Occasionally you need to make a piece of warped foam board straight and usable. For me it is the horizontal and vertical stabilizers, rudders, and elevators. Not so much a problem with fuselages and other parts that have panels that are bent and glued. Those tend to automatically straighten out any warps. So I usually take 2 warped pieces at the same time. Put a couple of strips of foam board under each end, then add some sand bags in the middle. If you get too aggressive with lifting the ends and adding sand bags you will end up putting wrinkles in the paper covering right where the sand bags sit. It normally takes a few to several days for the boards to straighten out. These pictures were taken outside in Chicago on a cold day. The warmth of being inside the house will be a better place to do this.
The little red pins are used to hold balsa parts together while the glue dries. Or to hold parts in alignment. They can also be used in foam board construction. The vertical stab and rudder are pinned down to make it easier to apply the tape hinge. Hard to do just holding the parts together while applying the tape.
The elevator of the Aeronca has a very narrow connection between the left and right side. If the elevator is being built with balsa and hardwoods there would be no concern about connecting the halves. But foam board does not have the torsional strength of balsa in this application. An exact foam replica from the plan would give a very narrow strip of foam board to connect the halves. So I decided to add a joiner made from 3/16″ x 1/2″ firm balsa. The middle pic shows what that looks like. Next is the need to cut a 45° bevel on the leading edge of the elevator. Normally cutting a bevel in foam board is easy, but with the addition of the balsa joiner the task becomes more challenging. Two possible ways to make a bevel in the balsa. One is to file or sand the bevel in the balsa before gluing it in to the foam board. Another is to use a power tool. I used a Microlux table saw. Just set the fence and make the cut. Comes in very handy.
This one comes from the Flite Test web site. If you build models from foam board eventually you will need to do a 50% score cut. A score cut will allow you to make a cut, then fold the foam board back on itself. You don’t want to cut all the way through. The tip from Flite Test is to take your cutting tool and round off the tip. Use whatever method you prefer. A couple choices are, a brick, sandpaper, or a file.
Seems like every time I hot glue something then try to find a scrap piece of foam board to wipe off the excess glue, there are none. Decided to solve that problem by making a couple dozen one inch squares to have handy.