Blanik L-23 Blanik L-13 SGS 2-33 SGS 1-26 ASK 21 93 mph 87 mph 98 mph 95 mph 108 mph 81 knots 76 knots 85 knots 83 knots 94 knots Maximum Aero Tow Speed MPH Knots in Chapter 7 of this handbook. A thoughtful glider pilot  communicates the intention to maneuver behind the tow  plane. However, the tow pilot should remain alert for  unannounced maneuvering. Glider pilot’s normally begin  the “Box the Wake” maneuver by descending vertically  from high tow position to low tow position. Once a similar  maneuver is detected, maintain a constant heading and a  wings level attitude. After the “Box the Wake” maneuver is  completed and the glider is stabilized in the hig-tow position,  turns can be resumed.  operating speeds. Also note fiberglass gliders, like the ASK- 21, are towed faster than other popular training gliders. During tow, the glider instructor may demonstrate and  practice slack rope recovery procedures. This maneuver  normally involves a climb to one side or the other followed by  a small dive to create the slack in the tow line. The instructor  will then have the student take the slack out of the tow line  without breaking the rope. Be alert for these maneuvers and  do not mistake the climb and dive maneuver as a release.  This maneuver is discussed in further detail in Chapter 8 of  this handbook.  Recommended towing speed is determined by considering  stall speed and maximum aerotow speed of the glider,  minimum speed for proper engine cooling of the tow plane,  and stall speed of the tow plane. Generally speaking, aerotow  should be conducted at the slowest speed possible considering  these factors and safety. Speed should be at least thirty  percent above stall speed of the glider and twenty percent  above the stall speed of the tow plane. Because of the potential for low altitude emergencies, the  initial climb must remain upwind and within gliding distance  of the airport. If circumstances do not permit an upwind  departure, plan the climb to remain in a position that allows  the glider to return to the traffic pattern with the existing  headwind component. The high tow is normally used for glider tow operations.  However, a low-tow position may be used in some instances,  a cross-country tow for example. The main goal of both  positions is to place the glider in a position that avoids the  wake of the tow plane.  [Figure 12-13] When towing, expect the glider to practice maneuvers such  as “Boxing the Wake,” which is explained and illustrated  Tow Positions, Turns, and Release Glider Tow Positions Figure 12-12.  Maximum aerotow speeds.  High tow position Wake Low tow position Wake Figure 12-13.  Aerotow climb-out. 12-8