UNN Torpedo plans and questions

[Bill S]

I'm working on plans for an UNN Heavy torpedo from the Expanse series. This one of the pictures I am working from:

Here is what I have so far:

Picture of rear showing the fins:

I wanted to use a BT-80 body tube as the main tube, and a BT-100 for the rear section, mainly because it is likely to be bigger and wider than the first Martian (MCRN) light torpedo I built. Overall length is 28.9 inches, weight with a D12-5 engine is 9.46 oz. I plan to use Aerotech D21 engines (530 - 550 feet altitute), or if I get perfectly calm condition possibly an Aerotech E30 ( 1150 feet altitute or so). D12's don't give the necessary initial thrust to stabilize the rocket.

The large light blue fins in the back will be 1/16" Lexan.

It will also have an internal long launch lug in the rear section, just like with the MCRN torpedo. I didn't really want to use BT-100 tube for the rear, but I couldn't find any other tube that gave the necessary clearance for a 3/16" launch lug.

I'm also enclosing the Rocksim file for it, though it isn't the final version.

A couple of potential issues come to mind. 1) With the rear 3-part outer fins that are close to the body, I don't see any easy way to build them, then prime/paint and attach them. I had considered attaching the support fin to the body and then assemble, prime and paint the 3-part outer fin, then attach it to the support fin somehow after the main body is primed/painted. I'd have to use some sort of mechanical fastener I would think though. Anyone have thoughts on this?

2) I am thinking that it might be a good idea to attach the support fin using the through-tube attachment method to give it extra strength. Good idea, or not?

I'm sure there will be more questions as I think of them...

 

[kuririn]

I would use TTW supports extending to the engine mount for the three part fins. And prime and paint before gluing. Same with the body tube. Cuz obviously reaching the inside of those fins is impossible after assembly. Internal epoxy fillets will make it very strong.
EDIT: The support tangs don't need to go all the way to the engine mount. Up to the BT-80 tube should be fine. That way you only need to slot one tube.

Question: What is an asteroid belter?
Answer: A really loud karaoke singer from Ceres.

Laters.

 

[Nytrunner]

Id give the 3-part fins 2 supports, and put them at the "folds" of the fins.

That single support is a recipe for endless reattachment.

Alternative, crenellate the support, and cut receiving holes in the fin panels

 

[Bill S]

Id give the 3-part fins 2 supports, and put them at the "folds" of the fins.

That single support is a recipe for endless reattachment.

Alternative, crenellate the support, and cut receiving holes in the fin panels

The 2 fin supports at the ends of the "crosspiece" that the 2 side panels attach to is a good idea. Why didn't I think of that?

I did consider drilling holes in the crosspiece with pins going into the main fin that attaches to the body - easier than the crenellation idea, though possibly not as strong. Hmm... have to think on this.

I also haven't figured out what is the best way to bevel the side fins that attach to the crosspiece. Some sort of beveling tool, I imagine, though I don't have one right now.

 

[Bill S]

So maybe something like this then? Viewed from the rear