Why not build a MINI Miss Riley?!?

I enjoyed designing and printing my Miss Riley from Ky Michaelson's Rocksim plans so much that I thought that, if scaled down a bit, it would be a nice desktop display item for my daughter.  My Miss Riley is 58 inches tall (from nose to the base of the nozzle):

OpenRocket lets you use the Edit/Scale command to resize any rocket by a percentage or to a specific diameter.  Choosing the smallest size body tube I have, the BT-20, I resized Miss Riley to a MINI Miss Riley that is 16 1/4 inches long and takes B and C engines instead of 29 mm F engines (Ky's was originally designed for 38 mm engines).  Here's my rescaled MINI:

Because the body is the size of the engines I'll use, I edited the fins to remove the fin tabs.  It took a couple of tries to export parts and print, since resizing led to very thin parts (~0.68 mm).  I manually resized the nose cone, fins and nozzle to 1.5 mm then re-exported then from OpenRocket for printing.  The nose cone required some manipulation in Tinkercad to add crossbars in the open base of the nose cone so I had a way to anchor the shock cord.  Using Tinkercad I uploaded the OpenRocket generated (1.5 mm) OBJ file, added a block next to the nose cone, then resized the block to 2 mm high by 3 mm wide by 17 mm long (after using calipers to measure the spacing on a test print), then duplicated that object, turned one copy 90 degrees, dragged it on top of the first copy then merged the two lines to make a large X.  I then dragged the nose cone on top of the X, nudging it until it looked good from the bottom, then merged these two objects and exported it from Tinkercad as an STL for slicing in Cura and printing.  For grins, I laid out the MINI parts next to the full size Miss Riley parts on my printer bed along with some pieces of the respective body tubes for comparison (BT-20 on left, BT-80 on right):

Comparison of Miss Riley and MINI Fins (blue), Nose cones (red), "De Laval nozzle" (grey) and body tubes

The MINI Miss Riley will only need an 8" plastic parachute (IF it fits into the body tube), compared to the 24" nylon parachute I plan on using in the full Miss Riley.  The MINI Miss Riley is too small for the JLCR, but will only go 123 feet on a B6-4 and 434 feet on a C6-7, with the parachute opening around 300 feet because of the long delay so will have the same effect as using the JLCR.

OpenRocket simulation of MINI Miss Riley on C6-7

I'll adjust the simulation with the final printed weights, then I just need to trim a couple of inches off the BT-20 in the above picture, glue in an engine mount so that there's still space for the nozzle, attach a launch lug, sand and paint the body then use my fin alignment guide to glue on the fins and print a resized "Miss Riley" decal.  If I can't get a folded 8" parachute to fit in the body I may end up using a streamer instead.  I'll try friction fitting the B6-4 and C6-7 using masking tape and friction fit to hold the nozzle below the engine.  It's printed with PETG instead of PLA so should be able to withstand the heat.  If the nozzle falls off, I can reprint one in half an hour for display and eventually figure out how to add retaining clips in Tinkercad when my skills improve.

I'll build it, launch it once for proof that it will fly before deciding to add it to my growing rocket collection or "loan" it to my daughter!  I'll update this page when it's finished.  Stay tuned for pictures and a launch report.  I still have to figure out a custom display stand for this rocket since it won't stand on the fins and the "De Laval nozzle" is too narrow to support it.  Of course, one advantage of building a MINI version is that things like the nozzle or nose cone print in less than an hour instead of the 18 hour or so for some of the full size Miss Riley parts.  I also have the Estes tube cutter for BT-20 and don't need to 3D print that either like I had to for the larger body tube.

April 12 update:

I've cut the 12" body tube, glued in the engine retainer and shock cord, and added some lead weights to the nose cone (OpenRocket suggested > 0.25 oz was needed).  I put in 8 gm of lead, then when I went to glue it the epoxy I had had gone bad so I used Titebond wood glue.  The final weight of lead + dried glue + nose cone is 16 gm (0.5 oz).  The finished weight of the rocket is 4.06 oz, 16.4" long with a diameter of 0.7 inches (BT-20).  Adjusting the weight in OpenRocket predicts the MINI Miss Riley should fly 138 feet on a B6-4 (optimal delay 2.48 sec) and 486 feet on a C6-7 (optimal delay 4.47 sec); I'll use slightly longer than optimal delays to open the 8" parachute later to reduce the chance of it drifting far, far away.  The body is primed, sanded and painted and now I just need to purchase some fresh epoxy to glue on the fins and print the decal.  I'll post a picture when it's finished.

April 15 update:

I bought new epoxy and attached the fins using the Estes fin alignment guide and attached the decal I printed while the fins were drying:

After everything dried, my MINI Miss Riley took it's place in shadow of some of my bigger rockets on my shelf.

The nozzle isn't permanently attached so I can remove it for display (using an Estes 18 mm display stand) but I think it turned out pretty nice.  I hope to make it to our club launch next weekend and see how it flies.