Saturday, February 9, 2008
Primer, Sanding Sealer, Balsa Filler, Paint, etc...
Do you really need all this stuff to build rockets?
Well the short answer is "No. " For the majority of the rockets we are building, we follow a pretty simple regimen for prepping and finishing them.
1. Sand the fins with tapered trailing edges, rounded leading edges and flat where they are glued to other surfaces.
2. After the rocket is constructed, paint with regular, inexpensive gray paint primer. This fills in some iregularities, but also provides a more even paint finish when parts that are originally dfferent colors, such as white or black plastic parts, balsa wood parts and various colored body tubes. We use gray colored primer because it works well under all light and dark colored paints.
3. Let the primer dry for a couple hours.
4. Paint a light coat of paint.
5. Let the paint dry for a couple hours.
6. Paint final coat of paint for good coverage.
7. Let completely dry for 24 hours or more. (Or you may end up with fingerprints, etc.)
Now go out fly it and have fun. Get out of the shop!
Now, on the other hand, if you are building an expensive scale model, a model that has fins that will be difficult to reach, once the model is constructed, or if you are building a rocket for performance over utility, then you will probably want to use fillers, fillercoats and sanding sealers.
Currently, we are building a Semroc Hydra VII that has some hard to reach, "internal" fins. For this reason, and because I wanted to follow the "exact" instructions, I decided to go ahead and take the time to use balsa fillercoat and sanding sealer.
The instructions below, from Semroc, came with the Hydra VII and have a good illustration of the smoothness achieved by using fillercoat and sanding sealer. This decreases drag and improves performance of the rocket. The rocket should be able to fly faster and higher.
* Note that for my 3rd coat, I used sanding sealer in place of fillercoat.
For this rocket, I used the following steps:
1. Sanded the flat sides of the fins before cutting them out of the sheets.
2. Sand the fins with tapered trailing edges, rounded leading edges and flat where they are glued to other surfaces.
2. Brush on two coats of balsa fillercoat and let dry in between each coat. You can use wax paper to set the pieces on after applying the fillercoat.
3. After letting the fillercoat dry completely, sand with fine sandpaper again. This all took a while with the Hydra VII as it has 21 fins in all!
4. Then I applied sanding sealer to all the fins.
5. After the sanding sealer dried overnight, I again sanded all the fins with fine sandpaper.
This process takes days, especially if the rocket has 21 fins. But seeing as I wanted to do it "by the book" on this rocket and because of how it is constructed, I followed these steps.
For this type of rocket with "internal fins," you could also follow a similar practice and spray on primer and sand it off before contruction as a lower cost alternative.
You can see by the picture of the Hydra VII below why it is hard to primer and sand the fins after the rocket has been assembled.
The Hydra VII kit is available from Semroc for $38.00 Postpaid from the following link: Hydra VII