whether a sunroof or window or the like is opened or closed in a vehicle as a result of this mass throughput the aerodynamic forces acting on the individual fan blades change as well as indicated by the reference mark p l shown as acting essentially in a circumferential direction for example in fig1 in addition to these aerodynamic forces which act opposite to circumferential direction d the centrifugal forces p z which are a function of the rotational speed act upon fan blades 9 and 10 and spokes 11 and 12 as a result of their deformability and as a function of the forces a certain equilibrium is established which determines the shape of the radial fanwheel in each case for example if the aerodynamic forces p l increase on the basis of the operating state shown at the center of fig1 a modified equilibrium of forces will occur wherein spokes 11 and 12 will have a greater curvature u03c11 1 r 1 at the same time the diameter of the blade ring formed by fan blades 9 and 10 will shrink fig1 right dashed lines since the blade geometry remains essentially constant the entrance angle u03b1 will decrease to a value of u03b1 1 and the exit angle u03b2 will decrease to a value of u03b2 1 this deformation and the associated adaptation to the changed load is reinforced further when a drive motor which changes its rotational speed as a function of load is provided since an increase in the load reduces the motor rpm so that centrifugal forces p z likewise become less increasing the tendency toward greater curvature of the spokes in the opposite case i e.