LESSON TWO: Fiberglassing the airframe tubes

In our last installment, we finished up the fiberglass fin sets that will add an unbelievable amount of strength to our models over the standard plastic styrene fins that the kits came with. In this installment, we will continue our hardening and strengthening campaign by fiberglassing the body tubes we will use for these builds.

As previously mentioned, the Maxi Brute Honest John kits come with BT-80 tube, which is perfect match for LOC/Precision's 2.56" body tubes and couplers. While I could glass the standard BT-80, I wanted the additional thickness of the LOC/Precision body tubes for additional strength. So to begin our class, we will be prepping full length LOC/Precision 2.56" tube for fiberglass sleeve reinforcement using Soller Composites 3" light grade fiberglass sleeving.

This information isn't something specific to just our class, it can be used on any rocketry project where you want to strengthen your airframes. Years ago, I got tired real quick of unreinforced airframes getting the kinks and dents of normal flight and recovery. One layer of properly applied fiberglass can significantly strengthen your airframes to protect against that from happening. A lot of people will tell you that fiberglass reinforcement isn't necessary, and they would be correct. Although it isn't necessary, if it adds an additional layer of protection so that you don't have to fix dings and dents all the time, isn't that of some value to you? It is to me, and the process isn't as difficult as some think.

For this class, I had three full lengths of airframe tubing, and although I would only need 1.5 of the tubes, I decided to laminate all three of them at the same time, and put the excess away for another project. Nothing like having some extra airframe tubing already fiberglassed to speed up your next project. I also glass my tubes full length and then cut them, and/or if needed, slot them. It makes it easier to work with rather than glassing different lengths of tubes.

So with my three lengths of tubing, I got out my supplies for the project. I had already purchased the light weight fiberglass sleeving from Soller at the beginning of the project. I mention the light weight grade specifically because Soller also has a heavy weight grade, but I felt the light grade was sufficient for what I was going to do.

In the photo above, I have set out my most common fiberglassing tools. In addition to the tube and fiberglass sleeving, and the items displayed above, you will need a coupler of couplers that fit the tubing you are glassing. The centering ring in the photo is one of two, the other one is already in a tube. I use them so I can insert a piece of 1.5" light weight conduit to rotate the tube while I work on it.

Before you begin, take your body tubes and sand them with 80 grit sandpaper, the full length, from end to end, roughing up the surface so the epoxy resin can get some "bite" into the tube. Once your tubes are sanded well enough, just enough to knock the gloss off the tube, you can start assembling the couplers to hold your tubes on the conduit rotisserie.

The couplers are already a snug fit in the tubes, so you can't just pile on wax paper and expect them to fit. I find the three step process in the photo above can really simplify the process. Take piece of wax paper long enough to go around the coupler one time. Where the two ends overlap, cut a single cut with a razor knife right down the middle of the overlap. Discard both scraps and use masking tape to connect the two ends.

Doing it this way, there is always one layer of wax paper (plus at the joint, a layer of masking tape), and the only place the masking tape is stuck to the coupler is at the right edge. I have slid the wax paper off the left end slightly and rolled it under the edge to make insertion into the body tube easier.

Once you have covered couplers for both ends with wax paper, put a centering ring inside each end and slide a coupler in each end, so that it looks like the photo above. Nothing is glued, it's just wedged in place with the wax paper holding it in place. If you knock the centering ring out of place with your rotisserie tube, you can pull it back into place with a piece of all-thread with a nut on the end like I show in my first photo above.

From the top, the inserted coupler looks like what you see above. Our couplers won't get stuck in the tubes with us doing it like this with the wax paper.

Next, you'll want to put your fiberglass sleeve over the tube and secure only one end. A few words about putting the sleeve on the tube: Take your time. Don't cut it until its on the tube. Don't mush it around too much playing with it, but don't be afraid to work out irregularities that can get in the fabric during handing. I have found that the less I mess with the sleeve, the better it lays on the tube, so I try not to stretch and distort the sleeve before I use it.

Feed the sleeve over the tube in whatever manner you find will allow you to get it in place with the least amount of fuss. You will see that the ends can get "belled" out quiet easily as the sleeve is expanded and contracted back over the tube. That is why I say don't cut it until you are putting it on the tube. Don't do trial runs putting on and taking it off the tube, as it will distort the fabric — put it on when you are ready to laminate it, cut it and be done.

When you get the sleeve on the tube and cut to length, leaving a couple of inches to lay over each end onto the couplers, secure one end with masking tape as in the photo above. Be careful, and take your time taping this end, being sure not to get any bunches or kinks in the cloth. You can not have a fold or pleat in the end or it will cause that end of the sleeve to not lay down properly when you put the resin on. It should lay down smooth just like in the photo.

This is my fiberglassing station in my shop. My benchtop is protected with additional cardboard to collect the drips I invariably make moving my brush from the cup to the tube. The two V-blocks positively position the tubes level on the bench and allow me to rotate the tube while I am working on it. As a right handed person, I place the tube end with the masking-tape-secured end on my left, because I will be working from the left to the right as I apply the epoxy resin. This photo is the second tube in my three tube run. The first tube is already done and trimmed at the back of the bench.

I start at the left end, and using disposable yogurt cups, I mix one "shot" of West Systems 105 epoxy resin with one "shot" of the 205 hardener. Disposable 2" paint brushes are used to apply the resin. The process is simple: Paint epoxy on. work it in and drag it to the right. Repeat. Mix more resin when needed, paint, work it in and drag it to the right, using the bristles of the brush to pull excess resin out and move it to the right end.

The bias of the fiberglass sleeving fabric, being oriented at 45 degree angles to the axis of the tube, dictates that the further the fiberglass sleeving gets pulled axially, the tighter it clings to the tube. The tighter it clings to the tube, and the more resin you extract dragging and pulling it to the right with your brush, the stronger the laminated matrix becomes. The key to doing this successfully is to have enough resin on the tube to wet the fiberglass sleeving and that's it. Do not worry about filling the weave at this point, that's handled in the next step.

When you have reached the right end of the tube, congratulate yourselves on successfully laminating an airframe tube. After the back patting, watch the tube — when the resin starts to gel, you'll know it, and you can then paint another layer of resin and hardener over the entire tube. This fills the weave with epoxy and give you something to sand off without sanding off the fiberglass cloth. You achieve a good chemical bond doing it this way, and I have even learned to time mine where I can use the same brush to do both coats of epoxy before having to throw it away. You may have to rotate the tube several times to keep drips from forming on the bottom of the tube — just rotate it 180 degrees a couple of times and let it flow.

When the tube's last coat of epoxy has hardened to what is called the "leather" stage (where the epoxy isn't hard but is firm enough not to leave a fingerprint), you can take a razor knife and trim each end of the tube close to the edge. If you take your time, you can even get to where you cut through the fiberglass and barely even touch the wax paper on the coupler.

After your trim the ends, remove the couplers and centering rings, and clean up your work area and materials. Once the tubes set up long enough, you can sand the ends flat. I use a piece of self-adhesive 80 grit disks stuck to a square of 1/2" plywood to sand the tube ends nice and square. After that, I cut them just a little longer than the proper length, 14.25", using a cut off saw with a combination blade. Wick a little CA in the fresh ends, sand square, and done.

And that's all there is to tube lamination. See, that wasn't that hard. Oh, wait, we still have to sand our tubes, right? I have to admit that I have started cheating lately when I have fiberglassed tubes to sand. I haven't always, as I used to hand-sand my tubes with 80 grit sand paper and a sanding block, so I know what it takes. But I found a little secret that makes the job so much easier.

I had an old wood lathe sitting inside my shop but I hadn't used it in a while. But when faced with hand-sanding three fiberglassed tubes, I started to have second thoughts about how I wanted to do this. The photo above shows what I came up with to simplify my tasks: a couple of properly sized plywood disks attached to the lathe allowed me to spin the tubes on the lathe to sand them.

With one 80 grit belt sander belt, I was able to sand all three of my tubes the same day I laminated them — all three in the same day. The fiberglass resin cut easier because it hadn't set up fully, but was still dry enough to sand effectively, yet the dust created was lower than normal. I finished up with a sheet of 150 grit paper and the job was done. I wished I'd discovered this earlier because it really made the job so much easier. To fiberglass three full lengths of tubing in the same day AND sand them ready for primer was, well, a wonderful revelation.