34FNC scratch build

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
I'll play around some more with fin orientation and placement later tonight — maybe I'll find something I like that uses the Viking fins and saves a lot of work. If I make it rear ejection, having the fins swept back won't be a problem.
 
Make a tube wrap the circumferential of your rocket. Put extra length on each end to hold it, you’ll trim lateral

Paint all fins except for root edge.

Mark where each fin is gonna be.

Tape it to your work surface.

Mount each fin, kind of like a deck of cards, all vertical, with parchment paper or waxed paper between them to keep them from sticking to each other. Launch lug on the end.

Once dry, wrap the wrap around the rocket.

They should fan out nicely, might need some tweaking, kind of like an artificial Christmas tree coming out of the box.
 
I'll play around some more with fin orientation and placement later tonight — maybe I'll find something I like that uses the Viking fins and saves a lot of work.
I've tried various combinations of the Viking fins, both flipped and not, and none of them especially appeal to me.

Except for all the fins swept back, which fits the "ordinary basic rocket" theme. But I think I still prefer the non-Viking fins for this rocket.basic-fins.png
 
I tried spacing the fins evenly with no extra gaps. Of course, that doesn't leave enough room for the launch rod, let alone the lug. (If the rod would fit, I'd just put the lug higher on the body.) I'm thinking I can mount one of the fins to the lug (I'd cut .173" off the root of that fin); by making it one of the long (green) fins, the lug will be pretty well hidden between the short fins. I expect there'd be plenty of strength with the lug basically wedged between two short fins, especially if I can get fillets down there around the long fin.

I'm leaning this way instead of the gaps because, well... no half measures.

rearview-even.png
 
I tried spacing the fins evenly with no extra gaps. Of course, that doesn't leave enough room for the launch rod, let alone the lug. (If the rod would fit, I'd just put the lug higher on the body.) I'm thinking I can mount one of the fins to the lug (I'd cut .173" off the root of that fin); by making it one of the long (green) fins, the lug will be pretty well hidden between the short fins. I expect there'd be plenty of strength with the lug basically wedged between two short fins, especially if I can get fillets down there around the long fin.

I'm leaning this way instead of the gaps because, well... no half measures.

View attachment 689745
that was my first thought as well when it came to the lug, it’s small enough that you’d have a very hard time noticing.
 
I found the inspiration behind this Rocket design. I hope you build it, we need more fun Rocketeers and fewer over Serious Rocketeers.
Donk! I've seen a few driving around here. For some reason it's usually a hoopty on those wheels — $700 car riding around on $5000 worth of ridiculous wheels.
 
38? I'd like to see that rocket and/or jig if you can provide a photo.
My BT-80 V32 rocket was destroyed 2nd flight (CATO) nose cone salvaged and reused. Fin guide disappeared in last move :(

David Qualman still has the guide CAD file. Guide looks like this (attached)
 

Attachments

  • V32_BT80_Upscale (1).png
    V32_BT80_Upscale (1).png
    27.1 KB
I tried spacing the fins evenly with no extra gaps. Of course, that doesn't leave enough room for the launch rod, let alone the lug. (If the rod would fit, I'd just put the lug higher on the body.) I'm thinking I can mount one of the fins to the lug (I'd cut .173" off the root of that fin); by making it one of the long (green) fins, the lug will be pretty well hidden between the short fins. I expect there'd be plenty of strength with the lug basically wedged between two short fins, especially if I can get fillets down there around the long fin.

I'm leaning this way instead of the gaps because, well... no half measures.

View attachment 689745
The old V32 model (and my up scale BT-80 version) glued the launch lug between fins.
 

Attachments

  • IMG_20250120_162042.jpg
    IMG_20250120_162042.jpg
    51.4 KB
at least few more options.

You could go with rear eject, take a load of the fins on impact.

If you went with rear eject pop pod, you could run an INTERNAL lug from rear centering ring to forward centering ring, lined up with a hole in nose cone. You would use a MicroMaxx body tube to run the length, so your rod doesn’t get mixed up with laundry.

Another trick with rear eject internal pop pod is to downside the chimney segment of the motor mount down one tube size. IF you to this, IMO you must protect the first 2 or 3 inches of the downsized tube just forward of the motor, otherwise it will burn through, possibly after only one flight.
 
Rear eject is the plan, but it will be a straightforward rear eject.

I am thinking I'll make the nose cone lock in but be removable, and mount the shock cord to it. That will make it easy to inspect and replace the shock cord. There will still be a seam between the nose cone and body, but I'm okay with that for a xFNC rocket.
 
Still haven't started assembly (too many other projects to deal with first) but I shared the idea with my dad and showed him the jigs and fins. His response: "Let me know when you're going to fly it. I want to see what it's like when that many fins come fluttering down." 😂😂😂
 
Still haven't started assembly (too many other projects to deal with first) but I shared the idea with my dad and showed him the jigs and fins. His response: "Let me know when you're going to fly it. I want to see what it's like when that many fins come fluttering down." 😂😂😂
OK your dad is awesome.
 
I'm too late to the party. I didn't realize you had parts cut already when I wrote the stuff below. Feel free to ignore it all.

you can probably get the jig 3d printed, and the fins cut by @DragonRocketry you probably should make the body tube as large in diameter is you can at the LPR scale so the spacing is larger.
You could also get the fin locations engraved on the tube by the laser machine. I fixture would make mean that's not really necessary, but it could still be a big help.

Alternatively, you could do 1/32" basswood for the fins... You'd need a skinny, round-ended tool to get between the fins and do the fillets though.
I'd go with 1/32" birch ply.

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

View attachment 689541

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.)
I agree yours are better, but not by much really. I think the Viking green fins and your yellow fins would be better still. But it's splitting hairs.

Let me guess, you're also not going to make each fin a different color?
You mean like this?
1738693006507.png1738693024830.png

For fillets, my thought is to drip some white glue in between fins and let it self level into a single fillet for both of them. The launch lug could go further out between a pair of fins, just as you say.
1738693711042.png
Obviously, not to scale.

I wonder what it would look like with alternating forward swept and rear swept fins.
 
Last edited:
With a hair over 3/32" of an inch between fins (.098), how are you proposing to get the glue into the joint, without getting it all over the fins?

What type of glue will you be using? Wood glue? What type?

If you glue every other fin, that would appear to be doable, but then when it comes to gluing the rest, it seems nearly impossible, especially with the height of the fins.

I use an oral syringe to apply fillets, and it's tip is 0.19"... and that's about twice the diameter of what is needed. :oops:
 
Last edited:
PHASE 1: glue down and fillet every other fin, the ones that stick out
PHASE 3: PROFIT!

In more seriousness, when it comes to phase 2, putting on the longitudinal fins, I'll have to try some things. I might be able to make fillets with a rounded toothpick. Put a drop of glue between the fins at the trailing edge, then drag it through the gap.

Worst case, if nothing works for the narrow gaps, I can just fillet the parts ahead of the other fins where the gaps are less narrow.
 
Last edited:
With a hair over 3/32" of an inch between fins (.098), how are you proposing to get the glue into the joint, without getting it all over the fins?

What type of glue will you be using? Wood glue? What type?

If you glue every other fin, that would appear to be doable, but then when it comes to gluing the rest, it seems nearly impossible, especially with the height of the fins.

I use an oral syringe to apply fillets, and it's tip is 0.19"... and that's about twice the diameter of what is needed. :oops:
I guess I'll take the strikethrough off of this part:
For fillets, my thought is to drip some white glue in between fins and let it self level into a single fillet for both of them. The launch lug could go further out between a pair of fins, just as you say.
View attachment 692770
Obviously, not to scale.
This comes with 22 gauge needles, which have 0.7 mm OD. Others range from 0.45 to 1.1 mm OD (from Wikipedia). The gap, 3/32" (thanks, John) is almost 2.4 mm. Of course, it would be difficult to push glue down a needle like that, so get the largest needle that will fit (there are probably some larger than are listed on Wikipedia) and use the thinnest glue, e.g. Elmers School Glue. (Some say that School Glue is not strong enough for LPR, but I have demonstrated that it is with my Office Supplies rocket; it used nothing but School Glue and survived an F motor, an F44 if memory serves. That flight suffered a shock cord break, so the airframe came in ballistic, and the glue joints survived that too. [The body tube did not.])

You'd want the School Glue or something else thin in order to get the self leveling no matter how it's applied, so this looks to me like a viable solution to me. Tack all 34 fins with CA, then apply the two at once, self leveling fillets all around.
 
I would just use the double glue method and skip the fillets.

Or "self fillet" Do all the shorter fins first with minimal glue.
When you go back to do the taller fins, be more generous with the glue so when you place the fin down, glue squeezes out of the joint. That glue will push against the two shorter fins on either side creating a fillet. You can have something small enough to fit down between the fins to smooth out the glue. But at least it is just trying to smooth the glue and not having to actually try to force glue into such a narrow space.
 
Back
Top