FAA on Powder Coated Wing Struts

[barnstmr]

Here's the latest FAA comment on Wing Struts. This time they are focusing on powder coating. Makes sense.

[Robert Lees]

Re: FAA on Powder Coated Wing Struts

I'm not going to read it. I assume they say "No".

Correct me if I'm wrong.

[barnstmr]

Re: FAA on Powder Coated Wing Struts

You might be surprized, Bob. I first expected the focus to be on the fact that powder coatings can mask deformities underneath, such as developing cracks. But this was not mentioned at all. Check it out... The focus is on how the elevated temperature during the powder coat process affects linseed oil and to watch out for repair shops drilling a ventilation hole in sealed struts to allow out-gassing. Certainly this is worth considering, especially for those who send out parts to repair shops expecting them to come back improved.

[Robert Lees]

Re: FAA on Powder Coated Wing Struts

OK, I read it

It only applies if your powder-coating company is STUPID enough to drill a hole in a sealed strut to relieve the internal pressure caused by the heat.

Discussion: The powder coat application process requires heating the wing lift struts to 450 degrees Fahrenheit. At this temperature, a sealed wing lift strut would expand (swell up). To vent the heat and gas buildup of this process, a hole is drilled at the fork socket located at the bottom of the strut. This vent hole in the wing strut ultimately means that the struts are no longer sealed.

It actually applies to Piper sealed struts, but applies to and has been quite rightly distributed to Taylorcraft interested parties.

In essence:

1. Don't powder coat anything on an aeroplane.
2. Don't drill a sealed strut.

Personally, I would like to know why anyone would powder-coat anything on a Taylorcraft?

[edit: all the above written before Terry's previous posting}

[flyguy]

Re: FAA on Powder Coated Wing Struts

Additional note. Somewhere I saw/heard considerable discussion of a corrosion problem when the coating is chipped. Seems the corrosion spreads outward under the coating from the chipped spot, unlike a properly painted surface.

The description made it sound similar to the problem the airlines had with the early single-coat epoxy paint getting "worm tracks" under the paint.

OK for wheel chairs, forget it for airplanes.

DC

[Robert Lees]

Re: FAA on Powder Coated Wing Struts

Correct, and under "commercial" powder-coated paint, where the stuff is thick and flexible, you won't see it.

I don't have any photos of corrosion under powder-coated steel, but I have seen it, and it's not pleasant.

It can also hide cracks, due to its flexibility.

Now, I'm no expert, but I like a brittle paint on steel-framed aircraft structures so that I can see any defects appearing on the underlying substrate.

[Ragwing nut]

Re: FAA on Powder Coated Wing Struts

we quit powdercoating all structural aircraft parts years ago. It only takes seeing one failed engine mount that was powdercoated to make you see it is a very bad idea period.

[N96337]

Re: FAA on Powder Coated Wing Struts

Yep...it's BAD stuff! Did an annual on a Super Cub and just noticed a noise in the tail area when I pushed it into the corner of the hangar... come to find out, there was a tube corroded off back there, and the powder coating was covering it up. No indication whatsoever unless you were there when the tube moved. I "red tagged" the whole plane... when it was pulled down, there was LOTS of corrosion under the powder coating. I wont let it in my shop! We had lots of problems with brake calipers on the goose with it too...they corroded something awful under the powdercoat.
Like was said...it's ok for a sewer grate...but not an airplane!
John