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Semroc LJ II

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jj94

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I haven't gone very far with this for a while. Most of it has been sitting in the bag, but I did get some of the fins done. So how well will these built up fins take landing stress? Should I do anything extra to reinforce the innards of the fin?
 

dwmzmm

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I haven't gone very far with this for a while. Most of it has been sitting in the bag, but I did get some of the fins done. So how well will these built up fins take landing stress? Should I do anything extra to reinforce the innards of the fin?
Built and flown mine several months ago; those built up fins are excellent. Just build them according to the instructions and you should do fine. BTW,
the SEMROC Apollo Little Joe - II build gives excellent practice in case you decide to go for the 1/70 Saturn 1-B, as it also uses the built up fins too.

Challenger 498 Club Launch @ Needville 033.jpg
 

foose4string

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I used a solid core for the fins on mine made up of 3/16" x 3/4", wedge shaped, trailing edge balsa. Most well stocked hobby shops will have it in their Midwest displays. I glued the cardstock skin directly to the balsa strip, lining up the trailing edge of the skin to the widest part of the balsa. Then, cut the fin away from the balsa strip at the root edge, using the fin skin as your guide. You'll have about 1/8" inside the leading edge that isn't filled or supported but the cardstock is plenty strong enough in that area. You'll have to fill that tiny bit on the outer edge of the fin with Fill N Finish or cut a small part of the balsa wedge that came with the kit. One thing I've noticed about making these built up fins is that it's difficult to avoid letting the frame show through the skin once the glue shrinks. Clamping down while the glue is drying makes things worse. It takes practice. A medium or slow gel CA works pretty well since it doesn't shrink as much as white glue might. Or, use the solid balsa core and have a nice smooth fin in about half the time. ;) I have to believe the solid core is stronger than the built up fins, but this model is so light , I doubt it makes much difference.

Little-Joe-Business-end.jpg


Little-Joe-II-topless.jpg


Little-Joe-II-complete.jpg
 
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jj94

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Built and flown mine several months ago; those built up fins are excellent. Just build them according to the instructions and you should do fine. BTW,
the SEMROC Apollo Little Joe - II build gives excellent practice in case you decide to go for the 1/70 Saturn 1-B, as it also uses the built up fins too.
Nice Little Joe II. Thanks for the advice.
I used a solid core for the fins on mine made up of 3/16" x 3/4", wedge shaped, trailing edge balsa. Most well stocked hobby shops will have it in their Midwest displays. I glued the cardstock skin directly to the balsa strip, lining up the trailing edge of the skin to the widest part of the balsa. Then, cut the fin away from the balsa strip at the root edge, using the fin skin as your guide. You'll have about 1/8" inside the leading edge that isn't filled or supported but the cardstock is plenty strong enough in that area. You'll have to fill that tiny bit on the outer edge of the fin with Fill N Finish or cut a small part of the balsa wedge that came with the kit. One thing I've noticed about making these built up fins is that it's difficult to avoid letting the frame show through the skin once the glue shrinks. Clamping down while the glue is drying makes things worse. It takes practice. A medium or slow gel CA works pretty well since it doesn't shrink as much as white glue might. Or, use the solid balsa core and have a nice smooth fin in about half the time. ;) I have to believe the solid core is stronger than the built up fins, but this model is so light , I doubt it makes much difference.
Well I already glued the balsa spars on the fin template. I just have to glue the other side of the fin template over to complete the fin, so I won't be making any new fins. But you say that it's difficult to hide the insides of the fin? Do you think adding another layer of cardstock over the completed fin will help? Or maybe putting small drops of foam in the crevices to avoid light from going through the fin?
 

foose4string

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Nice Little Joe II. Thanks for the advice.


Well I already glued the balsa spars on the fin template. I just have to glue the other side of the fin template over to complete the fin, so I won't be making any new fins. But you say that it's difficult to hide the insides of the fin? Do you think adding another layer of cardstock over the completed fin will help? Or maybe putting small drops of foam in the crevices to avoid light from going through the fin?

It's not that you have to worry about light shining through the fin, it's going to be painted anyway. The problem is having the paper shrink around the frame pieces, to where you see an impression of the frame. I think another layer of cardstock could possibly help but would probably be more trouble than it's worth. If you're careful you can avoid what I'm describing. I think CA is a better choice than wood glue or white glue. If you do use white glue, go very sparingly, a barely there film is all you need. Rather than clamping the paper with your fingers, find a way to hold the fin against a flat surface so that even pressure is applied across the whole fin.
 

jj94

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I've built the fins with CA for now, and I was going to add yellow glue fillets to it. But now that you brought up the topic of shrinking, I don't think I'll fillet them with yellow glue.
 

dwmzmm

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Josh, you haven't built the Apollo capsule/LES yet? That's going to be the hardest part. Have fun!! :D
 

MaxQ

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If you build them strong...I even went with built up fins on my upscale...

They are thru the wall to the MMT, though.

Take care and build them corectly..with adequate fillet joints...they'll handle a landing (as long as the parachute opens)

LBJ - II - fin sheet and substructure .JPG


LBJ -6aaa -  test fit.JPG
 

jj94

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Haha, I took one look at it. Then I thought, "Jeeze, this is going to take a while.":rolleyes:
 

jj94

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If you build them strong...I even went with built up fins on my upscale...

They are thru the wall to the MMT, though.

Take care and build them corectly..with adequate fillet joints...they'll handle a landing (as long as the parachute opens)
I think I'll fillet them with white glue. Yellow glue is out of the question because of shrinkage issues. White glue doesn't shrink too much so I suppose it should be fine. I was thinking of reinforcing the joints with tissue paper and white glue too. Not sure if it's worth the extra effort though.
 

MaxQ

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Haha, I took one look at it. Then I thought, "Jeeze, this is going to take a while.":rolleyes:

That tower is the real fun part....
rather than deal with wooden dowels and sanding them ...I went with plastic struts from the hobby shop.
Did the first one with superglue joints.

It rolled off my table and disintegrated.

My second effort used a liquid bonding plastic cement.
it has taken several landings (one w/o parachute inflation) and had no problem staying together...

I did sling it with a line from the base of the capsule to the LES skirt to hold the whole thing horizontal.

LittleJoe II buildTower.JPG
 
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jj94

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Well I don't have a problem with the wood dowels, it's just the point that the instructions ask you to sand some of them to smaller diameter. I'm skipping that step for sure. Other than that, it shouldn't be *too* hard...or am I just being a bit too optimistic. Haha.
 

Handeman

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............My second effort used a liquid bonding plastic cement.
it has taken several landings (one w/o parachute inflation) and had no problem staying together...

I did sling it with a line from the base of the capsule to the LES skirt to hold the whole thing horizontal.
Would that be the cluster flight at Battle Park this year?


Oh wait, I thing the capsule came down OK, I don't remember, I was too busy watching the rest of the rocket going up and down!
 
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MaxQ

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Would that be the cluster flight at Battle Park this year?


Oh wait, I thing the capsule came down OK, I don't remember, I was too busy watching the rest of the rocket going up and down!
Naw...the Culpeper flight was my large scale LJ -II.
That did go up and down....late airstarts make for a funny flight....

I was talking about my Semroc LJ - II (picture of it in my post).
 
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