devavu2

To Paint or Not to Paint?

The usual Gyrobee construction sequence runs something like this:

All the metal components are cut and drilled per the plans, typically in the sequence defined by the Phases in the Documentation package.

As construction proceeds, the components are assembled for fit, typically using "hardware store" grade nuts and bolts.

Once the airframe components are complete, everything is disassembled so that the airframe components can be painted.

Once everything has been painted, final assembly is done using aircraft grade hardware.

This time around, by purchasing a kit, we essentially skipped the first two steps since almost all holes are drilled and you can be confident that the parts fit. That meant that we were immediately faced with the decision as to how to proceed with the finishing phase.

Bare Aluminum

We were interested in getting the new machine into the air as opposed to spending lots of time building. One option was to skip any finishing steps and leave the airframe in its "natural aluminum" state. There were several problems with this approach:

The various tube, angle, and plate pieces all have a somewhat different "natural" finish, so the airframe would end up looking less than elegant. While we could care less about a showered finish, we didn't want a machine that looked like it came out of "Junkyard Wars".

Natural aluminum oxidizes quickly and also picks up finger and hand prints, not to mention corrosion from smashed insects and the like. Bottom line - in a short time it would look pretty crummy.

Aluminum can be kept shined to a fine mirror finish by virtue of very laborious polishing. The "laborious polishing" part tends to turn me off and, given the bolt-together construction, uniform polishing would be almost impossible.

I briefly toyed with the idea of a clear urethane sealing coat, but that was simply painting in another guise. Besides, I wasn't really sure how the surface would be prepared for such a clear-coat and how it would stand up to time.

Painting

This is the traditional approach and the one we used for the prototype. It is extremely labor intensive:

Chemical clearing of the aluminum

Multiple coats of an etching-type primer

Application of sufficient color coats to assure a smooth finish

To do this job right requires good spraying equipment (and technique) and works best if you have a dust/bug-free painting booth. Of course you can have it done, but, because it is tedious, detailed work, it will run up a significant bill. We would farm out a few items that had to be painted - like the tail group, but decided to pass on the airframe components.

Powder Coating

This is the current approach used by most manufacturers to get a picture-perfect paint job. There is concern in some quarters that the baking step may alter the metallurgy of some alloys, but I am not sure that is significant with the 6061-T6 used for the Gyrobee airframe. What did hold me back was the comparatively high cost if I went with a typical 2-color paint scheme.

Anodizing

Anodizing involves an electrochemical treatment of the surface of the aluminum, creating a range of finished surface characteristics, all of which are highly resistant to corrosion. It is also possible to get a reasonable range of colors by adding a dye step to the basic anodizing process. We elected to have all the aluminum components (except the axles and nose block) anodized with a clear satin finish. Looks great, essentially no maintenance, and the price was right - about $170 at a local anodizing shop!

Composites and Paint

I noted earlier that we intended to paint the composite tail group. High-end aircraft composites are typically done using pre-preg sheets and high-temperature (oven) curing of the lay-ups. This produces excellent results but, in virtually all cases, the finished materials should be painted a light color to avoid excessive heat build-up in the sun which could weaken the structure. This is even more critical with typical homebuilt composites since these involve wet lay-ups and room-temperture curing. Although it will limit your creativity, the use of light colors for all composite components is highly recommended.