Windshield Rain and Ice in Blender

[mroschk]

Hello,
i have 2 little Problems in Blender.

1. When i add a Material type of Windshield and sit the Aircraft looking to the Rain on the Windshield, the Raindrops are moving slowli up, and after a while again slowly down. After a little time it starts from the beginning. But i set the Wind to 0 kt in MSFS and the Raindrops should move from UP o DOWN only.
2. What means this Wiper option in the Material Settings ?
   

Thanks
Matthias