BBX Scratch Builds

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thzero

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There was a nice scratch build thread that was really detailed on a dual-deploy BBX on RF, and that inspired me some time ago to start plotting out some smaller scale dual-deploy builds. So I've built out or in process of building out a couple sport scale version of the BBX based on Peter Alway's books based on the BT60 tubes.

Both of these two versions are built to fly within certain parameters and within one of the rocket club fields I fly with and under the G limit.
  1. An Estes BT-60 based dual-deploy that launches on black power based Estes motors
IMG_20200801_181142.jpg

  1. A fiberglass BT-60 using Mach 1 tubes based dual-deploy that will launch on composite Cesaroni motors, and has a multitude of 3d printed parts. Build thread for this is over in HPR section since it'll be focused on HPR power levels
https://www.rocketryforum.com/threads/bbx-scratch-build.164178/
 
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thzero

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So for the Estes BT-60 based build... we'll start with the results.

Flew it on a D12-0 in booster and D12-5 in sustainer, but when I went back and sim'd it again it was below the 50ft/s I generally target to come off the rail. It is a long rocket with 3.75 cals of stability loaded, so a bit of weather cocking is to be expected.

Unfortunately the sustained landed deep in the reeds at the launching site and was not recovered; still need to go search for it in the snow.

launch video - Estes BT60 BBX

Oh, did use a JollyLogic CR on it (small field with lots of bushes and reeds).
 
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thzero

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Here are some photos during the build process.
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IMG_20200801_181251.jpg
 

thzero

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Couple of notes from the build process

The fins are papered, but I used epoxy instead of white glue to apply them to the fins. With compression while drying, it gave a nice surface that sanded a bit better (not that I ever did the paint job) than just exposed paper. I had used BS 15 minute epoxy, but think if I do it again I'll use BS 30 minute epoxy. Don't think its worth breaking out the West Systems for this purpose. Did all three sets of fins this way.

As far as the booster, it is gap staged. After reading bunch of powerpoints, pdfs, etc. on staging for BP rockets (google is your friend) it really boiled down to 10" seemed to be max gap for reliability. So the booster is cut-down version of the Terrier dimensions to the point that the gap staging was at 9.5". Seemed to work rather well!

The sustainer was built with as a no-zipper design - not sure I'll build it that way again, just to save some weight.
I used plastic rivets to attach components together. However, these are big and bulky - so need to revisit that and find another options.
 

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