Build Thread: Nibiru Interceptor

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neil_w said:
... Overall strength of a tabbed fin like this versus one surface-glued remains uncertain (there was a thread about this recently but I think it was inconclusive)...
Click to expand...

If we think about the failure mode of a typical fin just glued to the outside of a body tube, it is typically the top layer of the paper body tube that fails. The tabbed fin has to be much much stronger since it is a through wall joint. This is especially true if it is glued to the body tube both outside and inside. Sure, this is not as good as attaching the fin to an internal tube, true TTW construction, but it is much better than just sitting the fin on the outside of the tube.

And that being said, now the strength of the fin comes into play. Balsa, vs papered balsa, vs basswood, vs papered basswood, vs plywood.

It's all a game of "The Weakest Link".

But all that being said, with your ring fin.... this design is for sure hell-for-stout.

Beautiful build you've got going here Neil.
 
Pod Cones

I debated whether I should paint the pod cones separately and then glue them in at the very end with CA. That might have been a good idea but I had build fever so in went the cones. I had no idea how far to push them in.... Probably should have gone in a bit further, but I still think I got the look I wanted.

pod-cones-insttalled.jpeg
 
Wings

There's not all that much to say about the wings at this point, as the build heads into the home stretch. It has gone quicker than expected; too quick in fact which is a little bit of a bummer.

Anyway: using the built-in basswood default density, OR estimates the fin weight at 0.24 oz. The final measured weight, including label papering and primer, is...
wings_weight.jpeg
That's not bad. Since basswood is a lot denser than balsa, the % penalty for papering is much smaller, in this case 17%. Still, the weight of fin-papering is not to be ignored, it can have a big enough effect on CG that you need to be careful with it. I have actually entered some custom materials into OR for papered balsa, so I don't get surprised with it later on, but I haven't historically used basswood that much so I haven't entered that in yet. I will be doing so.

Not much to do except glue the wings on. Once again, eyeball alignment:
wing1.jpeg
And here we are.
wings.jpeg
That looks awfully good to me, can't wait to see it in paint. A great deal of paint scheme/decal design work has been going on behind the scenes, hopefully the results will be worth it.

Still just a bit more assembly to do though.
 
neil_w said:
Since basswood is a lot denser than balsa, the % penalty for papering is much smaller, in this case 17%. Still, the weight of fin-papering is not to be ignored, it can have a big enough effect on CG that you need to be careful with it. I have actually entered some custom materials into OR for papered balsa, so I don't get surprised with it later on, but I haven't historically used basswood that much so I haven't entered that in yet. I will be doing so.
Click to expand...
What weight increase do you typically see for papered balsa fins?
 
Well, you'd expect to see the exact same weight increase... except the balsa is about 1/3 the weight to begin with, so the percentage gain ends up being about 50%.

However, I can't find my old numbers, will need to re-measure.
 
boatgeek said:
What weight increase do you typically see for papered balsa fins?
Click to expand...
Technique is a big factor in additional weight...
  • Some folks use self adhesive labels
  • Some use regular printer paper and spray adhesive
  • I use heavy photo quality paper and Gorilla wood glue.
 
neil_w said:
Well, you'd expect to see the exact same weight increase... except the balsa is about 1/3 the weight to begin with, so the percentage gain ends up being about 50%.

However, I can't find my old numbers, will need to re-measure.
Click to expand...
OK, good to know. I papered some 3/32” balsa with epoxy (I know, but I had a batch of the thin stuff already mixed up) and it roughly doubled the weight using regular notebook paper.
 
Canards

Any surface mount fin of at least 3/32" thickness (and maybe even 1/16") should stand up straight on the bench.
canard-stand-up.jpeg
I didn't get the camera angle quite right here, but the one on the left is straight and the one on the right was leaning slightly to the right. So back on the sanding block went that one, until it stood equally straight up.

Actually, it should also stand up straight when placed on the body tube.

canard-stand-on-bt.jpeg
If they're sanded properly in this way, you don't need a jig: the fins will just naturally sit straight when glued on, e.g.:
canards-1.jpeg
It is amazing how fast a properly executed TBII double-glue joint will harden up. I was filleting these barely a couple of minutes after gluing them on.

I've been struggling a bit with my Q&T fillets lately, mainly in terms of dispensing the correct amount of glue. @Tobor submitted to the Tip of the Day thread the technique of covering part of the blue nozzle with tape... I had started doing that years ago but somehow either forgot about it or just became lazy. Seeing @Tobor mention it again knocked me out of my stupor and I covered about 2/3 of the Q&T tip (could have even covered a bit more):

qt-nozzle.jpeg

This helps, so, so much. In case it's not obvious, apply the glue with the open part of the nozzle bringing up the rear, so you're not dragging the tape through the newly-dispensed glue.

And so the finished canards:
canards-2.jpeg

This completes pre-paint construction of the rocket.
 
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Launch Lugs

I thought tucking the launch lugs under the pod supports was a good way to hide them. They should be mostly or completely invisible when looking at the top or side of the rocket.
lugs.jpeg
As I was looking down at them I realized it was going to be impossible to get paint in the nooks above the lugs in the picture. Will probably have to break out the touch-up brush for those spots.

OK, *now* pre-paint construction is completed, just under one month from when I started. This went too quickly. :(
 
jqavins said:
Quick progress now just means you can start on the conical alien monstrosity* all the sooner.

* I mean that in a good way.
Click to expand...
I will be working on that. :)

But there will be months of planning for that one (seriously I have a lot to figure out), so there will be plenty of time to squeeze in another build or two between now and then.
 
The rocket is now Rusto Winter Gray.
1683998584270.png
Unfortunately because in a hurry and I was juggling two rockets I was unable to get a picture. I think it went on OK, and I also think I got paint into all the nooks and crannies (even around the lugs).

One thing I've concluded, other than that I suck at painting, is that painting a complex model with nooks and crannies is a *very* different sort of task vs. painting a simple 3FNC or something like that.
 
Here it is in all of its gray glory. I would rate this particular paint job as "decent". I have no doubt I could make it better by sanding it and reapplying a final top coat.... but it's not nearly bad enough to make me want to spend that effort. Most important thing here is that I think I got coverage of everything, and hopefully the only touch-ups needed will be at the ring joints.
paint.jpeg
Now I need to finish up the decals. It has been a huge job, largely due to my own incompetence, but it's almost done.
 
That looks very good from here. Especially for painting, that was really quick. And no less than TWO rockets, so I'm curious about the second.
 
neil_w said:
When I say decals have been a huge job.... here is a snapshot of my decals folder showing all the different things I've tried. Thanks to @mbeels for suffering through this process with me and giving feedback.
View attachment 580693
Click to expand...

Dog like dedication to duty. I'm hoping you can figure this out.. so we can benefit from all your hard work.
 

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