NlltS & BOltS

Aircraft Building WHEN IT COMES TO seams. These encovering your airvelopes still exist plane with fabric, today, but builders one question scares can get envelopes people new to the with span-wise Fabric covering options for your airplane process—Do I have seams upon request to learn to sew? from manufacturers. RON ALEXANDER Not really. There Many people find are two ways to cover chord-wise seams on your airplane witha wing unsightly, out adding a sewing machine to your method, the top and bottom blan- and this is why span-wise seams toolbox and sewing to your list of new kets must overlap at their glue came into existence. The old CAM skills. But you still have to answer a joints on the leading and trailing 18 manual (predecessor of Advisory question—envelope or blanket? In- edges. The average wing is 60 Circular 43-13, Acceptable Methods, stead of sewing you can buy a presewn inches wide. In the early days cot- Techniques and Practices) required envelope that fits over the part, like a ton and linen was the fabric of fabric seams to be oriented with the wing, like a tight-fitting sock, or you choice, and it was only 48 to 50 airflow whenever possible. AC 43.13 can buy a roll of fabric, lay it over the inches wide. Because the fabric abandoned this practice. part like a blanket, and glue it in place wasn't wide enough for span-wise Finally, shrinking the fabric was with special cement. seams (wing root to tip), early another obstacle to the blanket In aviation's early days builders builders had to sew envelopes with method in the early days. Nitrate sewed envelopes because they didn't chord-wise (fore and aft) seams. and butyrate dopes continue to Then came 70-inch polyester fab- shrink fabric over time, and it didn't have a choice. The special glues that withstand the forces acting on the ric, which builders could lay on the have an adverse affect on chord-wise fabric in flight and make the blanket top and bottom of wings and glue in seams because the dope slowly tightmethod possible didn't exist then. place with the necessary overlaps at ened the entire surface, leaving the So they sewed. the leading and trailing edges. But seams straight. But the question today remains Glue wasn't the only thing that early builders and mechanics were kept early builders from using the creatures of habit (of course, we are envelope or blanket? Even with toblanket method. When you glue not today), and they continued to day's fabric covering techniques, fabric to a wing using the blanket use fabric envelopes with chord wise each method has its pros and cons.

Envelope or Blanket?

Laying the fabric over the structure is the first step in the blanket method of covering.

After laying the "blanket" over the structure, mark the fabric where you need to makes cuts. Always use a pencil. Sport Aviation

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Aircraft Building

Finally, cut the blanket to fit.

Blanket Method

Today's synthetic fabric (polyester) makes the blanket method of fabric covering more practical. You simply roll out one piece of fabric for the top of a wing or surface and then roll out another piece of fabric for the bottom

Seams must face the inside of presewn envelopes. Make sure they lay flat against the airplane's structure to get a pleasing appearance.

side, making sure the two pieces have the prescribed amount of overlap. (Using the Poly-Fiber system, you need a 2-inch overlap on the leading edge and a 1-inch overlap on the trailing edge.) Then you glue them together with the recommended fab-

ric cement. You can cover smaller control surfaces by wrapping one piece of fabric around the component like the shell of a clam and cement the one side where the fabric meets with the specified overlap. Today's fabric cement (such as

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Whether you use the blanket or envelope method of covering, you attach the fabric to the

airplane with special cement.

Poly-Tak or Super Seam) is strong enough to replace sewn seams. Both the Poly-Fiber and Ceconite supplemental type certificates (STC) allow cemented seams for all wing loadings and airspeeds. Thanks to polyester fabric's 70-inch width, covering wings using the blanket method is practical (depending on the width of your wing, naturally). You can cover an entire airplane by piecing fabric together with cemented, overlapped seams, but the cemented seams must have a hard structure underneath them. "Hard structures" are leading and trailing edges, longerons, structural tubes, etc. You cannot create a cemented seam in "thin air" such as between two wing ribs. As you can see, when covering the airplane with this method you should never have to get out your needle and thread, and most fabric-covered airplanes today require little, if any, actual sewing. Do not confuse sewing fabric with rib stitching or lacing, where you attach the fabric to a structure. Rib lacing is a different step and its purpose is to keep the fabric from "ballooning" on the top side of a surface that creates lift during flight. It does not join different pieces of fabric together. :

Fabric Envelopes

You can purchase a sewn envelope that fits each component of your airplane like a glove. Aircraft Spruce & Specialty has patterns for most aircraft and it will sew an envelope out of the type of fabric you desire. Then you slide the envelope over the structure and glue it in place with fabric cement. Because a properly sewn envelope fits

the structure like a glove, in most cases you have to cement the fabric in place on one end. For example, after you pull on a wing envelope you cement it at the butt end (root) of the wing. Envelopes save a lot of work and, therefore, time. On a wing, their disadvantage is a matter of preference. Some people don't like to see spanwise sewn seams. (Aircraft Spruce will sew the envelope with span-wise seams on the leading and trailing edges, but builders must request this.)

When you receive the envelope the seams will be on the outside, so you must turn it inside out to make sure the seams are inside the envelope and against the structure. The excess seam fringe can snake or bunch up along the structure and have an unsightly appearance. You can avoid this by making sure the fringe lays flat along the structure before shrinking the fabric. This requires some time and effort. The patterns used to sew envelopes are aircraft specific, and if you (or a

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Aircraft Building previous owner) have modified the structure in any way, the affected envelope will not fit. A 50-year-old

airplane with its sixth wingtip bow or a new cabin birdcage will not have retained its original shape. If this occurs, expect to spend a lot of time cutting and fitting the fabric. Heat shrinking an envelope presents another problem. You must shrink the envelope in such a way that its seams remain straight. If you start shrinking one side of a seam with an iron you can easily pull the seam in that direction. If you try to fix the problem by shrinking the other side you'll probably end up with a seam that looks like a spastic snake. To prevent this, begin the shrinking process directly over the

seam itself. Then work outward on both sides of the seam to balance the shrinking process to keep it straight.

You can sew your own envelopes if

Especially on aircraft fabric, even if it's just weekend war. Old Rhinebecfc Aerodrome values things that withstand the test of time. They cover their treasures with Poly-Fiber. Since 1958, fabric aircraft lovers have trusted the Stits Poly-Fiber process. And today, you get the same ease of application, the same consistent success, plus genuine been-there done-that factory support. So when your mission is critical, don't trust anything less than Poly-Fiber. Old Rhinebeck wouldn't.

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you have the desire, a commercial sewing machine, and the approved polyester machine sewing thread. Don't try to use a home sewing machine. Polyester aircraft fabric is tough stuff and it will wreak havoc on it. If you want to save yourself a lot of

time and grief, order an envelope

rather than attempt to sew it yourself.

Your Decision

With all of this information, which

method should you use to cover your airplane? It's up to you. Each type has

inherent advantages and disadvan-

tages, and there's nothing wrong with using both methods. Generally, it's easier to cover a fuselage with an envelope because the blanket method's "cutting-andpasting" takes a lot of time and can be confusing. The blanket method, however, easily covers wings and controls surfaces. Envelopes save you time when covering these components, but they are more expensive than buying just the fabric, cutting it to size, and cementing it in place. The choice is yours.