In a climb with reduced IAS and increased rev/min, what happens to the angle of attack of a fixed pitch propeller?

In a climb with reduced indicated airspeed (IAS) while simultaneously increasing the engine revolutions per minute (rev/min), the angle of attack of a fixed pitch propeller will increase. This occurs because as the aircraft climbs and speed decreases, the propeller's ability to generate thrust diminishes due to the lower airflow over the blades; however, with the increase in engine speed, the propeller blades move through the same air at a higher rate of rotation.

As the propeller spins faster, the effective blade angle of attack relative to the airstream increases, since the air is hitting the blades more forcefully due to the higher rotational speed. This results in a greater angle of attack for the propeller blades themselves. In simple terms, even though the aircraft is experiencing a decline in IAS, the increased rev/min leads to a greater angle of attack on the blades.

Thus, in this scenario of climbing with reduced speed and increased engine speed, the propeller's angle of attack increases, allowing for better thrust generation even in thinner air or at slower speeds, which is crucial for maintaining climb performance.