Rib lacing/stitching on challenger 2 Experimental

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Xivier44

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Hello all, i have two questions regarding rib lacing/stitching on my experimental challenger 2 aircraft:

1. Rib lacing was done on my wings but it was only done on the top of the rib, most literature I have found online references lacing through the entire wing from the top to the bottom of the rib. is lacing done is this manner ok? (see picture below)

2. The fabric is not secured against the bottom of the wing, after many hours of flying (upwards of 1000 hours) the fabric on the bottom of the wing can rub against the bottom cross members and weaken the fabric to the point it can be easily puched through. Without taking my fabric off (which is in really good condition) is there anyway i can reinforce the bottom fabric or protect it from rubbing against metal?

The plane is covered by polyfiber system with poly tone paint. Fabric is 15 years old but is in pristine condition only 300 total hours. All fabric passes punch test currently.

20220915_185839.jpg
 

pfarber

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Its an E/AB. There is no right way.

You may want to refer to AC 43-13.1B for all your questions.

But as an mx :

1 ac 43-13. But if its an E/AB then follow the plans.

2 no. You need to do whatever the manufacturer of the covering system recommends for a strength test. LOOKS MEAN NOTHING. DO THE TEST.

The punch test is useless. It is not accurate nor is it approved for certificated AC. That alone should tell you not to rely on it.
 

proppastie

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you perhaps could add a layer of fabric tape over the areas that are rubbing this would be poly fiber fabric tape....add it on the outside of the areas and if these areas are stitched re-stitch through the tapes....you would then re-finish these areas protect and match the color of the fabric.
 
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pfarber

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you perhaps could add a layer of fabric tape over the areas that are rubbing this would be poly fiber fabric tape....add it on the outside of the areas and if these areas are stitched re-stitch through the tapes....you would then re-finish these areas protect and match the color of the fabric.
If i understand the question the metal support is INSIDE the fabric envelope so adding a layer of tape to the OUTISDE is useless. The dope is in no way able to handle any stress. You are relying on the inherent ability of the fabric weave to stop rips. You could sew it in place but that will not stop the abrasion.

The only solution is either secure the fabric to the metal with lacing and add a layer or two of wear tape.
 

proppastie

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Were the fabric being installed new one would have fabric tape as in post 3 over each rib. According to link post 5 it seems you might sand down to the fabric and install the tape.
 

radfordc

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The factory approved method for attaching fabric on a Challenger is with pop rivets.
 

Dan Thomas

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The punch test is useless. It is not accurate nor is it approved for certificated AC. That alone should tell you not to rely on it.
Vast overstatement. From the FAA-Approved AC43.13-1B:

1664500008722.png

It's a good start, as pointed out in the last few lines of that clip.

Page 2-35 of the AC.

Also, from the Poly-Fiber Manual, another FAA-Approved document:

1664500379907.png
1664500587126.png


It's not useless and it's not illegal.
 
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Dan Thomas

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it is also not clear weather a 56 reading on painted fabric is airworthy.....does one remove the finish?.....is it possible a 56 reading is not airworthy?

View attachment 130397
Just use the tester on the painted fabric. If the fabric is that bad, the finish isn't going to save it all that easily. Airplanes I've seen that needed new fabric were so bad that you could pinch the elevator near the trailing edge, for example, and have your thumb go through the fabric.

With the Poly-Fiber process, as long as you don't have the Aerothane topcoat, you can remove a small patch of finish with MEK, do the test, and touch the area up with the original layers of finish. Lots of work even for a small area, but it's better than cutting out a strip of fabric to do the tension test on it. That makes a real mess, and takes much time to fix up. And it won't be on the belly, either; it will be up top where the sun gets at the fabric.

Here's the single-page Instructions for that tester:

Maule Fabric Tester | Aircraft Spruce

Easy to overthink some of this stuff. The FAA isn't going to bother with certification of that tool. How many fabric-covered airplanes are out there anyway? How many crashed because their fabric failed? How many people are going to pay $585 for the tool?

Like the Instructions say, the mechanic's training and experience matter a whole bunch in this matter. People without fabric experience, or training in its application and inspection, can't be expected to make accurate judgements here.

I took the Poly-Fiber course about 13 years ago. I did quite a bit of fabric work in the years before that. Licensed mechanics with that experience have become really rare.
 
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TFF

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I am going to assume that the tester was originally a Maule factory tool, and if used per the manual it’s legal on Maule’s fabric. I need to find an older Maule manual; I just looked up a Maule manual dated 2016 and it says the airplane had Razorback on it. Maule must have an inside because it hasn’t been available for a while. I would want Razorback on every fuselage I could cover and cover wood wings in Dacron. Metal wings or a Bellanca, I would use it all over. Maule must have switched to to because it doesn’t rot. I have never looked at the price for one of the testers, but wow.
 

TFF

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I get that. It’s got a different mission. It was invented for crop dusters because of the chemicals. If you have to leave your plane outside or drag it on bushes, it should be tougher. I know you have to use shrinking dope to get it to tighten up; heat doesn’t do anything to it, of course.
 

Xivier44

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All, thanks for the feedback here. I wanted to highlight a couple points and let everyone know my path forward.

Regarding rib lacing the factory manual specifies pop rivets be used on the top to secure the fabric. I'm not the originally builder of the plane so i had no choice in this decision. I have spoken with poly-fiber and they have no concerns about rib lacing their fabric in this way. The aircraft also has over 300 hours of flying and 15 years.

Regarding the fabric wearing through on the bottom of the wing surface. It seems modern day challenger builds are using tape/foam on the metal cross members of the wing to prevent the fabric from wearing through. My fabric punch tested good and i also took the liberty of punch testing the fabric near the cross members as well to make sure of strength. I spoke with poly fiber and they told me that if the fabric rips in these areas due to abrasion it can simple be patched over using their manual. This seems odd to me but they have had another person with a similar issue to mine do this.

Going forward i will take the time to do frequent punch tests near the cross members to verify strength and lack of abrasion.
 
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