One model of nonfeathering aluminum hub constant-speed  propeller utilizes oil pressure from a governor to move the  blades into high pitch (reduced rpm). The centrifugal twisting  moment of the blades tends to move them into low pitch  (high rpm) in the absence of governor oil pressure. This  is an exception to most of the aluminum hub models and  feathering models. Most of the Hartzell propeller aluminum  and steel hub models use centrifugal force acting on blade  counterweights to increase blade pitch and governor oil  pressure for low pitch. Many types of light aircraft use  governor-regulated, constant-speed propellers in two-bladed  and up to six-bladed versions. These propellers may be the  nonfeathering type, or they may be capable of feathering  and reversing. The steel hub contains a central “spider,”  that supports aluminum blades with a tube extending inside  the blade roots. Blade clamps connect the blade shanks with  blade retention bearings. A hydraulic cylinder is mounted on  the rotational axis connected to the blade clamps for pitch  actuation.  [Figure 7-24] The basic hub and blade retention is common to all models  described. The blades are mounted on the hub spider for  angular adjustment. The centrifugal force of the blades,  amounting to as much as 25 tons, is transmitted to the hub  spider through blade clamps and then through ball bearings.  The propeller thrust and engine torque is transmitted from  the blades to the hub spider through a bushing inside the  blade shank. In order to control the pitch of the blades, a hydraulic piston-cylinder element is mounted on the front  of the hub spider. The piston is attached to the blade clamps  by means of a sliding rod and fork system for nonfeathering  models and a link system for the feathering models. The  piston is actuated in the forward direction by means of  oil pressure supplied by a governor, which overcomes the  opposing force created by the counterweights. Hartzell and  McCauley propellers for light aircraft are similar in operation.  The manufacturer’s specifications and instructions must be  consulted for information on specific models. The feathering propeller utilizes a single oil supply from a  governing device to hydraulically actuate a change in blade  angle.  [Figure 7-25]  This propeller has five blades and is  used primarily on Pratt & Whitney turbine engines. A two  piece aluminum hub retains each propeller blade on a thrust  bearing. A cylinder is attached to the hub and contains a  feathering spring and piston. The hydraulically actuated  piston transmits linear motion through a pitch change rod and  fork to each blade to result in blade angle change.  While the propeller is operating, the following forces are  constantly present: 1) spring force, 2) counterweight force,  3) centrifugal twisting moment of each blade, and 4) blade  aerodynamic twisting forces. The spring and counterweight  forces attempt to rotate the blades to higher blade angle, while  the centrifugal twisting moment of each blade is generally  Mounting stud (K or R flange shown) Shaft O-ring Engine flange Oil Spinner adapter (if required) Hub Low pitch stop Pitch change rod Spinner dome Starter gear (Lycoming engine) Balance weights Blade Lubrication fitting Fork Blade retension bearing Spring Piston Cylinder (oil  pressure to increase blade angle and  reduce rpm) Figure 7-24.  Constant speed non-feathering propeller.  7-15 Constant-Speed Feathering Propeller