Tank s Hangar Aircraft Modeling

A Site Dedicated to Model Airplane Builders

The hardest part of the fuselage molding is making the plug. Essentially it is former cross sections glued to a piece of 3/4 MDF board with fillers placed in between the formers.  Scrap wood, foam, whatever solid is what you use. After you have taken up most of the space, a layer of plaster of Paris, shaved and sanded to the former heights then covered in fiberglass when cured, makes a mold.  It is some work, but the molds will last a long time. I have molds from the 60s still functional.

You cannot make balsa completely wrap around some curves, and you are not going to apply them to the model in whole sides either, so using staples in the formers where you want to cut the shells is a good idea. A pieces of wire centered along a longeron position will give you a cut line lengthwise.

Once you are satisfied with your molds, you need to deal with the balsa issues.  For lighter models, you need to mold wood that weighs between 5 and 6lb per cu. ft. using only A grain (Cathedral looking grain on balsa with long grain marks). A grain likes to bend in the width but resists bending in the length.  I edge join the wood using thin CA and masking tape to hold the boards together. Apply Ca liberally and wipe it with your finger. No kicker is needed!   As soon as you have joined the wood, and the glue has dried, remove the masking tape.

You can make a pattern using news paper and a marker to rough out the balsa sheet. Here you can see the glues joints because I mark the edges of the sheets with a felt tip marker so I know where to apply the CA.

I like using masking tape to secure the wood to the plug.  Al like to bind them with rags. Do what works best for you.

After soaking the wood in hot water, I align the board and wrap it in the tape securing one end.

You can see how the wood is wanting to act, sticking straight off of the mold. It is time to secure the front end next, being sure to keep the wood snuggly to the mold.

This causes a bulge in the middle that you have to compress down.  Sometimes you will actually crush the wood to get it to conform, but do not worry about that, we can sand, patch and or fill if needed.

Below you can see the final result.  In my climate I can usually let it dry a day or two pending the relative humidity.  A warm place will speed the drying but might induce splitting if it dries faster on one side than the other. 

I use a similar technique for molding leading edges, but over a white foam plug.

It took me less than 5 minutes each to make the wing tips on the small electric model using the brutish rasp and a sanding block.