Friday, December 14, 2018

A new project...

Weather continues to be wet and gloomy, but incremental progress is being made. The Estes Mercury Redstone is complete, the Centuri Sky Devil clone has a base coat of white, and I'm still sanding/finishing the 3D printed nose and fins for the Redstone missile and the plastic Jupiter. Sunday's humidity may be low enough to finish painting the Sky Devil and put a coat of primer on the Redstone. One can only hope...
The first page of the Zeta plans (Click to enlarge).
With the Mercury Redstone finished, time for another project. I'm still waiting on some parts for the Gemini Titan, so I decided to look through the old Estes Design of the Month plans for a quick build. I kinda have a love/hate relationship with the Design of the Month - some of them, like the Space Twins, I really love, and there are others - like the Blue Lightning - that I can't stand. Anyway, I was poking around these designs posted on JimZ's site, and ran across #58, from 1968. It's called the Zeta and has a nice retro look - I particularly liked the ring joining the fins. A quick check of the parts inventory showed that I had everything in my bins, so I gathered the components and set to work.

The Zeta is a fairly straight forward build - with the exception of the ring that fits into the fin slots. You have to be pretty exacting in cutting out the fins for this BT-70 sized ring to fit properly, so I resorted to making them using the Cricut Maker. Even with this, the ring was a bit too small, so I had to slice it and add about a 1/4" wide strip for it to slide into the slots. 1/4" sounds like a lot, but this translates to about a 0.04" (1/25") error in the slot distance from the body tube. Not much at all, and a slight import error in the sizing could easily account for it.

Zeta fin ring showing the added 1/4" strip (Click to enlarge)
The design calls for using a BT-55Z balsa tail cone to act as a transition from the lower BT-55 body to the BT-20 payload section. It's a nice concept, except that the BT-55Z does not smoothly merge into the BT-20 - after all it is a tail cone, and you have to leave some thickness of balsa around the end to support the motor tube and avoid chipping. Works fine on the tail end of a rocket, but that flat space around the BT-20 offended every aerodynamic sense in my aged body. So I made a small cardstock shroud to make things more aerodynamic and aesthetically pleasing. This means the build is not pure Zeta, as it deviates from the design; I guess I will have to call it the Zeta-A.

Zeta forward section showing the flat space at the end
of the BT-55 9Click to enlarge).
Same thing, with the cardstock shroud added (Click
to enlarge).
Everything is assembled and ready for finishing - here's the nekkid rocket shot. The ring is not yet glued in place, as I will finish it separately. My biggest issue now is deciding on a paint scheme - the plans show a checkerboard pattern and some horizontal stripes, but there is no way of deducing the colors. This model is not a common build (i.e., no pics to be found on the Internet), so I'm going to have to rely on my own color sense to come up with a decor. Hopefully it won't be ghastly.

The Zeta ready for finishing (Click to enlarge).


  1. Slick! I printed this off last winter, but never got around to buying the parts. Or did I?

  2. Bill E,

    I have the same problem. Just beginning to inventory 20-ish Semroc boxes myself. "Oh, good! I already have that, so I don't need to (re-)order it after all!" :D

  3. What? I'm persona non grata? AGAIN?

    --Jay G., "Tau Zero / Centuri Guy"

  4. Very cool!
    I wouldn't think that tail cone would have a "step" like that. Good fix! The big nozzle reminds me of the old Estes 260 Space Booster plan.