text: creates the differential 
  lift and the rolling 
  moment to accelerate the airplane in roll. The 
  roll rate increases until an equal and opposite 
  moment is created by the resistance to rolling 
  motion or “damping 
  The second 
  illustration of figure 4.29 defines the source 
  of the damping in roll. When the airplane 
  is given a rolling velocity 
  the 
  downgoing wing experiences an increase in 
  angle of attack due to the helix angle of roll. 
  Of course, the upgoing wing experiences a 
  decrease in angle of attack. 
  In flight at angles 
  of attack less than that for maximum lift, 
  the 
  downgoing wing experiences an increase in 
  lift and the upgoing wing experiences a de- 
  crease in lift and a rolling moment is developed 
  which opposes the rolling motion. Thus, the 
  steady state rolling motion occurs when the 
  damping moment equals the control moment. 
  The response of the airplane to aileron deflec- 
  tion is shown by the time history diagram of 
  figure 4.29. When the airplane is restrained 
  so that pure rolling motion is obtained, the 
  initial 
  response to an aileron deflection is a 
  steady increase in roll rate. As the roll rate 
  increases so does the damping moment and the 
  roll 
  the 
  acceleration decreases. Finally, 
  damping moment approaches the control mo- 
  ment and a steady state roll rate is achieved. 