drag and create a moment to yaw the WSC aircraft further  from the straight flight. Therefore, fins are sometimes put  on the carriage as needed so the carriage also has a yawing  aerodynamic force to track the WSC aircraft directly into the  wind.  [Figure 2-34]  Since the carriage has such a large effect on yaw stability,  the carriage is matched to the wing for overall compatibility.  Each manufacturer designs the carriage to match the wing and  takes into account these unique factors of each design. If the propeller thrust is above the CG  [Figure 2-35,  bottom ] ,  this creates a pitch-down moment about the CG when thrust  is applied and a resultant increase in speed. When reducing  the throttle, it reduces this moment and a nose pitch up results  with a decrease in speed.  These factors make the WSC aircraft track directly into  the relative wind and eliminate the need for a rudder to  make coordinated turns. Designs and methods vary with  manufacturer and wing type, but all WSC wings are designed  to track directly into the relative wind. With the thrust line above or below the CG producing these  minor pitch and speed changes, they are usually minor for  most popular designs. Larger thrust moments about the CG  may require pilot input to minimize the pitch and speed  effects. Most manufacturers strive to keep the thrust as close  as possible to the vertical CG while also balancing the drag of  the carriage and the wing for its speed range. This is why the  carriage must be matched to the wing so these characteristics  provide a safe and easy to fly WSC aircraft.  WSC aircraft designs can have different moments caused by  thrust based on where the thrust line is compared to the CG.  This is similar to an airplane except the WSC aircraft has no  horizontal stabilizer that is affected by propeller blast.  If the propeller thrust is below the CG  [Figure 2-35,  top ] ,  this creates a pitch-up moment about the CG when thrust is  applied and a resultant decrease in speed. When reducing  the throttle, it reduces this moment and a nose pitch down  results with an increase in speed.  As the AOA increases to large values on the wing chord,  the air separates starting at the back of the airfoil. As the  AOA increases, the separated air moves forward towards the  leading edge. The critical AOA is the point at which the wing  is totally stalled, producing no lift—regardless of airspeed,  flight attitude, or weight.  [Figure 2-36]  Stalls: Exceeding the Critical AOA  Thrust Moments  Yaw Stability Summary Thrust line below the center of gravity Thrust line above the center of gravity CG Thrust line CG Thrust line Figure 2-35. Thrust line moments.  Figure 2-34. Wheel fins for carriage yaw stability.  2-18