Several of the FT foam board designs use packing tape over the dihedral joint. The FT build videos show a tape dispenser that makes the process much easier than using the rolls of tape that you buy. This dispenser is weighted so you can tear a piece off with one hand. Here is a link to one that I bought on Amazon.
In this post I used a small, hobby table saw to cut the 45° bevel in the horizontal stabilizer. I left the stab in the surrounding foam board to maintain a line parallel to the saw blade, but removed the bottom few inches to adjust the saw cut.
The table saw is small so I needed to extend the fence to accommodate the the foam board that extended far beyond the table. To do that I taped a couple of yardsticks together then hot glued them to the table saw fence.
After the bevel has been cut I find it easiest to apply the tape hinge while the entire horizontal stabilizer / elevator assembly is pinned down.
To get the tape hinge centered I put a couple of pins toward the end of the stab as guides. The tape is 3/4″ wide so I put the pins in 3/8″ from the hinge line. Works great.
After you remove the fuselage sides from the building board the next step is to glue in the cross members. An earlier post showed how to accurately cut the cross members using a guide. Next step will be to glue the cross members in. If the wood was larger than 3/16″ we might use building pins to hold the parts together while they dry, but with small wood sizes you run the risk of splitting the wood. So instead I use tape.
As I mentioned in an earlier post, I am not good and cutting the bevel in control surfaces free hand. So I use a table saw. I have another post coming soon to further explain that process. And then I use Kraft tape as the hinge. The problem comes when you try to put the tape on the two parts properly centered. A classic case of needing three hands. To solve the problem I just use balsa pins to hold the two parts together while I apply the tape. Works great.
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 color of the FliteTest water resistant foam board is very similar to the color of cardboard. Wouldn’t it be nice if someone made tape the color of cardboard for use on that foam board? Well, someone does! I found this product at Amazon but it is probably available elsewhere too. Just what I needed. I tried to cut the elevator bevel free hand on my Old Speedster and cut through the paper hinge. The repair looks good and the tape added very little weight.