Full-Feathering and Constant-Speed Governing Systems
Besides the propeller, the other major component of the system is the governor. Each governor mounts on and is geared to the engine, which drives the governor gear pump and the flyweight assembly. The gear pump boosts engine oil pressure to provide quick and positive response by the propeller. The rotational speed of the flyweight assembly varies directly with engine speed and controls the position of the pilot valve. Depending on its position, the pilot valve will direct oil flow to the propeller, allow oil flow back from the propeller, or assume a neutral position with no oil flow. These oil flow conditions correspond to increasing pitch, decreasing pitch or constant pitch of the propeller blades. (Figs. 4A & 4B)
The flyweights change the position of the pilot valve by utilizing centrifugal force. The L-shaped flyweights are installed with their lower legs projecting under a bearing on the pilot valve. When engine RPM is slower than the propeller control setting, the speeder spring holds the pilot valve down and oil flows to the propeller in a full-feathering system and from the propeller in a constant-speed system. (Fig. 5) As engine RPM increases, the tops of the weights are thrown outward by centrifugal force. The lower legs then pivot up, raising the pilot valve against the force of the speeder spring so no oil can flow to or from the propeller. (Fig. 6) The faster the flyweights spin, the further out they are thrown, causing the pilot valve to be raised and allowing more oil to flow from the propeller in a full-feathering system and to the propeller in a constant-speed system. (Fig. 7)
The cockpit control lever is connected to the governor control lever which in turn is attached to a threaded shaft. As the lever is moved, the threaded shaft turns and moves up or down to increase or decrease compression on the speeder spring. (Fig. 8) For example, when the cockpit control is moved forward, the governor control shaft is screwed down, increasing compression on the spring. This increases the speed necessary for the flyweights to move the pilot valve and produces a higher RPM setting. The cockpit control lever allows the aircraft pilot to shift the range of governor operation from high RPM to low RPM or any area in between.
