Studying I have found a question that states that in a fixed-pitch propeller in flight at a given TAS, the blade's angle of attack will change if RPM increase, but I don't understand how can the blade's AOA change if the pitch of the blade is fixed.
Am I missunderstanding the concept of fixed-pitch propeller or the question is wrong?
Question answer and explanation for source:
Q:For a fixed-pitch propeller in flight at a given TAS, the blade angle of attack will:
A:increase if RPM increases.
E:For a fixed pitch propeller the pitch angle cannot be changed (it varies from root to tip to maintain near-constant angle of attack along the blade).
The angle of attack as in the case of a aircraft wing is defined as the angle between the chord line and relative airflow. With a propeller however the relative airflow is the resultant of the airflow due to rotation and forward speed. Change either of these values and the angle of attack will change.