Hamilton Standard 43E60 Propeller
The Hamilton Standard 43E60 is a hydraulically pitchable three blade propeller with a diameter of 15ft 2" (4.63m). It is equipped with an automatic constant speed mechanism and reversing capabilities.

This means that the pitch angle of the propeller blades is automatically adjusted depending of the speed of the airplane and the power settings of the engines.

Here you can see the gears which are usually hidden inside the propeller hub. The rest of the mechanism is removed.

Picture: The Dutch Connie

Thats the propeller hub in a cross section view.

It is "only" a propeller but besides the motor one of the most complicated systems in the airplane.

A diagram of the complete propeller system.

The so called governor is sitting on the top of the front motor housing and is driven from the crankshaft. It compares the actual rotational speed with the desired settings and adjusts the propeller blades if necessary.

If the RPM (revolutions per minute) are too low, the plades are adjusted to a flatter angle. In that way less air will be moved by the propeller, the load to the motor is reduced and the RPM can rise to the value set by the flight engineer. If the RPM is too high, for example when accelerating for takeoff, the blades were moved into a steeper angle to move more air. In that way, the engine gets more load and the RPM comes down to the desired value.

This means, if you push the contols levers foreward to accelerate, the engine speed increases shortly until the propeller blades have adjusted and the RPM speed remains constant. In other words - if you push the levers, you change indirectly the prop pitch, the engine is always running at optimal speed, but more air is moved. You actually change the power, not the RPM speed.