text: moments which 
  to equilibrium. 
  
  tend to restore the airplane 
  
  with control surface deflection. While it is 
  desirable to have a strong centering of the 
  stick near the neutral position, the amount of 
  force required to create an initial displacement 
  must be reasonable. 
  the control system 
  If 
  “break-out” 
  forces are too high, precise control 
  of’the airplane at high speeds is diflicult. As 
  the solid friction of the control system con- 
  tributes to the break-out forces, proper mainte- 
  nance of the control system is essential. Any 
  increase in control system friction can create 
  unusual and undesirable control forces. 
  The axis system of an air- 
  plane will define a positive yawing moment, 
  N, as a moment about the vertical axis which 
  tends to rotate the nose to the right. As in 
  is con- 
  other aerodynamic considerations, it 
  venient to consider yawing moments in the 
  coefficient form so that static stability can be 
  evaluated independent of weight, altitude, 
  is de- 
  speed, etc. The yawing moment, N, 
  fined in the coefficient form by the following 
  equation: 
  
  DEFINITIONS. 