Center of pressure with flaps extended Center of pressure – Lift Pitching moment Pitching moment Center of gravity Center of pressure – Lift Center of gravity Tail down force Tail down force position.  [Figure 11- 6]  To reduce power for climb or cruise,  manifold pressure is reduced to the desired value with the  throttle, and the engine rpm is reduced by moving the propeller  control back toward the high pitch/low rpm position until the  desired rpm is observed on the tachometer. Pulling back on  the propeller control causes the propeller blades to move to a  higher angle. Increasing the propeller blade angle (of attack)  results in an increase in the resistance of the air. This puts  a load on the engine so it slows down. In other words, the  resistance of the air at the higher blade angle is greater than  Figure 11-6.  Controllable pitch propeller pitch angles. Figure 11-5.  Flaps extended pitching moment. Low pitch – High RPM High pitch – Low RPM 11-5