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Ribstitching - Am I expecting too much?

N86250

Registered User
Elizabeth, WV
This is the fourth pair of wings I've recovered but the first set that needs ribstistched. All the Aeronca wings used #4 screws and these wings are original PA 12 so they get stitched. So I studied the Ceconite manual. I watched a bunch of youtube videos. I can do this, yeah, right. I'm sure I've got the knot down OK. The modified seine knot--flat cord--hidden knots. Actually my stitches LOOK very nice and snug. BUT---when I push the knot under the fabric, it puts ever so little slack in the anchor line from the previous knot. Then when I've finished a whole rib and everything looks so nice, I just have to slip a curved needle under any stitch and give it a little tug to test my work, and it SLIPS!! Not much. Only about a 1/16 or 1/8 of an inch. Just enough to worry me about the cord chafing on the rib over the years. The stitches slip just that little bit and it doesn't seem right to me. I was expecting a knot that wouldn't slip at all even if the cord stretched. The guys here I ask tell me they think my knots are OK but they have never tested a completed stitch by tugging on it. The comment was,"if you tied the knot right, why the H%** are you checking it?" The video I followed is the PolyFiber video with the blonde girl. Maybe I'm not pulling the stitch hard enough? Any clues why my stitches slip just a little bit? Or am I expecting too much from the cord and knot? jrh
https://www.youtube.com/watch?v=6Y-oU1ikcAA
 
I tried the rabbit and crocodile knot...

But the Staggerwing knot was much easier for me.

 
Your friends are right. Each knot only supports about 4 lbs of the airplane. That's 2 lbs per thread. You're over stressing the knot. The anchor line does nothing other than to make the project move faster and use less rib stitching cord. When you fasten down the tapes over the ribs, the stitches will be "glued" in place.

I would rather stitch than install the #4 screws. It's faster.
 
Those wing bows pulled into the ailerons are my pet peeve. Hardly any bracing in the Aeroncas and they move too easy if you over do the iron. That PA18 video was sad. A total waste of time and materials. Thank you Olibuilt, Skywagon8a, and Larry G. I'm going to try the Staggerwing knot to see if it goes better. I discovered today that I need a tool to pull the stitches with. Maybe a short dowel to wrap the cord around. I'm a bit arthritic and I'm crushing the flat cord in my fist when I pull. Not enough strength in my fingers to pinch the cord flat and pull. I think that is some of my problem. If changing knots or not crushing the cord doesn't work, I'll resort to exterior knots. If the exterior knots don't work for me, there always is .020 safety wire. Just kidding-- I think I'm squared away now. Thanks. jrh
 
I was looking at that video and I found this one. Supercub wing bad recover job. http://youtu.be/PZFkAS8o6Bc

This is troubling. I looked up the "N" number on the FAA site. It is a deregistered amateur built airplane that looks like a Cub that was listed in Big Lake AK. Do any of you Alaskans know this plane? What fabric process was used in the build? It looks like it was just pulled hand tight and painted. Hardly tight enough to bend the tip rib into the aileron. Lots of ??????? about this flying machine.
 
I've seen fabric do that when it gets cold, and the only reason we could come up with (it had happened to this "mechanic" on more than one cover job) was that he didn't follow the steps in shrinking. In other words, he just grabbed the iron and went right to final shrink temp and figured all that nonsense in between didn't need to be done. Every one of his cover jobs looked just fine when it was warm out, but as soon as the temps dropped to freezing, they sagged....just like that one in the video. To my knowledge, he still can't admit that it could have anything to do with it.... There's a reason for the steps, and we tried to explain "strand orientation" etc. to him, but he was sure it was a fault of the fabric.:roll:
John
 
Did you make yourself a pair of rib lacing gloves? A pair of thin leather tight fitting gloves with the finger tips cut off. My wings are Rib "Laced", not stitched. Each lace goes around the top and bottom of the rib. I used the round cord because I wanted the vintage look. I tied the modified seine knot and pulled them as tight as I could. It has been 15 years now and the cords around the ribs are tight as bow strings.
 
No. No rib lacing gloves. That did not cross my mind. I thought stitching and lacing were terms used interchangeably. I don't understand the difference? There are half stitches in the fuel tank bay and they are tighter than the full stitches. but I tied them each individually as square knots with the two half hitches. None of my stitches were tight as bow strings except the starter stitch. They were not slack but I thought they should have been tighter for as hard as I pulled the knot. I used a fish scale and found I was pulling 10 pounds or more before the finished knots slipped. What really concerns me is when I work a needle under a finished stitch and then remove the needle, the cord retains the deformed hump and doesn't go back flat. Push it back flat and it is slightly loose. I also found a 6 foot piece of cord will stretch and spring back about 2 1/2 inches so there is some stretch and spring in the cord. I am wondering if round cord would have been easier to work with than the flat. Initially I didn't expect there to be a difference. I'm going to cut the stitches off that first full rib for the second time and try it again, this time with the staggerwing knot. I'm also going to cut some wood strips and glue them to cardboard to experiment on. The cardboard worked nice to practice stitches on but without a backing the stitches couldn't be pulled very tight. I think the wood will let me pull harder while watching from all angles above and below so maybe I might see why my knots don't pull up really tight.
 
Be careful of over tightening on the original PA-12 ribs. By their design you could actually pull the top and bottom of the rib together thus changing the airfoil shape.
 
You need them tight enough to remove the stretch/ slack from the chord. If you do not cover regularly you need tape or gloves as your fingers shall bleed.
 
I just wrapped my fingers with anti-chafe tape, too cheap to buy special *new* gloves to cut the fingertips off of! Stitched my entire shortwing minus the fin. If you try to pull the cord too tight between stitches you'll end up with them going across the rib at an angle, guess how I know. :-\

I agree about the shrinking steps, I covered my controls and stabs in a hotel room (long story, it is over on the SWPO site), I had done the final shrink on all the parts execept one aileron, wow did it go slack when I walked out of the 72 degree hotel in December to put it in my van!

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Thank you all. I now have two ribs done to my satisfaction. As a newbie stitcher I learned some stuff. As advised the staggerwing knot is easier to tie. The hidden modified seine knot stitch is not that difficult either. I was not pulling the stitches tight enough. The wax in the cord can be a lubricant or it can be more friction to overcome. As of now it is mostly extra friction. It works best for me if I pull until I feel the "spring" in the cord at each step of tightening the knot.That has become my gauge for how hard to pull. Also it seems to make a difference if I pull the cord between the body of the needle and my thumb to flatten it when it gets twisted or crushed. It lays better that way and looks pretty just like the videos. I also learned to watch the knot as the first step of the knot is pulled and starts to tighten. If the loose line starts to bunch up or wrinkle in the knot any at all, stop and pull it left and right to take the wrinkle out and than proceed with the step one tightening. I found after the final step of tightening if the stitch wasn't tight enough to suit, I used a short piece of 1/2 inch wood dowel to wrap the free end around a few times and that gave me a good grip on the line to pull and hold the "stretch" in the line for a few seconds and the stitch would tighten up. I gave away a pair of tight fitting gauntlets when my motorcycle days ended. They would have been good to snip the fingertips and use. I'm watching for the right gloves now. I learned a small change in the angle of the pulls makes a difference in how well the knot and stitch tightens. I also see that after some successful stitches it will become almost natural to pull the knots and stitches tight without thinking about it. When I watched the videos of the ladies tying the knots I think it is deceiving how easy they make it look. I think those ladies have strong hands and fingers and they pull the knots much harder than it looks. It is going well. jrh
 
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