Metal back to Fabric Questions

[maintenanceguy721]

Hey Everyone,
Young A&P here and just soloed in my 140 four weeks ago. I have a 47' Cessna 140 and just started a wing recover project. Upon removing the fabric I noticed numerous holes drilled in a line on the spar caps and numerous extra holes drilled on the ribs in line with the fabric attachment rivet holes. There were also holes drilled in the leading edge skin. There is no mention of the wings ever being metalized or de-metalized back to 1959 (As that is as far as the logbooks go). So it has been flying like this for about 4000 hours and 66 years with no evidence of cracks, stress fatigue, or corrosion. Is this an issue or is there some corrective action required? I am hoping for some guys who have done metal back to fabric conversions to chime in and offer some factual advice.
Thanks,
Nathan

[8126]

Odd there are no replies to this question, everyone must be on Facebook. Embarrassing enough, I've been absent from this web site for quite awhile. I'm not an engineer but logic would seem to dictate that the strength of the spar cap has been reduced by those holes. It reduces the cross section area of the cap that sees compression and tension loads. The holes also create stress risers from which cracks might propagate. You note that the wing has survived quite a long time in this state but that would not make me comfortable. I'd find a DER and pose the theoretical question and see what he says. Then I'd ask if it is practical to repair the spar. It's possible that using those holes to rivet a doubler on might be acceptable. I shudder to think how many airplanes are flying like this. It's a major alteration to remove the metal skins and would require appropriate documentation.

[5149]

Nathan, Tim Mix here, I am an A&PIA and I personally would NOT fly these wing any longer! When the metal was removed from the wings it no longer has anything to "distribute the stresses of the holes" that are drilled in the spar caps. Each hole especially if they are close together are going to be a stress riser. I personally had a set of metalized wings that I was going to "take back to fabric" and when I open them up and saw the problems, I literally cut them up and parted them out. There are plenty of good wings that you can throw fabric on and not have to worry about. You have to remember these airplanes are 80+ years old. I'm not on here much but more on FB. But if you have any question let me know.
Cheers!
Tim
NC2404V
541-399-2731

[6643]

Tim's comments are pretty damning, and deserving of consideration. Another path would be to have a DER look at them. He may be able to come up with a way to reinforce them, probably by riveting a strip along the top and bottom of the spar. If so, his work is approved data and you can use that to fill out a 337 to record the repair.

What is this "facebook" of which you speak?

[V529]

What is this "facebook" of which you speak?
[/quote]

A place to spend (waste??) an inordinate amount of time at/on.