text: CONTROL IN ROLL 
  
  The lateral control of an airplane is ac- 
  complished by producing differential lift on 
  the wings. The rolling, moment created by 
  the differential lift can be used to accelerate 
  the airplane to some rolling motion or control 
  the airplane in a sideslip by opposing dihedral 
  effect. The differential 
  in 
  roll is usually obtained by some type of ailerons 
  or spoilers. 
  
  lift  for control 
  
  ROLLING MOTION OF AN AIRPLANE. 
  / When an airplane is given a rolling motion in 
  flight, 
  the wing tips move in a helical path 
  through the air. As shown in figure 4.29, a 
  rolling velocity to the right gives the right 
  wing tip a downward velocity component and 
  tip an upward velocity com- 
  the left wing 
  ponent. By inspection of the motion of the 
  the velocity of the tip due to 
  left wing tip, 
  roll combines with 
  the airplane flight path 
  velocity to define the resultants motion. The 
  resulting angle between the flight path vector 
  and the resultant path of the tip is the helix 
  angle of roll. From the trigonometry of small 
  angles, the helix angle of roll can be defined as: 