# How Propellers Work

## Propellers: A Rotating Wing

Propellers can be thought of as a rotating wing. The propeller blades are shaped similar to an aerofoil and the rotation of the propeller creates airflow over the propeller blade. Just like a wing, the airflow over the propeller creates a pressure differential, with relatively higher pressure behind the propeller blade compared to the front. The result is a force similar to lift, but the force from the propeller acts forwards and is called thrust.

The propeller blade also experiences a force similar to the drag on a wing, but in the case of the propeller it is called torque. The torque has to be overcome by the engine’s power to keep the propeller rotating and to continue to create thrust.

## Motion of the Propeller

In flight, the propeller is both rotating (because of the engine power) and traveling forwards (because of the aircraft’s forward airspeed). This results in the motion of the propeller being a combination of the two.

We can look at this motion as two vector components (remember those from the lesson on Forces?) One component is the velocity due to rotation and the other component is the forward velocity of the aircraft’s direction of flight. We can combine these two components into one resultant force – the propeller’s direction of movement in flight.

Just like the wing, the propeller’s relative airflow is opposite its direction of motion. The angle of attack (AoA) is the angle between the propeller blade’s chord line & this relative airflow.