The Beech & McCauley Types

The Beech and McCauley types of CSU operate in a similar manner to the units described above. However, with these types of units there are no heavy counterweights attached to the blades. The prop blades are turned towards fine/flat pitch by the centrifugal turning moment and towards coarse pitch by oil pressure acting on the moveable piston.

The Hamilton Standard Type

The Hamilton Standard CSU operates on the oil/counterweight principle. The major difference is the direction of movement of the blades due to oil pressure acting on the piston in the cylinder. The increased pressure moves the cylinder forward over the stationary piston The cylinder is connected to the blades by a system of cams and gears. An increase of oil pressure turns the blades to fine/flat pitch assisted by the centrifugal turning moment acting on the blades. The opposing force is supplied by the centrifugal force acting on the heavy weights attached to the blade hub and the aerodynamic turning moment acting on, and turning the blades towards coarse pitch. Note the oil pressure acting on the piston turns the blades in the opposite direction to that described for the Beech and McCauley CSU’s.

Air/Oil Type

The air/oil CSU works in the same manner as the Hamilton Standard CSU with the addition of compressed air pressure to assist turning the blades towards coarse pitch. The compressed air chamber is filled with dry air or nitrogen gas at a pressure of approximately 175 PSI. The reason for using dry air is to prevent corrosion and freezing of the moisture within the system. Compressed air is used on newer types of CSU in place of counterweights in order to save weight.