Building a Bohica’s Dead Ringer (part 1)

Last October I came across this YORF thread and this (archived) TRF thread having to do with rockets that use centering rings for drag stabilization instead of fins. Bohica’s two “Dead Ringers” — not to be confused with the FlisKits rocket kit of the same name — were similar but not identical designs using different motor mounts; there was a 13 mm one: 
and an 18 mm one:
Both used BT-50 tubing but the rings were different. Bohica provided a drawing with some measurements of the 13 mm version:

and a written description of the 18 mm. Solomoriah independently came up with a very similar idea, which he called the Spike, using BT-20 and three or four CR2060s. I haven’t found any posts indicating whether or not he ever built it.

Of course OpenRocket hasn’t a prayer of simming this design, although CPMcGraw put in an interesting effort which however may or may not have any relationship to reality. Bohica said his 13 mm version was “super stable” and I think he meant to imply the 18 mm one was too, with about 0.5 oz weight in the nose cone. Wbblair built an 18 mm one and reported it was stable during boost but flipped, once, to fly tail first after burnout; he had less weight (7 grams) in the nose, though. Micromeister built a T-3 based downscale:With 5.4 g nose weight he said it was “dead on stable… arrow straight boost…”

So with proper weight, it’ll work. And it is, to my eye, cool as all heck, so I’m building one.

I like Bohica’s 13 mm design best, so I’m working from that; but given how draggy the rings are, I’m going with an 18 mm motor mount.

Screen Shot 2013-11-04 at 10.18.43 PM

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