I would recommend using aluminum for the retainer. Steel will rust very quickly if it isn't a good stainless.
I would recommend using aluminum for the retainer. Steel will rust very quickly if it isn't a good stainless.
And, steel would probably be a violation of the safety codes, whereas brass, copper, or aluminum would not.
Hasn't Estes been using spring steel motor retainers for over 50 years?
Yes, in minimal amounts and where needed its specifically allowed by the safety codes. Same for eye screws. Its needed in the case of spring steel retainers because steel can be spring tempered.
It will be a big washer, not too different from the retainers Madcow sells.
https://www.madcowrocketry.com/motor-retainer-38mm/
If I make it from 28 gauge steel, it will mass something less than 10 grams. No part of it will extend outside of the tailcone -- so it will be, arguably, inside the rocket.
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Its light enough that it might be allowable, but why not make it from aluminum? For this application steel is not really required.
At the same time I realize its not much different than the nozzle washer for a snap ring case, which is heavier and steel.
Well, the steel isn't necessary, so I will use something else.
Dan's motor mount/retainer is beautiful. The Moonbat's will be hidden by the tailcone so I will not try to make it conspicuously pretty.
I sat for, and passed, the L2 written test yesterday. I also received my certification-allowance motor -- so I'll be able to get a real launch weight and COM when it is finished.
Not worth a picture, but I worked a little on the nosecone. Its slow going. I don't want to screw it up more than I've already screwed it up.
Started building the tailcone.
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I cut three conical transitions, each smaller that the last by the thickness of the card stock (a chipboard box), and stacked them like matryoshka dolls. Lots of fitting, and trimming, and refitting. I mis-measured the diameter of the blue tube by 0.4 mm, which meant all of the transitions were about 1.5 mm too long.
I had to do a little more fine-tuning on the fin slots to get the fins in tight to the tail-cone. I am not going put a tube inside the tail cone. After I get the final wall thickness I will cut plywood formers -- narrow rings -- for the forward and aft openings.
Beautiful work!
Made the holes for the rail buttons. Something I absolutely should have done before I started painting. I was dithering, trying to decide between screw-on buttons and glue-on guides. After I repainted the airframe, I decided that black delrin buttons would be less obtrusive than whatever that white plastic is that is used for the 3D printed guides.
I glued the rest of the obsolete aft centering ring to the back of the forward centering ring, then I printed a template (a large format inkjet printer is at least as useful as a 3D printer for rocket building). It took me a minute to figure out how to mount the round-stock holders the Stanley plastic saw horses.
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I didn't want to drill, because the blue tube is so plastic, I figured I'd end up sanding away a burr on the outside and then have to repaint. So I hung the tube on a piece of 2" round stock, strapped everything down with blue-tape, and hit the tube with a 6mm arch punch. The holes are clean. Only lost a little paint at the edges -- a defect completely covered by the button.
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Last dry fit, with a piece of 1" X 1" standing in for a 1010 rail.
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The tail cone gave me a lot of grief. After the finish empty cured, I sprayed it with coat of Dulpicolor Metal Cast ground coat. Instant orange peel. I sanded, primed it, sanded it again, but it looks like the outer layer of the paper is wrinkled. I put two coats of Rustoleum High Heat silver on it and am moving on.
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Prepping the balsa cone for paint -- two coats of thin CA, and lots of sanding.
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ProTip <grin>: The little paint brush you can see in the background above is one of THESE -- they are less than useless for paint, but they are great for CA. They don't smoke like cotton swabs, the CA in the bristles stays liquid for a long time, and the (eventually) hardened CA comes right off the bristles.
Also, I put two light coats of Rustoleum Automotive Metallic blue over the Metallic purple. It makes a two-tone effect. A dark blueish purple, with bright blue highlights.
I really expected this build to be done a month ago.
You are welcome to drop in on any Tri-Cities Rocketeers launch you chose. June 2018 is a 3 day event from the Fri-Sat-Sun Fathers Day weekend.<blush> thank you.
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While stacking the cones you see up in #39, I noticed that they they were tending towards a circular profile without a former or any real coaxing from me. I printed up another set of patterns with a tighter pitch between layers, and cut them from a thinner and more flexible cardstock (the white-on-one-side stuff commonly referred to as "shirt cardboard"). I guessed wrong about how tightly I could get the cones to stack and ended up leaving off the outermost cone (which is why it says "middle" on what is clearly not the middle layer). I used Beacon Frabri-Tac glue between the layers because it is flexible and has a long open time. Pressing the stack between pieces of plywood scrap, the tailcone came out nearly perfectly circular. I'll seal the edges with CA, and the whole assemble will get a coat of finish epoxy before I paint it. I will have to see how long/tall a cone I can fabricate in this way.
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I cut a retainer from 3mm aluminum/plastic composite panel. Light weight, high tensile strength and fire-proof. It bends a lot more easily than steel or solid aluminum, but not too worried about that with five points of attachment around the circumference. I dropped in a 38 mm DMS, and everything fits together.
I am still going to cut a steel one. I'll keep this on hand in case the RSO says no.
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I filled in the the seam on the one bad slot and I shot some more paint tests on earlier versions of the fins (when it was going to be a a Four-toed Moonbat). So far, I like the Duplicolor Metalcast yellow the best. The Spaz Stix color change paint is very cool, but it takes a lot of coats to get the effect.
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Final assembly this weekend. Because I am a grown-up with responsibilities I won't get out to Brothers to launch next weekend -- which is breaking my heart. If I get it finished in time, I might try to drop in on the June Tri-Cities launch. Otherwise it is looking like NXRS or Summer Skies. I've got too many rockets that have never flown.
Wow this build is phenomenal. So awesome!
Very cool design!
Thank you.
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Finished the recovery gear. The forward section of the airframe is nose-heavy and too aerodynamically stable by itself. On deployment, it is liable to be blown away from the aft end like a dart. I can't think of a way to make it tumble, so I am including a long section of elastic shock cord attached in parallel to a strip of velcro -- to act as a shock absorber. The idea is that the velcro will peel apart like a loomed-fiber fall-arrester -- dissipating the energy of the ejection. The worry, of course, is that something will go wrong that the tension exerted by the shock-cord will act parallel to the velcro -- and it won't peel. At which point, the integrity of the rocket will depend upon my joinery and the ultimate strength of the well-perforated piece of 3/16" aircraft plywood at the the top of the baffle.
I am interested in how this velcro shock absorber works - I think I understand roughly how you are using it (the velcro peeling absorbing ejection energy part) but I can't visualise how it is actually rigged (relation of elastic, velcro and shock cord). Is this something you can elaborate on a little?
I keep waiting for one of the vendors to discover what a hook pile tape lowering line is for and why I would want to buy a harness with that type of rigging baked in.
I had to Google that {hook pile tape..}.....
I think a Velcro energy dissipation system is a great idea. I considered it once but was worried that the hook side might snag the nylon parachute.
I’m not so sure about the riveted grommets in the ends of the strap (if I’m understanding correctly). I’ve not seen that for load bearing applications. I usually see loops sewn or tied into the ends of nylon straps. I would be concerned that the grommets would pull out under load.
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