Introduction to Glider Flying > Aerodynamics of Flight > Forces of Flight > Lift > Magnus Effect

The explanation of lift can best be explained by look-ing at a cylinder rotating in an airstream. The local velocity near the cylinder is composed of the airstream velocity and the cylinder’s rotational velocity, which decreases with distance from the cylinder. On a cylin-der, which is rotating in such a way that the top surface area is rotating in the same direction as the airflow, the local velocity at the surface is high on top and low on the bottom.

As shown in Figure 3-4, at point “A,” a stagnation point exists where the airstream line meets on the sur-face and then splits; some air goes over and some under. Another stagnation point exists at “B,” where the two air streams rejoin and resume at identical velocities. We now have upwash ahead of the rotating cylinder and downwash at the rear.

Figure 3-4. Magnus Effect.

The difference in surface velocity accounts for a dif-ference in pressure, with the pressure being lower on the top than the bottom. This low pressure area pro-duces an upward force known as the “Magnus Effect.” This mechanically induced circulation illustrates the relationship between circulation and lift.