Alien warship scratchbuild being considered

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Bill S

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Here's another design I am fooling around with. 20" long, uses BT-55 and 60 tubes, has unusual center wings with missiles on them. Flies on 24mm motors from D12-3 to E12-4, or an Aerotech E20-4. Stability looks okay even with E12 motors.

Here's the latest version (close to final): Not sure if I like the rear fins or if I should add something to them.

lengthened with side missiles and main body fins (like better).png
 
Rocksim says 3.9 oz, but I assumed 5oz. Hard to tell without all the parts on hand. :) Kind of draggy though. D12-3 should go about 475 feet, E12-4 should go about 750 feet, E20-4 about 950.
 
Rear fins need something or shaped a bit differently. Main part of the rocket is cool, but the simple rectangular fins don't quite make it..... Just my $.02 worth
 
Rear fins need something or shaped a bit differently. Main part of the rocket is cool, but the simple rectangular fins don't quite make it..... Just my $.02 worth

I tend to agree. The rear fins aren't rectangular, but not far off either. I tried a crosspiece on a fin and I dunno, not sure about that. I'll keep tinkering and hopefully I'll come up with something.
 
If it was mine, I would make it 4 fins aft. Two smaller ones in line with and echoing the weapons pods and two larger ones that echo the strakes.
 
I did up two versions with fins similar to what I put on the Talon scratchbuild I did. 4 fins gave a stability of 1.31 with an E12 motor, whereas 3 only gave 1.13.

4 fins, offset by 45 degrees:
lengthened with side missiles better rear fins.png

3 fins:
lengthened with side missiles better rear fins (3).png
 
Since it has 2 main horizontal "wings", it seems to me like it might only need 2 vertical fins, and maybe their shape could somehow align with the small, long vertical "wings". Just my 2 cents.
 
Here is a version being considered that fixes the potential issue I have with Rocksim not recognizing the proper nosecone diameter since I had to cobble together one. Doesn't incorporate Funkworks suggestion - I'll look at that.

v1.3 longer nose to fix stability issue with Rocksim.png
 
If there are 3 boxes on the nose I would use 3 fins on the rear to tie the design together.

I just tried that, here is what it looks like. I don't care for it, personally. Thanks for the suggestion though - its how we learn. :)

v1.3 merged long fin with nose (dont like).png
 
I just tried that, here is what it looks like.

View attachment 460842
That's not what I meant; I meant the drawing referenced in quoted material, as it was drawn, not a new and different thing.
Here, maybe expressing my thought like this will work,
[3 boxes on nose]+(body of rocket)+[3 fins aft]
3 and 3 visually "bookend" the design.
 
Here is a version being considered that fixes the potential issue I have with Rocksim not recognizing the proper nosecone diameter since I had to cobble together one. Doesn't incorporate Funkworks suggestion - I'll look at that.

View attachment 460841
I think that one is getting very close. There's a lot of good stuff in there.

I have a couple of further observations on the chute-snaggers rear fins.
  1. From here it looks like the left and right fins are really quite close to the missile pods in front of them (and they'll be right in their turbulent wake as well, for what it's worth). It seems like there should be some more separation there, although I'm not sure the best way to achieve it. One way would be to lengthen those fins so they extend further out. Or add another inch to the body between the rear fins and the stuff in front of it. OR, make it three rear fins but offset 60 degrees from the strakes (can you call them strakes if they're 1/2" wide? :)) That might look weird.
  2. Somehow the shape of the tip extensions just doesn't look quite right to me. Here's one suggestion that has been used on other designs and always (IMHO) looks good. As always you'll need to fiddle to get it just right.
    1619010901670.png
 
Neil, with the 4-rear fin design I favor, the fins are offset 45 degrees, so there should be clearance of the rear of the front wings. When I was fiddling with the design trying modeltrains suggestion, I re-oriented them, forgot to put them back. This is how they should look:

rear end 4-fin offset v1.3.png

As for the rear fins having more of a rear tip, never tried that, but you know what? I think it works better.

v1.3 with modified fin tips.png
 
Neil, those rear fin tips concern me. I would think they would be prone to breaking off if the rocket doesn't land squarely on the motor mount. Have you any experiences with that?
 
Neil, those rear fin tips concern me. I would think they would be prone to breaking off if the rocket doesn't land squarely on the motor mount. Have you any experiences with that?
I'm not sure, but now that I see them I don't like them anyway. Too much extra complexity on top of an already complex design. I don't have a great idea for it yet. Can you post the Rocksim file?
 
I'm not sure, but now that I see them I don't like them anyway. Too much extra complexity on top of an already complex design. I don't have a great idea for it yet. Can you post the Rocksim file?

I'll remove the fin tips and post the file for you. I think the dowels will work well enough.
v1.3 with dowels on fin tips instead.png
 
I went back to the older version with the fin tips to the front only, and made the fins a tad longer. I think the fin tips protruding out the back will be too fragile, and when I played around with dowels on the fin tips, stability went down significantly.

I updated the file again, so this is the current version:
 

Attachments

  • smaller missiles bt-5 10inch main body extra mid fins v3 .rkt
    157.3 KB · Views: 14
I find it hard to believe the the dowels, little more than toothpicks really, would have any effect on stability to speak of. I wonder if that's a RS anomaly.

I wonder what it would look like with the fins swept-ish, just so the trailing edge is perpendicular to the tube axis.
 
I have gotten all the materials I need start this project. It is next in the queue after I finish my current 2 rockets. I just need to tweak the RS file a little, and start weighing parts, etc.

I'll post updates as I get started.
 
After this project stalled for a while, I am revisiting it. Because Rocksim kept crashing with the rocket file, I redesigned it from scratch, and now it works. I made quite a few changes because I wasn't satisified with the design. Here's the new version:

latest version BT60 Aug 31 2021.png
 
I was just browsing around and this was an interesting thread title. I had totally forgotten that I responded to it back in June. Oh well.

So, this time through I looked at the original design and thought, like many others, that the three main fins needed some more interest. And I thought what they need is two more fins. Go back to more or less the original design but with five fins at the base. Make the fins more like the ones directly above, with or without the toothpicks ("pre-pre sticks", as I called them in one of @neil_w's threads).

I know you've built the rocket this design evolved into, as I have read, responded to, forgot, and then today re-read that thread too. So maybe I'll fool around with a five fin version.
 
The rocket is basically done, except for installing the shockcord+parachute, and decals. Decals are the stumbling block right now, as its very tedious working on them in Inkscape (despite this, the results are very good), and I can't spray the clear coat on the decals until its about 70 degrees - the spray stinks way too bad to do it in the house/garage.
 
The rocket is basically done, except for installing the shockcord+parachute, and decals. Decals are the stumbling block right now, as its very tedious working on them in Inkscape (despite this, the results are very good), and I can't spray the clear coat on the decals until its about 70 degrees - the spray stinks way too bad to do it in the house/garage.
The Vesta Intruder Nose Cone would look cool on your rocket design.
 
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