Dissymmetry of Lift

Dissymmetry of lift occurs when one side of the rotor disk produces more lift than the other due to differences in relative airflow.

Advancing and Retreating Blades

As an aeroplane moves forward through the air, both wings experience approximately equal relative airflow (RAF).

However, the rotor blades of a gyroplane or helicopter continuously rotate, causing them to:

• Advance into the oncoming airflow, increasing their RAF.

• Retreat away from the oncoming airflow, decreasing their RAF.

For example, if the rotor blade tip speed is approximately 300 kt and the aircraft's forward speed is 50 kt, then:

• Advancing blade: 300 + 50 = 350 kt

• Retreating blade: 300 − 50 = 250 kt

These figures illustrate the difference in airflow at the blade tips.

At a constant angle of attack, an increase in RAF produces an increase in lift.

For a rotor rotating anticlockwise when viewed from above, the advancing side is on the right and the retreating side is on the left.