Tech Questions - Attaching the Fabric to Wing Ribs


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Why are we so concerned about attaching fabric to wing ribs?

This is a very important step. When fabric is used to cover a wing certain precautions must be taken to ensure the fabric does not "balloon-up" in flight. Lift on a wing will cause the fabric to attempt to raise up on the top surface and separate from the ribs or from the plywood on a wooden airplane. This ballooning affect could be disastrous. You certainly do not want the fabric to separate from the ribs and spoil the lift on a wing. If this occurs in flight an accident is almost certain to follow.

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Should I only secure the fabric to the wings?

You must secure the fabric to any surface that creates lift-wings, control surfaces, etc.

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How do I do this?

It depends upon the type of airplane. Several methods are available. They range from sewing it to the ribs using a rib lacing cord to using screws. Rib lacing, screws, rivets, and fabric clips are the most common methods used.

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How do I know which one to use?

If you have a production airplane you must use the method originally employed by the manufacturer. If you have an experimental airplane you may use any method you choose.

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What about using fabric cement or another type of glue to attach the fabric to the ribs of a wing?

Do not use fabric cement to attach fabric to the ribs. If you do use it be sure to use another means of attachment. Fabric cement is not designed for this use and has no peel strength (that is required in this instance). Some kit manufacturers recommend attaching fabric in this manner. We emphatically do not recommend this method. Why take a chance-secure it properly.

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Did the first airplanes built attach fabric to ribs of wings?

They certainly did. They recognized the problem almost 100 years ago. They usually attached wooden strips over the fabric or laced it to the ribs.

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I have heard rib-lacing is a real challenge. Is the knot difficult to learn?

No, if you watch the video and read the manual you can easily figure out how to tie the knot. Go to an EAA SportAir fabric covering workshop and learn the technique. It is really easy to do.

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If I rib lace, do I have to tie a certain type of knot?

If you have a production airplane you must use the knot illustrated in the Poly-Fiber manual. If you have an experimental airplane, we still recommend that knot.

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What keeps the rib lacing cord from tearing the fabric over a rib?

Good question. If it were tied directly over bare fabric it would tear it. Instead, we first of all place a tape down over the rib (reinforcing tape). This tape then protects the fabric from the cord.

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Why not use fishing line or string to tie the knots?

You must use only an approved rib lacing cord. It is made of polyester material and has the necessary strength. All other cords are too weak and may cut through the reinforcement tape.

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I don't like the rib lacing cord showing above the rib. Is there anything I can do about that?

We make a flat rib lacing cord that is hardly noticeable. Also, we recommend using a method of rib lacing that actually hides the cord under the fabric.

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How far apart should the knot, screws, clips, etc. be spaced?

The spacing of knots, screws, etc. is dependent upon the never exceed speed of the airplane. A chart may be found in the Poly-Fiber manual that will provide you with the proper spacing.

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What type of needle is used to tie rib lacing knots?

Special rib lacing needles are available from Poly-Fiber distributors. These needles are usually 12 inches long and often have a curved tip to facilitate tying the knot.

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How long will it take me to rib lace a wing?

Of course, this depends upon the size of the wing and the spacing of the knots. Typically, you can rib lace a J-3 Cub size wing in about a day.

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Is it easier to use rivets, screws, etc.?

Yes, it is much faster and easier. However, you can only use these methods if your airplane had this type of attachment originally.

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If I use rivets, screws, clips, etc. should I still place reinforcement tape over the ribs?

Yes. The fabric must still be protected from the method used to secure it.

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How should I mark the wings for proper spacing?

Determine the spacing required for your airplane and then mark ribs at each end of the wing using a pencil (no pens). Then use a blue color chalk line and snap a line between these marks. (Do not use red chalk that bleeds through the topcoat.) That will provide you with a mark at each rib.

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I am still having problems learning to tie the knot. Any suggestions?

Purchase the new fabric covering video. It shows how to tie the knot very well.

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