Mid-Power K-48 Bandit upscale

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T-Rex

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When Semroc was shutting down and clearing inventory, I purchased 3 BNC-70H-AO nose cones. One of them is in an upscale Goblin, one is intended for a BBZ, and the other is for a Bandit.
Originally I was just going to build it with a normal motor tube, but after building the Semroc kit, got to thinking.... I am going to attempt using a 29mm motor tube with a 38mm baffle tube to channel the ejection gases.

Tonight I cut the 29mm & 38mm tubes to length, glued the 29-38 centering rings on along with one of the 29-BT70 rings.
Tomorrow is supposed to be a comfortable 63 degrees so hopefully I can get out in the garage to drill some holes in the tubes, and cut fins.....

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I do not work well in the abstract, and when I was able to actually see the space between the tubes, I started to get concerned. A ground test is in order to ensure it will not blow out.
 
This evening took the motor tubes out to the garage and drilled some seriously ugly holes. (Dear Santa, I need some sharp quality drill bits.) I wrapped some newspaper around a dowel to create a... not sure what to call it.... a backing so I didn't collapse the tube while drilling.
Stiffened the holes with thin CA and redrilled. Better, but still ugly. Cleaned the chads out of the 38mm.
Applied glue and slid the tubes together. Installed the forward centering ring.


After I had glued the tubes together, it occurred to me that the aft centering ring is now attached. I will have to do the internal fillets from the outside. Oh well, is what it is...
I covered the end of the motor tube and gave it a puff test. Didn't seem like it built pressure, so maybe it will survive after all.

EDIT: Added the photo that shows the drilled holes at opposite ends, thus creating the turns necessary for a baffle. The original did not have this many holes, but I am looking at loading 2 grams of BP....

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Cut the air frame tubes tonight. I measured twice and cut once. I should have scaled twice as well. Some where in the fiddling around with section lengths, I lost 1/2 inch. So I can re-cut one of the tubes, or I can just go with it.
I know this may throw the purists into a seizure but I am going to leave it as is for now. I have a long enough section that is currently scrape but I just don't think I can see the difference 43" and 43.5" total length.
 
Cut the air frame tubes tonight. I measured twice and cut once. I should have scaled twice as well. Some where in the fiddling around with section lengths, I lost 1/2 inch. So I can re-cut one of the tubes, or I can just go with it.
I know this may throw the purists into a seizure but I am going to leave it as is for now. I have a long enough section that is currently scrape but I just don't think I can see the difference 43" and 43.5" total length.

What's 1/2" among friends?
 
I still may add a 1/2 "switch band" at the coupling. Maybe I'll try cutting a band and see how it comes out.

Today's action... I am going to go into detail, just because I haven't seen it discussed in a while. Maybe it will help some of the newer folks....

Down loaded a wrap type marking guide from Payloadbay. Marked the tube the old fashioned way using a door jam. After the fin placements were marked, I folded the guide to locate the center between 2 fins, for installing rail buttons.

Got out my trusty aluminum angle, taped it to the tube and used it as a guide to cut the fin slots. Obviously you move it for each cut position. The reason we use an angle is because it will always lay straight along the long axis of the tube, unless it is damaged/dinged/bent. I use the blue painters tape because it does not stick hard enough to damage the tube when you move everything. I caution you new folks, it is possible for a razor knife (Exacto, etc) to slice off thing shavings of the aluminum, thus making your guide no longer straight (and placing razor sharp shavings on your work surface).
Score the tube lightly many times. Eventually you will cut through.

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I know this may throw the purists into a seizure but I am going to leave it as is for now. I have a long enough section that is currently scrape but I just don't think I can see the difference 43" and 43.5" total length.

My dirty little secret? My Optima is an inch short.
 
Been doing little things here and there, as well as working on a Little John repair...
Use a hobby knife to cut away sections of the most forward centering ring to allow ejection gasses to pass. Made a Y-harness and attached it around the motor mount. I hope that there is still enough room for gasses to pass.
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Went out to the garage and found 4pcs 1/8" plywood disc that look like they are from cutting 29mm centering rings. Sanded them a little until they fit snug in the end of the mmt. Didn't have a dowel the right diameter to fit the center holes of the discs, so I sanded a larger one down. Glued the discs and dowel together to make a bulkhead for the 29mm tube. Glued the bulkhead assembly in place at the forward end of the tube.
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Looks like the fins are the same shape, but it's a lot longer, correct?
 
Similar, but not. The trailing edge on the newer bandit are swept back. The trailing edge on the original are swept forward. Nose cones are also different.
The designed in ejection baffle is what makes the original special. Today we think nothing of using a baffle, but this rocket was released in '74.

Besides I have the nosecone, so why not...
 
Glued the motor mount / baffle assembly into the air frame. I hope that I got enough glue far enough in for the fwd centering ring.
Tomorrow is the last day before the big freeze comes to town, I will most likely get the fins cut while it is comfortable out......
 
Printed the fin template from OR. Used a glue stick and pasted it to a piece of poster board. Went out to the garage and proceeded to cut 4 fins. Just a few minutes ago I sat down and looked over at the Semroc version I built that is awaiting paint. The original only has 3 fins. Checked the air frame, and sure enough I cut 4 fin slots. Crapola..... Oh well I guess I'll build it with 4 fins.
 
That's an interesting baffle design. I don't know that I've seen that before. You mentioned OR. Did you not print the finwrap from it? It should automatically be for three fins.
 
That's an interesting baffle design. I don't know that I've seen that before. You mentioned OR. Did you not print the finwrap from it? It should automatically be for three fins.

I should have, but I went to Payload Bay and made one. For some reason I have never used the wrap from OR files.
 
I always use the wrap from OR. I like them better than Payload Bay, probably because I don't have to create it. I'm not lazy, I'm efficient.
 
I should probably start using the ones from OR. I think what happened is I am finishing a Patriot, rebuilding a Little John that I wrecked, and building the Bandit, with the BBZ in the back of my head (on vacation through the holidays sitting at the house trying to cram too much in..)
It will still fly, just not quite as high....
I was planning to laminate the 1/8" ply with 2 pieces of 1/32 basswood to make 3/16. I'll probably skip that part now.
 
I never thought about laminating 1/8" ply with basswood. That's a good idea. I've never been able to find any good 3/16" ply. I ordered some from Balsa USA several years ago, and it was warped really bad.
 
I never thought about laminating 1/8" ply with basswood. That's a good idea. I've never been able to find any good 3/16" ply. I ordered some from Balsa USA several years ago, and it was warped really bad.

I haven't tried it yet, not sure how good an idea it is. I considered trying 1/32 ply, but Hobby Lobby doesn't sell it any more, here anyway. I haven't looked online.
 
Have you tried Michael's? They sell various thicknesses, but I don't know how thin.
 
Found another length of the BTH070 out in the garage. Printed the wrap from OpenRocket. Laid out 3 fins and the rail buttons. Cut the tube to length.
Peeled the first tube off of the motor mount. It was interesting to find that it was not glued in very well. I'll have to do something different this time.

Since I know have an extra fin, I cut 2 pieces of 1/32 basswood and using wood glue and, laminated them to one of the fin blanks. (spread the glue thinly using the edge of an old NAR card) I wrapped the assembly in waxed paper then put a couple reams of paper on top to hopefully keep it flat. We'll see how it comes out tomorrow.
 
The lamination seems to have worked just fine, more or less. I measured the thickness with a tape measure, and found it to be between 3/16 and 1/4. (7/32?). Laid flat on the table, it is the same thickness as the 1/4" I have. I have not 'wasted' a piece of 1/4" to verify it, but I am also guessing that it is heavier than a fin cut from 1/4".

Might to play with different combinations and see what they make....

For this build, I'll stick with 1/8th.
 
Glued the motor mount/baffle into the replacement tube. Double glued the fins. Needs a fillet around the bottom and the motor retainer.
Picture is next to the Semroc version, also awaiting paint.....

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