#31
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Making these horrible cuts by hand is analogous to the reason people hit their thumb or finger with a hammer — because it feels so good when you quit.
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Lee Reep NAR 55948 Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor In the Paint Shop: Nothing! Too cold! Launch-Ready: Farside-X, Maxi Honest John, Super Scamp |
#32
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I think you are right! |
#33
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I've found it handy to have both 24 & 29 mm mounts for this rocket. Since I lost kit #1 on the 4x18, I had an extra 29mm mount from the 2nd kit, and just glued a 24mm adapter in permanently. Only thing different is that for both 24 & 29, I left the motor tube extend 1/4" past the cooling vanes, so that I could use a wrap of tape for retention. Your recessed motor hook looks great. I'll be interested to see how you color the vanes. Mine are all white, to match the 1971 catalog.
You're really going to enjoy flying this, with all the effort you're putting into it. It's a fantastic looking (and flying) model when done.
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Paul If we weren't all crazy, we would go insane - Jimmy Buffett NAR #87246 www.wooshrocketry.org |
#34
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I’m glad you had both 24 and 29mm mounts, validates what I’m doing. That is good advise to protrude the 29mm mount although I have had a bad experience with tape retention and a hot motor and tend toward positive retention. |
#35
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I’m trying to make some progress every day, yesterday I went back to the quad 18 mount. I ordered eb-7s from erockets because it was the Semroc part number listed on the mount. When I did a test fit the engine blocks were way too short, with the block glued at the end of the tube the motor would be all the way in the tube. The engine blocks need to be flush with the end of the tube because they are the primary gluing surface for a butt joint. The engine blocks were less than 1/4” long. It also occurred to me I wanted to fly qjets so need clearance for the delay module extension. Poking around the old Semroc site, it looks like the original eb-7s were 3/8” long. I had some old apogee 10.5-18 rings and peeled out a few of them to the right ID so I had enough rings for two in each tube. Two stacked rings leaves a little motor projecting from the motor tubes and the qjet delay module fits. I glued two rings in each tube and put qjets on top to keep them compressed. Today after that dried, I made a plywood star to mount a wood insert for a bolt that will be the motor retention. I drilled a hole for the insert then used a sanding drum to get it to the right size. Next I will epoxy the insert about an inch down between those tubes. Wish I used motor hooks, what was I thinking?!.
Last edited by 5x7 : 11-28-2019 at 10:29 AM. |
#36
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Don’t try this at home
I mixed some JB weld since the expoxy will be between four motors and will take some heat. I swabbed the inside hole of the wood plate that holds the insert and glued the insert into the plate. I swabbed epoxy between the motor tubes. I used the bolt as a handle threaded into the insert and swabbed epoxy onto the edges of the wood plate and set the wood plate with the wood insert between the tubes about 3/8” down, then swabbed epoxy around the wood insert and over the wood plate. JB weld takes hours to cure so I’ll leave it overnight and see how it comes out. I say don’t try this at home because using motor hooks would have been better in hindsight.
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#37
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I use threaded inserts with no issues. But I think you’d find that a faster curing epoxy makes it simpler. JB Weld is super strong, but for something like this, it means lots of cure time that can cause runs.
I even used threaded inserts on clusters like 3x18mm in a BT-60. A normal threaded insert won’t fit, so I use a clevis from the RC airplane world. I clip off the arms and epoxy in the threaded barrel piece. The engines are held in by a 4-40 cap screw and washer. (Washer not shown in picture).
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Lee Reep NAR 55948 Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor In the Paint Shop: Nothing! Too cold! Launch-Ready: Farside-X, Maxi Honest John, Super Scamp |
#38
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That’s similar to what I had in mind, but I didn’t realize when I decided against the hooks that the space between the tubes was so much to fill. I have used #4 and #6 brass wood inserts in other rockets but a clevis is a great idea. The JB is really thick and seemed to stay put, I’ll see tomorrow. |
#39
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There is one advantage to using a bolt for retention in that I don’t have to use tissue and glue to block the inside of the tubes but I’ll probably do it anyway to keep the bolt hole cleaner and prevent that area from being pressurized. The JB weld cured great and didn’t run at all. I used Qjets from a bulk pack of As I had and noticed that they had flash at the fwd end of the casings which made them appear initially to have slightly different lengths. I was able to knock down the high spots with a fingernail and they evened out, pictures are a test fit using Qjets.
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#40
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Just wondering how easy (or difficult) it is to light the Q-Jets in a cluster, since they are composite motors. I haven't tried it yet.
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I like the unusual, the off beat, the avant-garde. No 3/4 FNC for me! |
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