34FNC scratch build

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Azamiryou

Learn from your mistakes. I learned a lot today!
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Once I thought of it, I had to design it: 34FNC rocket.

screenshot.png

Yes, that's thirty-four fins and a nose cone.

I love the warning there in the bottom right corner. I guess I'll need to do a swing test rather than trust the sim!

The fins are spaced 10 degrees apart, which would make for 36. I left two out on opposite sides, and put the launch lug in one of the gaps. I did two different fin shapes just to make it more interesting.

rearview.png

I feel like I have to build this now, even though those fins will truly be a challenge. I think maybe I should find someone with a laser cutter so I don't have to cut out 34 fins by hand. And I'll definitely need to make some sort of jig for fin positioning.

I've attached the ORK file, even though it's just a quicky - no centering rings, recovery system, etc. yet.
 

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  • 34fnc.ork
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you probably should make the body tube as large in diameter is you can at the LPR scale so the spacing is larger.
Agreed. You are presently using a BT55. Circumference is PI*d, so 4.16". Divide by 36 is .116" 1/16" thick fins which are .0625 thick, that leave only .053" from one fin to the next. Your alignment is going to have to be "perfect". And good luck doing any fillets....

Just another thought. Your arrangement is fin gap fin "gap" skip "gap" fin gap fin....
There are then 2 gap areas plus a missing fin width which totals to 0.169". You will just fit a 1/8" (0.125) launch rod, but the outer diameter of your lug is 0.173 so it will not fit between 2 fins. Granted, it is only .004" diff so the fins could be scooched over. But also need to consider the dimensional tolerances of everything....

And whichever 1/16" fin it lands on will be highly subject to breakage.........
 
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the outer diameter of your lug is 0.173 so it will not fit between 2 fins.
My thinking is that the lug doesn't have to be actually on the body tube. I can just glue it as far down between the fins as it will go.

And good luck doing any fillets....

I might skip fillets just this once...

And whichever 1/16" fin it lands on will be highly subject to breakage

I might slide the fins forward a bit to encourage it to land motor first.

Or maybe it will be my first rear eject rocket..
 
And whichever 1/16" fin it lands on will be highly subject to breakage.........
put a forward sweep on trail edge and maybe mount the rear edge of the finds about 1 cm forward of tail of tube.

Use a big chute.

I suspect the inner closely spaced fins are gonna act like a plate, like long length to diameter tube fins act like cylinders.

Didn’t someone design and fly a rocket with a flat circular plate in place of fins?
 
I'm thinking it would be much easier to paint the fins before gluing them on the rocket. Leave the root bare wood and skip the fillet. I think it needs a ring wrapping around the fins to "lock" them in place :)

-Bob
 
put a forward sweep on trail edge and maybe mount the rear edge of the finds about 1 cm forward of tail of tube.

They already have a forward sweep. I definitely agree on moving them forward a bit. For extra insurance.

If you wanted to make it easier, you could align two sets of 17 fins and have one set in front of the other.

I considered this. Or things like a "stack" of fin cans, like 9-9-9-7, or 12-12-10. Or 8-8-8-8 and a couple of canards.

But I sort of think that's just split fins, and not really 34 fins. No half measures! 😁

Boo.

Let me guess, you're also not going to make each fin a different color?

Probably not, though I haven't actually come up with the livery for it. I might go with the generic product look from the 80s.

font-used-on-1980s-ralphs-generic-items-as-seen-in-repo-man-v0-ap2lzamfygwc1.jpeg
 
They already have a forward sweep. I definitely agree on moving them forward a bit. For extra insurance.



I considered this. Or things like a "stack" of fin cans, like 9-9-9-7, or 12-12-10. Or 8-8-8-8 and a couple of canards.

But I sort of think that's just split fins, and not really 34 fins. No half measures! 😁



Probably not, though I haven't actually come up with the livery for it. I might go with the generic product look from the 80s.

View attachment 689295
like the livery idea!
 
These fins aren't that far off from Estes Viking fins. Amazon is currently offering a sixty-pack of Viking fins for $36 (bonus: I'd also get a bunch of BT-20 tube and nose cones).

Estes Viking Rocket Bulk Pack Pack of 12
https://a.co/d/5GGcryZ

That price is so far below everyone else, though, that it doesn't ring true...
 
There are then 2 gap areas plus a missing fin width which totals to 0.169". You will just fit a 1/8" (0.125) launch rod, but the outer diameter of your lug is 0.173 so it will not fit between 2 fins.
The widest part of the launch lug is 0.173/2 = .087" outside the BT. At that distance, gap+fin+gap is 0.199".

The fins' closest point to the lug will actually be narrower than that where the fins would touch it, since the fins are 20° from each other... but that point is also slightly closer to the BT than the center of the lug, so the available circumference is slightly less. I believe these two factors are close enough to a wash that in the end we're basically putting a .173" tube in a .199" gap, and it will fit.

(Nevermind that these calculations are way more precise than the tolerances innate to the materials 😂😂😂)
 
Estes Viking Rocket Bulk Pack Pack of 12
https://a.co/d/5GGcryZ
Ordered, should arrive tomorrow. Guess we'll see if it's a legit deal or not.

Even if I decide these aren't the right fins for this project, it's a hard price to beat for adding that many parts to the build pile.
 
I bought the Viking bulk pack a few years ago when it was $43, because it was a lot of parts for cheap. This is even better, but I don't need all those parts. At the time, it was a pile of NCs and white-glassine body tubes. I was playing with finishing methods where white vs. kraft made a difference. And I can now clone all the Vikings and Wizards I want, and whatever other random BT-20 builds with that NC. If you just want the NC and BT and don't care if they're kraft tubes, AC Supply has bulk packs of both that are a better deal because the tubes are longer.

One downside of the Viking cardstock die-crushed fins is they aren't flat. I intend to actually build a Viking in the next few months and will be flattening some of them so my rocket flies straight. Will post up my method when the time comes.
 
One downside of the Viking cardstock die-crushed fins is they aren't flat.

We've had two Vikings in our household in the last year, and both had flat fins.

Hopefully I can find 34 flat ones among the 60 in the bulk pack.

Although... I'm actually starting to think they'll be too small and not look right on a BT-55. I need to put 'em in OR and see if I like the look.
 
Once I thought of it, I had to design it: 34FNC rocket.

View attachment 689256

Yes, that's thirty-four fins and a nose cone.

I love the warning there in the bottom right corner. I guess I'll need to do a swing test rather than trust the sim!

The fins are spaced 10 degrees apart, which would make for 36. I left two out on opposite sides, and put the launch lug in one of the gaps. I did two different fin shapes just to make it more interesting.

View attachment 689255

I feel like I have to build this now, even though those fins will truly be a challenge. I think maybe I should find someone with a laser cutter so I don't have to cut out 34 fins by hand. And I'll definitely need to make some sort of jig for fin positioning.

I've attached the ORK file, even though it's just a quicky - no centering rings, recovery system, etc. yet.
I would deffintly look at getting the fin jig printed for sure. Should be an easy print
 
Pretty awesome idea @Azamiryou.

Perhaps some homemade basswood plywood for those tall fins (2 pieces of 1/32" basswood glued together) and 1/16" regular basswood for the intermediate fins?

A rear eject configuration would bring the rocket down nose 1st and would also protect the fins?

34FNC.jpg
 

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  • 34fnc.ork
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Viking fins are fine size-wise, but I think I still like mine better. What do you think?

fin-comparison.png

As you can see, I do like @lakeroadster's yellow and green fin scheme, at least for helping visualize what's going on in pictures. (It probably won't be the final colors I'll choose. Still leaning towards "generic" for that.)
 

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