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L3 Build - Gratuitous Excess

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Dustin Lobner

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How’s the build coming?
Haven't done too much on it lately. Have had a couple other side projects going on, so I've been staying busy with other things.

Planning on a launch sometime in the spring next year, maybe Mini-Midwest Power in May.
 

DMehalko

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Haven't done too much on it lately. Have had a couple other side projects going on, so I've been staying busy with other things.

Planning on a launch sometime in the spring next year, maybe Mini-Midwest Power in May.
Good deal! Thinking about this kit for a possible L3 build as well, maybe swap the fins out to match a big nuke upscale or something
 

Dustin Lobner

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Good deal! Thinking about this kit for a possible L3 build as well, maybe swap the fins out to match a big nuke upscale or something
Highly recommended for a first build of this scale. I'm lucky enough to work about 15 min from LOC...I got the kit initially, then decided I wanted to go away from their multiple motor mount system and went to a straight 75mm mount. Called up LOC, they burned the fins (longer tabs than stock), I brought all the parts back for the stock mount and we did a straight up swap for free. No BS. Jay has answered every email in a timely fashion, gave suggestions on how to organize it (there are some decisions you can make in terms of how to orient things...great for flexibility, but not the greatest if this is your first build of this size), and has been very helpful.

The kit is solid, reasonably priced, and has great support. Dunno how to recommend it more than that.
 

Dustin Lobner

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Actually started doing some things on here again. Was able to make it to the January TRA launch at Bong to show my TAPs the progress so far. One of them had concern that the coupling between the two 30" body tubes in the booster would buckle and needed to be reinforced. In the vein of "Gratuitous Excess", I took the two short coupler stiffys from the Av Bay and are putting them in the booster as reinforcement in that coupling. The top double centering ring will be between the two halves of the stiffys. I sketched it up quick to explain to the TAPs what I'm doing and got approval...the fins would be on the right hand side in this pic:
Overall.PNG

Closeup.PNG


Got the first stiffy put in last night:
IMG_20210117_212846511.jpg



So now it's the centering ring. Once that's in, the next stiffy goes in over the top of that. So at that point, that will be 30oz of glass, the body tubes, a coupler tube, a stiffy tube, and the motor mount will also traverse the gap and secure at the other side. If the rocket doesn't survive the flight...something has happened that it wouldn't have survived anyways. :headspinning:
 

Dustin Lobner

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Got the top bulkhead plate put in tonight, at least some what. Recall that for the top and bottom I'm using two bulkheads that are slightly split from each other. I first sanded some notches in one of the set:

IMG_20210122_172748705.jpgIMG_20210122_174301384.jpg

So, put some epoxy on the back of it and put it in... except that wasn't going to work. Realized that I wouldn't be able to align the rods, so I cut some holes in the thin coupler. Was then able to guide the rods into the bulkhead. These holes will be covered with the stiffy and will be reinforced with epoxy.

IMG_20210121_194416803.jpgIMG_20210121_194421403.jpg


So, the tube is spending the night upside down so the epoxy I put on things will run to where it's useful. Tomorrow I'm going to flip the rocket right side up and then inject epoxy into the holes I ground into the edges of the top disc. The goal here is to basically fill the gap between the bulkheads with epoxy and of course to epoxy them to the tubes.

Then smear epoxy everywhere inside and slide the 2nd stiffy in. Hopefully that's all done tomorrow.
 

Dustin Lobner

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Got the top rings put in this morning - the notches worked great, I was able to "inject" epoxy into the holes, and as it's sat here it's continued to flow into the groove, so it's going where it should.

Hoping to put the stiffy in later today...then I can turn my attention to fin fillets and the bottom centering ring set.

IMG_20210123_104102691.jpg
 

Dustin Lobner

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Put some more epoxy down the notches, and then put in the upper stiffy. Everything looks good...

IMG_20210123_140008004.jpg
IMG_20210123_140003637.jpg


...except one of the 3 windows I cut got cut a bit low and the stiffy ended up not quite sealing there. Going to let this epoxy cure and then going to lean the rocket at an angle and put a "generous" fillet there. It'll have the body tube plus 30oz of glass on it so I'm not worried about the strength, but might as well reinforce it given how easy it'll be.

IMG_20210123_140116878.jpg
 

Dustin Lobner

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Got the bottom centering rings in place. After fiberglassing, the tube wasn't quite round down by the fins, so ended up with a pretty significant gap between the rings and the ID of the body tube. Filling that with epoxy as best I can.

Prior to installation, I set the nuts on the metal rods about 0.010" taller than the back of the fins. Put epoxy on the washers, on the motor mount tube OD, and on the back of the fins. Put the rings on and then used nuts on the rods to tighten the plate down to the nuts/washers already on the rods. I'm pretty sure this is not at all the right way to use these rods...I put them in as something of an experiment, and at this point I'm calling it a failed experiment. That's fine, not the end of the world or this rocket.

High quality gauge block setting washer height to just taller than the back of the fins:
IMG_20210126_184003725.jpg

Prep for center ring insertion:
IMG_20210126_184814336.jpg

Ring in and epoxy everywhere:
IMG_20210127_214929502.jpg


Debating what to do with the bottom of the rocket. I wanted the bottom centering rings pushing on the backs of the fins to help carry that load...left that small gap between the ring and fins to allow epoxy to flow into the seam. So, now the motor mount tube protrudes a bit...considering just filling the bottom of the rocket (the bottom where the motor mount tube is protruding, not like the whole fin can) with epoxy (plus glass fibers as a filler since I have a crapton of it) and just fill the whole bottom flush with the bottom of the motor mount and body tube.

From this point, I'm drilling holes in the sides of the body tube above the bottom ring and shooting epoxy onto the top side of the centering ring... Because, you know, Gratuitous Excess. (-:
 

Dustin Lobner

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Talked it over with TAPs and they agreed with the glass fiber + epoxy back end fill, so that was tonight's job. Worked out pretty well I believe. Time to sketch out the tailcone/motor retention for this so I can get it 3D printed.

IMG_20210128_210517652.jpg
 

Dustin Lobner

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Got it sketched out...emailed the TAPs to ask if it's OK if the tailcone crumples a bit on landing. I had one rocket with a cone like this land on a boulder and it took a chunk out of the tailcone. It would've worked again, but yeesh. If some damage is OK, I'm planning on printing the bottom half of it (further from the rocket body) a bit weaker and allow it to work as a "crumple zone". There's a 50/50 chance I'm flying the cert flight at Bong, and the chances of landing on a gravel runway are pretty decent. Planning for that possibility.

Tailcone 1.PNGTailcone 2.PNGTailcone 3.PNGTailcone Section View.PNG
 
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