotow should occur.
If the CG hook sits in the landing gear well, retracting the gear on tow may interfere with the tow line. For any type of tow,
retracting the gear should wait until the glider achieved the desired tow altitude and releases the tow cable. Leaving the
gear down also allows the glider pilot more time to assess the best landing options.
A CG hook makes a crosswind takeoff more difficult since the glider can weathervane into the wind more easily. In
addition, a CG hook makes the glider more susceptible to kiting or rising too rapidly on an aerotow takeoff, especially with
the CG near the aft limit.
Signals
Prelaunch Signals (Winch/Automobile)
Prelaunch visual signals for a ground launch operation allow the glider pilot, the wing runner, the safety officer, and the
launch crew to communicate over considerable distances. When launching with an automobile, the glider and launch
automobile may be 1,000 feet or more apart. When launching with a winch, the glider may start the launch 4,000 feet or
more from the winch. Because of the distances involved, members of the ground crew use colored flags or large paddles to
enhance visibility, as shown in Figure 7-18. When relaying information over large distances, direct voice communication
between crewmember stations augments visual prelaunch signals, adds protection against premature launch, and facilitates
an aborted launch if an unsafe condition arises.
Check controls
Open towhook
Close towhook
Raise wingtip to
level position
Take up slack
Hold
Begin takeoff
Stop operation immediately
Release towrope or cut towline now
Thumb moves through circle
Arm moves slowly
back and forth
through arc
Arms straight out and held steady
Arm makes rapid circles
Wave arms Draw arm across throat
Figure 7-18. Winch and aerotow prelaunch signals. The raise wingtip to level position is given by the pilot.
Inflight Signals
Since ground launches occur quickly once the tow begins, inflight signals from the glider pilot to ground personnel only
inform the winch operator or ground vehicle driver to increase or decrease speed. [Figure 7-19]
Glider pilot yaws glider repeatedly to signal
ground operator to reduce tow speed.
Glider pilot rocks wings to signal ground
operator to increase tow speed.
Figure 7-19. Inflight signals for ground launch.
Tow Speeds
The pitch attitude to airspeed relationship for a tethered glider during a ground tow presents a unique flight experience.
Provided the tow mechanism has enough power to meet the energy demands of launch, a greater diversion of tow force
from horizontal to vertical results in an acceleration to higher glider airspeed if the pilot pitches up. During the launch,
pulling back on the stick tends to increase airspeed, and pushing forward tends to reduce airspeed.
Proper ground launch tow speeds ensure a safe launch. Figure 7-20 compares various takeoff profiles that result when tow
speeds vary above or below the correct speed.
Tow speed correct: Glider climbs to altitude safely
Tow speed too high: Glider cannot rise to climb because doing so would exceed maximum permitted ground launch airspeed
Tow speed too low: Glider cannot climb because it is not possible to achieve safe margin above stall speed
Figure 7-20. Ground launch tow speeds.
Each glider certified for ground launch operations has a placarded maximum ground launch tow speed. This speed usually
applies to both automobile and winch launches. The glider pilot should stay at or below this speed during the ground tow
to prevent structural damage to the glider.
Automobile Launch
Before the first launch, the pilot and vehicle driver should determine the appropriate vehicle ground tow speeds by
considering the surface wind velocity, the expected wind gradient for the climb, and the glider speed increase during
launch. The pilot and driver should agree on a maximum vehicle ground tow speed as a safety factor.
If a crosswind condition exists, the crew should position the glider slightly downwind of the takeoff heading and angled
into the wind to help eliminate glider control issues during the initial portion of the tow. Due to the slow acceleration of the
glider during an automobile ground launch, the tow line lay out should allow time for the glider to obtain sufficient speed
while still in a headwind. [Figure 7-21]
Airborne here
WIND
Grass or dirt runway
Figure 7-21. Ground launch procedures.
The tow speed calculation works as follows:
1. Subtract the surface winds from the maximum placarded ground launch tow speed for the glider.
2. Subtract an additional five miles per hour (mph) for the airspeed increase during the climb.
3. Subtract the estimated wind gradient increase encountered during the climb.
4. Subtract a 5 mph safety factor.
• As an example for a glider with a placarded maximum ground launch tow speed of 75 mph and with the following
conditions:
Surface winds 10 mph ................................. –10 mph
Airspeed increase during climb 5 mph.......... –5 mph
Estimated climb wind gradient 5 mph .......... –5 mph
Safety factor of 5 mph ................................... –5 mph
• The calculated automobile tow speed works out to………………..50 mph
Winch Launch
During winch launches, the winch operator applies full power smoothly and rapidly until the glider reaches an angle of
30° above the horizon. At this point, the operator begins to reduce the power, reaching approximately 20% power as the
glider reaches a point about 60° above the horizon. As the glider reaches the 70° point above the horizon, the operator
reduces power to idle. [Figure 7-22] The winch operator monitors the glider continuously during the climb for any signal
to increase or decrease power, which would result in a change in the glider's speed.
Release point
Idle power
20% takeoff power
Begin reducing winch power
70°
60°
30°
Figure 7-22. Winch procedures.
Crosswind Takeoff & Climb
The following are the main differences between crosswind takeoffs and climb procedures and normal takeoff and climb
procedures:
• During the takeoff roll, the glider tends to weathervane into the wind.
• After liftoff, the glider drifts toward the downwind side of the runway.
• Strong crosswinds create a greater tendency for the glider to drift downwind.
• If space is available in the takeoff area, the tow line or cable should be laid out in a manner that the initial takeoff
roll is slightly into the wind to reduce the crosswind component of the glider. [Figure 7-23]