1932 Volume 10 Issue 11 Pages 645-647
When an aeroplane flies over undulating land surface the aerodynamical forces that act upon it are different from those experienced over plain. The aeroplane seems to be repulsed when it approaches to a mountain and attracted when it crosses over a valley. This phenomenon is explained hydrodynamically and the general expressions for the forces are obtained assuming the aeroplane as a point-vortex.