Composite cracks. Serious or cosmetic?

[oceanplexian]

I have had some hairline cracks on my wing that have been there a long time, but are starting to get worse. It seems like this area probably encounters a lot of flex and it's just cosmetic.  Are there any hidden dangers or things that might be occurring that are not visible (delamination)?  Or is it just a matter of sanding it down, sealing and repainting?

Before (~2020):

 

Current (2024):

 

Close up, it's about large enough to get a fingernail into and ~4 inches in length:

 

 

[FlyingMonkey]

I have a lot of small cracks all over my airplane.  The paint on these airplanes is a bit brittle, and seems to crack along areas that have flex, or where a very stiff area meets an area with more flex. However, my cracks are very light hairline affairs that look like paint cracks, yours are significantly wider and deeper.  And I don't love the puckering/buckling along the edges. 

I asked Flight Design USA about this years ago, and they said if there's any concern that it's more than paint cracking, you should sand a small area (about the size of a quarter) in the middle of the crack down to the composite so that you can determine if the composite is cracked or compromised.  If the composite's good you'll probably want to sand out the whole area and re-paint, and if the composite is cracked that starts a new conversation regarding how to repair it.

For reference here's an image of one of my cracks, this is very close-up it's about 2" long:

[Anticept]

Those areas flex a lot.

The filler agent flight design uses to smooth out the surface between fabric layups and paint is relatively brittle. Far less than the fabric or paint.

Because of that, over time the filler cracks and the paint will eventually crack with it.

I see no threads sticking out in your photos so I believe it is cosmetic. You can do a quick and dirty check with a pick and pick away at the paint but don't dig into it and create damage.

The proper fix is as recommended by FD, sand the area down and if you don't see any delam or  cracking in the fabric, recoat with USC icing filler and then paint over.

You will probably need to get some USC icing from a body shop, its not sold in small quanities. Best filler there is though.

WARNING: this area has an anchor to the fuselage. There is a remote chance this could be a symptom of a bigger problem and it should not be ignored; early detection is key, in composites the sooner you fix a flaw the SUBSTANTIALLY cheaper it is.

[FredG]

My main concern with paint cracks like those is the entry of water with subsequent lifting of the paint.  I would want to seal them, one way or another.

[oceanplexian]

Thanks, a lot of helpful info in here. I live in the desert southwest and the plane lives indoors in a hangar, so I think it's more likely mechanical due to constant flexing than chemical or water. I'm pretty obsessive about using PH neutral soap and distilled water when I occasionally clean it.

I looked inside the crack and I can see composite material but it's not "pushing up through the crack" if that makes any sense. The area around is pretty solid but I'm going to run back to the hangar and try to tap around it to see if anything sounds off. It seems like sanding-inspecting-filling is probably route I'll end up taking. 

[FlyingMonkey]

On 1/4/2025 at 3:13 PM, FredG said:

My main concern with paint cracks like those is the entry of water with subsequent lifting of the paint.  I would want to seal them, one way or another.

Not just paint damage, but water (particularly alkaline water) in the can cause foam core collapse in the composite areas that are foam filled.  And that is *really* nasty.

[FlyingMonkey]

On 1/4/2025 at 6:08 PM, oceanplexian said:

Thanks, a lot of helpful info in here. I live in the desert southwest and the plane lives indoors in a hangar, so I think it's more likely mechanical due to constant flexing than chemical or water. I'm pretty obsessive about using PH neutral soap and distilled water when I occasionally clean it.

I looked inside the crack and I can see composite material but it's not "pushing up through the crack" if that makes any sense. The area around is pretty solid but I'm going to run back to the hangar and try to tap around it to see if anything sounds off. It seems like sanding-inspecting-filling is probably route I'll end up taking. 

Like Corey said, jam a toothpick or dental pick in there and wiggle it around a bit.  If it catches or you can feel a seam, sand it out and check.  It's probably cosmetic, but if it's not, it's really no joke.