Can an axial fan fit on the glass?
If the vibration on the glass, more than a certain value, then the strength of the glass will be a great impact, may produce resonance.
Fan is a rotating part, long time to use, the balance is relatively high.
If installed on the glass, the weight is a problem, the second problem is the quality of the fan.
No matter where the installation of the fan, are the need to support the framework.
