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## 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] 

## Improper Wing Flaps Setting 

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 During Launch 

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 

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