Hinge pockets made easy.

Get a piece of balsa half the thickness of the item to be hinged. 1/4 inch thick flaps use 1/8 inch firm balsa. Cut 4 strips at least 1/16" wider than the hinges to be used. Cut the same width strip off the flaps or elevator leading edges. Cut a 6" strip of coarse sandpaper that is a bit wider than the hinge. That will give you some wiggle room when assembling the parts to it's mating surface, flap to wing or elevator to stab. Lightly coat the sandpaper with spray glue and stick it to a flat surface.  Mark the hinge locations on each pair of balsa strips and mark the sides to be cut so you end up with mating parts in the end. Place the balsa strip on the sandpaper with the hinge pocket marks straddling the sandpaper. With some downward pressure push the balsa back and forth three times, or back twice and forth once, three passes over the sandpaper. Use a flat item and place it on the balsa and holding downward pressure make one more pass over the sandpaper. This evens out the depth of the pocket. Repeat that procedure for all the hinge locations on all 4 balsa strips. Using a straight edge glue the balsa pairs together so the cuts align into pockets all along the strip. Now glue the strips to the flap or elevator. A little sanding and your done. I use a fork shaped slotting tool to cut the pockets into the wing or stab.

  To get glue in the pockets I attach a pointed tip from a cya bottle to a tube of "Quick Grip" "all purpose permanent adhesive". I got it at a "Benny's" store. It's clear and dries fast and stays a bit rubbery. Sticks to everything. Using the tip as an injector needle I squirt some glue into each hinge pocket and install the hinge. I glue the hinges to only the flap or only the wing at a time not both at once. You don't have top work as fast and you have time to straighten the hinges. Once the glue has cured you can final assemble the two items. You don't have to worry about the hinges moving around while you work.