Werner Sobek developed a frame-less umbrella whose textile skin is stretched by rotation and the resulting centrifugal forces. The mast of the umbrella remains rigid. In the head of the mast there is an electric motor that rotates the textile surface, which is slightly reinforced in the hub area.
Umbrella with Optimal Tension Distribution
The textile surface is not simply smooth, but its shape was calculated with specially developed computer programmes from the ratio of span width/fabric weight/rotation speed. This resulted in extremely complex, pagoda-shaped cross-sections with an optimal distribution of tension in the fabric. A slight bulge at the edge improves aerodynamic stability.