Wing Leading Edge Crack

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Derek
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Re: Wing Leading Edge Crack

Post by Derek »

My experience with composite is it ages better than metal or other materials. Certain elements within composite are susceptible to UV radiation breakdown and must be covered with paint or something like that. Other than that 40 year old composite should be as strong as new, no? Composite boats, for example, age better than wood or aluminum ones.
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Colin
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Re: Wing Leading Edge Crack

Post by Colin »

Boats are what prompted my question for source. I believe that the composite material of the spar is good for long past my own lifetime and probably that of my children. A lot of the skin I know I need to protect with paint, and there are composite boats out there which became salvage because they sat in the sun without getting new paint every ten years (or, I suppose, "as needed"). But protected from the sun and heat, what is going to break down?
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Re: Wing Leading Edge Crack

Post by rwtucker »

We would be well informed by a materials scientist specializing in fiberglass matrix, epoxy resins, etc. Such a person might be able to comment on the chemical and mechanical causes of degradation. Microscopically, I would think that every flex of the composite material results in a mechanical change. The questions are how much, to what effect, and to what cumulative effect.

I also recall our discovery that Diamond did not take measures to prevent galvanic action in some areas where composite meets other materials. Would this not be life limiting? I have read Diamond's 4 January 2006 "no life limitations applicable to major structural components" but what does this mean other than that the statement is valid until it is not? Additionally, some of the composite may not qualify technically or legally as "wing spars & load bearing structures." Don't know.
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Re: Wing Leading Edge Crack

Post by Diamond13 »

From this photo, I would say that is cosmetic, some simple body work (with epoxy based filler) and an area 'blow-in', buffed, ready to go.
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Re: Wing Leading Edge Crack

Post by ihfanjv »

Colin wrote:
Composite does not age well in the elements.
What is your source for this? Examples?

And do you mean even when protected by paint, as with on the Diamond planes?
rwtucker wrote:
I also recall our discovery that Diamond did not take measures to prevent galvanic action in some areas where composite meets other materials. Would this not be life limiting? I have read Diamond's 4 January 2006 "no life limitations applicable to major structural components" but what does this mean other than that the statement is valid until it is not? Additionally, some of the composite may not qualify technically or legally as "wing spars & load bearing structures." Don't know.
There is no long term history on composite aircraft to set precedent for how they will hold up over time, especially in the elements. One case of the water intrusion and electrolysis issue has been documented here:

viewtopic.php?f=8&t=3203&hilit=electrolysis

...and you see this kind of water intrusion damage to most composite aircraft that live outside on the ramp.

And this thread with the following quote:

viewtopic.php?f=8&t=4247
Keith M wrote:Interesting. My Da40D had to be reweighed when it was 4 years old, after installing a TAS600, and it had put on 13 Kg. The TAS600 was 6 Kg, but I never did find out where the rest of the weight increase came from. Perhaps it is moisture.
...discusses the water-weight gain of composite aircraft over time. If these aircraft are becoming water logged, that is not a good thing over time.

Absent sever corrosion, aluminum aircraft can generally be refurbished. With composite, it could be that there reaches a point where the effort to repair the composite consumes the value of the aircraft - or that repairs cannot be done at all.

The real problem with composite is that it is difficult to know what is really happening under the surface. The leading edge crack looks like it could be caused by delamination of the two halves of the wing - but there is probably no way to know without destroying the wing to find out. But, a cause might be improper build up of the wing during construction, like the "failure to use enough adhesive" problem that led to the "skin spar void" AD on pre-2008 the DA40 fleet which seems to be largely ignored.

As far as comparing fiberglass aircraft to boats, it is probably a fair comparison. But, good boat builders have learned to do things to keep water out of the composite that aircraft manufacturers have not. For example, for any hole that goes through the composite on a boat, a good boat builder will enlarge that hole, then seal the inner walls of the hole with epoxy or resin, then re-drill that hole so that the inevitable water that goes through that hole cannot seep into the laminate (the water is sealed out by the solid resin hole). In composite aircraft, they just drill through the laminate and leave the core exposed to the air and pass-through fitting - that might be partly a consequence of the metal-mesh-in-composite bonding that requires the mesh to be bonded to metal fittings through the composite, but then that creates the electrolysis issues mentioned in the linked post above. Boeing and Airbus have probably figured out ways to deal with these issues, but they have invested billions on solving these problems, and it looks like that knowledge has not trickled down to the small composite aircraft market.

These are just practical realities, and these are just engineering problems. People are notoriously good and solving engineering problems.

Time will tell if we see 30+ year old composite aircraft on the ramp! I hope we do!
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Re: Wing Leading Edge Crack

Post by cgray80244 »

blsewardjr wrote:I'm in the process of my first annual of my new-to-me 2003 DA40. During our work today (I'm doing an owner-assist annual), we discovered a six inch or so crack on the leading edge out near the lights. I can't recall seeing this before. I've reviewed the forum for posts on cracks, but didn't see any that matched this location. I'd appreciate any advice you might have. Thanks. Bernie

I had a similar crack on my 40. I went around and around stressing about it. It was just the paint. After much research I learned that the paint becomes brittle. My crack occurred when a well meaning helper pushed on the leading edge. Long story short...most likely your paint guy can get it handled.


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Re: Wing Leading Edge Crack

Post by Colin »

good boat builders have learned to do things to keep water out of the composite that aircraft manufacturers have not. For example, for any hole that goes through the composite on a boat, a good boat builder will enlarge that hole, then seal the inner walls of the hole with epoxy or resin, then re-drill that hole so that the inevitable water that goes through that hole cannot seep into the laminate (the water is sealed out by the solid resin hole). In composite aircraft, they just drill through the laminate and leave the core exposed to the air and pass-through fitting - that might be partly a consequence of the metal-mesh-in-composite bonding that requires the mesh to be bonded to metal fittings through the composite, but then that creates the electrolysis issues mentioned in the linked post above.
I would love to see that happen on my plane. I think I would even throw a grand at that problem.
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Re: Wing Leading Edge Crack

Post by blsewardjr »

I had Glenn Lawler at Southtec Aviation look at it. His view is that it is non-structural and can be easily fixed. I plan to do so when I get the plane painted. Highly recommend his business.
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Re: Wing Leading Edge Crack

Post by Lance Murray »

Weight gain is not exclusive to composite aircraft. Airplanes of all types seem to gain weight over the years. Just like the Pilots.
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Re: Wing Leading Edge Crack

Post by Rich »

Weight gain due to moisture absorption certainly hasn't happened to my 15 year old DA40.

The first 13+ years it was based in the Seattle area, which is plenty wet. For 8+ years it was in a hangar and the last 5 it was parked outdoors. Even the hangar it was in wasn't really good at keeping it dry, as often, during rainy periods, there was water on the floor and condensing on everything inside in the winter. And, of course, when traveling it was often parked out in the rain from time to time. In summer of '15 it was moved to this much dryer climate and has been in a hangar since.

The plane was delivered at about 1701 pounds, as weighed by Diamond. Then in 2004 the extended baggage was added by Diamond and they weighed it again, coming it at 1709 pounds. Over the years I added this and that, as far as I could tell adding something like 4 pounds. Then last spring I added the thinner gear to increase MLW, which should have removed about 3 pounds. So I figured I was at about 1710 pounds. After this mod the plane was weighed (with me observing) and it came in at 1711 pounds. And no, I didn't tell the shop the expected result, this is what it came in as.
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