Aircraft fabric testing, ultralight aircraft sail fabric testing,  how to test fabric on ultralights light sport aircraft.

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Student pilot to irate instructor: "Think about it. I navigated through a boiling fluid swirling around a rotating sphere that is hurtling around a fusion reaction source at thousands of miles per hour. This system is moving in a circular motion around a black hole at who knows what speed, while the space it takes up is expanding. And I bounced 6 inches. 6 MEASLY INCHES! You need to get off my back, man"

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Underside of wing is bright the
way the fabric should be.

Top side of wing is faded indicating the fabric has suffered UV damage and is NOT airworthy!

Ultralight aircraft fabric testing,  fabric testing for ultralight aircraft.

Ultralight Aircraft need protection for U.V. - ultra violet rays!




The pilot had been working on the ultralight aircraft for about an hour; he then took off, flew for about 10 minutes, and landed. About 10 minutes later, after he had donned a jacket, the pilot took off again far another local flight. Minutes later witnesses observed the ultralight in level flight and at about 100 feet above ground level (agl). They then heard a loud report and saw the aircraft descend rapidly and strike the ground. The aircraft was destroyed and the pilot was fatally injured. 

The wind was calm and the sky was clear at the time of the accident. Weather was not a factor in this occurrence.

The pilot trained and was licensed to fly ultralight aircraft in 1983, and was trained and licensed as private pilot in 1985. He did not maintain an up-to-date pilot log book, but there was evidence that he had about 200 hours flying experience. He had not flown for several months before the accident flight.

The aircraft was manufactured in 1982, and the accident pilot purchased it, ready to fly, in 1983. No maintenance history of the aircraft was found; however, a sales receipt indicated that the dacron fabric wing sails were replaced in 1986.

The aircraft had been kept in a barn on occasion. It was also reported to have spent long periods outside, unprotected from the elements and in direct sunlight, most recently during the several months prior to the accident. There was no evidence that the wings had been covered when the aircraft was kept outside.

The quicksilver wing consists of an upper surface formed by a Dacron fabric wing sail stretched over the wing frame. The sail is composed of several Dacron panels, sewn together. On inspection, the upper surfaces of the sails were found to be severely faded when compared to the lower surfaces. Further, the dacron fabric was weak and tore easily when stressed.

A sample of the dacron wing fabric was examined by the University of Alberta's Textile Analysis Service. The fabric specialist determined that the fabric had been degraded by sunlight. The tests determined that the tensile strength of the unfaded fabric sample was about 120-130 lbs/in and the faded sample's strength was about 25-40 lbs/in.

There are no Transport Canada regulated design, construction, or assembly standards established for the Quicksilver ultralight aeroplane. Ultralight aeroplanes are exempt from airworthiness certification requirements, and neither a Certificate of Airworthiness (C of A) nor a Flight Permit is required.

The Airframe Maintenance Schedule in the aircraft operating manual recommends that the sail be covered when not in use and that the wing fabric should be removed, inspected and replaced if necessary every two years or 400 flight hours.


The dacron fabric sail was not maintained in accordance with the manufacturer's recommendations. Because the dacron fabric was often exposed to the elements and the sun's ultraviolet rays during the eight~ years since the sails had been replaced, it was severely weakened and it tore when it was exposed to aerodynamic flight loads.


1. The dacron fabric sail was not maintained in accordance with the manufacturer' 5 recommendations

2. The dacron fabric sail was severely faded and weakened by ultraviolet light.

3. The dacron fabric sail tore when it was exposed to aerodynamic flight loads.

4. The pilot lost control of the aircraft when the sail tore, and the aircraft crashed.

Causes and Contributing Factors

The dacron fabric sail was not maintained in accordance with the manufacturer's recommendations, and was severely weakened by exposure to the sun's ultraviolet rays. The dacron fabric tore when it was exposed to aerodynamic flight loads.

This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board, consisting of Chairperson, John W.. Stants, and members Zita Brunet and Hugh MacNeil, authorized the release of this report on 10 May. 1995


 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 had 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 did not hurt a 'good sail'.

Maule Fabric tester - A fine quality tool to test fabric covered aircraft for minimum FAA requirements without removing or punching holes in fabric. Also used to test struts for inside rusting as required by FAA on all Piper aircraft with struts.
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.

Your sails a little faded? Are they safe to fly on? Click here for more information!

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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