Sunday, March 18, 2018

Decals and wraps in Open Rocket

Centuri Payloader from 1962 catalog (Click to enlarge).
HARA has received an email from Levi's (the clothing company) looking to do a late 1950's/early 1960's period photo shoot involving model rocketry in Huntsville. So yesterday, I started inventorying my retro clones and noted that I had plenty from the 1970's, but very few from the earliest days of our hobby. This realization planted my carcass in front of my computer, where I began a search of the early catalogs on Ninfinger's site, looking for some models that could be quickly cloned. The 1962 Centuri Payloader - a shorter, skinny ancestor of the popular Payloader II - caught my eye; simple 3FNC with a clear plastic payload section and white decor with a black roll pattern. Easy peasy, and there was a Rocksim file for this model posted on the Rocket Reviews web site.

However, I did not like the fins in the Rocksim simulation - they seemed to have too great a span, so I went back to the catalog image and made a few measurements, assuming a ST-7 (0.759" diameter) and a rocket length in the vicinity of 15". I then created a simulation in Open Rocket, which looked to be a much better match to the catalog, and dashed off a quick order to eRockets for the parts. This ought to have made me happy, except that a plain white rocket in Open Rocket is, well, blah. So how do I get that roll pattern into the sim?

Past attempts at incorporating decals into Open Rocket had failed miserably, leaving me to think those that could were possessed of some great arcane knowledge not dispensed to ordinary mortals. But last night a Google search turned up this thread on The Rocketry Forum, the second post of which was like reading the Rosetta Stone. All you have to do is:
  • Use a paint program (MS Paint, Pixelmator, etc.) to create an image wrap for the body tube. This wrap should have dimensions length x (pi x diameter), scaled by a suitable factor to permit easy drawing. In my case, the body tube was 10" long, so the clipboard should be at least 10 x (0.759 x pi) or 10 x 2.38. This is way too small, so I converted to centimeters and multiplied everything by 50, yielding an image size of 1270 x 303. This is usable, and soon I had it drawn up in Pixelmator (see below). Rotate it 90 degrees, save it to a JPG file, et Voila! You are done with the hardest part.
Centuri Payloader wrap in Pixelmator (Click to enlarge)
  • Now open the simulation in Open Rocket, select the body tube and click on edit.  Choose the appropriate color for the body tube (white in my case) and then change the "Repeat" option to "Clamp Edge Pixels". Under Texture, select From File, find and select the image wrap file, then click OK. Switch the view in Open Rocket to 3D Finished and you should see your rocket's body tube nicely decorated with your wrap,
Finished Payloader design in Open Rocket (Click to enlarge).
There's more stuff in the thread dealing with fins, but this was enough to get me started. I am pretty pleased that my designs and sims now will be a lot less plain!

Centuri Payloader in Open Rocket's Photo Studio (Click to enlarge).

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