5.5 Loc Goblin build

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Troy3003

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Goblins are no stranger to this community but I wanted to do a little build post on this one.
First I'd like to give props to Loc for a really nice kit. Most everything is included, although I'll be subbing in a few misc items. The kit came well boxed, and all pieces included look to be of high quality.
My plans are to use this rocket for my level 1 certification flight. It will be using basic motor ejection. I decided to go with an I297SM for a couple reasons. First, using this motor I can take advantage of the CTI cert offer and get a 5 grain case free. Second reason is because skid mark engines are just plain cool. It sims in open rocket to about 1500ft with a good launch rail velocity and around an 8.5:1 thrust to weight ratio. I considered using a JLCR but I may leave that out to keep things as simple as possible.
 

Troy3003

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First I dry fit all the parts. Everything looked good. The fin slots were very tight, I did do a slight scuff inside the slots to ease installation but very little material was removed. I will be building the fin assembly outside of the body tube.
Next I removed the glassine layer from the 54mm motor mount tube. It was not very cooperative but eventually got it all removed. Then the mmt was marked for the fin/centering ring alignment.
I decided to use an Aeropack flange mount retainer so during the earlier dry fit I marked the location where the holes needed to be drilled for the inserts. Holes were drilled and a light coating of JB was applied to the inserts before threading into the rear centering ring. Also a dab on the outside of the inserts to help keep them from turning if I ever have to remove the flange.
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Troy3003

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Next with the flange bolted on I had to try out the 54/38 adaptor and casing. Then I started installing the centering rings on the motor mount tube.
I used aeropoxy laminating epoxy straight for the initial bonds. This really penetrates very well into the cardboard and plywood. I applied a layer of epoxy on the tube slightly before the mark so it would push up under as it was moved into place.
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Troy3003

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After that sat for a day to cure I started on the fins. Like I said the slots were very tight so there was not any need for a centering jig. I just double checked for straightness and it looked fine. I epoxied the fins onto the unit using the same laminating epoxy as I used on the centering rings. One thing I didn't catch was the insert position for the retainer. If you notice in the bottom pic I had to make a clearance notch on two of the fins.
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Troy3003

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Last thing I have had time to do was add fin and centering ring fillets. I used the same Aeropoxy laminating epoxy thickened with West 406 and a small amount of 404 blended in as well. I didn't spend much time smoothing these since they will be hidden.
Fins will be lightly sanded and sealed. I planned to leave fins square, but it bothers me so I may just do a light round over.
I'll be working on the body tube and rail buttons next chance I get, with more pics to come.
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Troy3003

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Been a busy weekend with the family so not much time to work on this project.
I did get the fin notches sliced open(do this after sanding to make it easier, unlike me)
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, worked on filling spirals with spot putty, and sanding. Alot of sanding... The glassine layer looks smooth at first but once you start block sanding you really notice high and low spots. I sanded off all the filled spirals and still could notice alot of random shiny spots. I basically just kept sanding until I was able to get rid of all the shine, which should mean a straighter, smoother surface. Any prep before primer you can do really improves the finish. And cuts down on the amount/coats of primer also.
Next on the list will be the 10/10 rail buttons installation and the installation of the fin can assembly when time permits.
 

Troy3003

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Made a little more progress today. Marked out centering ring locations for initial glue lines and installed fin can. I'll go back after this tacks up and start doing a fillet or two on the cr's so it can be curing overnight.
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rfjustin

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Been a busy weekend with the family so not much time to work on this project.
I did get the fin notches sliced open(do this after sanding to make it easier, unlike me)View attachment 461627View attachment 461628View attachment 461629View attachment 461630, worked on filling spirals with spot putty, and sanding. Alot of sanding... The glassine layer looks smooth at first but once you start block sanding you really notice high and low spots. I sanded off all the filled spirals and still could notice alot of random shiny spots. I basically just kept sanding until I was able to get rid of all the shine, which should mean a straighter, smoother surface. Any prep before primer you can do really improves the finish. And cuts down on the amount/coats of primer also.
Next on the list will be the 10/10 rail buttons installation and the installation of the fin can assembly when time permits.
I like that, you split the tube just enough at the rear. Most folks hog off the entire width of the fin. Nice, clean build!
 

Troy3003

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It is a little tougher to get fin section inserted but I think once its dry and finished you won't see any evidence of cuts at all. The thin epoxy soaks in really well to and gives a good firm seam.
 

jd2cylman

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That’s how I did both of my 4” LOC Goblins. And how I’ll do #3... 🙄
 

Troy3003

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Today I did the fillets. I marked with a popsickle stick coated with a sharpie. Then taped off with painters tape. This works pretty good at keeping things clean.
One thing I've been doing is 'prime' the fillet area with unthickened epoxy first. It soaks in and I think it may help the thickened epoxy bond better to the wood and cardboard. I didn't do huge fillets as the fin can is pretty solid already. I still cant do the front ramp very good so it will probably need a little spot putty to finish it out. Also did the fillets on the centering rings to finish up those.
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Theory

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Agree with this: One thing I've been doing is 'prime' the fillet area with unthickened epoxy first. It soaks in and I think it may help the thickened epoxy bond better to the wood and cardboard.
 

Troy3003

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Just some sanding tonight, and tomorrow some fin work and the start of the primer job.
Fillets need some work at the leading edge but so far no filler needed. A couple dowels wrapped with sandpaper makes nice sanding of the radius.
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Troy3003

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Back to the workbench. Almost done, primering, sanding and repeat. I already have my decals and paint scheme ready.
Right now I've done the final paint, installed the Stickershock decals and waiting for clear to dry, so I thought I would catch this up while I wait.
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Troy3003

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Done, ready to go fly tomorrow I hope. I went old school Green Goblin. The green wasnt quite the shade I was wanting but the automotive paint wasn't in the budget this round.
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