The bulkhead formers are cut from 3/16" foam board, allowing the reed to be glued and wrapped around it. Note the vertical and horizontal lines important in the alignment process before stringers are attached.
Most rubber scale fuselage construction comes in one of two basic types: the traditional "half shell" found in most of the early kits and designs from the 1930s up until the present; and the "box with formers style", which came into vogue as modelers became more concerned with the relationship between model weight and flight duration. Beyond these two basic categories, there are probably as many other fuselage construction schemes to retain strength and build in lightness as there are modelers
My particular venture into an alternative fuselage construction method was prompted by a fellow club member who brought in a lifetime supply of reeds, which he got at a local craft shop. The reeds had a circular cross-section, nominally about .070 in diameter. Their light weight, flexibility, and strength got me to thinking about how they might be used for round or oval fuselage formers for those sleek WWII designs that I love.
To enhance the naturally flexibility of the reeds and allow them to be bent to a very small diameter, I decided to soak them in water. I have some plastic tubes which used to house 36" lengths of piano wire and have plastic end caps, so the reeds were stuffed into the tubes, the tubes filled with water, and everything just allowed to soak away until needed.
The construction method I developed using reeds has very distinct steps to it, so I’ll try to describe each step clearly enough so that anyone can duplicate the process. Hopefully, the accompanying photos will also help. Before starting, the materials you will need are a sheet of 3/16" foam poster board (white foam overlaid with cardboard on both sides); a piece of 3/4" blue foam insulation a bit longer and wider than the fuselage you intend to build; a length of .062 music wire as a skewer for the bulkhead assembly; and, of course, a supply of .070 reeds.
Step 1: I use a simple CAD program to draw the cross-sections of each bulkhead and mark them with vertical and horizontal center lines for the important alignment process to come. They are then printed out, and pasted onto the 3/16" poster board. My little jigsaw cuts them out to size, leaving room for the .070 reed and the balsa stringers. A bit of touch-up sanding evens out any saw kerfs or waviness.
Step 2: The reed is wrapped around each bulkhead and marked where it overlaps. It is then taken off the form and a diagonal scarf joint is used to glue the reed into a closed circle. It is put back onto the form to fully dry. If it is too loose, it is removed, re-cut and re-glued to get a "slight push" fit back onto the form. If it is too tight, well, you have plenty of reeds!
Step 3: Using the blue foam plank as a platform to hold the bulkheads in alignment, I draw a centerline and perpendiculars at each bulkhead location. I use my bench drill press as a router and fabricate a slot for each bulkhead. The blue foam gives good support to the bulkheads as you begin adding the stringers.
Step 4: I spear the center of each bulkhead with the .062 music wire, and then insert the bulkhead shish kabob skewer into the slots in the blue foam platform. The music wire skewer is pinned to the foam for stability, and the bulkhead horizontal and vertical centerlines are lined up.
Step 5: Now comes the rewarding part. The jigged assembly allows me to pin down and glue in place the centerline side stringers, so at least I start with two perfectly straight stringers along the centerline of the model. After the top half of the stringers are installed, the assembly is pushed out of the foam base. By now, it is pretty rigid and the remaining stringers are added "in the air".
Step 6: When all stringers are installed, the music wire skewer is removed and the bulkhead forms are freed from the reed formers. There may be some glue spots that have to be dealt with if much CyA was used initially, but the reed is very strong and can be used as a prying surface to the foam board forms.too
So far, I have done a fuselage for a 24" span Macchi-Castoldi MC-72 Schneider Cup Racer (the fuselage weighed six grams), a Henschel p87 pusher canard bomber, and a P-39 Airacobra using this method, and I am pleased with all of them.
At one point I tried sanding the reed to a flat-sided cross-section after it was joined and before it was put on the form. I was able to save a grand total of one half gram on a total of 10 formers, which seemed futile, given the care and effort needed to complete the sanding process. As I noted in the opening paragraph, there are multiple methods of fuselage construction that have become favorites of individual modelers. This method lets me work with simple tools and materials and feel confident that I can make a light, strong model every time.
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