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convair880mfan
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Protective corrosion coatings and aerodynamics

Sat Jul 17, 2021 12:48 am

Does anyone know if protective corrosion coatings especially applied to wings degrades their performance capabilities? I am assuming they add a bit [?] of weight to the wings and are not as smooth as original wing skins but maybe the performance penalty is miniscule or minimal ???

I sometimes cannot tell the difference between composites used on ailerons and trailing edge flaps and corrosion prevention paints or coatings. One "appears" light grey and one a darker shade of grey. Maybe it is an optical illusion.

Also, are the dark stains and streaks on this material caused by normal hydraulic fluid loss or leaks? It seems that the airlines often have little desire to clean these up or perhaps it isn't worth it. They make the trailing edge of the wings look nasty in comparison with wings that are all metal and don't have composites or corrosion protection.

What do you know about this or what do you think? Thanks in advance for all replies.
 
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fr8mech
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Re: Protective corrosion coatings and aerodynamics

Sat Jul 17, 2021 1:02 am

convair880mfan wrote:

Also, are the dark stains and streaks on this material caused by normal hydraulic fluid loss or leaks? .


These stains are not necessarily leaks. Sometimes a mechanic might have gotten a little overzealous with the grease gun. A couple of couple of cycles and you get these streaks.
When seconds count, the police are minutes away, or may not come at all.
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convair880mfan
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Re: Protective corrosion coatings and aerodynamics

Sat Jul 17, 2021 1:11 am

Can these grease gun stains be cleaned off or are they sort of etched permanently in the material?
 
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fr8mech
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Re: Protective corrosion coatings and aerodynamics

Sat Jul 17, 2021 11:30 am

convair880mfan wrote:
Can these grease gun stains be cleaned off or are they sort of etched permanently in the material?


They can be cleaned off. Might take a little elbow grease if the stain has been there a while, but it should come off.

Airlines have cleaning schedules, just like any other maintenance schedule they keep. Some are more robust than others.

Chances are, those types of stains will be cleaned by a mechanic that needs to do some sort of inspection or is looking for an actual leak.
When seconds count, the police are minutes away, or may not come at all.
It’s hard to win an argument with a smart person, but it’s damn near impossible to win an argument with a stupid person. ~B. Murray
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gregorygoodwin
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Re: Protective corrosion coatings and aerodynamics

Sat Jul 17, 2021 10:48 pm

Maybe I can provide some answers. Composites on aircraft, especially on the exterior of the plane, are virtually always painted surfaces. This is because ultraviolet light, such as sunlight, will degrade the composite resins. Most of the resins used in fiberglass, carbon fiber, and hybrid lay-ups, such as Kevlar-fiberglass or Kevlar-carbon, are epoxy resins. If left unpainted out in UV light they will start to get a milky opaque appearance and the surface resin coat will start to flake which exposes the fibers thus weakening the lay-up. On our B767-300F's, the composite surfaces of the wings are a light grey while the main wing surfaces, which are aluminum plate, are a dark grey color. The dark grey coating is called AeroFlex. It has a metallic look to it in the paint can and also when you apply it to the wing surfaces. It goes on very smooth and I would say it doesn't add very much weight to the plane. It's better to have the coatings than to start having corrosion or composite problems which can ground a ship for long periods of time at great expense. One surprising aspect of the AeroFlex is that it isn't very fluid resistant, Hydraulic fluids and solvents will quickly dissolve it, why it was engineered this way I can't answer. The paints you see on the composite surfaces and on the metal fuselages are a epoxy or polyurethane base that can stand up to leaks better but will eventually begin to fail if exposed for long periods of time.
Aircraft move around a lot. To wash a plane, it generally needs to get to a heavy maintenance base. Scheduling this can get complicated. As for degraded paint, here at IND, we always try to touch up the paint if it needs it and we have a paint and appearance inspection that grades the aircraft's appearance and , if really bad, gets it lined up for a paint job.
I hope this answers some of your questions.

Gregory
 
JayinKitsap
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Re: Protective corrosion coatings and aerodynamics

Sun Jul 18, 2021 7:49 am

Newer aviation and marine paint types can be quite slick. Racing sailboats get some exotic paints that improve performance. Similarly on a plane, a design for a paint that works miracles that is only a few mills thick and makes teflon seem rough.

https://www.ppgaerospace.com/getdoc/28a ... earcoat-(1).aspx
 
StereoTechque
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Re: Protective corrosion coatings and aerodynamics

Sun Jul 18, 2021 10:18 am

gregorygoodwin wrote:
.
Gregory


That was a fantastic read. Thank you for your inputs.
Looking California.. Feeling Minnesota.... R. I.P. Chris Cornell...
 
extender
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Re: Protective corrosion coatings and aerodynamics

Mon Jul 19, 2021 1:23 pm

Which is one reason why you see a lot of speed tape on the 787. When the paint chips off, you need to protect it from exposure to UV. All composite flight controls are painted.

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