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Find me a place to put the launch lugs

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neil_w

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I posted this design in another thread a while ago. I quite like it, even though in some respects it's sort of a remix of other stuff I've done. But I can't for the life of me figure out where to put the launch lugs without really uglifying the whole thing. Anyone have any clever ideas? The CG is an inch or two (depending on engine) in front of the double transition.

lln_photo2.png
View attachment launch_lug_nightmare.ork

I actually have an idea of one thing I might do, but first I'll wait to see what others can come up with (if anything).
 

dhbarr

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Seems like you could do through lugs on the transitions, maybe? Could make a symmetric pair, splitting the distance between the two archstrakes.

Might interfere with the canards, though.
 

Amsterdam

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I've never done this, but you could try wire lugs. There's a couple methods out there. This one from apogee's newsletter is interesting, in my mind music wire should be sturdier than a paper clip.
 

K'Tesh

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I've never done this, but you could try wire lugs. There's a couple methods out there. This one from apogee's newsletter is interesting, in my mind music wire should be sturdier than a paper clip.
+1 on that. However, sturdy likely wouldn't be a problem unless this is a lot bigger than I'm imagining it.
 

Cabernut

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I'll go way out on this one:
Make it a cluster with the rod going straight through the center?

Otherwise go the sane route and use one lug flush next to one of the bottom fins, the other with a tall standoff that's airfoiled a bit.
 

Gary Byrum

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Show me a profile drawing and a rear view that clearly shows the fins. FWIW, I can't view ork. files. PDF prolly?
 

ratchet01

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Third the wire loops. There's a thread somewhere on here about fishing line guide's.
 

BABAR

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Inside the fin can, through the transitions (small holes just big enough to fit the rod.). Should be almost invisible.
 

sl98

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Flis Kits has a pop lug, which is sort of like a break away rail guide. You might be able to use or come up with something similar.

This might also give you some ideas (see last page)

http://www.oldrocketplans.com/cmr/cmrC9/C9.pdf
 
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KenECoyote

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One at the root of one of the rear fins and then one above it in-line on the arched section? Should all be in the back and hidden when viewed from the flight line.
 

neil_w

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Wow, lots of great input. You guys are quick.

Here are diagrams for those (*ahem* Gary) without OR:
lln_diagram.png
lln_back.png

The natural location for the forward lug is somewhere in the BT-50 wasteland. Note that I am willing to modify the design to accommodate the lugs, but not to ruin it. Whatever that means. Also, at some point I'll have to decide if this design is worth the trouble; right now I like it but have been known to change my mind. :)

One idea I've been marinating for a while is to figure out a way to mount the edge of one of the canards. This would require at least one (if not all) of the canards to be just a bit taller, and it would somehow need to stay with the main BT and not be above the split like it is now. Also it would need to be not in line with any of the rear fins. Maybe not practical but interesting to think about.

I've never done this, but you could try wire lugs. There's a couple methods out there. This one from apogee's newsletter is interesting, in my mind music wire should be sturdier than a paper clip.
I'll read up on that. I thought a wire lug could be a solution but I will have to learn a bit first.

Seems like you could do through lugs on the transitions, maybe? Could make a symmetric pair, splitting the distance between the two archstrakes.

Might interfere with the canards, though.
Maybe. It'd be tricky, though. The lugs would have to be lifted ~0.16" off the BT50 to clear the BT60 payload section. In that case the rod would actually go inside the rear BT70 and through the aft centering ring. And the forward lug (through the double transition) would still be an inch or two behind the CG. I don't know how much that really matters, but I would certainly *prefer* to have the forward lug at at or in front of the CG.

Flis Kits has a pop lug, which is sort of like a break away rail guide. You might be able to use or come up with something similar.
That would work but I'd prefer not to have to fiddle with something like that, just want to affix a lug or two and be done with it.

One at the root of one of the rear fins and then one above it in-line on the arched section? Should all be in the back and hidden when viewed from the flight line.
Doable but that again puts the forward lug quite a bit behind the CG. How much should I worry about that?
 

Gary Byrum

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The red line dictates where the rod would go if you mounted a lug on the root edge of the aft fin. Unfortunately, there is no other place for a 2nd one, w/o a stand-off. If those forward fins were a little wider, then you could use one of those.

Neil  LL.jpg
 

jflis

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Have had this issue on a number of designs. What I do is run the lug up through the shrouds.

For this design, you can run a long one up through the BT-70, such that it clears the OD of the BT-60. A second lug would be needed through the shrouds just above that. Trimmed neatly, flush against the shroud, and they look quite nice.

We do this on the Nantucket Sound, Decim8 and the upcoming MIRA kits...
 

neil_w

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Have had this issue on a number of designs. What I do is run the lug up through the shrouds.

For this design, you can run a long one up through the BT-70, such that it clears the OD of the BT-60. A second lug would be needed through the shrouds just above that. Trimmed neatly, flush against the shroud, and they look quite nice.

We do this on the Nantucket Sound, Decim8 and the upcoming MIRA kits...
That comes back to the same question again, though, which is: how much does it matter that the forward lug will still be behind the CG?

If we don't care about that *at all*, then I could just put a single (long) lug on the rear BT70. If it's OK to be behind the CG but we want it as close as possible (how close?), then there are a few different ways (including the scheme you're suggesting) to get the forward lug into/onto/around the forward shrouds. If we *really* want the forward lug to be at least at or in front of CG, then we start moving down the list to the more difficult and/or uglier solutions.

If I fiddled with the design and made the forward shrouds further forward, then I could possibly get the point where they are close enough to the CG that I would stop worrying about it. Have to see if I can do that without screwing up the proportions of the design.

If the forward shrouds are an acceptable lug location (either in the current design or the above-described modification) then I could also do something like this:
lln_lug_proposal.png

Here, there's a standard lug on the BT70, and a wire loop anchored to the centering ring at the middle of the two transitions. Alternatively, the forward one could be made longer and glued to the side of the arch fin (like what Ken suggested):
lln_lug_proposal2.png
Here I made the forward lug white just so it's visible in the picture.

I had been trying to get the forward lug more forward, but if I don't need to then there seem to be several reasonable solutions.

All this staring at this design and it's making me want to tweak some details (particularly the paint scheme), but I still like it so far, I think.
 

dhbarr

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Aah. I pictured the wire loop on the very front most bt60 section, north of the canards; w/ througholes in both aft bt70 sections ( the double and the tail ).
 
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Gary Byrum

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View attachment 295499
Here I made the forward lug white just so it's visible in the picture.

I had been trying to get the forward lug more forward, but if I don't need to then there seem to be several reasonable solutions.

All this staring at this design and it's making me want to tweak some details (particularly the paint scheme), but I still like it so far, I think.
That looks like a remotely possible solution, but I too would question if that was forward enough for that lug. You'll still have a majority of the rocket in front of both lugs which could present a problem still. If you're like me at all, you too, don't entertain the notion of going through those shrouds with a rod. There are times when it's an acceptable approach, and I have done it a few times myself. But when it digs into the aesthetic value, I have to question, "can I live with that?"

When all else fails, is where my ingenuity kicks in and I develop a solution. I'd prolly mount a lug on that fin root (or where ever on the BT 70) and build a cockpit on the BT 60, as a disguise for a standoff.
 

KenECoyote

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Have had this issue on a number of designs. What I do is run the lug up through the shrouds.

For this design, you can run a long one up through the BT-70, such that it clears the OD of the BT-60. A second lug would be needed through the shrouds just above that. Trimmed neatly, flush against the shroud, and they look quite nice.

We do this on the Nantucket Sound, Decim8 and the upcoming MIRA kits...
I was actually going to suggest the same! While more work, it does seem to be the better solution if you want to keep the rocket looking clean.


Neil - Regarding whether the forward lug is too far back, I think it would be fine; however make sure they're on straight. There are a few rocket designs which just have the lugs on the lower portion/quarter (I think the Hi-Flier does this). I think a while back when there was discussion of rail button location, someone did a bunch of tests and said it was best to have both of them at the bottom close to each other. One issue is that there will be more stress if the lugs are farther from the CG due to the greater levering force applied, so you would just use a longer or stronger lug.
 

neil_w

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When all else fails, is where my ingenuity kicks in and I develop a solution. I'd prolly mount a lug on that fin root (or where ever on the BT 70) and build a cockpit on the BT 60, as a disguise for a standoff.
That actually brings up another good question: is there anything inherently problematic about having the upper lug be attached to the rocket above the split? Certainly one would have to align top and bottom carefully before threading onto the rod (alignment markings on the shoulder of the coupler and inside the BT could help here). Is there any likely danger of the upper portion trying to twist (for whatever reason) while the rocket is heading up the rod? That could also be addressed, but I'm trying to figure out which of these issues need to be considered at all.

If it's safe/kosher to mount the forward lug to the payload section, I probably have an assortment of solutions available.
 

Gary Byrum

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Is there any likely danger of the upper portion trying to twist (for whatever reason) while the rocket is heading up the rod? That could also be addressed, but I'm trying to figure out which of these issues need to be considered at all.

If it's safe/kosher to mount the forward lug to the payload section, I probably have an assortment of solutions available.
FWIW, that rocket is coming off that rod real quick. I can't imagine what would cause any kind of "twist". I never have problems with at least 1 lug above and below CG. In my opinion, it doesn't matter where you put them as long as CG is between them. Take it from an 'Old School Dood", and try not to think this thing to death. Simple rocket science doesn't have to be difficult...or hard.
 

neil_w

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Take it from an 'Old School Dood", and try not to think this thing to death.
But that's my *true* hobby... This rocketry stuff is just to provide overthink fodder. For which it succeeds most excellently. :)
 
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