Scale Fuselage Stringers

Scale aircraft of the Thirties is my personal obsession and one aspect of modeling a large number of those "Golden Age" aircraft is reproducing the wooden stringers used to shape the fabric covering of the fuselage. I just love that fabric covered look on the Gee Bee's, the Staggerwing Beech's, and the old bi-planes.

If you look at the construction of those aircraft, for example, a Waco bi-plane, you will find a rectangular tubing framework that forms the structural core of the fuselage. Plywood formers are then added to provide a lightweight aerodynamic shape fairing back to the rudder tailpost. Finally, long strips of spruce or mahogany are set into the formers to further fair in the desired fuselage shape and provide attach points for the fabric covering.

In the case of square fuselages like the Curtis Robin, the stringers are needed to space the fabric away from the steel fuselage tubing so it will not 'beat against the tubing while in flight and create wear points.

Years ago most flying model kits came with 'print wood' sheets with the former shapes simply printed on the thin sheet balsa and the modeler was expected to carefully cut each former from the sheet. Each stringer position was printed and, naturally, most modelers would cut the notches for each of those sometimes many stringers. I know I did. The wood often split as I tried to cut notches sometimes less than a quarter of an inch apart. With a circular former, there was no way to have the grain running the right way for all the notches to be cut easily. Long live laser cutting!

The next immediate problem was that due to errors in printing or building, the notches for a given stringer didn't line up smoothly with the notches in the former in front of or behind the one you were trying to fit the flimsy 1/16 square stringer into. When scratch building, plans often have faulty patterns. The final result was that when the covering was applied, the line formed by the stringer was one wobbly wave down the length of the fuselage. Darn, I hate that.

There is an answer to having smooth stringer lines, and it is a fairly simple one too. First of all, do not cut the notches in the formers when you cut out the former. You can mark the suggested positions on each former, but do not cut them at this time. When the fuselage is framed up you will use a special tool to cut the individual notches, one at a time. The special tool is a piece of balsa or hardwood of the same thickness as the stringer to be installed and glue a piece of 22 grit sandpaper on the edge only. Starting from the front or rear end point, carefully sand in a notch just deep enough to hold the stringer material. Fit a stringer into that notch and hold the stringer over the marks made on each former. The stringer will form a natural and smooth arc on the formers. Mark each former (I use my Exacto knife) and then remove the stringer. Sand in the notch in each former. Install and glue one stringer in place.

Going to the opposite side of the basic framework, install the next stringer in the same way. Work carefully from one side to the other so the fuselage will stay straight and not be sprung into that familiar banana shape seen on models that were improperly built. Back and forth from one side to the other and soon you have all the stringers glued in place.

If you were to cover the model at this point, the covering would look terrible. Each former, especially if a rounded shape, would show through the covering. Ugh.

Another easy fix. Just take a dowel and wrap a piece of 22 grit sandpaper around it so you can scallop the former between each stringer. Do not scallop the first or last former in each section. They will need to hold the fuselage contour. Now, when you apply the covering, the formers will not show and the covering will flow smoothly across the stringers just like that beautiful full scale restoration you saw at the airport last week.

Some stringers are fairly deep and, if installed on a built up stick type fuselage, will need triangular braces to stabilize each stringer and keep them from twisting with the sometimes considerable force applied by the covering as it is shrunk to tighten. Most finishing materials will also cause at least some shrinkage too. Early aircraft were finished in nitrate dope that never stopped shrinking, so some older aircraft will have badly warped stringers, formers, and even trailing edges, caused by the shrinkage of the dope finish.

The really nice apart of all this drill is that you will have duplicated the method actually used on so many of those lovely old antiques.