text: GUSTS AND WIND SHEAR 
  
  The variation of wind velocity and direction 
  throughout 
  the atmosphere is important be- 
  cause of its effect on the aerodynamic forces 
  and moments on an airplane. As the airplane 
  traverses this variation of wind velocity and 
  direction during flight, the changes in airflow 
  direction and velocity create changes in the 
  aerodynamic forces and moments and produce 
  a response of the airplane. The variation of 
  airflow velocity along a given direction exists 
  flow direction. 
  to 
  with shear parallel 
  Hence, the velocity gradients are often re- 
  ferred to as the wind “shear.” 
  
  the 
  
  The effect of the vertical gust has important 
  effects on the airplane at high speed because 
  of the possibility of damaging flight 
  loads. 
  The mechanism of vertical gust is illustrated 
  in figure 6.5 where the vertical gust velocity 
  is added vectorially 
  to 
  produce some resultant velocity. The principal 
  effect of the vertical gust is to produce a change 
  in airplane angle of attack, e.g., a positive 
  (up) gust causes an increase in angle of attack 
  
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