Final answer:
Centrifugal force does not help the Seminole propeller to feather. Instead, it usually works against the feathering process by driving the blades towards a low pitch position, while oil pressure, spring pressure, and, to a lesser extent, aerodynamic forces support the feathering action.
Step-by-step explanation:
In the context of the Seminole propeller system, the mechanism to feather the propeller usually relies on specific forces. When the propeller feathers, it is positioned such that the blades are aligned with the airflow to reduce drag during an engine failure. Let's consider the options given one by one:
- Oil pressure is often used to move the propeller blades into the feather position. In many aircraft, including the Piper Seminole, the feathering pump increases the oil pressure in the propeller hub to drive the blades toward the feathered position.
- Spring pressure can also be a component of the feathering system, as springs may return the propeller to the feathered position when there's a loss of oil pressure.
- Centrifugal force dictates the blade angle under normal operating conditions and helps move the blades toward low pitch, not feather. So, centrifugal force does not help in feathering the propeller but rather opposes it.
- Aerodynamic forces usually act on the blades during operation and can assist in driving the blades toward low pitch when combined with centrifugal force. However, these forces do not contribute directly to the feathering operation. In the feathered position, the blades are designed to minimize these aerodynamic forces.
Therefore, the option that does not help the Seminole propeller to feather is centrifugal force.