Testing wing fabric, how to test your ultralight aircraft wings fabric.

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When was the last time you did maintenance on your K & N Airfilter? Is you filter safety wired? Click here to see how to clean and safety wire your airfilter!

How to test your ultralight aircraft wings fabric.

How can one tell if their old sails are still airworthy? My sails are a bit bleached, but seem quite strong. Is there a home built device that will test  the fabric?

Sail condition can be quite deceiving unless a proper test is performed. The fading of the sail definitely means degradation has occurred. If the blacks are grey and the reds are close to pink, the sail is shot and needs replaced.

However, there are chemicals available to rejuvenate the colors which can mislead the eyeball type tests, since the faded colors means a bad sail but so-so colors don't mean a good one.

The other concern is the thread used in the sail. Quality sails will use thread that is immune to UV compared to the basic dacron material. A sail made with non- stabilized thread will fail often in the seams while in use.

Often , an accident involving the wings, will make large tears in the sail, other than puncture tears. Any sail which exhibits such damage is not airworthy. A good sail will tear only when severely punched by jagged material from the accident, not due to the shear loads from the impact with an object.

The best place to check a sail is in an existing slit where battens enter pockets. If the existing slit can be propagated with little effort the sail is shot. Another method is to give the sail a good solid poke with a finger in a suspect area. If it tears, you will not hurt a 'good set of sails'.

Maule Fabric testerMaule Fabric tester
Belt tension tester, can be purchased
with special end for testing fabric.

A new piece of material will require almost more effort than you can muster to get the point to penetrate the material, the tester will be stopped as the 45 degree area tries to go through and the actual penetration will make a sound about like a 22 cal 'short' going off in a small pistol.

Whenever I sell the tester, I include a sample of new cloth to allow some comparative testing.

An example may help

Once, many years ago, when an MX was still hot stuff and I knew who owned the Quicksilver company, I and two friends were standing under the wing of an MX that had just flown into the local airport to be hangared there.

This plane was originally owned by one of the guys there with me. He commented that the new owner had left the plane outside for the past year and we all thought it was just good luck that no storm damage had occurred to the plane. I had lost several plans to a freak wind storm just two years before.

The owner had gone into my hangar to get a Coke from the machine. As the three of us stood there looking the plane over, the third person, not the previous owner asked "I wonder what shape the sails are in?". We then discussed the finger-poking method of testing them. Since the sail pattern was a Lakeland Custom, mostly white, it didn't show the typical fading that the darker colors did when left out for a year.

I noted that the sails were probably not in real good condition after being outside for a year and just as I was about to say, don't my friend did. And his whole fist went through the sail!!

There we were, standing under the wing, with a major hole in it. It surprised me and both guys with me. We then discussed how to tell him that the plane he just flew in, now had a rather large hole in one wing panel. As it turned out, he too, had concerns for the sail, and thanked my friend for 'checking' it for him. Luckily, I had a stock Lakeland Special MX sail in stock, and had it installed by the next afternoon.

The proper tool for doing sail tests is a modified belt tension tester. It has a calibrated spring scale and a special end which has a 1/16 inch diameter flat area, with a 45 degree taper above it. The intention is that the small diameter will penetrate the sail and the tapered area will not go on through, just the small 1/16 flay point. This does put a small hole in the sail, but such a hole in many areas is more than acceptable.

When using the tester, it is also possible to press until a minimum reading is obtained and not press until the hole is made. Typically, a poor sail can be diagnosed by the faded colors and the tester will push through easily without even getting much of a scale deflection.

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You may not believe it, but there are people that believe that duct tape will work to patch and even hold their sails together. This email was sent to me from a person on one of the many Weedhopper talk groups. Please read it and remember it each time you inspect your sails.

Hello Everyone,
I would like to share a story with all Weedhopper Pilots and other ul interests. It was A day I'll remember for the rest of my life. I was at a local fly in 4 years ago and there were 3 Weedhoppers to show up. One of which was a Weedhopper model C in "DESPERATE" need of new sails. The sails were dry rotted and had about half a roll of duct tape on them. After the pilot landed, people couldn't help but notice the condition of the sails as they were a tragedy waiting to happen. An uncle of mine at the fly in offered the guy to take his Weedhopper home on a trailer. The guy refused the offer of my uncle's and stated " He had been flying them like this for years"

After the pilot had eaten at the fly in, He decided he was gonna take her
back up. The plane had a 503 Rotax, He got in and put on his seatbelt, and
started the engine. At this time the crowd was gathering to watch him take
off including his son. The pilot held the homemade brake down while he pushed the throttle to full power. I was standing directly behind him. He was off the ground in 60 feet. As he climbed to approx 80-100 feet the unthinkable

Everyone was screaming in terror. The plane hit the ground in a straight nose down position, motor buried itself about half a foot in the wet field. The pilot was unconscious, hurt very badly. Most people, thought he was dead. Bleeding like a stuck hog, His right leg was over his head. The impact was so severe it pushed his ankle through A PAIR OF LEATHER COWBOY BOOTS.
He sustained a broken  leg, severe concussion, shattered ankle, fractured skull, and extensive back injuries.

The pilot survived the near fatal crash after months in the hospital. Doctors amputated his right ankle. All of this over dry rotted sails.

Please Everyone, Take my advise!!!!

Top of wing faded,
fabric is not safe to fly on!

Bottom of wing bright.

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