There is a longer thread on powder coating in tech tips. But for those interested in the ACA process, here is a summary of what I learned. The actual specification sheet is posted in the Current ACA Specifications thread in this sub-forum.
- The factory powder coats their frames, as do most other TnF manufacturers.
- There are a wide variety of types of powder coats with different performance characteristics, ranging from melted plastic on playground equipment to industrial grade powders used on aerospace and mining products.
- You will occasionally see someone on the internet claim that power coat does not protect from corrosion and should not be used on airplanes. This is typical internet bullshit. Someone somewhere used cheap thermoplastic powder on a bike and had it rust, and extrapolated from there. That's like painting your steel boat trailer with rattlecan enamel and then proclaiming all paint sucks because it rusted.
- The types of powder most suitable for aircraft frames are urethane and epoxy powders. They have the same performance characteristics as paints of those types; the main difference is the means of application. Powder coats are applied electrostatically and cured by heat, while paints are sprayed on in a solvent medium and cured by chemical reaction. Powder coating provides 2 advantages over painting: less wastage, and thicker coatings.
- The ACA lists specific product codes for acceptable powders. According to Dale, the usual factory powder is Axalta Black Magic II, which is a urethane thermoset powder in matte black. You may not be able to get this exact powder, since most powder coating shops tend to stock a few preferred brands which they have been certified to apply. However, all the major power makers will have a powder with similar chemical composition and performance characteristics.
- Also according to Dale, the iron phosphate wash is important for corrosion protection. And when you pick up the coated frame, wipe it with a q tip soaked in MEK to test the cure.
- Before coating, plug any hole where a bolt or bushing will go, and anywhere clearance might be an issue. You will still need to ream out the holes because of powder on the edges. I put a zip tie through every hole I wanted plugged. The powder coater has special silicone plugs for this. Also mask grounding threads and any tube that fits tightly into another tube, such as the horizontal stabilizer mounting stubs. Don't worry too much if you miss a few spots; it is easy to remove powder with an abrasive disc on a die grinder or with a drill bit. You will do that a lot during assembly to insure electrical bonding.
- I paid about $4K to have my frame, tail surfaces, engine mount, seats, and assorted steel parts media blasted and powder coated. You could probably find it cheaper, maybe as low as half that cost. However, beware of high throughput shops that compete on price, as they tend to have minimum-wage "crews" doing the work. I felt it was worth the extra money to have mine done by a small shop where the owner did the work personally.
- Airplane people talk about soda or media blasting, but I could not find anyone in the powder coating industry that does that. It takes too long and the media costs too much. Everyone uses sand. Material loss is controlled by the size of the grains, blasting pressure, and nozzle distance. The key here again is to find an owner-operated shop where you can speak directly to the blaster and make sure they understand this ain't garden furniture.
- Most shops will be comfortable blasting the frame to remove the paint, then letting you take it back to your shop for inspection and mods/repairs. They will have to lightly blast it again before coating to remove flash rusting and oils.
Last edited: