Which type of propeller allows adjustment on the ground?

The correct type of propeller that allows adjustment on the ground is the adjustable propeller. An adjustable propeller is designed with blades that can be repositioned or set to different angles while the aircraft is stationary, allowing for optimal performance based on specific flight requirements or conditions. This capability is particularly beneficial for maximizing efficiency during ground operations, such as takeoff and landing, where different blade angles can be selected to provide better thrust and performance.

In contrast, a fixed pitch propeller has blades that are set at a single angle during manufacture and cannot be adjusted by the operator. Controllable propellers typically allow for in-flight adjustments, meaning changes to the blade angle are made during operation rather than from the ground. Rotational propellers is not a recognized term in the context of propeller adjustment and thus does not accurately describe a type of propeller related to ground adjustments.