View Full Version : HOW TO TEST FABRIC
09-08-2006, 06:14 PM
What is the proper way to test fabric to see if it's good or not?ceconite/poly stits. thanks for your help
09-08-2006, 06:34 PM
Maule fabric tester
Nathan K. Hammond
09-08-2006, 06:44 PM
The FAA only accepts a pull test from the factory or a lab. But in order to do that, you have to cut off a sample piece of fabric. The Maule tester is the best way to get a good idea of condition in the field.
09-08-2006, 06:54 PM
The proper way, is to cut a 1-1/4' strip of it, unravel the edges to 1" clamp one end and then see how much weight it takes to tear it, as per 43-13. The Maule fabric tester, as I understand it, is not an approved method of testing fabric, although it may give a useful indication of the strength. One thing about the Maule tester, if you just push it against the covering with no prep, you aren't testing the strenght of the fabric, you're testing the strength of the fabric and the finish. Depending on what finish is applied, the finish may throw off the results considerably.
09-08-2006, 07:24 PM
what psi would be acceptable or passing if you are pull on it?pass or fail
09-08-2006, 09:16 PM
If you are buying it, take it outside, remove some inspection plates, and look up toward the top. You are looking for light - a spot here and there is no big deal, but a big grey haze is not good, and zig zag light showing along each pinked tape is really not good. If it is really dark in there, and the finish is ok with you, then you have lifetime fabric. Pull it off only to check the underlying structure.
I know of no one who cuts a 14" swatch out each year, and I won't let a Maule tester anywhere near my finish.
09-09-2006, 12:14 AM
My fabric will break at 45 lbs with a Maule tester when I push against stiff dope....60+ lbs when I dissolve the dope off with acetone. Pull test breaks at 68lbs/inch....clean off the dope!.... :o
09-10-2006, 12:16 PM
I have heard that the Maul tester will give greatly differing results based on where you test. For example, the fabric at the base of the rudder flexes a bunch and as a result will often fail a punch test at this point, whereas the fabric in another location will punch just fine. A useful tidbit to know if you are buying an airplane and want to convince the selling party that his fabric is shot, therefore he should knock 20K off the price. :D
My understanding is the Maul tester is pretty useless.
12-20-2006, 02:32 PM
Seems like any approved fabric testing method would be in the STC paperwork. Look under "Instructions for continued airworthiness". Maybe the older STC's don't address this aspect of things, but newer STC's and field approvals do. I've been told that there is no approved test method for Ceconite & Stits. Punch test may only be good for reference/peace of mind.
Seems to me that you'd want to test the fabric the way it is on the airplane: doped,painted, whatever. The fabric & finish together is a system, and together is what's hanging out there in the breeze subject to failure (god forbid).
12-20-2006, 03:25 PM
I believe a maule tester is approved for cotton or maybe Irish linen. But who uses these anymore? Guess I'm dating myself
12-20-2006, 03:38 PM
43.13 says take off the dope before testing, either by pull test or other means. Tensile strength is what you are supposed to be testing for, and shear strength is only slightly related to tensile, especially with a flexible materal. Maule tester is (unofficially) tolerated as a screening test, only because it is non-destructive. You are testing the fabric for UV damage and mold damage, etc...the dope when stiff distorts even further the relationship between shear and tensile failure.
12-20-2006, 08:45 PM
But isn't 43-13 talking about cotton and linen? These STCs are sort of stand-alone deals. Check with American Champion; they do not use an STC since dacron/dope is approved type data.
Maule testers are very pricey. I have been borrowing my friends punches for the biennial strut test, but am looking for one at the $75 point. I do not think they are useful for Ceconite; all they do is put a small round ringworm on your fabric. I have never heard of one going through . . .
12-21-2006, 02:56 AM
My wings have original cotton on them (1966) .....pull test at 68lbs/lineal inch
punch test at 46lbs with stiff dope,55 lbs with somewhat softened dope, 65 lbs with removed dope....
12-21-2006, 03:14 AM
I for one will not take a piece of fabric off my airplane or take the dope off and ruin my surface just to test it. When it comes to Ceconite (synthetic material) which is what I have used mostly. Assuming the application was done properly in the beginning and it is maintained by patching properly with tapes or patches ect, maybe rejuvinated, what ever is needed at the annual you can get 25-30 years out of fabric. It will not be necessarily pleasing to the eye toward the end but is airworthy. This is assuming that at the cover job everything was done properly, which includes making sure the airframe is properly repaired and preserved so it will last 30 years. I have seen a few cubs with 5 year fabric and the airframe rusting because of poor prep work. Usually with a good fabric job and maintenance the fabric will hold up. Sunlight (ultra violet rays) is what ruins fabric, so if your dope cracks or chips it needs to be repaired to stop the sun from getting to it. Deterioration will usually start at trailing edges of the wing or along stringers or where the fabric makes a tight turn around the structure.
12-21-2006, 04:19 AM
Bob American Champion has written their own procedure for covering their aircraft IAW their Production Certificate, QA manuals and such. American Champion has never used Dope. Pre production certificate days all the aircraft were covered under Superflite's System IV STC and a 337 was written for the cover job. Bellanca on the other hand covered all in Dacron/Dope. I spent some time reading that procedure manual at one time not really that much different than the old Ceconite manual.
12-21-2006, 01:50 PM
I haven't seen the new ACA prpcedure manuals, but my Citabria and Decathlon Service manuals are very clear. They do not follow any STCs that I know of - for instance, Dacron fabric is all that is required. If you use dacron tapes, they must be pre-doped (yuk!). And if you use the blanket method, you must attach using3M EC47 Adhesive, at least in certain spots. All clear coats must be nitrate! If you do all that, there is no STC involved. If original factory aircraft were done under an STC, a copy of that would have to come with the initial logs.
12-22-2006, 10:48 AM
Lunchmoney, you asked the original question as "What is the proper way to test fabric to see if it's good or not?" The Maule Tester is an "Acceptable" as opposed to an "Approved" method of testing fabric. The difference is with with the FAA and Legal Professionals. The FAA Defines a method that is Approved as having all the Supporting Data by reports and tests, submitted by Type Certificate holders. Manufactures, STC holders etc. These are the organizations that are legally responsible if there becomes an issue. "Acceptable Method" puts the burden on the person that is performing the work. Most A&Ps that work with Fabric aircraft are very confident with the results obtained from the Maule Tester for testing Fabric Strength, (Heck I have seen some old timers that can tell if the fabric is good just by pushing it with their finger)... Just remember, cotton being "Organic" is going to get weak with age regardless if it is kept inside or outside. The dacrons will last indefinitely if kept inside, and out of the direct sunlight.
One last area to watch for on an aging dacron job, is cracks along the edges of ribs and structure. These edges will sometimes crack, and sunlight will penetrate these areas. The Fabric will test Good out in the middle of of a bay, but will be EXTREMELY weak along the rib where the bare fabric has been exposed to sunlight. This is the worst spot on an older cover Job. Good Luck, and feel confident with the results you do obtain from the Maul Tester.
12-22-2006, 01:52 PM
Hum, I must be an old timer!
12-22-2006, 07:05 PM
Yeah, me too. I won't let anybody near my airplanes with a Maule tester. Just those stupid struts . . .
12-22-2006, 09:12 PM
You mean Len hasn't gotten you to buy a set of sealed struts? I'm gonna have to talk to him! :lol:
12-22-2006, 09:23 PM
Len has actually aided and abetted my perfidy. He gave me a pair of older struts which get rotated on and off every two years. Len, and I, and others obviously including the FAA, think these struts are perfectly safe if they are checked and corrosion-proofed. However, a number of us are starting to worry about linseed oil peeling off the bare steel surface, thus allowing corrosion. I may convert to some other fluid next summer - I'll pick a very warm day, hoping that all the linseed oil will heat up and roll out, then flush with turpentine.
An aircraft parked outside, not being flown, is a target for discrete corrosion. It doesn't make any difference what you do, the water will get in there, and sit forever in the same spot. Deadly. The cure is daily flight, and/or a hangar.
12-28-2006, 07:02 PM
Have been an IA for about 30 years and find myself to be the old goat that understands at least a little about fabric in this area. I have never seen a case of questionable poly fabric that I didn't already give the thumbs down on other airframe issues. Our local FAA feels all fabric needs the same test (pull) but by the time synthetic rag will fall below minimum, the airframe is generally feeling it's age and in need of help.
I have a Maule tester and feel it works real good, after I have enough heartburn about the rag to put a punch tester to it. I also have an "approved" tester (Seiboth ? or some such name) that punches a 1 square " circle to give a reading, doesn't see daylight as I don't run very fast anymore and it could get my butt whopped.
You have to consider a lot of factors before calling the fabric bad, and be willing to probably expose yourself (as an IA) but cutting chunks out of the airplane yearly is a bit much.
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