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Thread: Dangerously stupid information in Vintage Airplane

  1. #1
    FlyingRon's Avatar
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    Dangerously stupid information in Vintage Airplane

    Why on earth do we have an article on fabric punching in Vintage Aviation. Fabric punching is specifically disallowed by the FAA for finished dacron fabrics and Poly Fiber officially disparages it as well. Punching is a relic of the old cotton fabric days (and not even the die hard vintage guys are still using cotton fabric).

    Nice looking guy on page p 37 though

  2. #2
    rwanttaja's Avatar
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    Quote Originally Posted by FlyingRon View Post
    Why on earth do we have an article on fabric punching in Vintage Aviation. Fabric punching is specifically disallowed by the FAA for finished dacron fabrics and Poly Fiber officially disparages it as well. Punching is a relic of the old cotton fabric days (and not even the die hard vintage guys are still using cotton fabric).
    Ron, do you have a reference to the FAA disallowing punching on dacron. Need something to show my A&P this annual....

    Ron Wanttaja

  3. #3
    FlyingRon's Avatar
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    Straight out of acceptable methods AC 43-13.1B 2-34 FABRIC TESTING
    4. FABRIC TESTING. Mechanical devices
    used to test fabric by pressing against or
    piercing the finished fabric are not FAA approved

  4. #4
    Jim Hann's Avatar
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    Quote Originally Posted by FlyingRon View Post
    Straight out of acceptable methods AC 43-13.1B 2-34 FABRIC TESTING
    4. FABRIC TESTING. Mechanical devices
    used to test fabric by pressing against or
    piercing the finished fabric are not FAA approved
    FR, is that why you didn't include the entire sentence or the rest of the paragraph? How do you test Dacron fabric in an FAA approved way?

    2-34. FABRIC TESTING. 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. Punch test accuracy will de-pend on the individual device calibration, total coating thickness, brittleness, and types of coatings and fabric. Mechanical devices are not applicable to glass fiber fabric that will easily shear and indicate a very low reading regardless of the true breaking strength. 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. Cut a 1-1/4-inch wide by 4-inch long sample from a top exposed surface, remove all coat-ings and ravel the edges to a 1-inch width. Clamp each end between suitable clamps with one clamp anchored to a support structure while a load is applied (see table 2-1) by add-ing sand in a suitable container suspended a few inches above the floor. If the breaking strength is still in question, a sample should be sent to a qualified testing laboratory and breaking strength tests made in accordance with American Society of Testing Materials (ASTM) publication D5035.

    NOTE: ASTM publication D1682 has been discontinued but is still referred to in some Aerospace Material Speci-fication (AMS). The grab test method previously listed in ASTM D1682, sec-tions 1 through 16, has been super-seded by ASTM publication D5034. The strip testing method (most com-monly used in aircraft) previously listed in ASTM D1682, sections 17 through 21, has been superseded by ASTM publication D5035.
    Jim Hann
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  5. #5
    FlyingRon's Avatar
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    Well since I deal with PolyFiber I use the guidance in their manual and assume that as long as the finish is in good condition that the underlying fabric is. Once you lose the finish with dacron, the weave is likely suspect.

    Punching is inherently unreliable.

  6. #6

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    The internet is sort of the wild west and the advice that you read is worth what you pay for it.

    One entertaining aspect of what you read are the folks who publish statements that can be summed up as "I think I know a lot about the one narrow topic so my knowledge must apply to every other topic that people post about." You find folks with this life view in other activities, not just aviation. Unfortunately the world just isn't that simple.

    So the official FAA guidance seems to advise that the punch test tool can be used with caution to determine whether further investigation should be pursued. Seems pretty reasonable as a first screen for condition, combined with other observations of the material being scrutinized.

    There are still some airplanes out there covered with cotton. Pitts Specials are an example. The factory did not switch to the new fabrics until the late '80's. And today there are fewer and fewer mechanics who know what to do with those airplanes at annual time. I think that the article is valuable for the owners of those airplanes and the mechanics that they work with.

    Best of luck,

    Wes
    N78PS

  7. #7
    One entertaining aspect of what you read are the folks who publish statements that can be summed up as "I think I know a lot about the one narrow topic so my knowledge must apply to every other topic that people post about." You find folks with this life view in other activities, not just aviation. Unfortunately the world just isn't that simple.


    Wes,
    You are so right about the internet! I have owned a 1974 Aerotek Pitts S-2A for over 20 years , it has never been recovered and I can assure you with absolute certainty that it was factory covered with Ceconite fabric/dope finish .

  8. #8

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    My 1974 S-2A is serial number 2068. It came to me as Butyrate dope over Ceconite. But what always has puzzled me is why the factory build the early S-2B's with dope over cotton. And I am told that they got a bad batch of Grade A and had to bring some airplanes back and redo them. In the last few years I have seen two flying B's that are still wearing their original Grade A cotton. I can only guess that at annual time the IA looking at the airplanes think that the fabric is still OK..... 30 years later.

    Best of luck,

    Wes

  9. #9

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    I spoke to 2 experienced shops, one of which does deal with a number of fabric surfaces. They both have the Maule punch tester, and as I read the FAA note you give , it seems that the a&p has some discretion as to how they determine fitness. I doubt if many owners would like to hear that the mech wanted to cut out a piece of the upper wing fabric.
    They told me that ceconite really seems to last a long time.
    There are still a few who use cotton. It can last 20 years, ( a lady at Smithsonian told me it was on her plane) if hangared and out the the sunlight.

  10. #10
    FlyingRon's Avatar
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    Cutting a hole is a valid test, but it's not what the manufacturer recommends. The recommendation is to keep the finish service in good order and as long as you do so the underlying weave will last forever. If you allow the surface to deteriorate the underlying weave is suspect and you can punch it all you want and there's no guarantee of anything.

    All this punching and other fabric lore dates from the old cotton/linen days. Polyester is a different beast. As already pointed out there are underlying differences from surface prep of whatever parts of the airframe that you are going to apply this to, to how you stick it down, to how you apply the UV protection coats, it's only once you get above these functional layers that you can even begin to think about safely deviating from the manufacturer's recommendations with regard to the color coats.

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