The ASK-21 is mainly a fibreglass construction.
However, the bearings for the airbrakes and their control rods are fitted into small pieces (some 10 cm wide) of what seems to be plywood molded into the fibreglass.
The following picture shows the plate holding the bearing for the airbrake, seen from the rear side in the space in the fuselage where the wing spars are joined. The bolt that sticks out holds the bearing of the linkage that transfers the brake movement to the rods in the wing.
The last picture shows the bearings in the wing where the rod to lift the actual air brake is fastened.
What is the reason for this choice of material - could the bearings not be fitted into the fibreglass structure without extra pieces of plywood?