Buy the manual for your chosen process, which will have a copy of the STC in it. This manual will take precedence over AC 43.13, since STC’s are approved FAA data. In order for the STC to be signed off legally, the STC manual must be followed to the letter. Some have videos available, and I would recommend getting that, too. Of course, the manufacturer’s maintenance manual is required. Having AC 43.13 is a good idea for any questions not covered in the STC manual or the manufacturer’s maintenance or service manual. Just remember which publication takes precedence, and prioritize which will be consulted first, second, and third.
Securing the fabric
These instructions are general guidelines. Consult the appropriate manuals for specific instructions applicable to your project. Some STC’s will have you buy fabric by the yard, while others have a choice of by the yard or a pre-sewn sleeve for areas like the wings. For the fuselage, the fabric is glued to the tubing structure and to itself for the overlap seam using the special glue called for in the STC Procedure Manual. The amount of overlap in specific areas will be defined in each STC manual. Some aircraft will have the fabric clipped, sewn, or screwed to metal strips in certain areas to keep it aligned. The manufacturer’s maintenance manual will have the specifics on this. Some wings will need to be rib stitched. If neither the STC manual or maintenance manuals explain how to do this, AC 43.13 still has instructions on how to do the different stitches. Essentially, the STC manual will pertain to the fabric process; the manufacturers manual will define what specifics for their particular aircraft; and AC 43.13 will have general guidelines and instructions on how to do a baseball stitch or a rib stitch if neither of the other manuals calls out for it.
Iron it smooth
Once the fabric is glued, most of the modern processes call for lots of ironing with a temperature-calibrated iron. The fabric is ironed at a low setting first, then at a higher setting to get the desired shrinkage and shape around the form. If the iron is not heat- controlled and gets too hot, it could loosen the fibers in the fabric permanently, rendering the fabric unworkable. Take it off and start again. There is no way to fix this problem. Ironing is time consuming to get it done right, but if not done correctly, the appearance of the finished product will suffer. This step, especially, is where having good technical assistance can be invaluable — there’s no substitute for experience in this step.
Next, the fabric gets its first sealing coat. This is usually brushed on. If you are doing Ceconite, or a dope-based process, the butyrate will stick to nitrate, but it will not stick to the polyester fabric. The highly flammable nitrate must go onto the raw fabric. Then, butyrate goes on over that. Poly-Fiber is a vinyl product that does not use dope in its process. The first coats in that system will be Poly-Brush to the raw fabric.
Using a temperature-calibrated iron to obtain desired shrinkage and shape.
From here, the rib lacing is done, as is any other attachment needed for the fuselage and tailfeathers by use of screws, clips, stitching, or whatever is specified in the aircraft manufacturer’s maintenance manual. Then, the reinforcing tapes are applied over the stitches or attaching hardware. These tapes are also used on seams, leading and trailing edges, and fuselage longerons and stringers where two layers of fabric are needed for reinforcement. This tape is made of the same material as the covering fabric. Tapes come in different widths, and usually have pinked edges that give the tapes over 40 percent more edge area. At the same time the tapes are applied, the rings for the future inspection holes and their fabric coverings need to be put on (to be cut later), as well as the drain grommets. If using a dope process, remember these tapes are raw material, and nitrate dope must be used to apply them. Poly-Brush™ is the Poly-Fiber brand name for the product that is used until the aluminum pigmented Poly-Spray coats are applied. After more ironing to smooth tapes and any fabric that may have been missed before, the first spray coats go on. Then, the sanding starts. Spray, sand, spray, sand. Iron some more. Then go in with your UV blocking aluminum pigment coats. Sand some more, and iron if needed.
Poly-Fiber is the world's best-selling fabric-covering system. For over forty years, the all-vinyl Poly-Fiber system has proven to be the easiest to use, most forgiving, and most durable system on the...
There are a large selection of colors for the tinted dope, with everything from basic white to yellows and reds to metallics.
Scheduled for Sept. 26 and 27, it will be held at Wicks facility in Highland, IL.