Building the (scratch) Rxiiiab (part 2)

So here’s a start on the 13 mm motor pod. The two BT-5/20 rings are to close the gap and align the tube while the BT-5/50 acts as a thrust plate.IMG_6207 Here it is in the end of the BT-50 body tube.IMG_6210 I made two cardstock shrouds (from the patterns generated by OpenRocket), picked the one I liked better (a coin toss really) and glued the other inside it, making what Chris Michielssen calls a super-shroud.IMG_6213 I glued it in place, then started cutting a notch for the launch lug. A longer notch than I expected. I kept cutting to what I thought would be a good length, trying the lug, and then cutting it longer. It’s a sloppy cut; for the RX, I need to figure out how to lay out and cut the notch before gluing the shroud together and on. Note the inner shroud sticking out at the back. Later on I trimmed it even with the outer shroud.IMG_6216 Next I glued a BT5/60 centering ring (with a notch for the hook and a hole for the launch lug) onto the rear end of the pod. The pod could’ve stood to be another quarter inch or so longer.IMG_6219 I removed the pod and stuck it in the top of the body tube to hold it upright while I glued the launch lug in. The rear end got trimmed off later.IMG_6222

Before anything else I peeled off a layer of paper from the BT-5/20 rings, to loosen up the pod’s fit a bit, then tried blowing through the body tube with the pod in. It ejected. There may be hope.

Another lug was glued to the airframe; a piece of Kevlar was glued to the pod and the other end was attached to the inside of the shroud with a trifold mount; the nose cone was glued in.IMG_6226 That’s almost all. I checked the CG against OpenRocket and found a discrepancy — which turned out to be because somehow I cut the body tube about an inch too short. Once I modified the OR model it claimed the CG with an A10-3T loaded was right bang on top of the CP. Not that there’s necessarily any reason to believe OR’s CP, but I think it’s probably not terribly far off. I rammed 8.5 grams of clay into the top of the airframe, bringing the CP to about the bottom of the forward launch lug, which OR claims is 1.4 calibers ahead of the CP. Seems a good starting point.IMG_6230

I plan on flying this thing naked tomorrow. The rocket, not me. I’m bringing more clay along.

It’s unpainted, therefore not really done, but it’s entering the fleet, so I’m taking it out of the “in progress” category along with the Big Blinka. Now that category is back down to single digits, but no one’s going to be fooled by that.

 

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