Patriot downscale build

I had sort of a logical reason for building a Goony Patriot. This one, not so much. Well, there was some logic in building a cardstock rocket: Launch coming up in a week, two rockets in progress both held up by painting-unfriendly weather. I printed out a downscale Satellite Interceptor. And then I decided to design a downscale Patriot instead. For some reason.

This is my first cardstock rocket of my own design. In fact it’s my second cardstock rocket, and my first round one. The PDF file is here: Patriot downscale.

I drew it up in Intaglio, scaling measurements off my Estes Patriot by 33% to make the body tube accommodate a 13 mm motor. It could be built with a balsa or plastic BT-5 nose cone if you have one, or want to buy one, but I went purist and adapted the “Sprint Style” nose cone from Eric Truax’s 13mm nose cone pack (the nose conesthe instructions). The Sprint cone is a little too short so I used Matt Stum’s transition template to print some transitions that gave something closer to the right length. Some assembly required. Adaptation instructions in Cantonese. Batteries not included.

I printed the pattern onto 90 pound cardstock and got started. First the body tube.IMG_1995Wait a minute, that’s not a tube.

I fixed that. I flipped it over, drew a line down the center, and wrote “glue” on the half behind the printed part because I have the attention span of a canary.IMG_1996

I rolled the piece over the edge of the workbench to start giving it a curve.IMG_1997 I applied glue stick to the “glue” half, and then rolled it around a couple of used 13mm motor casings.IMG_1998

Then I did the whole thing over again because the first time didn’t go so well. Second try was pretty good. I rubber banded it to my aluminum angle piece, with the seam against the aluminum, to hold it together for a while.IMG_1999

Next the fins. I cut the fin pieces out of the cardstock, not along the edges but outside the edges (not shown here). These are to be laminated with cereal box cardboard. Or actually Pop-Tarts box cardboard. I roughed up the printed side with 220 grit sandpaper.IMG_2001

Then I cut pieces of similar size and shape to one side of a fin. The leading edge was cut with a straightedge. The other edges, anything goes.IMG_2002

I used the back side of an Xacto blade to score the fold line for each fin (which will become the leading edge)IMG_2003

Then I put glue stick on one side, inserted the Pop-Tarts cardboard piece, put glue stick on the top of that, and folded the cardstock fin piece over it. I didn’t photograph any of that very well, sorry. The result is a cardstock-cardboard-cardstock lamination, with a fold along the leading edge and the other edges needing to be trimmed. I put these pieces between layers of wax paper and applied weight so they can get flat and happy.

Back to the body tube. I cut out the strip for the thrust ring, curled it up, and placed it (without glue) in the end of the body tube.IMG_2005

Then I glued the inner end down (here I used Alleene’s Tacky Glue) and made sure it wasn’t sticking to the body tube. Once it had set I pulled the thrust ring out and glued down the outer end. Then I applied glue inside the body tube, pushed the thrust ring in, and used a 13mm motor casing to push it forward far enough, with the motor sticking out a little.IMG_2006Then I removed the motor casing, since gluing a used motor inside a rocket is considered bad form.

And then I remembered I’d intended to tie a piece of Kevlar to the thrust ring before installing it. Oh well, I’ll have to use some other way of attaching the Kevlar.

OK, then came the fun part. The nose cone!

There are three pairs of transition patterns. The top one of each was cut out on the lines.IMG_2012

The bottom ones would become the gluing tabs. Here I’ve sketched how one would be cut out. The number and shape and size of triangles isn’t particularly critical.IMG_2013 Here are the three tabs cut out.IMG_2014

I also cut out the tip piece and cut notches about halfway into it. It looked pretty sketchy. I figured I’d probably have to redo this but decided not to decide until morning.IMG_2010

The tab for the tip piece along with the shoulder piece and strip “T” were cut out from Eric Truax’s original pattern.IMG_2011

Here are the tabs glued to their respective pieces.IMG_2015

Then the shoulder piece was rolled up and inserted into the body tube.IMG_2016 At this point I deviated from the nose cone instructions in part because I didn’t really understand them. Instead I made a pencil mark at the inner end.
I removed the shoulder piece from the body tube, unrolled it, and applied glue stick to the part left of the pencil mark. Then I rolled it up again, bringing the inner end back to the pencil mark and verifying it fit back into the body tube. I pressed the glued surfaces together with the handle of my hobby knife inserted into the ring.IMG_2018 Strip “T” was trimmed so it would fit around the shoulder with a gap just big enough for the first transition’s tab.IMG_2019 And it was glued on.IMG_2020

Next morning I decided the tip piece was indeed too ratty to use. I added some lines for cutting the notches to the drawing, since improvising those clearly wasn’t working, and cut out a new one. Then I joined up all three transitions and the tip.

Meanwhile I noticed the edge on the body tube was starting to pull up. I put Tacky Glue under the edge with a toothpick, and then rubber banded the body tube to the aluminum angle again for a while.IMG_2022 Here are the top three pieces, and bottom two pieces, of the nose cone glued together.IMG_2023And here’s the whole thing. A bit rustic but I’m okay with it.IMG_2025 Here’s the nose cone on the body tube.IMG_2026 I pulled the fins out from under the weight. The two sides are printed with different size quadrilaterals. The two on the left are small side up, the other two are big side up.IMG_2027 I trimmed along the edges on the small side. (In spite of everything, a couple of the fins had a little white showing on the other side. I went back to the drawing and made the big side a little bigger. Too late for me, though.) Then I put a bead of glue on the trailing and outer edges.IMG_2028 Next I glued the fins to the body tube. They’re only 1/32″ thick, so to use the Estes fin tool I put pieces of Pop-Tarts cardboard between the fins and the tool.IMG_2029 I cut out the launch lug piece, rolled it loosely around a 1/8″ rod, and glued it together.IMG_2030 Here’s the launch lug glued in place.IMG_2031 I added fillets on the fins and launch lug.IMG_2033 I made a 1″ x 10″ crepe paper streamer. I considered just going with nose blow recovery but decided to go with the streamer. It can always be removed.IMG_2034 Here’s where I paid the piper for forgetting to tie Kevlar to the thrust ring. I made a shock cord mount following an idea by James Jason Wentworth. Piece of bond paper 3/8″ by 2″, folded in half, with three holes poked:IMG_2035 Kevlar’s fed through and doubled back:IMG_2036I glued the top half down to the bottom, applied glue to the side with the holes, then used a pencil with some tape around it, sticky side out, to maneuver the mount down into the body tube and press it down.IMG_2037 You can see it down in there. This is thinner than a tri-fold mount, which is good when you only have 13 mm to work with.IMG_2038I reinforced the end of the tube with some CA. Then I tied on the streamer, rolled it up and put it in, put on the nose cone, and installed the biggest, meanest unused motor I ever intend to use on this thing: 0.625 newton-seconds of sheer muscle. No, really. Hold that thought.

Before adding nose cone weight, with a motor in place this thing is very tail heavy. It probably would’ve been smart to increase the fin size, but I didn’t. Probably would have been smart to make this an MMX, but I didn’t. So I have a 1/4A3T-3 in the back, and OpenRocket says the CG should be about 11 cm from the front. To get it there I had to add a little more than 3 grams of weight. I used clay. (Final weight of the rocket without motor was 8.2 g, of which 4.7 g was the nose cone.)

For a 1/2A or A, I would have had to go to more like 4 or 5 grams to get well over 1 caliber stability, which would be kind of nuts. Anyway, I have some 1/4As I have no other immediate use for. OpenRocket says the 1/4A3T-3 should take this up to 210 feet, and I’m good with that. A rocket this tiny, I’d probably lose sight of it if it went any higher. I may lose sight of it anyway. And if I’m ever sick of looking at it, OpenRocket says it’s still 1.0 calibers stable on an A3T-4 and will go to 880 feet.

So 1/4A it is, and after nearly filling the nose cone with clay and doing a quick swing test to verify stability, I tied a knot in the end of the Kevlar, buried it in the last part of the clay,IMG_2039and put a layer of glue on top of that to hold it in. Well, that’s the theory.

And that’s about it. I did a little cleanup, and since this was printed on an inkjet printer it’ll definitely need a coat of clear, when and if we ever get painting weather again. Aside from that, it’s done. This version anyway. I might consider replacing the nose cone with a plastic or balsa one, or possibly even a redone paper one; this one’s definitely in the not bad for a first attempt category. Anyway, I’m pretty happy with this model. We’ll see if I’m still happy after launching it…IMG_2040 IMG_2041 IMG_2043


One thought on “Patriot downscale build

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s