Fabric attach methods that are legal

[Bruce Caldwell]

Looking for a 337 that approves either rivets or PK screws for a 46 BC12-D. Had planned on rib stitching but looks like that is not approved. I tried the fabric clips from A/C spruce but they don't fit. HELP!

Bruce Caldwell
N95893

[3Dreaming]

Re: Fabric attach methods that are legal

http://www.taylorcraft.org/docs/Taylorcraft%20Wire-replace%20with%20rib%20stitching.pdf

[Edwin Otha]

Re: Fabric attach methods that are legal

I don't know if it would be "illegal" or even meet the major repair standard. What ever you use it needs to be installed and maintained to a standard. Should you stitch it and the stitches break, it would not be in an airworthy condition.
The minor alteration will need to be logged as accomplished. Should any issue arise, you will need to be prepared to explain your position of this minor repair. If you do not log this, the discussion will be about the violation of FAR 43.12.
Should the FAA not agree with your conclusion of this being a minor repair, they would then ask for the major repair documentation to be provided.
EO

[Hank Jarrett]

Re: Fabric attach methods that are legal

What we NEED is one of the tools that made the Taylorcraft wire! The tool could be adjusted to make the clips any pitch needed (the Taylor wire was NOT the same pitch as Martin wire that is sold today, which is why the new wire doesn't fit). SOMEBODY out there must have at least a photo of the machine they use to make this wire.

Hank

By the way, looks like bending the Martin wire doesn't work very well. Looks terrible under the tapes.

[Bigdog]

Re: Fabric attach methods that are legal

I have a friend who owns a spring manufacturing company that is capable of bending the wire. I didn't have the specs but a while back he made a sample from a picture. I let it drop when someone posted they had a stockpile of correct wire. Given that the wire can be reused my impression was the stockpile could last a while. I've got L-2's so don't need it for myself but I can pursue it further if the stockpile runs out and I can get the specs, i.e. wire size/material, bend geometry and spacing.

[Mark Bowden]

Re: Fabric attach methods that are legal

Hi

In '56 some one in the flight school put 39911 on her back. Repairs were done on a 337 as appropriate for all the work needed.

Relevant to this issue, new ribs were installed and stitched. New ribs = stamped ribs.

It flew fine from this way for 40 years prior to the restoration and since '99 flying another 19 years this way.

The 337 doesn't prove that it is minor repair, but provides supporting evidence that it is approved.

Recovering of wings which includes stitching of formed ribs, "all work performed according to Manual 18 of the C.A.R."

The photo is from 2006 when an internal issue unrelated to rib stitching need to be redone which shows the rib mix from the 1956 repair.

Mark

[Mark Bowden]

Re: Fabric attach methods that are legal

Hi,

I had one of my engineers make an engineering drawing of the Taylorcraft wire form a sample of NOS Taylorcraft wire sufficient for an owner produced part. I also have a copy of the the Luscomb rib wire drawing which is basically the same part but pitch is different.

I also found/spoke with a company that makes CNC wire bending machines that could do this as well but felt that the wire diameter was a bit small. Like Greg, I dropped it too when it appeared that some NOS was still available.

Happy to revisit & assist if there is sufficient interest from the group.

Mark

[Guest]

Re: Fabric attach methods that are legal

In case it makes a difference I have no more NOS wire left.

I had about 2200' ten or twelve years ago and sold the last roll this year.

Dave R

[N96337]

Re: Fabric attach methods that are legal

Just went through this with the local FSDO and according to them, the "standard" is rib stitching and going back to the "standard" is a minor alteration, so only a log book entry required.
As far as being unairworthy with broken stitches, it's not any different than anything else.
John

[astjp2]

Re: Fabric attach methods that are legal

Looking for a 337 that approves either rivets or PK screws for a 46 BC12-D. Had planned on rib stitching but looks like that is not approved. I tried the fabric clips from A/C spruce but they don't fit. HELP!

Bruce Caldwell
N95893

Its in the tech references section. I also got rib lacing approved, because it was an alteration to the type design....Tim

[Scott]

Re: Fabric attach methods that are legal

Looking for a 337 that approves either rivets or PK screws for a 46 BC12-D. Had planned on rib stitching but looks like that is not approved. I tried the fabric clips from A/C spruce but they don't fit. HELP!

Bruce Caldwell
N95893

HI Bruce
Never able to resist the fabric attachment debates, here are some facts to hopefully help you make a decision:
1. None of the methods you mentioned, or martin wire, were factory original, with the possible exception of lacing, because it was used by the factory on all BC12D ailerons (same basic structure as the wings) and the tail feathers. Stamped ribs were also approved to be used as replacements for truss ribs and fabric attached by stitching.

2.If you apply the criteria, either FAA or Transport Canada, to determine if an alteration will be considered major or minor, it is difficult not to conclude that lacing is a minor alteration and therefore requires no extraordinary approval (assuming it is done in accordance with acceptable data, like your covering manual and AC43.13). I have not done the assessment for rivets or screws but I suspect you can reach the same conclusion (my personal view is that you risk ending up with double holes in the rib flanges but I guess if the proper care is exercised it's doable).

3. The polyfiber manual suggests that substituting lacing or other method for the original method from the manufacturer needs FAA approval. However I interpreted that as their opinion, and I don't interpret that the STC is invalidated through this minor modification.

4. Wire was used on BC12D's because it reduced labour and therefore costs, not because it was better from and airworthiness, durability, weight, appearance or other reason. In fact if you look at your ribs, I suspect you will find a large number of the holes for the wire are torn (keyholed) so reusing wire will require drilling
new holes or repairing all of the damaged ones. This is why one of the supporting rationale contained in the published 337's for lacing is that lacing represents a solution to the keyhole rib damage problem. see here:

So, regardless of which method you choose, you've got some decisions to make. For me the decision was straight forward. I wanted the best solution from an airworthiness, durability and appearance perspective and I considered my sweat equity to be free. Given these criteria lacing is the clear choice, and I had zero problems obtaining a new C of A from Transport Canada with lacing entered in the work report as a minor alteration.

I have no specific experience with the FAA but there appear to be many examples out there of US registered BC12D's with laced wings (including mine before I started the restoration). It seems that some have been done using the minor repair philosophy and other with supporting 337s. I think it is largely up to you and your AI to decide how you do the certification or if you prefer, speak to your FAA office. I haven't heard of anyone experiencing a hassle with this but perhaps others have?

The actual job of lacing the wings, while time consuming, is not particularly complex and, as stated, it is all standard practice including taking proper care to protect the lacing from abrasion, ensuring the spacing of the stitches is such that clearance from structure, cables etc. is maintained, and resist pulling the lacing too tight! (cuz if you're over zealous the ribs will flex).

hope this helps
S
https://2.bp.blogspot.com/-W0UZ5Ehe7...0/DSCN6059.JPG

[astjp2]

Re: Fabric attach methods that are legal

Scott, its a Major per the FAA, that is why there are field approvals for changes...its a major structural change for attaching the skin of the aircraft. Stamped ribs are supposed to have the taylorcraft wire, truss ribs were laced. It was the subject of several IA seminars in Alaska. Tim

I also have an old 337 field approval for rib lacing for N3576T on my old computer. I may have posted it on here somewhere if I can find it.

[Scott]

Re: Fabric attach methods that are legal

My point was that if you work through the criteria (FAA or TCCA) for what constitutes a major alteration, fabric attachment doesn't qualify, and some aircraft altered in this way do have paperwork i support of a major and many don't. (and nobody seems to be having problems) and irrespective of which method chosen, other than factory wire, you need to make a determination of major or minor (in other words the major/minor debate is a wash... just choose the best attachment method for you)

Fabric is not structure. There are no alterations to structure in substituting lacing for wire. Lacing is the standard for attaching fabric as has already been stated. The reasons for using alternatives were all production related.

Bottom line is this really isn't a big deal in the whole scheme of things. There are many more critical issues to deal with in restoring a BC12D.

[Edwin Otha]

Re: Fabric attach methods that are legal

When talking with the FAA ASI's each of them have an opinion, sometimes differing. I always ask them for the FAR related to the subject. As far as rib stitching no one so far have supplied an FAR to substantiate that any rib lacing deviation is considered a major alteration. Their opinions vary, but no regulation has been produced. Their advise was to log it as a minor alteration. Should a differing interpretation arise, the log entry was made for the work performed and the subject will about the major/minor alteration. I have never had an ASI be concerned with this method of entry on many different subjects. I'm not as wise as some of you, I've only been at it since Jimmy Carter was in office.
During subsequent inspections should there be a problem the fabric attachment, this becomes a maintenance item and repaired.
The FAR's are written in a way that they never tell you what is allowed, but always tell you what's prohibited. I interpret them the same way, if not prohibited it is allowed.
EO

[Miguel]

Re: Fabric attach methods that are legal

What about PK screw or pop rivet and washer?
Miguel.