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Peeling paint on composite surfaces.

Posted: Sun Jan 23, 2022 12:53 am
by gregorygoodwin
Hello everyone,
As some of you may have read, Qatar Airlines and Airbus are in a disagreement over the peeling paint on Qatar's new A350's. If you have seen photographs of the paint, it looks like the paint has bubbled or blistered up, cracked and left voids that exposed the underlying anti-static mesh and composite surfaces. Airbus has stated that this is not a airworthiness issue.
I have seen this same problem on our aircraft for several years now. It seems to occur on carbon fiber surfaces of all of our aircraft. Especially on our B757's, MD11's, and to a lesser extent on our B767's. The paint seems to not adhere to the carbon fiber substrate. We are currently replacing the elevators on a MD11 for this very problem, an expensive undertaking. For those of you who do not know, the elevators are a balanced flight surface, any work you do on them requires a balance calculation or to remove the surface and re-balance it in a fixture. We will remove the elevators and replace them and send the damaged ones out for re-work.
As I work in the structures side of maintenance, I must adhere to aerodynamic smoothness requirements. For example, fasteners that are not too high, or composite repairs that are as smooth as possible. So, I am somewhat confused as to how you can have bubbled up and peeling paint over an area of the aircraft and it is not considered critical to aircraft performance. It would seem to be detrimental. It is time consuming to fix on any surface, but very expensive and time consuming on a critical flight surface such as a rudder, elevator, or aileron.
Do any of our pilots or maintenance techs out there see this condition on your walk around inspections? Does anyone have any ideas on what may be the cause of this problem?

Gregory

Re: Peeling paint on composite surfaces.

Posted: Sun Jan 23, 2022 8:26 am
by zeke
The QR thing is not about paint peel it’s about other issues like paint missing from fastener heads, paint cracking where dark/light paint livery join.

I think the reasons that vary however fall into four areas
1) surface preparation
2) paint system used
3) environmental conditions
4) dissimilar materials (eg combination of metal and composite) on the surface

Re: Peeling paint on composite surfaces.

Posted: Mon Jan 24, 2022 11:58 am
by extender
The 787 has similar issues. Carbon flight controls have been around for over thirty years now and haven't seen the same degree discrepancies as the A350/787 paint adhesion issues. The primer isn't sticking. The anti-static and top-coat are just along for the ride. At least on the 787 issues, I think that the primer needs to be more elastic, and compressible.

Re: Peeling paint on composite surfaces.

Posted: Tue Jan 25, 2022 4:13 am
by celestar345
On the 787 the most problematic area is the wings and looks like it's similar on the A350. Yes composite has been used for a long time but it's until 787/350 where it's used on the wing and see flexing all the time.

On the 787 the paint system is revised and looks like it's fairing better now, so will see how Airbus will get on and solve this problem.

Re: Peeling paint on composite surfaces.

Posted: Fri Jan 28, 2022 4:46 am
by JayinKitsap
Composites are stiff in the direction of the fibers, quite springy (E about 1/3 that of wood) in the resin only direction. Resins, especially epoxies can have quite slick surfaces, many have strict limits on recoat times or one starts over, also include a light sanding in the prep between surfaces. I've seen a pressure washer blast off the top coat in large chunks, 1 to 2 SF each with little effort, it took a complete replacement of the coating systems to stop it. So there is the structural composite, the metal mesh, and coatings. All have different thermal expansion, bond strengths, stress/strains, and issues with primer compatibility. Thermal cycles approaching 150 F in 24 hours, 180F cycles occur across a year. Flexing lightning, hail stones, rain drops at 600 mph, buffeting winds. A really tough place to get it right.

Re: Peeling paint on composite surfaces.

Posted: Mon Jan 31, 2022 11:17 am
by LoganTheBogan
The Q400s I work with have terrible paint peeling issues, even to the point where the paint peels off exposing the lightning mesh. One in particular was only painted three years ago. I'm not sure how to add photos but if someone pointed me in the direction I'd be happy to share some, albeit I cannot mention the airline at all.

Re: Peeling paint on composite surfaces.

Posted: Thu Feb 03, 2022 11:25 pm
by gregorygoodwin
We changed out yet another MD11 outboard elevator last week for severely deteriorated paint. In this case, it seems the aluminum flame-spray under the paint was either burnt or melted, maybe from a heavy lightening strike. Anyway, the amount of surface that would require rework would have meant that the elevator would need to be removed and re-balanced. Instead, we removed it, installed a new elevator, and will send the damaged one out for repair at a overhaul station. We see this cracked, peeling, and missing paint quite often on carbon surfaces on our B757's and MD-11's.

Re: Peeling paint on composite surfaces.

Posted: Fri Feb 04, 2022 12:07 pm
by extender
gregorygoodwin wrote:
We see this cracked, peeling, and missing paint quite often on carbon surfaces on our B757's and MD-11's.


We see it pretty much on all composite parts; TR sleeves, fan cowls, nose cowls, wing-to-body fairings, you name it. Some paints are better than others. I haven't seen it on components painted with Jet-Glo.

Flame spray is horrible on some panels. Applying that is an art.

Re: Peeling paint on composite surfaces.

Posted: Fri Feb 04, 2022 12:20 pm
by StereoTechque
Conventional aluminium alloy surfaces are far better for paint adhesion as compared to composites especially Carbon fibre.

Re: Peeling paint on composite surfaces.

Posted: Fri Feb 04, 2022 3:34 pm
by extender
Yet even though radomes are not immune to this type of damage, you would expect to see more of it. You see more peeling from the previous scuff & squirt.