Improper Elevator Trim Setting The elevator trim control position also contributes to PIO  in pitch attitude. The takeoff checklist includes a check to  confirm the proper takeoff elevator trim setting. Trim set  properly for takeoff results in normal elevator pressures felt  through the control stick is normal, and the likelihood of PIO  is reduced. If the elevator trim is set incorrectly, however,  abnormal elevator pressure is felt through the control stick  and may contribute to PIO.  Excessively nose-down trim requires the pilot to hold back  pressure on the control stick to achieve and maintain the  desired pitch attitude during launch and climb-out. If the trim  is set excessively nose up, the pilot needs to hold forward  pressure. The more pressure is needed, the more likely it is  that the pilot overcontrols the glider. Although all gliders exhibit these tendencies if the trim  is improperly set, the effect is most pronounced on those  gliders with an aerodynamic elevator trim tab or an antiservo  tab on the elevator. The effect usually is less pronounced  on those glider fitted with a simple spring system elevator  trim. Regardless of the type of elevator trim installed in the  glider, error prevention is superior to error correction. Use a  comprehensive pretakeoff checklist and set the elevator trim  in the appropriate position prior to launch to help prevent PIO  attributable to elevator trim misuse.  [Figure 8-1] The likelihood of PIOs increases if the wing flaps are not  correctly set in the desired takeoff position. For the majority  of flap-equipped gliders, most Glider Flight Manuals/Pilot  Operating Handbooks (GFM/POH) recommend that flaps be  set at 0° for takeoff. Pilots should review their GFM/POH  for the manufacturer recommendation for takeoff settings.  If the flaps are incorrectly set for takeoff, a positive flap  setting increases wing camber and wing lift, the glider tends  to rise off the runway prematurely, perhaps even before the  elevator control is sufficient to control the pitch attitude.  Attempting to prevent the glider from ballooning high above  the runway, the pilot may exert considerable forward pressure  on the control stick. As the glider continues to accelerate,  this forward pressure on the control stick exerts a rapidly  increasing nose-down force on the glider due to the increasing  airflow over the elevator. When the glider eventually pitches  down, the pilot may exert considerable back pressure on the  stick to arrest the descent. Severe pitching or PIOs are likely  to result. If allowed to continue, hard contact with the runway  surface may result in glider damage and personal injury. If the wing flaps are incorrectly set to a negative flap setting,  decreasing wing camber and wing lift, then takeoff may be  delayed so long that the towplane lifts off and begins to climb  out while the glider is still rolling down the runway, unable  to get airborne. Excessive back pressure on the control stick  may eventually assist the glider in leaving the runway, but  the relatively high airspeed at lift-off translates into a very  effective elevator, and ballooning may occur as a result of the  extreme elevator position. Overcorrecting for the ballooning  with excessive forward pressure on the control stick increases  the magnitude of this pitch excursion. A series of PIOs may  result. If this condition is allowed to continue, the launch  could lead to a premature termination of the tow. Pilot-induced roll oscillations occur primarily during launch,  particularly via aerotow. As the tow pilot applies full power,  the glider moves forward, balanced laterally on its main wheel  by the wing-runner. After the wing-runner releases his or her  balancing hold, aerodynamics or crosswind could cause a  wing to drop. If a wingtip begins to drop toward the ground  before the glider achieves significant speed, aileron control is  marginal and considerable stick displacement must be applied  to elicit a response from the glider’s ailerons. As the glider  accelerates, the control response improves and the latency of  response from the glider shortens. As acceleration continues,  the pilot must recognize the increased responsiveness of the  glider to avoid overcontrolling the glider.  [Figure 8-2] Although roll oscillations can develop during ground  launch operations, they occur less often than during aerotow  operations because excellent aerodynamic control of the  glider is quickly achieved due to the rapid acceleration. Since  control improves as acceleration increases, operations that  Pilot-Induced Roll Oscillations During Launch Improper Wing Flaps Setting Premature takeoff resulting from mismanagement of elevator trim setting or wing flap position setting. Low airspeed  at lift-off results in sluggish response to elevator. Startled pilot overcontrols the elevator and PIOs result. Figure 8-1.  Premature takeoffs and PIOs. 8-3