Each glider certificated for ground launch operations has a  placarded maximum ground launch tow speed. This speed  is normally the same for automobile or winch launches. The  glider pilot should fly the launch staying at or below this  speed to prevent structural damage to the glider during the  ground tow. Automobile launches today are very rare. During automobile  ground launches, the glider pilot and driver should have a  thorough understanding of the groundspeeds to be used prior  to any launch. Before the first launch, the pilot and vehicle  driver should determine the appropriate vehicle ground tow  speeds, considering the surface wind velocity, the glider speed  increase during launch, and the wind gradient encountered  during the climb. They should include a safety factor to avoid  exceeding this maximum vehicle ground tow speed. If a crosswind condition is present, the glider should be  positioned slightly downwind of the takeoff heading and  angled into the wind to help eliminate control problems until  sufficient airspeed is obtained. Due to the slow acceleration  of the glider during an automobile ground launch, the towline  should be laid out to allow the glider to obtain sufficient speed  for control while still in a headwind.  [Figure 7-17] The tow speed can be determined by using the following  calculations: Automobile Launch 1.  Subtract the surface winds from the maximum  placarded ground launch tow speed for the particular  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. Figure 7-17.  Ground launch procedures. 7-14 Airborne here WIND Grass or dirt runway 4.  Subtract a 5 mph safety factor. 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 should start  to reduce the power until the glider is about 60° above the  horizon where approximately 20 percent power is needed.  As the glider reaches the 70° point above the horizon, power  is reduced to idle. The winch operator monitors the glider  continuously during the climb for any signals to increase or  decrease speed from the glider pilot.  [Figure 7-18] The following are the main differences between crosswind  takeoffs and climb procedures and normal takeoff and climb  procedures: Crosswind Takeoff and Climb •  During the takeoff roll, the glider tends to weathervane  into the wind. •  After liftoff, the glider drifts toward the downwind  side of the runway. •  In strong crosswinds there is a greater tendency for  the glider to drift downwind. •  If space is available in the takeoff area, the towline  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 7-19] Maximum ground launch tow speed .................... 75 mph 1. Surface winds 10 mph................................. –10 mph 3. Estimated climb wind gradient 5 mph .......... –5 mph 2. Airspeed increase during climb 5 mph.......... –5 mph 4. Safety factor of 5 mph................................... –5 mph Automobile tow speed.......................................... 50 mph