Model Rocket Body Tube

Scratch-Built Model Rocket
Part 1: Airframe Body Tube
Made from posterboard and spray glue

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It delights me that one can buy such a vast array of rocket parts nowdays. So many suppliers, so much good stuff, so little time. Nose cones, G10, phenolic tube that fits standard motors....

And I've learned a lot from buying kits and building them. Like how to put an airframe together. Every kit has something new to teach me.

But I have this character flaw that requires me to do as much for myself as possible, and then some. Good thing. My personality is of the type that deals with emergencies well. So well, that I have developed habits that tend to create them. Unfortunately, that's not a joke. Procrastination, for instance, is a crude, common, but very effective technique for creating emergencies. I use it a lot.

Back in October I had scheduled a session of Rocket Science 101 through Community Education here. Checking the roster a week before it was to begin, I was surprised to find that six people had signed up for it. The previous class in Spring was cancelled because nobody registered, and I had kinda thought this one would go away too. I am now delighted by the prospect of meeting six prospective rocketeers, sharing the little bit I know, and learning from them.

So I went to the storage room, found my box of Estes Alpha kits which I have students build in these classes. It was empty. Should have ordered another box of them from Dennis at New Horizons Hobbies back when I signed the contract. Oh, well. I can always go buy them at retail. What's money for, anyway!

So a week before the class began, I went to Mall Wart and and wound my way to the rocket department. It was bare too! Oh yeah, they had some boxed almost-ready-to-fly kits, complete with launch controller and stand. But that is not what I needed for this class. No Alpha kits, nor anything like it.

So not to panic.... Over the years I have made a number of model-rockety airframes from stuff lying around. I had been thinking of consolidating the better bits into a standard model, and here is an opportunity with a pitchfork.

So these pages are a tribute to the students of that class, a documentary of some things I learned from making these "kits," and of some things I learned from the students themselves.

Body Tube Materials:

There are three essential materials, posterboard, double-stick adhesive tape, and 3M Super 77 spray glue.

Double-stick tape is sticky on both sides. One of its more common uses is for mounting photographs in albums.

Here is a photo of a sheet of posterboard:

It is 22 inches wide by 28 inches long.

I say these things are "essential," because the 3M spray and the double-stick tape make this technique so quick and easy that this is now my standard practice. But there are some good substitutes. On other pages I have illustrated the rolling of paper tubes using diluted Elmer's glue, Titebond, or some similar water-based wood glue.

That being said, I still use Titebond for making motor tubes, as it is stronger and more heat-resistant. Cheaper, too, as if that mattered.

One can also use plain copy paper instead of posterboard. And they are much stronger, especially when using wood glue.

Why the double-stick tape? Well, Super 77 is a contact cement. It adheres immediately. If you spray the part of the posterboard board that will contact the dowel, you will glue it to the dowel and have a hard time getting it off. So the first turn of the roll is secured with tape instead, then the remaining posterboard is sprayed with glue and rolled up. More on that later.

Since Super 77 adheres upon contact, the tubes do not need to be secured with rubber bands while the glue dries. They become strong within a few minutes of rolling and can be used almost immediately. They stink for an hour or so, but not too bad.

Another advantage is that the solvent-based adhesive does not soften the paper like water-based glues do, so the tubes are much straighter and smoother.

By the way... this technique is good for making casting/inhibitor tubes as well. I used it in making grains for the Big Sugar launches recently, and in the tidy tubes for my 38mm loads.

Doing it

A few tools are needed, a ruler to measure, scissors or sharp knife to cut, and three wooden dowels.

The dowels should be each a foot to 14 inches long, round, straight, and smooth. I recommend sanding them.

Sizes are:

3/4 inch diameter, for making the body tubes themselves.
1/2 inch diameter, for making coupling tubes
1/4 inch diameter, for pre-rolling the posterboard

The larger two sizes should be covered with something that makes them less attractive to glue. In the photo, note that the largest dowel is covered with Nashua 324 aluminum foil duct tape, giving it a metallic look. The 1/2 inch dowel is covered with red plastic-wrap. Both work OK.

The 1/4 inch dowel is not covered with anything, it just looks that way. It is painted flourescent pink. I use these as stabilizing sticks for crude motor tests, and I like to be able to find them. They are hard to look at, but easy to see.

A sheet of posterboard is cut into four equal rectangles, each 11 inches wide by 14 inches long. Each rectangle will make one body tube, 11 inches long.

It is important to pre-roll the posterboard at both ends, to make it "want" to roll. Just wrap the edge of the paper around the 1/4 inch dowel and force it to curve around the dowel as smoothly as possible. It will resist. Persist. A smoothly curved edge now will make a smoothly rolled tube in a minute or so.

If you don't pre-roll, you will have trouble at both ends. At the first end, there will be difficulty getting the first roll tight on the dowel, and the tube will not be size-conformal. At the finish, the final edge will want to pull away from the tube, and you will have to rubber-band it or something to make it lay down. Pre-rolling pre-empts these predicaments.

Having done all that hard pre-rolling, it is time to unroll one of the ends and flatten it a bit. That is so we can put double-stick tape on it.

A strip of double-stick tape is torn off just a little longer than the width of the posterboard. It is stuck to the edge

The taped edge is curled over the 3/4 inch dowel, tucked in evenly, and the first roll made. The double-stick tape secures the first turn of the tube, making the spray-glue operation much simpler. Note that the far end of the posterboard is not properly tucked. It was the best I could do and still get a photograph. Rest assured that error was corrected before I actually did the roll.

So the first turn is now secured with double-stick tape.

Remove the dowel from the tube to keep it from getting glued. Take the paper to a spot you don't like and spray it with glue. It doesn't take much, but do strive to get an even coating. Take it back to the flat rolling-board, re-insert the dowel, and roll it up.

I guess you could mask the dowel with tape and not have to take it out. But I haven't tried that yet.

Be especially careful to get the far edge of the posterboard stuck down evenly and firmly. Otherwise, it will peel away and be ugly and non-aerodynamic. This is the purpose of pre-rolling that edge, so that it lays down without a struggle and sticks to the tube.

The finished tube can be worked within a few minutes. Here I am holding it to a fin-attachment guide, which is used to space out the fins at the right interval and to get them on straight. But we are getting a bit ahead here.

Another tube we will need: Thrust ring tube

A smaller tube is made in the same manner, except this one is a strip 20 inches long and wrapped around a 1/2 inch dowel. 20 inches of posterboard makes for a nice fit inside the 3/4 inch tube. It slides in with just a little resistance, so it will glue in well. This tube will be cut into short sections to make the motor thrust-ring.

Such close fits can also be used to make extended airframes, either as coupling tubes to add another 3/4 inch ID tube, or by itself to make a reduced-diameter upper airframe. But beware! Long, skinny airframes make ejection more difficult, and lawn-darts are common with this model already.

Just in case you don't have any double-stick tape lying around, or have a yen for doing things the old-fashioned way...

You can mask the side to be rolled around the mandrel. Just draw a line 2.375 inches (2-3/8ths) from one edge. Pre-roll it and mask it with something. Here I am using a scrap of posterboard and green masking tape. Spray the remainder with Super 77, remove the mask, and roll it up!

Actually, I realize that this works very well, now that I have tried it again. Forget the double stick. Make that two essential materials.

Next: Let's make some fins!

Jimmy Yawn
jyawn@sfcc.net
Recrystallized Rocketry

rev. 11/26/05