Caudron C.59 advanced trainer; covering of the horizontal stabilizer

Suomeksi

Caudron C.59 was an advanced trainer used by the Finnish Air Force in the 1920s. The restoration of the individual aircraft CA-50 was commenced at the Tuesday Club in 2019. The work has advanced in stages. After the Finnish Aviation Museum acquired from abroad cotton fabric designated to covering aircraft, we could start covering the horizontal stabilizer of the Caudron, which had been waiting for some time. We had earlier refurbished the Caudron’s horizontal stabilizer, which had been in very poor condition, by taking it apart and reassembling it for covering.

Prior to the covering, it was decided to lacquer with nitro cellulose lacquer the fabric strip covering, wound around the leading edge of the stabilizer. It was made of 50 mm wide linen band according to the original. By lacquering the band covering, the gluing of the covering fabric will be enhanced on the surface of the leading edge of the stabilizer.

Photo by Jukka Köresaar.

The linen band covering wound on the leading edge of the horizontal stabilizer was lacquered with 75% nitrocellulose lacquer. As lacquer we used NC Speed nitrocellulose lacquer, and it was tinted red with iron oxide powder. After the lacquer had dried, the edges of the linen band had, as we expected, risen as well as the fabric fuzz. So the band covering was sanded smooth, and another layer of lacquer was applied. Even after the re-lacquering, the leading edge band was uneven and the band had to be sanded once more, after which it was lacquered with 100% nitrocellulose lacquer. So the linen band wound around the leading edge had been smoothed, and we could start covering the horizontal stabilizer.

The width of the horizontal stabilizer is 60 cm and its length 120 cm, so a 130 cm wide piece was cut from the 140 cm wide cotton fabric. This way the fabric has enough working allowance to work both in length and width way. The fabric was wound around the stabilizer, which was laid the table, so that the lapels of the fabric reached past the horizontal stabilizer’s trailing edge. We meant to make a bag out of the fabric, which would be open at the trailing edge.

To achieve this, at both ends of the stabilizer the lapels were joined with pins. The lapels were then sewn together with a sewing machine, along the line of the pins. So the fabric was formed to be a bag, open at the trailing edge. When the ends had been sewn, the fabric was turned inside out, leaving the sewing seams of the lapels inside the fabric bag.

The fabric bag, open at the trailing edge, was drawn on the horizonal stabilizer. The sewing of the fabric was very successful, because the fabric bag had become tight, or rather “skin-tight” on the horizontal stabilizer. Now it was time to sew together the still open trailing edge fabric lapels. For the sewing extra parts of the lapels were cut off, so that the lapels met at the outer edge of the trailing edge batten.

To keep the lapels of the fabric in place when they were sewn together, the fabric was fastened with staples from a stapler at the side of the trailing edge batten. The lapels of the fabric were sewn together with a thin double yarn cotton thread. As a needle we used a curved needle, which was handy for this kind of sewing.

Photo by Antti Laukkanen.

The sewing of the covering fabric lapels was done so that the seam formed a continuous serrated shape. When the lapels had been sewn, the covering fabric formed a closed bag over the horizontal stabilizer.

Photo by Antti Laukkanen.

The next phase in the work was the water-tightening of the fabric. The stabilizer covering fabric was soaked with boiled, but cooled water, and was left to dry. With water-tightening, the fabric is pre-tightened, because when dried the covering fabric has already tightened a few percent on the stabilizer.

Photo by Antti Laukkanen.

The proper tightening of the covering fabric to resemble a drum head, will be made with nitrocellulose lacquer.  Before tightening the covering the fabric needs to be sewn on the stabilizer ribs. The sewing will be done by following the original 1920s Caudron stabilizer sewing method. This way of sewing was documented, when the decayed covering fabric was stripped off the Caudron’s stabilizer. According to that, the covering fabric was sewn onto the fabric strips, which were fastened to the stabilizer ribs, with tacking interval of about 3 cm. The fabric strip was for its part tied to the rib’s surface with an edging ribbon. We had done similarly, when refurbishing the stabilizer.

The places of the stitches were marked at each rib on the surface of the covering fabric, using a thin template made of plywood. The stitching places of the sewing needle were marked on the fabric surface with a thin felt pen, through the template holes. Using a curved needle and double yarn thin sewing thread, the covering fabric was sewn stitch by stitch to the edging ribbons that ran along the ribs. A regular space between the stitches made it possible that the needle occasionally pierced the edging ribbon which tied the fabric strip to the rib. When the sewing had been done, the staples could be removed from the fabric surface.

The covering fabric was now sewn to the horizontal stabilizers’ ribs, both on the upper and the bottom surface, so it’s time to move on the next phase of the covering. There the horizontal stabilizer’s covering fabric will be tightened to drum head tightness with nitrocellulose lacquer. As lacquer we use NC Speed nitro cellulose lacquer. Applying the lacquer is started with 25 % thinned lacquer, and from there in stages to the full 100% nitrocellulose lacquer.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.