Punch test?

[Michael Horowitz]

the punch test on fabric... are the results a go/no-go decision, or
can an A&P make a determination as to how long the covering will last
based on the test? - Mike

[RST Engineering]

I argue that the punch test is go-nogo, but there are those who argue that a
lab test may be required for marginal fabric. My answer is that "marginal"
is like being a little pregnant. IT passes or it doesn't.

It says NOTHING about how long the fabric will last. That is a function of
environment -- hangared or outside, humid or dry, hot or cold...

Jim



"Michael Horowitz" > wrote in message
...
> the punch test on fabric... are the results a go/no-go decision, or
> can an A&P make a determination as to how long the covering will last
> based on the test? - Mike

[Michael Horowitz]

Jim - I'm looking at a fabric a/c with 25 year old fabric. A recovery
will run into 5 figures. Assume we don't know the entire history of
this coating; no log entries stating "under cover from X to Y" so I
have to guess at how long we have remaining on the fabric.

Any suggestions on how that can be done? - Mike




"RST Engineering" > wrote:

>I argue that the punch test is go-nogo, but there are those who argue that a
>lab test may be required for marginal fabric. My answer is that "marginal"
>is like being a little pregnant. IT passes or it doesn't.
>
>It says NOTHING about how long the fabric will last. That is a function of
>environment -- hangared or outside, humid or dry, hot or cold...
>
>Jim
>
>
>
>"Michael Horowitz" > wrote in message
...
>> the punch test on fabric... are the results a go/no-go decision, or
>> can an A&P make a determination as to how long the covering will last
>> based on the test? - Mike
>

[RST Engineering]

No way in hell other than extrapolating 100% strength to where the fabric
punches right now and drawing a straight line through 25 years to the
ultimate fabric strength limit. What kind of fabric is it?

Jim

[Michael Horowitz]

Dacron/Ceconite - Mike

"RST Engineering" > wrote:

>No way in hell other than extrapolating 100% strength to where the fabric
>punches right now and drawing a straight line through 25 years to the
>ultimate fabric strength limit. What kind of fabric is it?
>
>Jim
>

[[email protected]]

The punch-test gives an approximation of the tensile strength of the
fabric. It has nothing to do with how long the fabric will last.

New Grade 'A' cotton ('standard' weight; about 6oz per square yard)
must have a minimum tensile strength of 80 pounds, equal for both warp
& weft. When applied to a wing or control surface, once the strength
degrades by 30% the fabric should be replaced. (The test is normally
done to the upper surface; that which has the most exposure to
sunlight.)

For comparison, new 2.7oz/yd polyester (ie, Dacron) has a tensile
strength of about 85 pounds, 3.7 oz about 130, although those numbers
may vary slightly from one manufacturer to another. When warp & weft
are not equal you must use the lower strength for your calculations.

Other than fiberglas, all fabrics used for aircraft covering are
subject to degradation. And even WITH fibergals (ie, 'Razorback') the
airframe UNDER the fabric requires periodic maintenance, making claims
of 'Lifetime' coverings a bit iffy :-)

The fact a 20 year old covering measures high-green on a strength test
is no guarantee the thing won't fall apart next week. There could be
corrosion, dry-rot or rampant rusting going on under that slick,
always-hangared fabric skin.

-R.S.Hoover

[Cy Galley]

No!

"Michael Horowitz" > wrote in message
...
> the punch test on fabric... are the results a go/no-go decision, or
> can an A&P make a determination as to how long the covering will last
> based on the test? - Mike

[RST Engineering]

Bob...cut me some slack...


> wrote in message
oups.com...
>
> The punch-test gives an approximation of the tensile strength of the
> fabric. It has nothing to do with how long the fabric will last.

That is the absolute truth. The condom is only so strong from manufacture;
how many times can you use it before it breaks catastrophically?




> The fact a 20 year old covering measures high-green on a strength test
> is no guarantee the thing won't fall apart next week. There could be
> corrosion, dry-rot or rampant rusting going on under that slick,
> always-hangared fabric skin.


Which was not the question. The question was the fabric itself. The
remainder of the airframe is quite another matter.

Jim

[[email protected]]

RST Engineering wrote:
> Bob...cut me some slack...
>
----------------------------------------

Okay. But I wasn't aware you needed any.

My msg was in response to Mike's. The fact it appeared after yours is
an artifact of my ISP, which has taken as long as 24 hours to upload a
message to a Usenet newsgroup.

My closing para was to make sure Mike understood that the condition of
the covering is not the only criteria for re-covering.

-R.S.Hoover

[RST Engineering]

> RST Engineering wrote:
>> Bob...cut me some slack...
>>
> ----------------------------------------
>
> Okay. But I wasn't aware you needed any.

Moi? {;-)


>
> My msg was in response to Mike's. The fact it appeared after yours is
> an artifact of my ISP, which has taken as long as 24 hours to upload a
> message to a Usenet newsgroup.

Got it.


>
> My closing para was to make sure Mike understood that the condition of
> the covering is not the only criteria for re-covering.

Absolutely true.


>
> -R.S.Hoover
>

Jim

[Ernest Christley]

Michael Horowitz wrote:
> the punch test on fabric... are the results a go/no-go decision, or
> can an A&P make a determination as to how long the covering will last
> based on the test? - Mike

Mike, I haven't read RAH in a few days, and I'm just now catching up,
but your question has drawn a emphatic response from Jim Weir, R.S.
Hoover, AND Cy Galley that you should replace the fabric.

I've been reading this group for a while now, and think I have learned
who knows what they're talking about and who might blow a little smoke
now and then. I would have to say that this is a unique situation.
Dude, if you value your hide, you better ground that plane until the
fabric is replaced no matter how much it cost.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

[[email protected]]

Ernest Christley wrote:
> Michael Horowitz wrote:
>
>> the punch test on fabric... are the results a go/no-go decision, or
>> can an A&P make a determination as to how long the covering will last
>> based on the test? - Mike
>
>
> Mike, I haven't read RAH in a few days, and I'm just now catching up,
> but your question has drawn a emphatic response from Jim Weir, R.S.
> Hoover, AND Cy Galley that you should replace the fabric.
>
> I've been reading this group for a while now, and think I have learned
> who knows what they're talking about and who might blow a little smoke
> now and then. I would have to say that this is a unique situation.
> Dude, if you value your hide, you better ground that plane until the
> fabric is replaced no matter how much it cost.
>
Just because the fabric is 25 years old does not mean that it needs
replacement.
It means that it needs a good close inspection, which includes punch
testing.
Is the dope cracked anywhere? Anywhere there is a crack there could be
UV damage.
Check for ringworm, pretty much the same thing as cracking. Get inside
it on a bright day and see where the light comes through the fabric.
Look for loose spots where the glue may have come loose. Squeeze the
training edges of the control surfaces and see if there is any
crunchyness. That will indicate corrosion.
Discoloration of the dope along metal parts will indicate rust.

If it all seems good, buy it with the understanding that it may need
recovering in the next few years and the price should reflect that.

But like all old aircraft, it's not so much age but condition.


Dave

[RST Engineering]

BULL****. DO NOT put words in my mouth. Nowhere did I say that the fabric
should be replaced. NOr did Bob or Cy. We simply said that a punch test
should be taken at face value. If it punches green, fly. If it punches
grey replace it. NOWHERE did we say that the fabric should be replaced.

Jim




"Ernest Christley" > wrote in message
om...
> Michael Horowitz wrote:
>> the punch test on fabric... are the results a go/no-go decision, or
>> can an A&P make a determination as to how long the covering will last
>> based on the test? - Mike
>
> Mike, I haven't read RAH in a few days, and I'm just now catching up, but
> your question has drawn a emphatic response from Jim Weir, R.S. Hoover,
> AND Cy Galley that you should replace the fabric.
>
> I've been reading this group for a while now, and think I have learned who
> knows what they're talking about and who might blow a little smoke now and
> then. I would have to say that this is a unique situation. Dude, if you
> value your hide, you better ground that plane until the fabric is replaced
> no matter how much it cost.rt them (and ourselves)."

[Cy Galley]

How can one take a ONE word answer to the question... "will the punch test
tell how much longer the fabric will last?" and turn it into replace the
fabric is beyond me!
--
Cy Galley - Chair,
Air Emergency Aircraft Repair
A Service Project of Chapter 75
EAA Safety Programs Editor - TC
EAA Sport Pilot

> wrote in message ...
>
>
> Ernest Christley wrote:
>> Michael Horowitz wrote:
>>
>>> the punch test on fabric... are the results a go/no-go decision, or
>>> can an A&P make a determination as to how long the covering will last
>>> based on the test? - Mike
>>
>>
>> Mike, I haven't read RAH in a few days, and I'm just now catching up, but
>> your question has drawn a emphatic response from Jim Weir, R.S. Hoover,
>> AND Cy Galley that you should replace the fabric.
>>
>> I've been reading this group for a while now, and think I have learned
>> who knows what they're talking about and who might blow a little smoke
>> now and then. I would have to say that this is a unique situation. Dude,
>> if you value your hide, you better ground that plane until the fabric is
>> replaced no matter how much it cost.
>>
> Just because the fabric is 25 years old does not mean that it needs
> replacement.
> It means that it needs a good close inspection, which includes punch
> testing.
> Is the dope cracked anywhere? Anywhere there is a crack there could be UV
> damage.
> Check for ringworm, pretty much the same thing as cracking. Get inside it
> on a bright day and see where the light comes through the fabric.
> Look for loose spots where the glue may have come loose. Squeeze the
> training edges of the control surfaces and see if there is any
> crunchyness. That will indicate corrosion.
> Discoloration of the dope along metal parts will indicate rust.
>
> If it all seems good, buy it with the understanding that it may need
> recovering in the next few years and the price should reflect that.
>
> But like all old aircraft, it's not so much age but condition.
>
>
> Dave

[Ernest Christley]

Cy Galley wrote:
> How can one take a ONE word answer to the question... "will the punch test
> tell how much longer the fabric will last?" and turn it into replace the
> fabric is beyond me!

Quite right. I read WAY to much into your postings. I was being to
clever by half.

I began reading to much between the lines with Veedubber's comment that
it just isn't the fabric, but also the supporting structures underneath
that have been hidden for 25yrs.

I explained to Veedubber that I'm a scaredy-cat about what Father Time
and his insidious sidekick Water Vapor will do to a structure over the
years. Personally, I'd replace the fabric, but Veedubber informed me
that there are devices that can ultrasonically test for hidden rust and
defects. (Is it safe to assume that questionable wood can also be picked
up?)

Cy, Jim and Veedubber, please accept my apologies.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."