I believe that was to keep the atmosphere breathable for the occupant, as IIRC the fly-cycles were capable of going supersonic. The air cushion was to deflect the supersonic airflow around the occupant. I believe it was to act as a sort of light-weight cockpit. However, the pressure exerted to form the air cushion acted like an airbag too, so it should have definitely deflected rain, especially considering that it was likely designed to stop rainfall at supersonic speeds.<p>I can't really remember this with accuracy, it's been a while since I read the series.