in climb. Consequently, engine power is again reduced by  lowering the manifold pressure and increasing the blade angle  (to decrease rpm). The higher airspeed and higher blade angle  enable the propeller to handle a still greater mass of air per  second at still smaller slipstream velocity. At normal cruising  speeds, propeller efficiency is at or near maximum efficiency. Blade Angle Control Once the rpm settings for the propeller are selected, the  propeller governor automatically adjusts the blade angle to  maintain the selected rpm. It does this by using oil pressure.  Generally, the oil pressure used for pitch change comes  directly from the engine lubricating system. When a governor  is employed, engine oil is used and the oil pressure is usually  boosted by a pump that is integrated with the governor. The  higher pressure provides a quicker blade angle change. The rpm  at which the propeller is to operate is adjusted in the governor  head. The pilot changes this setting by changing the position  of the governor rack through the flightdeck propeller control. On some constant-speed propellers, changes in pitch are  obtained by the use of an inherent centrifugal twisting  moment of the blades that tends to flatten the blades toward  low pitch and oil pressure applied to a hydraulic piston  connected to the propeller blades which moves them toward  high pitch. Another type of constant-speed propeller uses  counterweights attached to the blade shanks in the hub.  Governor oil pressure and the blade twisting moment move  the blades toward the low pitch position, and centrifugal  force acting on the counterweights moves them (and the  blades) toward the high pitch position. In the first case above,  governor oil pressure moves the blades towards high pitch  and in the second case, governor oil pressure and the blade  twisting moment move the blades toward low pitch. A loss  of governor oil pressure, therefore, affects each differently. Governing Range The blade angle range for constant-speed propellers varies  from about 11 1 ⁄ 2° to 40°. The higher the speed of the airplane,  the greater the blade angle range.  [Figure 11-8] The range of possible blade angles is termed the propeller’s  governing range. The governing range is defined by the  limits of the propeller blades travel between high and low  blade angle pitch stops. As long as the propeller blade angle  is within the governing range and not against either pitch  stop, a constant engine rpm is maintained. However, once the  propeller blade reaches its pitch-stop limit, the engine rpm  increases or decreases with changes in airspeed and propeller  load similar to a fixed-pitch propeller. For example, once a  specific rpm is selected, if the airspeed decreases enough, the  propeller blades reduce pitch in an attempt to maintain the  selected rpm until they contact their low pitch stops. From  that point, any further reduction in airspeed causes the engine  rpm to decrease. Conversely, if the airspeed increases, the  propeller blade angle increases until the high pitch stop is  reached. The engine rpm then begins to increase. The engine is started with the propeller control in the low  pitch/high rpm position. This position reduces the load or drag  of the propeller and the result is easier starting and warm-up  of the engine. During warm-up, the propeller blade changing  mechanism is operated slowly and smoothly through a full  cycle. This is done by moving the propeller control (with the  manifold pressure set to produce about 1,600 rpm) to the high  pitch/low rpm position, allowing the rpm to stabilize, and then  moving the propeller control back to the low pitch takeoff  position. This is done for two reasons: to determine whether  the system is operating correctly and to circulate fresh warm  oil through the propeller governor system. Remember the  oil has been trapped in the propeller cylinder since the last  time the engine was shut down. There is a certain amount  of leakage from the propeller cylinder, and the oil tends to  congeal, especially if the outside air temperature is low.  Consequently, if the propeller is not exercised before takeoff,  there is a possibility that the engine may overspeed on takeoff. An airplane equipped with a constant-speed propeller has  better takeoff performance than a similarly powered airplane  equipped with a fixed-pitch propeller. This is because with  a constant-speed propeller, an airplane can develop its  maximum rated horsepower (red line on the tachometer)  while motionless. An airplane with a fixed-pitch propeller, on  the other hand, must accelerate down the runway to increase  airspeed and aerodynamically unload the propeller so that  Constant-Speed Propeller Operation Design Speed (mph) Blade Angle Range Pitch Aircraft Type Low High Fixed gear Retractable Turbo retractable Turbine retractable Transport retractable 160 180 225/240 250/300 325 11$^{1}$/$_{2}$° 15° 20° 30° 40° 10$^{1}$/$_{2}$° 11° 14° 10° 10/15° 22° 26° 34° 40° 50/55° Figure 11-8.  Blade angle range (values are approximate). 11-7