Dangerously stupid information in Vintage Airplane

[Aaron Novak]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.