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View Full Version : Dangerously stupid information in Vintage Airplane



FlyingRon
10-24-2013, 07:09 PM
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

rwanttaja
10-24-2013, 07:58 PM
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

FlyingRon
10-24-2013, 08:11 PM
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

Jim Hann
10-25-2013, 01:58 AM
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.

FlyingRon
10-25-2013, 05:35 AM
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.

WLIU
10-25-2013, 05:48 AM
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

Jerry Petro
10-25-2013, 08:48 AM
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 .

WLIU
10-25-2013, 11:54 AM
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

Bill Greenwood
11-02-2013, 09:24 AM
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.

FlyingRon
11-02-2013, 10:02 AM
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.

Aaron Novak
11-04-2013, 09:00 AM
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.


Ron,
Relying on the condition of the fabrics finish to determine the condition of the fabric takes a couple of assumptions into account:

1-That the fabric is not recieving any kind of UV from the back side (i.e. through a cockpit)
2-(the big one) That the person doing the finish actually followed the STC.

You can have a beautiful finish that lacks UV protection (lack of silver coats etc), so unless YOU did the work yourself to know for sure the STC was followed, what is one left with to test their fabric?

Tom Downey
11-04-2013, 09:41 AM
You can have a beautiful finish that lacks UV protection (lack of silver coats etc), so unless YOU did the work yourself to know for sure the STC was followed, what is one left with to test their fabric?Unless you know what fabric system you have there is no way to tell its test method.

The first paragraph in the vintage mag article makes the assumption that the fabric system is not covered by an STC which will have the requirements for testing. That is why the FAA has never approved the Maule fabric tester for Ceconite systems.

two of the most popular systems do not require a silver UV blocker, It is formulated into their base coat. So just because you do not see a silver layer does not mean there isn't any uv blocker there.

Stewert system (Ecofil) prior to top coat.

Aaron Novak
11-05-2013, 09:26 AM
Unless you know what fabric system you have there is no way to tell its test method.

The first paragraph in the vintage mag article makes the assumption that the fabric system is not covered by an STC which will have the requirements for testing. That is why the FAA has never approved the Maule fabric tester for Ceconite systems.

two of the most popular systems do not require a silver UV blocker, It is formulated into their base coat. So just because you do not see a silver layer does not mean there isn't any uv blocker there.

Stewert system (Ecofil) prior to top coat.

Tom,
I understand the non-universal use of silver, thats why I said silver etc. My question is then, how is the mechanic to determine the condition of the fabric if not for punch testing? Obviously the condition of the finish cannot be used unless he knows for sure of the system used and that it is not recieving rouge UV from the backside. He probably is not going to tear off a piece from the wing for testing. Honestly the only thing left seems to be some kind of punch test. Put yourself in this situation, you are asked to do an annual on an aircraft you have never seen before, but is covered with polyester fabric and some sort of finish. How do you determine the condition of the fabric?

WLIU
11-05-2013, 11:45 AM
One likely answer is that modern finishes fail before the fabric so external observation of the condition of the finish is all that is needed.

The Grade A and dope covering has the characteristic that the cotton is attacked by moisture and bacteria (mold) in ways that modern polyester fabrics are not. And the cotton absorbs the dope. When the finish is observed to be failing, that means that both the dope and the cotton are failing.

In contrast, my experience and observation of modern fabrics and finishes leads me to believe that the finish, be it dope or Cooper Superflite, has the failure mode of losing its bond to the fabric, leaving the fabric at full strength initially. If the finish is not repaired, then synthetic fabrics will start to degrade, but usually the owner responds to the ugly looking situation by repairing the finish. Or if the finish and fabric is old or too ugly, ripping off the old fabric and recovering. My Pitts S-2A was recovered when the work of fixing the butyrate on Ceconite got to be too much hassle. Looked at some sections of the old fabric and an informal pull test between two guys seemed to indicate that the fabric was fine but the dope had simply gotten brittle and the dope to fabric bond was failing.

So perhaps we do not need any testing of modern finishes at all beyond the old mark 1 eyeball. When it looks bad, fix it. Skip messing with testers.

Best of luck,

Wes
N78PS recovered with Cooper Superflite

Aaron Novak
11-05-2013, 10:06 PM
One likely answer is that modern finishes fail before the fabric so external observation of the condition of the finish is all that is needed.

The Grade A and dope covering has the characteristic that the cotton is attacked by moisture and bacteria (mold) in ways that modern polyester fabrics are not. And the cotton absorbs the dope. When the finish is observed to be failing, that means that both the dope and the cotton are failing.

In contrast, my experience and observation of modern fabrics and finishes leads me to believe that the finish, be it dope or Cooper Superflite, has the failure mode of losing its bond to the fabric, leaving the fabric at full strength initially. If the finish is not repaired, then synthetic fabrics will start to degrade, but usually the owner responds to the ugly looking situation by repairing the finish. Or if the finish and fabric is old or too ugly, ripping off the old fabric and recovering. My Pitts S-2A was recovered when the work of fixing the butyrate on Ceconite got to be too much hassle. Looked at some sections of the old fabric and an informal pull test between two guys seemed to indicate that the fabric was fine but the dope had simply gotten brittle and the dope to fabric bond was failing.

So perhaps we do not need any testing of modern finishes at all beyond the old mark 1 eyeball. When it looks bad, fix it. Skip messing with testers.

Best of luck,

Wes
N78PS recovered with Cooper Superflite


Wes,
I see where you are coming from. I have however seen finishes that looked perfectly fine, on polyester that was in poor condition. One example was covered using stitts material, but the person had used a third party UV blocker in the polytone instead of the silver in an effort to save weight. Push too hard and your finger would go right through it, looked great though.

FlyingRon
11-06-2013, 05:29 AM
Correct, and punching solves that problem how? You're in a world of hurt if someone cut corners on the process and unless you can remove a piece of fabric and do forensic analysis on it (as well as to whether the underlying surface was prepped right), you're always got a suspect job. Such is the perils of buying a homebult. Similar to not knowing much what's under the surface on a fiberglass ship. At least with a certificated ship, you hope that the people did the maintenance in an approved fashion.

I_FLY_LOW
11-06-2013, 08:33 AM
At least with a certificated ship, you hope that the people did the maintenance in an approved fashion.

Just like airliners never crash due to poor maintenance...

Tom Downey
11-06-2013, 09:35 AM
I agree with Wes, 100% The fabric (ceconite) will out last any of the paint systems in use today. Cracking is the first sign of the paint system failing, when you see the system is starting to crack, it is time to recover the craft.

Tom Downey
11-06-2013, 09:41 AM
You make the assumption that there is an approved testing for the ceconite system, and thus an approved method of using the punch test. when neither exists.

A better test is to apply a strip of tape to the surface, and pull it off, if the top coat comes off with the tape, the system is not protected and needs to be replaced.

Aaron Novak
11-06-2013, 10:08 AM
You make the assumption that there is an approved testing for the ceconite system, and thus an approved method of using the punch test. when neither exists.

A better test is to apply a strip of tape to the surface, and pull it off, if the top coat comes off with the tape, the system is not protected and needs to be replaced.

Tom,
What I am saying is that the mechanic needs to use some common sense and logic when determining the condition of the fabric. Not saying the punch test is the answer, however I do not feel a pure visual test of the finish is the answer either. Like anything, it will be a combination of tests and factors that determine condition. Maybe a modified punch test could be developed? Different tip design, loads etc that would be more appropriate to polyester.