Building the (scratch) R13 (part 1)

I’ve started building the R13, an oddroc I conceived of almost a year ago. I’ve been referring to it here as RX, but forget that. I decided last year to build a smaller, less odd prototype, the Rxiiiab; I built it, flew it, painted it, declared victory, and this year I build the real thing.

This will be a finless, tail cone stabilized rocket. Like the Rxiiiab it’ll be rear ejection, with the laundry — a chute this time — packed inside the cone. If that’s not odd enough, it’ll… but no, just wait, you’ll see.

I started with the motor mount:IMG_7920 This is ST-7 tubing. The big centering ring is ST-7 to ST-16 and the small ones are ST-7 to ST-115.

Yeah, I’m using ST tubing, not my usual Estes-type BT. There’s a reason. ST-115 is close to the right diameter. BT-50 is too skinny and BT-55 too fat. “Right” for what? Spoilers!

I expect this thing to be heavy enough to need a D motor, but I don’t think there’ll be enough room inside the cone to pack the chute around a 24 mm motor mount. So I’m going with 18 mm and expecting to fly it on Aerotech composite D motors.

Next I cut a piece of ST-115 about half an inch long and removed a slice to make something that’ll slide into the ST-115. IMG_7916 Didn’t bother closing up the gap, not needed. And in fact the slice I took out was a bit too wide, so I don’t really want the gap fully closed. What I would have liked to do with that piece would have been to glue a ST-115 bulkhead to it, but as far as I can tell there’s no such thing on the market. And I didn’t feel like trying to cut one myself, so I took the lazy way out: I glued a -7 to -115 centering ring on, and then glued a BT-50 bulkhead on top of that.IMG_7917I glued Kevlar cord to one side and coated the other with epoxy. Which is taking its own sweet time hardening in the cold basement. So I’m calling it a night.

 

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2 thoughts on “Building the (scratch) R13 (part 1)

  1. The ST-7 and ST-10 tubing is so much better than BT-20 and BT-50 tubing.
    I use it every chance I can. After a hard landing, the tube wall thickness won’t buckle and crimp above the fins leading edge.

  2. It’s more habit than anything else that I tend to use BT tubing — that, and it (and compatible parts) is more readily available, e.g. at the LHS.

    ST-115 is heavy walled stuff, apparently about twice the thickness of BT-55.

    Due to a mixup I now have a lot of ST-7 to -16 and -7 to -115 centering rings, so I may have to build more ST-16 and ST-115 rockets…

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