In this paper the precessional phenomenon of the modal pattern of a ro
tating hemispherical shell gyro excited parametrically by electrostati
c forces is investigated. Niordson's thin shell theory, which included
the extensional deformation of the middle surface and was derived in
an invariant form; is employed and the rotary inertia is added. The mo
dal equations of motion are coupled by the Coriolis force and the appl
ied electric field. The method of multiple scales is used to determine
quantitatively the vibrational displacement of the shell from which t
he precessional rate of the modal vibration pattern can be extracted.
It is also shown that the modal precessional rate for the parametrical
ly excited vibration case is found to be the same as that of the freel
y vibrating one. Experiments are performed on a rotating quartz hemisp
herical shell excited electrostatically to verify the theoretical resu
lts.