blade angle (pitch). The low blade angle keeps the AOA,  with respect to the relative wind, small and efficient at the  low speed.  [Figure 11-7] the torque, or power, delivered to the propeller by the engine,  so it slows down to a point where forces are in balance. When an aircraft engine is running at constant speed, the  torque (power) exerted by the engine at the propeller shaft  must equal the opposing load provided by the resistance of the  air. The rpm is controlled by regulating the torque absorbed  by the propeller—in other words by increasing or decreasing  the resistance offered by the air to the propeller. This is  accomplished with a constant-speed propeller by means of a  governor. The governor, in most cases, is geared to the engine  crankshaft and thus is sensitive to changes in engine rpm. At the same time, it allows the propeller to handle a smaller  mass of air per revolution. This light load allows the engine  to turn at maximum rpm and develop maximum power.  Although the mass of air per revolution is small, the number  of rpm is high. Thrust is maximum at the beginning of the  takeoff and then decreases as the airplane gains speed and  the airplane drag increases. Due to the high slipstream  velocity during takeoff, the effective lift of the wing behind  the propeller(s) is increased. As the airspeed increases after lift-off, the load on the engine  is lightened because of the small blade angle. The governor  senses this and increases the blade angle slightly. Again, the  higher blade angle, with the higher speeds, keeps the AOA  with respect to the relative wind small and efficient. When an airplane is nosed up into a climb from level flight,  the engine tends to slow down. Since the governor is sensitive  to small changes in engine rpm, it decreases the blade angle  just enough to keep the engine speed from falling off. If the  airplane is nosed down into a dive, the governor increases  the blade angle enough to prevent the engine from over- speeding. This allows the engine to maintain a constant rpm  thereby maintaining the power output. Changes in airspeed  and power can be obtained by changing rpm at a constant  manifold pressure; by changing the manifold pressure at a  constant rpm; or by changing both rpm and manifold pressure.  The constant-speed propeller makes it possible to obtain an  infinite number of power settings. For climb after takeoff, the power output of the engine is  reduced to climb power by decreasing the manifold pressure  and lowering rpm by increasing the blade angle. At the higher  (climb) airspeed and the higher blade angle, the propeller is  handling a greater mass of air per second at a lower slipstream  velocity. This reduction in power is offset by the increase  in propeller efficiency. The AOA is again kept small by the  increase in the blade angle with an increase in airspeed. At cruising altitude, when the airplane is in level flight, less  power is required to produce a higher airspeed than is used  During takeoff, when the forward motion of the airplane  is at low speeds and when maximum power and thrust are  required, the constant-speed propeller sets up a low propeller  Takeoff, Climb, and Cruise Figure 11-7.  Propeller blade angle. 11-6 Forward motion Stationary Chord line (blade face) Plane of propeller rotation Plane of propeller rotation Relative wind Thrust Relative wind Forward airspeed Angle of attack Angle of attack Chord line (blade face)