John's Build

[PapuaPilot]

I primed mine and painted it with a urethane paint. It is holding up very well and only has a couple small nicks in it.

[jrevens]

Several folks have had their Grove gear powdercoated. Looks good and seems to be durable.

There are potential pitfalls with powder coating of these structures also. These gear are a 7075 alloy, probably something like a T-6... I'm not sure exactly what Grove uses. In general, there is a degradation of static strength (yield & tensile strengths) as well as degradation of cracking resistance when it is exposed to elevated temperatures, a percentage of which remains when the material is returned to "normal" temperature. If the material has been shot-peened for strength that will be affected too. Effects can occur at lower temperatures than you might think - probably somewhere around 250 deg. F, and certainly at 350 deg. and higher, which some powder coating processes use. I think the Grove gear are probably over-designed for airplanes like ours (maybe depending on how much rough back-country flying you do!), so I wouldn't necessarily be too worried about it, but it would be good to ask the powder coating firm what temperature they will use. The higher the temperature & the longer the exposure, the more potential degradation of strength there is. This all comes from some "ancient history" part of my brain, so I'm sure if someone was inclined to research it, what I've stated could be confirmed, or not.

[jrevens]

I primed mine and painted it with a urethane paint. It is holding up very well and only has a couple small nicks in it.

Your airplane is really beautiful, Phil! Urethane paint is good, IMHO.

[Flybyjim]

Interesting read guys, thanks for sharing your knowledge. One can't go wrong with painting as far as not changing the integrity of the metals but powder coating does seem to hold up well. It's also nice to drop off the piece and pick it up the next day and it's done! I have only had some small parts powder coated on other projects (planes, coke coolers, 1937 Sinclair gas pumps) as I do like to paint, painting is easy, it is all the prep and clean up that takes most of the time.

[rv9ralph]

John, here is the reference to the heat used in powder coating affecting the integrity of the metal. In AC 43-13.1B, in the section on metals and heat treating. There is a reference to not raising the temperature of heat treated aluminum above the temperature of boiling water (212 degrees F). It applies to certain alloys, however, why do anything that may weaken the integregrity of vital structural parts.
Also, in reference to anodizing, there was an article last year in the November 2016 Kitplanes. The subject aircraft was an award winning RotorWay that had suffered a failure of a critical control tube. The tube was anodized for cosmetic purposes and had failed within the first 6 months it was put in service. Post-mortem on the part revealed stress fractures on the anodized surface that promoted the complete failure of the piece.

Ralph

[jrevens]

John, here is the reference to the heat used in powder coating affecting the integrity of the metal. In AC 43-13.1B, in the section on metals and heat treating. There is a reference to not raising the temperature of heat treated aluminum above the temperature of boiling water (212 degrees F). It applies to certain alloys, however, why do anything that may weaken the integregrity of vital structural parts.
Also, in reference to anodizing, there was an article last year in the November 2016 Kitplanes. The subject aircraft was an award winning RotorWay that had suffered a failure of a critical control tube. The tube was anodized for cosmetic purposes and had failed within the first 6 months it was put in service. Post-mortem on the part revealed stress fractures on the anodized surface that promoted the complete failure of the piece.

Ralph

Thanks for verifying my thoughts, Ralph.

[SSFoxBuilder]

Great info on the anodizing! When it came time for our gear, I simply figured that if Grove recommended anodizing for corrosion preventative for their landing gear then it should be safe. They did recommend a specific process, but I cannot recall what that was. Took a few calls in the Portland area to locate an anodizer who could comply with what Grove recommended.

[David47]

Hi Guys, just chiming in an interesting discussion regarding anodizing aluminium. Sulphuric acid anodiing is the most detrimental to fatigue life. We stopped calling out Sulphuric acid on anodised parts long time ago because of this and use less aggressive processes such as Chromic,Acetic etc. I've posted (hopefully) an internet address for an interesting article that helps to explain some of this.

dspace.dsto.defence.gov.au/dspace/bitstream/dsto/10291/.../DSTO-TN-1180%20PR.p...

If you paste into the browser hopefully you'll get access to the .pdf article. If not, let me know and I'll try again.

It's released for public access so all good.

[jrevens]

"Smoke" tested my panel today, and all the smoke stayed in, so that's a good sign. Fun to see things light up & come alive. Now it's time to "permanently" install the boot cowl. I also finished a few little details on the lower cowl piece. I fabricated some short extensions of the radiator air scoop out of 1/16" reinforced silicone rubber that I had. This gives a little better/closer match-up with the front surfaces of the radiator and oil cooler, and hopefully less air loss, while still being easy to remove and install the lower cowl.

[jrevens]

These pics are for Carl ("Cherrybark") -

This is basically how I did these panels Carl. I've seen many others done a little differently that looked very nice. As I mentioned on your thread, I used "Tric-nuts" on the 4 little steel tabs (along with SS machine screws). In retrospect, the Tinnerman clip nuts would have been just as good or better to use there also. I "formed" the edges of the panels with a slotted wood stick to make it fit a little nicer against the fabric.