Ham Standard Propeller

VOLUME 3  |  FEBRUARY, 1950  |  NUMBER 5  |  MODEL 18 SERVICE NOTES AND CHANGES

Hydromatic Propeller Care
Single-acting, hydromatic, Hamilton Standard propellers are offered as optional equipment for the Model D18S airplanes in lieu of the constant speed Hamilton Standard Propellers provided as standard equipment. These hydromatic propellers are standard equipment on the Model D18C and Model D18C-T airplanes. These propellers are controlled by individual, single-acting, Hamilton Standard propeller governors, and feathering or unfeathering action is accomplished by individual, electric motor-driven pump feathering systems. The feathering pumps are located in the engine nacelles and the propeller feathering oil supply is contained in the engine oil tank. A standpipe extending into the oil tank at the engine oil outlet fitting prevents the escape of oil below the level of the standpipe opening through the engine oil system, thereby insuring a sufficient supply of oil for propeller feathering in an emergency.
Three fundamental forces are utilized to control the blade angle variation required for constant speed propeller operation.
1. A centrifugal twisting moment which tends at all time to move the blade into low pitch.
2. Oil at engine oil pressure on the inboard piston side *the outboard piston side on early model propellers) which is introduced to supplement the blade centrifugal twisting moment toward low pitch.
3. Oil, taken from the engine supply and boosted in pressure by the engine-driven propeller governor, is supplied to the outboard piston side (the inboard piston side on early models) to balance Forces 1 and 2, and used to move the blades toward high pitch.
These hydraulic and centrifugal forces are transformed into mechanical force by the piston and cylinder, and the cams transmit this force to the blades through the bevel gears. The required balance between the three control forces is maintained by the propeller governor which, in addition to boosting the engine oil pressure, meters to or drains from the piston the exact quantity of oil necessary to maintain the proper blade angle setting for constant speed operation. See figure 4