Ripstop tape revisited

[pchapman 261]

Has anyone looked at aging and strength issues with modern adhesive ripstop tape?

A few brief tests I did of some F-111 material with adhesive ripstop patches, 18 to 20 years after the patches were made, shows very little if any deterioration of the canopy fabric. This is for tensile tests of the edge of the patch, of the material away from the patch, of the material underneath the patch, and other comparison material of probably similar age. That's the short answer.

My few tests also are of some general interest when considering issues of nylon aging, and the strength of older vs. newer parachute fabrics. All the tests were on F-111 style fabrics, and not zero-P material.

Riggers are all told about how evil adhesive ripstop tape is, and people have honestly reported how they've seen material that tore easily from around ripstop tape that had been applied for a longer time. I myself have seen some pretty ugly and crackly ripstop repairs on 40 year old Para-Commanders. It is often mentioned that patches "may be detrimental" [Parachute Rigger Handbook] to the strength of the material. Or that "some brands" [Poynters I, 7.13] may degrade the material. Some people have said that the glue may be acidic and weaken the nylon in that way.

I have even been told by one authority that using ripstop tape at all on a modern main canopy is a poor rigging practice, and that anything but a temporary patch should be a proper sewn patch, no matter whether a jumper asks a rigger for a quick and cheap solution to the problem of a small hole. The Parachute Rigger Handbook, in contrast, [in 7.7] still allows permanent patching of mains with it, showing sewing around the edges to keep it affixed to slick zero-P material.

Ripstop tape has changed over the years. Poyters I has some specs for a minimum 2.5 oz material, that would have made sense on heavy canopy fabrics, but also in another section mentions that ripstop is 1.5 oz material -- closer to the 1.1-1.2 or so of F-111 style fabrics.

There are only a few threads on this site about ripstop. While some riggers find it a handy tool for quick fixes on main canopies, others would rather do a proper patch in any case. Still, even if one has the skills as a rigger to do a proper patch, not everyone keeps a large selection of fabric colours, while translucent white ripstop works reasonably well with about any colour.

The Parachute Rigger Handbook technically allows ripstop for round reserve canopies (as does Poynter) to a limited extent, but there is a caveat that the manufacturer must allow it, something that is unlikely these days. It is however prohibited on certificated square canopies. There are other parts of the PRH that say not to use it on certificated canopies in general, but that appears to be more about general good usage than what is technically allowed. In any case, just about nobody wants to see it used on a reserve. Still, I have seen ripstop to cover minor wear holes in reserve pilot chutes, as an alternative to completely disassembling the pilot chute for repair or replacing it entirely. While that doesn't necessarily fit with rigging standards, it seems to be a quite practical fix for small areas of damage.


My tests:

I had put a few pieces of ripstop tape on some F-111 style fabric of unknown but likely young age in 1994, and then in 2012 and 2014 did a number of tensile tests. Unfortunately the pieces I had were small, so I couldn't do all the tests I would have wanted. Still, these are tests on 18 to 20 year old ripstop patches.

-- Did anything become extremely weak?
No. Thumb tests didn't show any weakness.

-- Was there an acidity problem?
No.
Bromocresol tests on the original F-111, on the adhesive ripstop tape, and on the F-111 underneath the tape (when the tape was peeled back) showed no sign of acidity.

-- Was there any loss of strength?
If there was, not by a whole lot. We'll get into the tests later after having a closer look at tensile tests that establish baseline information.

Due to the small size of the test samples, the tests with clamps couldn't follow the normal standards of having material surrounding the test area. Almost all the tests were done on 1" wide strips. This does decrease the strength of the fabric, as there is no surrounding fabric to give it support.

a) For comparison to the fabric that had been patched for 18-20 years, I had some plain F-111 that must be at least 10 years old and probably 20 for all I know. Let's call it the "medium age F-111", and assume it could be 20 years old. Pull tests on a larger piece went to an impressive 50 lbs before snapping, or once maybe even 55 lbs.

When cut to a 1" wide strip, it usually breaks at only about 40 lbs. So 40 is still good for a 1" wide strip of fabric.

Comparing the 50+ and 40 values against the old 45 lb military specification for F-111 style fabric, it shows the medium age F-111 exceeds it if tested in the skydiving manner of a larger piece, but no longer meets the spec when tested purely as a 1" wide strip -- perhaps what the fabric manufacturers consider the proper test, although I don't know their methods.

b) Some essentially brand new F-111 style fabric was available, bought just a few years ago from a major retailer. In tests in a larger piece, it went to 65 lbs before tearing. (Even with slightly poorly aligned clamps, where it started to tear progressively instead of all at once, it went to 60.) In a 1" wide strip, it would break at 48 to 52 lbs, usually about 52.

So it is quite a bit stronger than the "medium age" F-111, such as 52 vs. 40 lbs for a 1" wide strip. Nylon aging may be involved, but also very likely improved production processes in the last 20 years.

-- What about the strength of the ripstop tape itself?
1" wide pieces pull tested to 45 lbs. The ripstop was 'new', purchased from a major vendor just a few years ago. So it is better than older F-111, and not quite as good as really modern F-111, and probably was never intended to be of quite the same quality.

-- Is the sudden transition between ripstop reinforced areas and non-reinforced areas a weak point?
From a general engineering perspective, it should be, as one is going from about 3 layers of material that is now stiffer, to a single layer of less stiff material. The flow of stress and strain in the region of a patch will be less evenly distributed and may put extra loads on the material just around the patch. On the other hand, we always deal with areas of different strength and stiffness in parachutes, such as rolled seams and reinforcing tapes on canopies.

-- Let's look at pull tests of patches that haven't been aged::

I put pieces of the 'new' ripstop tape on both sides of a 1" wide strip of the medium age F-111. Pull testing the joint between the patch and the base fabric, it didn't break until 43-45 lbs. (With a slight variation when having the clamps close together vs. the standard 1" apart.)

So that result shows a new patch provides a higher breaking strength at its edges than the base material alone (typically 40 lbs). This wasn't seen with brand new F-111 however, where a test at the edge of a patch gave basically the same strength as the material alone, 52 lbs in more than one test.

I'm guessing that the ripstop reinforces the F-111, so that even when there is unreinforced F-111 that can rip, now there's less unreinforced material that can start to randomly tear between the clamps. If the clamps were a lot further apart, one would expect the breaking strength to go down to the 40 or so for the F-111 alone. While there might be issues with the stiffness of two layers of ripstop tape on F-111 (as mentioned above), that is perhaps more of a problem with randomly oriented forces. When everything is nicely lined up for a standard tensile test, it looks like the patch - at worst - doesn't decrease the overall fabric's strength.


-- Now finally let's look at the old test pieces of F-111 with ripstop tape on both sides, that had been sitting stuck together for 18-20 years:

The reason it is "18 to 20" is that I did some tests 2 years ago and more this year, on the patches I applied in 1994 to some scraps of F-111 material that had been sitting around, and were likely not new at the time.

- Testing the F-111 away from the ripstop tape, it broke at 42 lbs in a 1" wide strip - Good! The basic material hadn't degraded just from being near the ripstop adhesive for years. Strength was similar to other old F-111. (While 42 is more than 40, I doubt there is much statistical significance to the small difference from just one test.)

- Testing the junction between the F-111 and where a ripstop patch had been applied on both sides - For a 1" wide strip, in the one good test I was able to do, it broke at 40 lbs.

(In another case it was about 35 lbs, but that was with only a 1/2" long strip of F-111 past the patch to grip onto, which always lowers the breaking strength. Other tests with new patches shows that not having a full 1" by 1" square of material to clamp to, can reduce the breaking strength from say 40 lbs to 27 lbs for example. Just not enough material to grip it properly -- more like pulling strands off the edge of a piece of material.)

-- Was any of the old material from under the old patch, now 20 years old, degraded on its own?

I was able to strip both of the patch pieces off the F-111 and test them individually. All were 1" wide strips.
- The ripstop tape broke at 40-45 lbs, so not a whole lot less than new ripstop tape (45 lbs).
- The F-111 that had been sandwiched between the ripstop tape and its evil glue for 20 years, broke at 40 lbs.

So given that 1" wide pieces of medium age F-111 were breaking at around 40 lbs, and the edge of an 18-20 year old patch breaking at around 40 lbs, and the F-111 underneath when stripped of the patch also breaking at around 40 lbs….therefore:

The conclusion is that there really was very little deterioration if any of the F-111 due to the adhesive ripstop patch. Nor was there any evidence that any of the material was in any way acidic.


I can't rule out some small strength loss. That would be possible, hidden in the variability of testing with hand held clamps and by the limited size of the test material available, which limited the number of pull tests and data points that could be collected.

I also can't rule out that some adhesive ripstop tape material, from some manufacturers in the past (or the present?) might cause deterioration of the material it is attached to.

Without having adhesive ripstop that is guaranteed to a certain specification, and without much better testing, this doesn't mean that anything goes with ripstop tape. But it does suggest that ripstop tape, even from some years ago, will not necessarily degrade the material it is attached to.

Unrelated to ripstop tape issues , one can also see that older F-111 style fabric can be significantly weaker than brand new fabric.
E.g. roughly 50 vs. 65 lbs in tensile tests of larger areas (old vs. new), or 40 vs. 52 lbs for 1" wide strips. The old standard for F-111 style fabric was for a minimum strength of 45 lbs per inch. So there may be some deterioration due to nylon aging, and perhaps a larger improvement in new fabrics due to improved design & production.

[Boogers 0]

Excellent work!

[riggerrob 558]

Thanks for doing the detailed research ... er cutting through the B.....S.....

I suspect that many of the cases of fabric tearing - at the edge of a sticky ripstop patch - were caused by the salt and grit found in desert soils. The adhesive held the salt in contact with the fabric until it frayed the fabric.

[RiggerLee 61]

A lot of the edge tearing I've seen around old rip stop patches on canopies has been on ones with UV damage. So think about this. The rip stop patch is very stable. The material is stiff. No stretch, no give, no bias stretch. It can't move stretch or give along with the rest of the fabric. You see this in engineering with dissimilar materials with different modulus of elasticity. It concentrates the stress along the edge. And over time as the canopy gets more UV damage and just general wear it becomes the natural fail point. So in the examples I've seen, I suspect that the canopy over all had deteriorated and the strength of the rip stop simple centered the strain and caused the tear in what was just over all weak material.

I know that really isn't a glowing recommendation but at the same time I don't think it deserves the pariah status that some people assign to it. In a since the patch out lived the canopy and the canopy failed around it. I don't use a lot of rip stop because I know how to sew. But I don't see any thing wrong with it.

Lee

Lee
[email protected]
www.velocitysportswear.com

[airtwardo 6]

I use to use it on canopies that had actual burn holes from using pyrotechnics.

I'd cut two pieces 1/4 inch larger than the hole - or slightly larger for bigger holes...both patches would be round or oval shaped as they held better than the square edges.

One on the inside - one on the out...and used a flat spring clamp on the patch for 1/2 an hour or so. They held up really well!

Had a 270 sqft Wizard that must have had 30 or 40 holes patched like that.

~ If you choke a Smurf, what color does it turn? ~

[jimmytavino 16]

yes back in the day we'd always make a 2 sided patch
using the peel and stick repair tape..
You know?? i have a need right now, for enough white ripstop to fix a one inch sized 90 degree tear in a panel, on a 28 foot orange and white cheapo which i bought, a few years ago..
if Anyone HAS some white they could spare, i would be grateful And would put it to a good use... you can reply here or PM me, thanks

jmy

[airtwardo 6]

jimmytavino

yes back in the day we'd always make a 2 sided patch
using the peel and stick repair tape..
You know?? i have a need right now, for enough white ripstop to fix a one inch sized 90 degree tear in a panel, on a 28 foot orange and white cheapo which i bought, a few years ago..
if Anyone HAS some white they could spare, i would be grateful And would put it to a good use... you can reply here or PM me, thanks

jmy

PM me your snail mail I'll get it in the box tomorrow...

~ If you choke a Smurf, what color does it turn? ~

[jimmytavino 16]

done,,,,and done.
thanks twardo

jmy

[airtwardo 6]

jimmytavino

done,,,,and done.
thanks twardo

jmy

In the box & on the way.

So is yours Peter - I forgot I had it in the truck to send ya - until I hit the post office this morning.

~ If you choke a Smurf, what color does it turn? ~

[jimmytavino 16]

Thanks airtwardo..
it arrived in my mailbox a couple of days ago.
and thanks pchapman, for raising the subject of ripstop.
jmy
A3914
D 12122

[pchapman 261]

Just a little update on what I wrote before.

First, I think the ideas others have posted are great, that some of the traditional problems with ripstop are probably:

a) attracting grit that wears the canopy at or under any peeling edge of ripstop
b) adding stiffness to the canopy, so that small patches create localized areas of increased stress on the canopy, which may become important for aged canopies where the fabric strength is already low


Twardo kindly sent me some of his 27 year old ripstop tape, which I did a couple tests on:

1. The glue showed no signs of acidity in a bromocresol test.

2. As I had seen in Poynters, some old ripstop is much heavier than modern ripstop, with a wider box pattern, much like some early parachute fabrics.

One F-111 style ripstop tape ripped at about 43 lbs, while the heavier, stiffer ripstop tape wouldn't rip at 65 lbs and that's as high as I wanted to go with my hand scale. (In both cases, using 1" wide test pieces)

3. The glue on the old ripstop tape had somewhat worn out, so it wouldn't stick well to canopy fabric, making it impossible to do some other tests with the old ripstops.


Just for fun, and unrelated to ripstop tape, I did a couple tensile tests on the top skin of a Stiletto that had 3200 jumps on it before being retired because of repeated rips happening at the topskin seams. One area would only go to 25-27 lbs before tearing, while other bits went to 32-33.

[riggerrob 558]

Also remember that sticky, ripstop tape was originally designed to repair goose-down filled sleeping bags. Then some cheap-skate skydiver used it to repair his "Cheapo" military-surplus parachute and the Western World started to collapse ....
Hah!
Hah!

[airtwardo 6]

riggerrob

Also remember that sticky, ripstop tape was originally designed to repair goose-down filled sleeping bags. Then some cheap-skate skydiver used it to repair his "Cheapo" military-surplus parachute and the Western World started to collapse ....
Hah!
Hah!

Back in the late 70's...my college roommate saved up his cigarette money for a month & bought an extremely WELL used para-plane from some guy that should have cut the lines off and made it a car cover years before.

The shot & a half lugs on the risers were so corroded that I scraped off an 1/8 of an inch of crud with a pocket knife before even trying to polish 'em back 'into spec'.

The risers themselves made a cracking sound when bent the first dozen times we tried to pack it...which was hard enough to do period, all the cells stiff as cardboard & nearly impossible to fit it into the 35.00 contained he bought at a flea market.

The lines did 'look' much better after he ran a zippo up & down 'em a few times to mush down the fuzz.

I came home from class one afternoon to see him modeling the container with smug satisfaction...the main fit 'damn tight' but looked right.

Figured out what he did when I went into the kitchen...on the table was a beach ball size wad of rip-stop tape!

He'd pulled off every inch of it from everywhere in, on or around that canopy...heck even the slider had foot or so on it collectively.

Next day was his first jump on it...which resulted in a short ride on the 26 Navy - but that was because he'd hooked up the R-3's wrong and the whole thing separated on deployment. (pretty cool to watch from 20' away @ 1800 feet!)

Two hours later we were back in the air...and she worked perfectly!

Looked about like a screen door coming down with sunlight glowin' all the holes...and talk a stable canopy in deep brakes!!

He jumped that POS for another 3 years - we kept the ball of red rip-stop hanging from the ceiling like a 'disco ball' for a few years...he hung it on the Christmas Tree as an ornament after graduation...

That is until the cruel, unreasonable, vindictive slut he married....errrr, I mean his wife, made him quit jumping - and threw out everything he had that even smelled like a dropzone.

~ If you choke a Smurf, what color does it turn? ~

[wmw999 2,122]

Sounds like a dream setup -- jumpable gear for cheap .

Wendy P.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)