FAA Powerplant Written Practice Test

How do hydromatic propeller systems differ from other constant-speed propeller systems?

1. They require no maintenance

2. They do not use oil for control

3. They do not include counterweights

4. They cannot change blade pitch

The correct answer is: They do not include counterweights

Hydromatic propeller systems are unique in that they utilize a specific mechanism that sets them apart from other constant-speed propeller systems, particularly in their design and operational features. One key characteristic of hydromatic propellers is that they do not employ external counterweights to achieve blade pitch adjustment. Instead of relying on counterweights to facilitate pitch changes, hydromatic systems utilize a system of oil pressure and centrifugal force to move the blades to the desired angle. As the propeller spins, oil pressure acts on the blade, and the design of the propeller allows for the adjustment of the pitch based on the engine's power setting and speed. This eliminates the need for additional counterweight mechanisms that can complicate the design and maintenance of other types of constant-speed propellers, which typically use both oil pressure and counterweights to manage blade pitch. Understanding this distinction is important as it highlights the operational efficiency and reduced mechanical complexity of hydromatic systems compared to their counterparts.