Tips for Building Model Rockets

Adhesives

A lot of people aren't quite sure what kind of glues should be used to build a rocket. From my experiences and what I hear from others, there are a few glues that are good to use. I always use Elmers white glue on my small models. It holds good and finishes well with little effort. On my Phoenix, which is a very big rocket, I used mostly Elmers Carpenters glue and some epoxy. I used the epoxy in the engine mount because it is very strong and the Phoenix can take E engines. I used the carpenters glue to attach and fillet the fins, it should be strong enough. For plastic parts, I recomend tube-type plastic cement from Testors. Epoxy also works on plastic, but is a little overkill.
There are some glues that are not so good to use. Hotmelt glue, or hotglue, is one example. Although it can be used to some success, it is not very good. It tends to stay a little gummy and flexible, even after it dries, which is not good for the fins. Hot glue is also very heavy and can drastically reduce your rocket's altitude.

Slick Fins

Finishing fins so they come out good can be a challenge if not done right. Through my experiences with balsa wood fins, I have found many different ways of finishing fins. Believe me, I wasn't that good at it in the beginning either!


One of the oldest and most common way of finishing balsa is with sanding sealer. You can get a bottle at most hobby shops and it can be applied to almost all balsa parts. You simply brush on and sand it. Then you just repeat 2 or 3 times until you get a smooth finish. Prime and paint. Suprisingly, if you do this right, it comes out very good!

Just recently, I saw a new way of finishing fins on Sven Knudson's homepage. It involved rollng some glue on printer paper and gluing it to your fins then cutting it out. I tried that and it works fantastic! Your fins come out soooo smooth, I love it! Although, I found that it worked a little better with some 3M spray adhesive. You just spray the glue on a sheet of paper and stick your fins on it. Smooth out any bubbles or wrinkles and let dry. Then just cut them out with a hobby knife. Hint: don't use water based glue, it will wrinkle and bubble the paper.

Since most of my sport rockets aren't for competition, I wanted a quick and simple way to finish the fins. In the instructions for the Big Dawg, it didn't tell you to use sanding sealer on the fins like it normally does. It said to use 2 or 3 coats of automotive primer, sanding in between coats. I tried it and it works good enough to use on non-scale or sport rockets. It may leave some grain unfilled, depending on how much you use. The only problem is that you go through primer like water!

Painting and Finishing

Most often, I spray paint my rockets because you don't get brush marks or uneven coverage. I'm not saying that you can't get a perfectly fine finish, I'm just not that willing to slave over a sport model. The only time the kind of paint matters is when you're spraying certain plastics or foam. You can buy Testors paint that is specifically for this type of model. Here are some helpful tips and tricks used in adding that extra flair to a model.

Spray Painting: I've seen alot of models ruined because of a bad paint job. Sometimes, people put one heavy coat on and get drips or lose some fine details in a pool of dried paint. While painting, it is important to take even strokes and do many thin coats. The last coat should be a little thicker to get that shiny look. Before you start painting though, it is important to put down a good coat of primer. Primer should be sprayed on thinly and sanded lightly to help the paint stick.

Masking: Whenever you paint a model with more than one color, it is usually necessary to mask off certain parts of the rocket. This gives you a clean edge and sharp colors. Usually, masking is done with masking tape (DUH). Try to find a tape that holds well, but doesn't leave any residue behind. If you need to cover a large area, you can use sheets of paper or plastic bags with the edges stuck down with tape.

Trim: Trim is the smaller details that make a model more interesting. This can be done a variety of different ways. On my Tomcat, the box showed all these complex panel lines and stuff. I went to the hobby shop and bought some dry-transfer pinstripe decals. They were easy to apply and turned out great (follow the directions very carefully).
While finishing some rockets of my design (no decals to work with), I wanted something quick and good looking. I reached into my shelves of stuff and pulled out a roll of plastic tape(3M). This tape is slightly conformable and is relatively thin. I used it to make some high-visibility patterns on my fins, but I imagine you could use it on any number of projects(numbers?). I also found some small self-adhesive stamps with American flags on them. I saved them and eventually cut out the flags and put them on some of my rockets.
Maybe these were attempts for a good finish out of lack of anything else to stick on a rocket, but they worked very well! Normal people do trim with hand paint and masking tape. That works too.

Decals: Applying and aligning decals can be a difficult task for many builders. Most people have trouble with water-slide decals common in a lot of kits. One tip that always helped me is be patient! If you follow the directions, getting the decal prepared is easy. Getting it off the paper and on the model is another story. I have become quite good at it. After the decal has been soaking for 30-45 sec., remove it, let it rest on a towel for a second or two. This will remove some of the excess wetness. Place one edge of the decal where you want it and hold that end in place. Then slide the paper out from under the decal, keeping it as close to the model as possible. You can then slide it around (very carefully) and into position. If it doesn't slide very easy, put a drop or two of water on it. When it's where you want it, put the edge of a tissue near it to wick away some of the water and let the rest dry.

Stability

It is always a good idea to do some stability checks on your rocket. This isn't really necessary on a manufactured kit because it's already been thuroughly tested. The first thing you have to do is find the C.G. of your rocket. First of all, you have to put an un-used engine in it. Then you tie a string around it and get it to balance as shown



Once it balances and there are no twists in the string, you can begin to spin the rocket around your head on the same string. First, though, you must make sure there is nothing around you that your rocket could hit. If you start the rocket facing the direction you want to spin, it should always face forward as shown below.



If your rocket tumbles around, it's probably not stable to fly. To fix this, you can do one of two things. 1) you can add fin tabs that extend off the back of your fins to make them more effective. 2) You can pack some nose weight (clay, filler, etc...) into the nose cone. For some odd reason, this helps alot and can add alot of stability to your rocket.
Not all rockets test well, either. Rockets that are very long or often scale models won't test very good. Just because a rocket doesn't pass the test, doesn't mean you can't fly it.