text: percent of the stall speed for propeller air- 
  planes or 90 percent of the stall speed for jet 
  airplanes. This feat must be accomplished on 
  a smooth runway at all normal service takeoff 
  loading conditions. 
  
  forces 
  acting on an airplane during 
  toll. 
  When the airplane is in the three point attitude 
  at some speed less than the stall speed, the 
  wing lift will be less than the weight of the 
  airplane. As the elevators must be capable 
  of rotating to the takeoff attitude, the critical 
  condition will be with zero load on the nose 
  wheel and the net of lift and weight supported 
  on the main gear. Rolling 
  friction resulting 
  from the normal force on the main gear creates 
  the 
  an adverse nose down moment. Also, 
  center of gravity ahead of 
  the main gear 
  contributes a nose down moment and this 
  consideration could decide the most aft loca- 
  tion of the main landing gear during design. 
  The wing may contribute a large nose down 
  this 
  moment when 
  increase 
  effect may be countered by a slight 
  To balance these 
  in downwash at the tail. 
  nose down moments, 
  tail 
  should be capable of producing sufficient nose 
  up moment to attam the takeoff attitude. at 
  the specified speeds. 
  
  Figure 4.19 illustrates the principal 
  
  takeoff 