Rocketry Works, which is a fairly new rocketry vendor in Tucson, Arizona, has a focus on the educational market, along with being a general supplier of stuff for our favorite hobby. They also are doing some interesting things with 3D printed parts for both GSE and for rockets themselves.

One result of this is a new kit for the educational market which, to me, seems very much like an updated (modernized?) interpretation of Balsa Machining’s great School Rocket. This kit is called Socrates, and like the BMS School Rocket it is a BT-50-based 4FNC with streamer recovery, set up for 18mm motors. And like the BMS School Rocket its four fins are TTW and made from laser-cut 3/32 inch balsa. Further, again like the BMS School Rocket, it has an all-Kevlar shock cord and a shiny streamer for recovery.

But thanks to some clever use of ABS 3D printed parts, it has a screw-on motor retainer instead of a hook, a 3D printed nose cone that is hollow with an open shoulder (and therefore a good place to stash a small altimeter) and a 3D printed launch lug. The motor mount’s centering rings and the launch lug have holes in their mounting surfaces so that it is possible to use wood glue (or white glue) to assemble the whole model. No other adhesives are needed, so it can be built in a group setting with no worries about CA or having to deal with plastic model cement.

What follows is a build and then some comments after putting 15 flights on one with motors ranging from an Estes A8-3 through Q-Jet Cs.

Let’s start with the obligatory parts picture. At the top is the streamer and two Rocketry Works stickers (one gets used in the build). Below is the slotted body tube. This tube is the same pearlescent white BT-50 as used in the current AstroCam and Ghost Chaser models. More on that later.

Then, starting on the left, the fins, the shock cord, the motor mount parts (with the launch lug below) and the nose cone.

In the next post we’ll do the motor mount assembly and install it.

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Bernard Cawley
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The motor mount itself includes four parts, three of them 3D printed. The front of the mount is a part that is a combined motor block and centering ring. Then there is a motor tube which is a bit shorter than the standard 2.75 inch BT-20J. The rear centering ring also doubles as the threaded retainer, and finally there is the screw-on retainer itself.

To put the centering rings on the tube, a thick bead of Titebond II is used. You want enough that some of it extrudes out the holes in the portion of the rings that interface with the motor tube. Adding a little glue through each of the holes to assure that there are “rivets” of glue is not a bad idea.

A slot is provided in the forward ring through which you can tie the Kevlar shock cord. A little glue on the knot (and some distance up the shock cord) is helpful.

Then, to install the assembly, another sloppy bead of Titebond should be spread inside the tube just forward of the front of the fin slots, then the mount is inserted part way, and another sloppy bead of glue put on the aft ring forward of the flange. Then the mount is pushed all the way in. (Of course it helps to have pulled the shock cord back through the mount before the installation). Wipe off the excess glue and there you are.

Because the clearances are pretty generous, and the rings are plastic not wood or paper, there’s no real danger of the motor mount seizing up on the way in as there would be in a more conventional model.

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Bernard Cawley
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Round fin leading edges and tips if you like (I do), then install them normally. Since they are TTW, alignment is pretty much assured. I still use the double glue method and then use one of David Qualman’s lovely fin jigs to hold the fins perpendicular to the body.

Visible above the fins in the first picture is the laser-marked location for the launch lug.

The lug itself, which has a conformal-to-BT-50 “foot” on it is installed with a good glop of Titebond. Again the object here is to have little glue “rivets” in the holes.

Then, after a suitable time, one layer of Titebond glue fillets for the fins can be added.

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Pull the shock cord back through and tie it to one of the holes in the shoulder of the nose cone. The other hole is a convenient spot for tying a small altimeter’s lanyard.

Then finally use one of the Rocketry Works stickers to attach the streamer a foot or so down from the nose cone.

At this point the model is quite flyable. I went ahead and put three coats of Brodak Sanding Sealer on the fins on both of these that I have built to protect the fins against landing on damp grass, and to make them nice and smooth.

I’ve built two of them. One weighed 0.98 ounce at this point. The other (the one in the pictures) weighs exactly 1 ounce.

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Bernard Cawley
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I’ve put 15 flights on one of these, as I mentioned. That’s probably 13 more flights than most of these models will ever see if they’re built in a classroom/Scout context.

Again like the BMS School Rocket, the Rocketry Works Socrates is a reliable flyer, and with the screw-on motor retainer it’s about as easy to prep for flight as a streamer-recovery model gets.

However, that all-Kevlar shock cord tied to the upper centering/motor block ring is right in the ejection charge blast. So eventually it gets cooked through. In my case this happened on the 12th flight. It was reattached with a tri-fold after that.

Earlier on the ejection charge from the first C18-6W I flew it on was quite strong and the shock cord tore loose from the nose cone. Fortunately it was a calm day and the nose cone landed near the pad. I glued the crack with thin CA and moved the shock cord to the other hole in the nose cone shoulder and have had no more problems even with another C18-6W.

That pearlescent white body tube seems to be weaker than the average BT-50 (either brown or white) and after 15 streamer landings on moderately firm surfaces there is quite a bit of crumpling of the tube above the fins. I have applied my usual fix for this (tiny pinholes in the glassine layer, pull the tube as straight as possible and flow thin CA into the pinholes) and it is still quite flyable, if ugly now.

The Rocketry Works sticker that holds the streamer on will eventually tear. I’ve reinforced with Scotch Multi-Task tape. I also had the streamer tear in half almost but not quite at the middle fold, but I don’t know why as there has been very little fraying of this 2 mil Mylar otherwise. Again Scotch Multi Task to the rescue.

Altitudes are just under 200 feet on A8, 500-600 on various Bs, and 900-1200 on various Cs, with the best altitude on the C12-6FJ.

Pictures are liftoff frames from video: Estes C6, Q-Jet C18, Q-Jet C12.

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Bernard Cawley
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Thanks for taking the time for the write-up.

Interesting that the Titebond II worked for the 3D plastic to tube joints.
Yep - Kevlar usually gets charred enough to break after 10 to 15 launches.

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You’re welcome.

Yeah, that whole idea that Titebond would work for these parts intrigued me, but the holes/glue rivets seem to be quite robust. I had expected to pop that launch lug off but it’s even held up to launches with C18Ws (two so far on the one I’ve been flying) just fine.

The motor mount is as solid as you could hope for.

I knew the Kevlar was going to die, it was just a question of how long. I think it took over 20 flights with my first BMS School Rocket.

The record for short Kevlar life in an arrangement like this, for me at least, was the Rocketman ‘Chutes small Miss Riley kit. It let go on the second flight. But that one has the Kevlar right in the middle of the blast from the ejection charge, not off to one side as in the School Rocket or Socrates.

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Bernard Cawley
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Updated a few pictures (orientation, mostly) and added one of the repaired crinkled body tube in post 5.

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Bernard Cawley
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Very nice writeup Bernard.

Any idea what the cost of the kit will be?

Also, I'm curious as to how much time is required to print the 3D pieces. I've recently seen a number of kits using 3D parts but to produce them in any quantity takes a ton of printer time.

Steve

Steve,

The are shown at $6.99 on the Rocketry Works web site. https://www.rocketryworks.com/socrates-model-rocket/

One of us would have to ask James how much printer time is involved. I get the impression from poking around the site that he has more than one printer. And I’d think he could print batches of the various parts in one session unless the build volumes of his printers are really tiny.

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Bernard Cawley
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SAM 0061
AMA 42160
KG7AIE