Fliskits classroom aid -- low power motor model

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Well-Known Member
Jan 17, 2009
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Fliskits CutAway model rocket motor

I recently worked on a ‘beta’ version of a new FlisKits kit and would like to share my experiences. The new product is a non-flying teaching aid, useful for illustrating what all the goodies are inside a blackpowder model rocket motor. Assembly instructions were well documented, fairly straightforward and should be easy for all skill levels. The resulting model is a really neat item with colorful highlights and clear labels and is a good size for holding up in front of a group of students.

At the start of this project, Mr. Flis asked me to complete the build in a couple days. Of course, I completely blew that plan (SORRY, Jim!), especially after I messed up the paint job (that Jim did NOT ask for) and my little digital Nikon broke (Jim, can I turn in an expense report for a new camera?). If you don’t screw around (like I did) this kit is easily build-able in a couple evenings for a few hours total build time. And you don’t really need paint.

When I finally finished this project we submitted a review to EMRR, and they did a great job of making all my notes and snapshots look good. Just in case anyone here on TRF does not ever get over to EMRR (and WHY DON”T YOU?!!) I am putting the info here as well; also, here on TRF you are a little more free to post questions and add comments. I am going to work on getting this review completed and then I’ll come back to answer any questions you guys might post.

The new Fliskits Cutaway Model Rocket Motor should become one of our standard teaching items, just like Stine’s Handbook and the Estes Starter Specials. The only down-side I can think of is that this new model has me wasting a lot of time daydreaming about an actual working blackpowder motor this same size…..

If you have ever been at a loss for a giant version of a model rocket motor, a teaching aid to hold up in front of a class, this is your ticket. This little kit provides a good illustration of the internal parts, gives you a model in a good, usable size, and is easy to assemble in a couple hours of total work-time. It requires primarily a sharp X-acto knife and some Elmers-type white glue.

When I first opened the kit I was impressed with the high quality of the laser-cut sheet, both the material and the laser work. The sheet material from which components were cut was a cardboard-type product that was very light while still having good strength and stiffness. The faces of the sheet were finished with a “plastic” layer that made me think of the exterior of Estes-style body tubes. The laser-cut lines were (to me) very narrow (0.1 to 0.2 mm?) but were straight, neat, and without any noticeable scorch marks on the surrounding material. Parts were connected to the main sheet by tiny webs that were easily severed with the tip of a sharp X-acto. Parts fit so snugly within the sheet that a little patience and care was needed to separate them without damaging the edges of the parts.

Before separating any parts from the laser-cut sheet it would be good for the builder to check Figure 1 (Step 1) and make a clear identification of all parts before separating them. Builders should note that the spine is slightly different from the two casing caps (and may want to pencil a label on the parts to note which is which). Similarly, the four nozzle parts (the half-disc-shaped items down the center of the sheet) should be noted and identified. It is not difficult to see a difference between the nozzle 1/nozzle 3 parts and the others because 1 and 3 have a large center cutout (and if I am not mistaken, nozzle 1 and nozzle 3 are the same size and interchangeable). The most important difference is that nozzle 2 has a small center cutout and might be mistaken for nozzle 4 if the builder gets in a hurry.
For Step 2 the builder must remove the spine, casing caps, and ribs from the laser-cut sheet. These parts should be handled carefully as they are relatively delicate until they are assembled. It is easy, for example, to bend the long, thin, narrow spine and casing caps, but they need to be quite straight for this kit to work. It might be a good idea for the builder to separate these parts by cutting the connecting sprues, then placing the sheet on a flat cutting surface for support and cutting away the surrounding sheet material from one end (see Figure B). This makes it much easier to remove these parts gently from the rest of the sheet and keep them straight.

I found the four parts needed for Step 2 and checked them for flatness and clean edges. I used only a very small amount of glue to assemble each rib to the spine; a dot of glue from the tip of a toothpick was enough to prep each connecting joint. Large amounts of glue are really not necessary at this point (or at any point in this kit) and would just make a mess. The parts are pre-cut with tabs and slots, and the fit was very good.

I had no difficulty completing Step 2 but worked quickly (before the glue dried completely) and checked for proper part alignment by placing the finished assembly upside down on a good flat surface. All six rib tips should sit squarely on the flat surface. I also used a framing square (two tablets of paper could also form a 90 degree corner) and a plastic triangle to check that the end ribs were square and the spine was straight (see Figure C). I handled this thing very carefully to set it aside, and let it dry while working the next steps.

In Step 3 the nozzle pieces and the propellant plate are assembled. Again, I used the tip of a toothpick to apply glue to the joints, this time because I wanted to be able to adjust them a bit (if needed). I used my plastic triangle again to check alignment, but the corner of a business card or any small object with a square corner could be used. It was easy to clear the waste material from the pre-cut slots and I found the pre-cut tabs fit cleanly and firmly into the slots. (Jim, have you given any thought to completely cutting these slots, with no sprues, so the tiny little pieces just fallout?) Once these parts are properly assembled the builder can add more glue but it really isn’t needed. This assembly is shown in Figures D and E.


For Step 4 the two casing caps are added to the edges of the assembly from Step 2 (the delicate one). The casing caps appear to be symmetrical, and can be turned either way and will still fit properly. I used my trusty toothpick to place a small dot of glue on the tips of the ribs and spread it across the joint. I worked quickly to complete this assembly and re-checked everything with my framing square and plastic triangle, trying to keep everything square during and after handling these delicate parts. Finally, I placed the assembly upside down on a flat surface and laid a light object (the plastic triangle) across to top to gently hold all the parts in alignment while the glue dried (see Figure F). Let the glue dry thoroughly; do not proceed if this rib assembly is “soft” or loose.

In Step 5 the BT60 is finally glued to the inside of the rib assembly from Step 4. I think the best way to glue this whole thing together is to use only small amounts of glue on the inside of the rib framework for the initial assembly to the BT60. This way the glue dries quickly, and if the framework needs to be repositioned it will not be as difficult to cut through all the glue joints. Once the rib framework is in place the builder can add more glue to all the joints, but more glue should only be added to the “framework” side (shown in Figure G) but should be kept clear of the opposite side (shown in Figure H) to make life easier in following steps.


In Steps 6, 7 and 8, follow the directions. Jim provides a normal wrap-around marking guide for the outer BT70 tube and did a good job of describing how to mark and cut. Builders will end up with two sections of BT70 (as shown in Figure I) that are two slightly different widths…and they are supposed to be that way.

Don’t do what I did; I split them neatly in half. And then each half was just a sliver short of covering the framework. I had to get out some more BT70, and actually follow the directions (and hey!, if you follow the directions, THEY WORK!). I completely wasted eight inches of BT70. Did I mention that I HATE wasting ANY bits of body tube? The rocket-builder police will no doubt be on my case now for body tube atrocities.

For Step 9 the assembly from Step 5 (Figures G and H) will be glued into the wider of the two pieces of BT70 from the previous step. In order to get a good glue bond in the middle of this thing, I used an end rib as a marking guide and made a pencil mark where the center rib would touch the inside of the BT70 (shown in Figure J) so I could apply glue while this area was still open (Figure K). Note the expendable Q-tip that was used to spread out the glue—a little handier than cleaning the bristles of a small brush.

The figure on the left shows how I used the previous assembly as a guide for marking where the center rib will fit. The figure on the right shows how I applied glue on the areas where the assembly from step 5 will attach to the inside of the BT70.


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In Steps 10 and 11 the model motor case will really take shape. In Step 10 the builder trims off the excess BT70 so the edge of that BT matches the flat surface of the casing cap (remember how the BT70 is supposed to be WIDER than half of the circumference?). Hold the cutting edge of the X-acto at a shallow angle (see Figure L) and make several passes. Try really hard not to twist the X-acto and cut into the casing cap because any gouges or divots you leave will only be making that much more repair work for yourself later. In fact, if you leave a little bit of BT70 after cutting with an X-acto, you can finish it off with an emery board (see Figure M).


In Step 11 the builder will make the same kind of cut but will trim the inner BT60. Again, hold the X-acto cutting edge at a shallow angle, make several passes, and the BT60 will soon cut through (see Figure N). If you concentrate on holding the side of the X-acto blade so it is flat against the face of the casing cap you should get a nice even cut through the inner BT60.

In Steps 12, 13 and 14, follow the directions. Jim already has these well described. I might add that Step 13 is another place where a small amount of glue, applied by toothpick, will be plenty to attach and hold the caps onto the ends of the delay plate. (And a small amount of glue gives a second chance to adjust the position of the caps, if necessary.) If it makes you feel better, after the first glue dries and the assembly is firm, you can put all the glue you want on the inside corners.

Step 14 is another wrap-around marking guide that is sized for the CPL60 coupler, and has uneven marks just like the guide used for Step 6. Builders will end up with two sections of coupler (as shown in Figure P) that are two slightly different widths…and they are supposed to be that way.

The CPL60 coupler material was much easier to cut than I expected (going from past experience with Estes coupler material). It is still necessary to make several light passes and cut progressively deeper each time, just as when cutting body tube cardboard, but the FlisKits CPL60 material is only slightly tougher to cut than normal BT60. Builders should have no trouble completing these cuts, but should observe all normal safety measures when using an X-acto knife.

In Step 16 one of the cut pieces of CPL60 is trimmed to width and glued to the delay plate assembly from Step 13. When I built my preliminary version of this model kit, this assembly was designed slightly differently from the final production version. It still was a good representation of a motor’s delay charge (see Figure Q), and is an optional part of the motor model that represents the delay and ejection charges (and end cap retainer) for single stage and upper stage motors. If this assembly is removed, the motor model illustrates a booster motor loaded only with propellant.

And speaking of propellant, this is the point where I inserted the propellant plate assembly (from Step 3) into the aft end of the motor case assembly (from Step 12). Because the fit of these two assemblies was so snug, I was concerned about my ability to slide them together, with glue already applied, and get them properly positioned before the glue “grabbed” and possibly locked them in the wrong position. So, I assembled them dry. I placed the propellant plate assembly about 1/4 inch forward of the aft edge of the motor case assembly because most blackpowder motors have the ceramic nozzle stamp-formed a short distance inside the back end, not flush with the end of the motor case. I pressed the propellant plate into the motor case assembly until the outer face sheet made a flush fit with the casing caps. After the propellant plate was seated where I wanted it, I was able to apply glue through the openings in the propellant plate and around the aft nozzle part (see Figure R; look closely to see where I applied glue). I also applied a thin bead of glue around the front propellant end cap (see Figure S), but builders should avoid using a thick fillet at the front cap so that the delay plate assembly will be able to fit.

This was a teeny oops in the beta instructions because….it was left out. Hey, it can happen to anybody. That’s what beta builds are for.


Well, this step is supposed to be part of the delay assembly from Step 16, and this step of the instructions works just fine if you are building the released version of the Cutaway motor model. Since I was doing a beta check we did not use step 17, but this step looks like an easy one for anyone.
For Steps 18, 19, and 20, I can only recommend that builders should not try to hurry through these steps. It is not critical to construct perfect little conical sections for nozzle #1, #2, #3, and #4, because only half of these parts will remain in the finished motor model. Builders can position the glue tabs so they are in the upper, exposed part when installed (see Figure T); this is the part that will be trimmed and removed in Steps 19 and 20.


The kit instructions recommend using a sharp X-acto blade to trim the nozzle parts, and I would go even further and recommend using a brand-new-sharp X-acto blade. It will make trimming these parts so much easier.

Micromeister, you can use one of your old blades because you know how to re-sharpen them better than new.
At this point I will sympathize with people who don’t like teeny origami projects. I used spackle to fill in gaps and cracks, and in the middle of spackling, it occurred to me: I could have just packed the whole rear end with spackle, let it dry, and used a small jeweler’s file or a Dremel to carve out the nozzle throat and the propellant chamber. But I’ll also say that working with these little bitty pieces of paper wasn’t really all that bad. No, this idea wasn’t in the Fliskits instructions, but I thought I’d toss it in at no charge.
The construction part of my beta build was complete at this point. This step was included to point out that builders could leave the delay assembly loose, and have the option to display a motor model (with the delay module removed) of a booster. Or, the delay module could be glued permanently in place. Decisions, decisions.
Getting close to the end: I think that soaking a few drops of CA (cyanoacrylate, or “superglue”) into the four outside corners of the motor case model would greatly improve the durability of this model. If handled with reasonable care, this model will probably stand up well to handling, transport, and other demands, but I think it couldn’t hurt anything to use a touch of CA for an extra bit of reinforcement on the corners.

I should point out that this model really does not require any painting at all, but adding an overall color was my own choice (yeah, I’m one of those obsessive-compulsive people that likes to add my own little extra touches). The motor model works just fine without any paint. The kit instructions didn’t even mention paint. I guess I should have taken a hint.

I applied a thin layer of spackle to the “show” face of my model and sanded it smooth (and mostly removed) before proceeding with primer and paint. I think the smoothed faces just make the appearance of the whole model a little more slick, and it makes a little better surface to apply paint and paper wraps. Any sort of normal water-based spackle from the local hardware store can be used (I would recommend avoiding any oil-based spackle products). Use 400 or 600 grit sandpaper to smooth the surface, wipe any remaining dust off the surfaces for better paint adhesion, and use appropriate colors. The first time I painted, I used a brown that (AFTER I painted, of course) I decided just didn’t look right. I sanded a little, and re-primed a little, and ended up using a combination of tan and medium brown to get a more authentic “cardboard” color (TOLD you I was obsessive). I also masked off the areas around the nozzle and used a gray spray paint to color the nozzle surfaces that the paper wrap would not cover. (My doctor is opening a new therapy lab at the end of my block.)

In hindsight, all this priming and spray painting was probably more work than it was worth—I will probably just use brown and gray highlighters next time. Or re-work the outer paper wrap to extend over the inside edges of the motor.

The paper wraps were assembled using “Duro All-Purpose” spray adhesive on the back face of the paper and on the matching areas of the motor model. (There are other brands such as 3M spray adhesive that will also work quite well.) I masked the model to prevent getting adhesive spray all over areas where I didn’t want it, but that was pretty easy. As always, after spraying both surfaces with adhesive you have to align the joining pieces very carefully before letting them touch. I thought I got the outer paper wrap just a teeny bit crooked and started obsessing over whether to remove it and print a new one—my wife (an actual full time classroom teacher) said that the label position was just fine. The inner paper wrap went on very easily and fit the nozzle edges well. The paper wrap for the delay and ejection charge was a little mis-sized for the model I built, but I think that was because I had a “production” wrap and a “beta” model that was a different size.


The completed motor model is very scale-like in appearance and should go a long way toward answering questions from new rocketeers about what is inside the motor. The wraps are designed with bright colors to highlight the important components, and also have good labels for internal parts. All internal components are separately represented (even the clay cap over the ejection charge) so there is something to point to when explaining any part of the motor’s operation. The removable delay/ejection part is an excellent way to show how booster motors function. The model is designed to a good size that works very well for talking around a table or for standing in front of a classroom.

Since I made this beta build, FlisKits has added a matching demonstration model of a model rocket igniter. This looks like a great tool for illustrating the parts of an igniter, how to use it, and how to handle it properly. I don’t have one of these yet but it is definitely on my “gotta get” list.

Overall, I think part quality and fit is very good in the new FlisKits Cutaway model rocket motor. Instructions are clear and follow a logical approach, matching illustrations are very good, and beginners and inexperienced modelers should have no trouble building this motor model. Not being a “flight” model rocket, this kit automatically becomes much more forgiving of misplaced (or left out) glues, and does not require some of the more intricate assembly and heavy-duty adhesives of flying rockets. Undoubtedly, some wise guy will still insist this kit must be fiberglassed…just wait and see.
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I made a fairly major mistake in the construction of this kit, and it is not mentioned anywhere in the preceding text, but it is clearly documented above…somewhere. I am offering a prize to anyone who correctly identifies the screw-up and posts a note in this thread. The winner will receive one of these Cutaway kits, sponsored by me (because I think it’s a really great kit idea), delivered to your door. (If you have a door.) Employees of Fliskits are not eligible because---well, they just aren’t.
Hi Powderburner,
The only thing I can see (after re-reading the entire review) is the positioning of the "Delay Charge" copy block. It's flipped 90 degrees and set very close to the wall of the propellant section. It doesn't look like the FliKit illustration in your first post. The whole delay/ejection charge section seems longer too.
So - how'd I do?

Hans "Chris" Michielssen
We are glad you could join in. The more the merrier!

You made a good observation but no, you were only picking up one of the little differences between the 'beta' and production versions.

The mistake I made was all my own, for not following directions, and for getting ahead of myself. It is very very clearly shown in one of my pix.

Keep trying!
I'll try- in step 16 the coupler stock should cover the ends of the frame rather than going inside of it. That would affect the fit of this unit in the outer tube. Also, the portion of the nozzle that goes into the propellant section should be colore red.
The lines on his rear paper cover should be horizontal rather than vertical, so the line does not show when finished, without painting it?

You guys are coming up with some interesting stuff, but so far it has all been minor 'cleanup' stuff that showed some of the differences between the beta and production versions. I'm trying to fess up to a spot in the directions where I totally blew it. I'll give one hint: builder fever.

But you are all making some very very good points.

And when I tell you what the mistake was, it's one of those things that was right under your nose, and you're gonna groan....and I'm gonna reveal what an idiot I am.

I think I'll let this challenge run for another day and then pick some winners.