fibreglass breaks down

[floats]

When I bought my CTSW new there were bumps and dimples (surface of wings, tails and stabilizer were not flat). Now after storing my plane in a heated airport hangar for six months, I noticed that things got worst. The bottom part of the tail is totally out of shape and brittle, It cracks when I touch it. I have the feeling that it would just break if I press a lot. Anybody with that experience. I find it totally abnormal I was not to happy when I got the new plane with non flat wings and tails but the breaking down does not make sense to me.

[Znurtdog]

How old is this airplane?

[mocfly]

Floats,

What was used to heat the hangar?

 

Is this the only portion of the plane to exhibit this type of distortion?

 

Has this part ever been repaired? Or Replaced?

 

Have you sent pictures to Flight Design?

 

 

[floats]

The floor of the hangar is heated but at minimum. The part has never been repaired. I just sent picture to flight design. I have to check the rest of the plane this week end. Very disturbing

[floats]

The plane is a 2007 model. Delivered in April 2007

[Roger Lee]

I have seen this on the underfin and a couple of other places. It probably was not caused by a heated hangar. It is usually caused by water from being left outside or it was just a defective layup and the Rochelle foam collapse. FD should absolutely be included with pictures. The underfin can be re-finished and it isn't a major structural component.

 

I suppose it could also be caused by excessive water from washing mixed with a ph based cleaner/solvent.

[mocfly]

I wonder if a process called laminate hydrolysis occurred? This occurs more in the boating industry, I wonder if your problem was caused by the retention of water on the inside of the structure.

 

Gelkote blisters and more importantly, deterioration of the laminate caused by water is, by now, a well established phenomenon

 

The cause of the problem was well established in the 1987 University of Rhode Island study by Thomas Rocket and Vincent Rose, The Causes of Boat Hull Blisters. In simple terms, what happens is this. Water penetrates the gelkote both as water vapor and as liquid water. Water is particularly good at this due to the small size of the H2O molecule. The gelcoat is a rather poor barrier against water penetration when constantly immersed. The glass fibers assist by acting as capillary tunnels to transport the water molecules into the laminate. Once adjacent to the resin in the gelkote and laminate, the water goes into chemical solution with what are known as "water soluble materials (WSMs)" in the resin in the gelkote and laminate. These WSMs include phthalic acids, glycol, cobolts, mekp and styrene which have not gone to full cure in the hardening process. To varying degrees they are present in all cured polyester resins. Five percent is an excepted norm. In some rare cases the quality of the materials or their application may be inferior causing a higher than normal percentage of water soluble elements.

 

The cause of the problem was well established in the 1987 University of Rhode Island study by Thomas Rocket and Vincent Rose, The Causes of Boat Hull Blisters. In simple terms, what happens is this. Water penetrates the gelkote both as water vapor and as liquid water. Water is particularly good at this due to the small size of the H2O molecule. The gelcoat is a rather poor barrier against water penetration when constantly immersed. The glass fibers assist by acting as capillary tunnels to transport the water molecules into the laminate. Once adjacent to the resin in the gelkote and laminate, the water goes into chemical solution with what are known as "water soluble materials (WSMs)" in the resin in the gelkote and laminate. These WSMs include phthalic acids, glycol, cobolts, mekp and styrene which have not gone to full cure in the hardening process. To varying degrees they are present in all cured polyester resins. Five percent is an excepted norm. In some rare cases the quality of the materials or their application may be inferior causing a higher than normal percentage of water soluble elements.

 

Though this all sounds rather like it is taking place on a "micro-chemical" scale, the affects of hydrolysis of the laminate are visibly apparent. It appears to be effecting all conventionally built polyester fiberglass bottoms that are continually immersed. It is our experience that all boats built with conventional polyester resin and gelkote, show signs of hydrolysis deterioration of the outer laminates after 5 to 10 years of immersion. These signs include "sediment piles" where hydrolysis fluid is exiting the hull, increased moisture content in the outer laminates, reduced resin and glass fiber clarity, reduced resin hardness as well as the obvious and well documented blisters. It should be noted that in the last five years, real progress has been made by some manufacturers in addressing the problem. A switch to using vinylester resin for all or a substantial part of the outer layers of the bottom seems to have been one of the most successful methods to date.

 

So what about these blisters you might ask. Well, blisters form when the flow of water into the laminate exceeds the flow of hydrolysis fluid back out. It is that simple, FLOW IN EXCEEDS FLOW OUT. To understand technically what happens, we have to understand osmosis and osmotic theory.

 

 

There are several stages of inspection one can use to assess hydrolysis damage to the laminate resin.

 

The first is to have a look at the exterior:

 

Identify the size and frequency of blisters. Blister diameter is often associated with the depth of the blister and thus a rough gauge of the depth of the hydrolysis. Though it is risky to place too much emphasis on blister size, bigger blisters mean bigger problems.

Look for cracks, crazing and pin holes. These may be letting lots of water into the laminate and accelerating hydrolysis.

Look for sediment piles. These typically indicate active hydrolysis, even though there may be no blisters

Look for hull distortion. Distortion may be the result of lower laminate rigidity from hydrolyzation

Take moisture meter readings. It is hard to draw conclusions from high moisture readings on the surface, but low readings usually rule out the possibilities of ongoing problems.

One cannot, however gather sufficient information from the exterior to define the extent of the hydrolysis damage or to design a repair. For this, one has to look into the laminate interior.

 

 

THE "WINDOW" INTO THE LAMINATE:

 

To look into the laminte, we need a "window". The window is a shallow grind, about 6" - 8" in diameter through the bottom paint and gelkote, into the laminate structure of the boat. .

 

First the repairer chooses a site for the window. The site should be in an unreinforced area, usually 1-2 foot below the waterline. A small hole is drilled all the way through to determine the full thickness of the unreinforced laminate.

 

The repair then grinds away the bottom paint to expose the gelkote. He visibly inspects the surface, takes a moisture meter reading, a BarCol hardness reading and zeros out a depth gauge. He then grinds through the gelkote, exposing the first layer of fiberglass laminate. Again the surface is visibly inspected. A dry laminate in good condition is clear, dense and bright. White glass fibers, porosity and opaque resin are associated with hydrolysis. Blisters can be clearly seen if present. Moisture and hardness are again tested. The depth gauge is used to give the thickness of the successive layers. The process of grinding and inspection continues until a layer is reached that is considered in good condition, unaffected by water.

 

The repairer analyzes the data, using his experience and understanding of the repair process to design a repair. Primarily, the repairer is trying to determine how much damage has occurred to the laminate and how far he will have to go into the laminate to make a repair.

 

The depth of laminate removal is a critical decision point in the repair process. As a general rule, the laminate will be of poor quality at least to the base of the deepest blisters. Usually, there is some hydrolyzed laminate below this level, but eventually, a solid, resin rich, laminate with little residual moisture is usually (but not always) reached. We often see all of the exterior matt (outside of the first woven roving) is in poor condition.

[floats]

Thnaks for your analysis. I have not seen the inside of the fin yet. But from the outside it does not seem to be osmosis. I am a ocean sailor more than a pilot and I had to repair osmosis on sailboats in Spain. I had to clean all bislters one by one and let them dry for several months to get the fibreglass fully dried before recoating. In this cas there is no blister, I do no see delamination but the whole fin is now soft like a rubber piece. I do not see it as repairable. We shall see how FD replies to this. CT planes should obviously not delaminate. Although my plane is on amphibious it never stays in water and did not even land on floats (on water) for the last two years. I have never seen anything similar not on a plane nor a boat. I have seen some osmosis ont he CTSW at the location where the tiedown strap provided by FD attached to the tail boom. After leaving the strap under rain, blster have developped around it.

[floats]

I have seen this on the underfin and a couple of other places. It probably was not caused by a heated hangar. It is usually caused by water from being left outside or it was just a defective layup and the Rochelle foam collapse. FD should absolutely be included with pictures. The underfin can be re-finished and it isn't a major structural component.

 

I suppose it could also be caused by excessive water from washing mixed with a ph based cleaner/solvent.

 

It is washed once a year with the product provided originally by FD. In addition to the kinking the strange thing is that the fin became soft and rubbery.

[FastEddieB]

Are you continuing to fly the plane? I would be hesitant to.

 

I really think Flight Design needs to step up and address this.

 

Give them every chance to make it right. But failing that, it may be time to get lawyers involved.

[floats]

I would not fly it without the fin. Particularly on floats where you lose longitudinal stability. On Cessnas they add a fin of that type when they install floats. Will see what FD says..

[mocfly]

We almost had to replace ours a couple years ago, and they are pricey. I can't remember what they quoted but I do remember it was North of 1000.00. The other factor was the long lead time.

 

I am very curious to learn what the guys at Flight Design have to say about this obvious laminate failure.

 

Please keep us informed.

 

 

[Roger Lee]

The carbon fiber on the inside should be fine. This should only be where the foam collapsed and messed up the gel oat and paint. From the pictures this is one of the bad ones. Many just had small areas affected.

[floats]

The carbon fiber on the inside should be fine. This should only be where the foam collapsed and messed up the gel oat and paint. From the pictures this is one of the bad ones. Many just had small areas affected.

 

Did FD consider this as a design or fabrication failure and replaced it ?

[mocfly]

Roger,

Does flight design use foam or honeycomb? Do you know if they use an autoclave during the cure cycle? Obviously they use the vacuum bag technique. Curious if the use pre-preg or do manual lay ups.

[Tom Baker]

The core is foam. Lay ups are by hand and post cured with heat, but I don't think it is in an autoclave. Something alkaline got to the foam on this sub fin.

[Tip]

Does water splash up on the tail when landing?

[Roger Lee]

There would have to be a lot of splash it to make any difference. There would have to be enough water to get in there to really soak things and possibly be a repeat scenario. Not too likely. This foam collapse can happen even without water. Things like this happen at times when planes are left out in the rain and or the drain holes are clogged. Using a hose to wash the plane and allowing water to directly enter that area. It's not always just about the water itself, but the PH level.

[floats]

No water splash as the plane has not been in water for two years. Did not fly at all last year for float problems

[PDG]

I have had my underfin repaired 3/4 times and mine was just plain fiberglass with a few stiffeners. (no carbon fiber and no foam filler!)

 

Paul

[Ed Cesnalis]

I believe that my fin as well as my wheel pants are fiberglass and not carbon fiber.

[WmInce]

I have had my underfin repaired 3/4 times and mine was just plain fiberglass with a few stiffeners. (no carbon fiber and no foam filler!)

 

Paul

 

Paul,

 

Do you have a protective skid attached to the underfin?

[PDG]

No protective skid. The repairs were for similar damage as the OPs, one when the $#^# drain hole clogged, and when I broke it off getting it out of the mud in the tiedown.

 

Paul

[floats]

How easy is it to remove. I see some tape inside the tail where there is no access. Do the four screws attach to the fiberglass or there is some kind of reinforcement inside

[Roger Lee]

The under fin is only held on by the 4 screws on the upper sides. Then you need to disconnect the wire if you have the fin light. Easy to remove and and easy to repair. I always tape the edges when put back in place including the screw holes to prevent water entry.