text: In order to visualize the forces and moments 
  on the aircraft; it is necessary to establish a 
  set of mutually perpendicular reference axes 
  originating at the center of gravity. Figure 
  4.4 illustrates a conventional right hand axis 
  system. The longitudinal or X axis is located 
  in a plane of symmetry and is given a positive 
  direction pointing into the wind. A moment 
  about this axis is a rolling moment, L, and the 
  positive direction for a positive rolling moment 
  utilizes the right hand rule. The vertical or 2 
  axis also is in a plane of symmetry and is estab- 
  lished positive downward. A moment about 
  the vertical axis is a yawing moment, N, and a 
  positive yawing moment would yaw the air- 
  craft co the right 
  The 
  lateral or Y axis is perpendicular to the plane 
  of symmetry and is given a positive direction 
  out the right side of the aircraft. A moment 
  about the lateral axis is a pitching moment, M, 
  and a positive pitching moment is in the nose- 
  up dlrection. 
  
  (right hand rule). 