i bought one from taobao as well, but i dont seems able to find the middle poin ...
This is very normal.
Once you keep it neutral, both motors will start to spin, so there is air cushion, and the hovercraft will move forward slightly.
Once you put on full reverse, the both motors stopped, not only the forward motor stopped, but also the downward motor. So there will be no air cushion and the brake pad at the bottom of hovercraft will rub against the ground for braking.