Yaw momentum of the  mass of the glider’s wings  and fuselage contributes to  overshooting the desired  heading. This tendency is  aggravated if the pilot holds  corrective rudder  pressure too long. Figure 8-3.  Pilot-induced yaw oscillations during takeoff roll. Gust-Induced Oscillations Vertical Gusts During High-Speed Cruise Gusty headwinds can induce pitch oscillations because the  effectiveness of the elevator varies due to changes in the  speed of the airflow over the elevator. Crosswinds also can  induce yaw and roll oscillations. In gusty crosswinds, the  effects on glider control change rapidly depending on the  speed and rate of the crosswind component. A crosswind  from the right, for instance, tends to weathervane the glider  into the wind, causing an uncommanded yaw to the right.  Crosswinds tend to lift the upwind wing of the glider and  push the tail downwind.  Local terrain can have a considerable effect on the wind.  Wind blowing over and around obstacles can be gusty and  chaotic. Nearby obstacles, such as hangars, groves or lines  of trees, hills, and ridges can have a pronounced effect on  low altitude winds, particularly on the downwind side of the  obstruction. In general, the effect of an upwind obstacle is to  induce additional turbulence and gustiness in the wind. These  conditions are usually found from the surface to an altitude  of 300 feet or more. If flight in these conditions cannot be  avoided, the general rule during takeoff is to achieve a faster- than-normal speed prior to lift-off. The additional speed increases the responsiveness of  the controls and simplifies the problem of correcting for  turbulence and gusts. This provides a measure of protection  against PIOs. The additional speed also provides a safer  margin above stall airspeed. This is very desirable on gusty  days because variations in the headwind component have a  considerable effect on indicated airspeed. Caution: Do not exceed the glider’s tow speed limitations when  adding safety speed margins for takeoff in windy conditions. Although PIOs occur most commonly during launch, they  can occur during cruising flight, even when cruising at high  speed. Turbulence usually plays a role in this type of PIO,  as does the elasticity and flexibility of the glider structure.  An example is an encounter with an abrupt updraft during  wings-level high-speed cruise. The upward-blowing gust  increases the angle of attack of the wings, which bend upward  very quickly, storing elastic energy in the wing spars. For a  moment, the G-loading in the cabin is significantly greater  than one G. Like a compressed coil spring seeking release,  the wing spars reflex downward, lofting the fuselage higher.  When the fuselage reaches the top of this motion, the wing  spars are storing elastic energy in the downward direction, and  the fuselage is sprung downward in response to the release of  elastic energy in the wing spars. The pilot then experiences  reduced G-load, accompanied perhaps by a head bang against  during the early portion of the takeoff roll and during the  latter portion of the landing rollout. Even highly proficient  glider pilots find takeoffs and landings in these gliders to be  challenging. Many of these gliders are designed for racing  or cross-country flights and have provisions for adding water  ballast to the wings. Adding ballast increases mass, which  results in an increase in lag time. Low time pilots and pilots new to such high performance  gliders should review the GFM/POH thoroughly prior to  flight. It is also recommended to review normal procedures,  emergency procedures, and the glider’s fight characteristics  with a qualified pilot or instructor pilot before attempting  flight in any high performance glider. 8-5