Rib stitching

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TEAM says rib stitching is not necessary, the fabric manufacturer says it is. To make matters worse both are technically right.

On the Minimax, fabric glue is sufficient to keep the fabric attached to the ribs. But what would happen is there was some sort of failure?

Pirate Pilot over on www.lonesomebuzzards.com posted a link to a video that makes some convincing arguments. The video discusses the cause of a Bushmaster ultralight (C-IAUE) crash that resulted in two deaths. The aileron gap seal broke away from the main structure allowing the fabric to separate from the entire top of the wing. While the Minimax wing has slightly different construction there have been numerous maxes that have had partial separation of the aileron gap seal so it is conceivable that a Minimax could have the same type of catastrophic failure.

I can’t say that rib stitches would keep the fabric attached to the wing if my aileron gap seal were to separate from the wing. However I am sure that without the stitching the glue alone is not strong enough to keep the fabric attached if the gap seal separated.

Rib lacing is not exactly cheap the lacing cord, reinforcement tape and finishing tape set me back around $150. It is time consuming too took me about eight hours to do the left wing, bet the right wing will only take about five hours now that I have some experience.

I have read about some people stitching their wings without reinforcement tape and in my opinion all they did was waste time and materials. OK maybe they added a little strength but using the reinforcement tape increases the strength by orders of magnitude. The lace holds just a 1/4″ piece of fabric on the bottom and since I installed rib caps 1/2″ on the top. A 1/2″ by 1/8″ strip of fabric at each lace is not very strong and could easily allow the fabric to rip around the lacing.

I used three inch spacing for a total of twelve stitches on each rib. Without reinforcing tape that gives a total surface area of just 0.75 square inches of the fabric being mechanically attached to each rib top. The reinforcing tape is extremely strong, it will not rip under the forces imposed on the Minimax. The tape drastically increases the surface area holding the fabric to about 18 square inches on each rib top! 

You will need a special needle to stitches around the compression members. I made mine with some music wire a hammer and drill. It’s the curved needle in the picture below. The straight needle purchased and put a small bend on the end to make it more useful.

Rib lacing needles

I used the flat lacing cord because it gives a nicer appearance .

Rib stitch and reinforcement tape

You might have noticed I used a blue chalk line to mark where the laces go. Having them all in nice straight rows looks great, I think it looks nicer than not lacing.

To finish the job I used 2″ finishing tape to cover the stitches and holes.

Finishing tape over rib stitches
Finishing tape over rib stitches
Fully stitched Minimax wing
Fully stitched Minimax wing

After applying primer they already look great.

Stitches after paint primer
Stitches after paint primer

I basically followed the directions in the polyfiber book. To learn how to do the lacing I watched this video.

You won’t regret rib lacing your wings and it very well could save your life.

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