Stitts Polyfiber Age

[flybuoy]

How old is too old for wings covered with Stitts Polyfiber? Looking at a nice 140, but the wings were covered 33 years ago. The plane is now hangered, but I don’t know how it was stored before 2019. Should I be more concerned about the fabric or the wing structure?

[beaverbill]

I think that there is no hard and fast answer to the question of simple fabric age. I have had personal experience with fabric that was still airworthy well beyond 40 years. And that was on an airplane that spent all of its life outdoors in Northern Alaska to the best of my knowledge. On the other hand, an airplane that sat in the Arizona sunshine probably wouldn't have near the life expectancy. The quality of the original silver UV protectant paint job would figure into things as well. I'd have someone with experience have a look at the fabric if that would give you peace of mind. All that being said, 33 years doesn't seem particularly concerning to me.

[4004]

I agree with Beaverbill. There is an FAA test by cutting a strip of fabric and making a pull test on the uncoated fabric sample. Also, there is punch test that should be done at an uncoated fabric area- this has been generally accepted over the years but if the aircraft has been painted, one can cheat the tester.
Since you're looking, these test may not be welcomed. However, if you kinda want a "quick look" to see if the fabric was done right, as Beaverbill pointed out, the most critical item in a recovery is putting enough UV protection coats on.
In a darken hangar, nite time or doors closed, remove an inspection plate from under the wing, then using a bright light held directly to the top fabric surface on top of the wing just above the hole, look thru the inspection plate hole to the underside of the top fabric to see how much lite comes thru. If UV protection wasn't done right, it will be evident. Granted, this test is highly subjective, based on experience, etc.

[6643]

As far as I know there is no life limit and no prescribed testing procedures for polyester fabrics such as Ceconite, Stits, Polyfiber, and Superflite. Punch testing and pull testing (which is destructive) were for cotton and linen coverings.

[4004]

Respectfully, suggest that one review the entire Section 3 of AC43.13-1B CHG 1 pg 2-33 (my copy, there may be a later change) then Pag 2-34 "Fabric Testing".
I go back to the old Grade A cotton and nitrate dope, with bed mattress ticking doublers around the fuel tank caps fabric.

I also spoke with Ray Stits, hemself, in the 1960s, concerning a problem I was having and he talked about how robust his polyfiber was. "Strip the enamel ( I had used before the days of poly paints,etc) with remover, wash the fabric good and recoat. I'm not trying to sell product but you may be wise in opening the wing so you can inspect throughly, then recover".' !IIRC exact quote"! I recovered the wings!!

My main emphasis was about using the light, just thru-in the other as education.

[6643]

I have the same version. Para. 2-34, Fabric Testing, is on page 2-35 of my copy. My point is, nowhere does it say "you must perform this test."

It does say "Mechanical devices used to test fabric by pressing against or piercing the finished fabric are not FAA approved and are used at the discretion of the mechanic to base an opinion on the general fabric condition."

and "If the fabric tests in the lower breaking strength range with the mechanical punch tester or if the overall fabric cover conditions are poor, then more accurate field tests may be made." ("may" is not mandatory!)

At that point, you're talking about cutting a strip out of the covering and testing it to destruction. So, "if the overall fabric cover conditions are poor" you might as well skip ahead and strip the wing and recover it. Who wants to cut a hole in a wing that is in poor condition, then patch it back up if it passes the pull test? Then, you have wing in poor condition with a patch.

[meloosifah]

As everyone seems to be saying, the fabric may or may not be good - have an AP familiar with fabric look at it. My wings were recovered in ‘92 I think - they are in GREAT condition.

The bigger issue is what’s inside. Tripacers really need recovering periodically because they rust! My wings still have cloth covered wires and there is no easy way to replace. What is the state of the aluminum? Do you have adequate inspection plates to see both sides of the spar?