I am suspicious that this could lead to problems due to the differing
stiffness of the two. 
When a structure like that is put under load, the stiffer material carries
more of the load and there becomes a large stress where the different
materials join.
Maybe someone has tested this and can make a recommendation for us all.

Mark,

 

With respect to 320/360s, we are all testing this every day - our spar caps have carbon fiber enclosed by pre-preg glass and the webs are pre-preg glass, not to mention the that the spars are bonded/glassed to the glass wing skins.  I would think that, in the spar cap case, the stiffer core material would put less stress on the more flexible encasement and web material.  Also, those that fly under the forward hinged canopy used uni-directional carbon fiber layups between the canopy skin, foam and pre-preg glass to stiffen the forward part that is under stress from the gas struts.  Aye, she's still holding together!

 

Scott Krueger