Having six fins, pods between them, and a larger tube above makes sizing the fins a little tricky for me. It doesn't look like there's much taper between the root and tip. I can't recall anything without taper off the top of my head. My first thought is the Aerobee 350, but it has some taper to it and maybe too small. The Taurus/Orion fin looks pretty darn close.

__________________
I love sanding.

What about the Rubicon? Is that fin pattern pretty close?


David

Attached Thumbnails

 

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD

No. the Rubicon's fins are clipped. I edited the previous post to state that I think it's probably the Taurus/Orion fin. Once you stuff all those pods around it, I believe that it will be about right.

Edit: Nope. I pulled the Orion out and stuck some tubing up against the fins to get a look. The fin is tapered too thin at the tip. The decal rocket's fins are darn near parallelograms.

__________________
I love sanding.

Yup. I think you're right. I was able to download a pattern of the Taurus Fin.

Attached Files

Tarus fin pattern.tif (350.3 KB, 36 views)

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD

Looking at the color picture, I'm pretty certain the root edge of the fins are at least 3 inches. I think the tip edges at a little longer that the tip edges on the Taurus fin pattern, but I may be able to scale something from the Taurus fin pattern if I don't find an exact match.

David

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD

Have a look at the Centurion fin. I believe that's the one. After downloading the image and zooming in, it looks like that little curve on the trailing edge might be there. All you would need to do is trim the tip to sharpen the lower corner and you will have it.

__________________
I love sanding.

That's definitely a much closer match than the Taurus fin. You're pretty good at this.

David

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD

OK. So I did the math on the two different engine tube sizes.

With an 18mm (ST 7) engine tube, the circumference of the lower body tube cluster will be larger than the main body tube by 0.1874 inches, this is assuming that the main body tube is an ST 13, to which I think we are all in agreement that it is.

As for the 24mm (ST 10) engine tube, the maths works out like this:
The circumference of the lower body tube cluster will be larger than the main body tube by 0.2436 inches.

So based on that and studying the color picture closely, I think I'm gonna go the the ST 7 tube as my motor mount, essentially making this rocket powered by an 18mm rocket motor.

Does anyone see where I may be going wrong on this conclusion?

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD

Take six pieces of BT20/ST7 tube and make yourself a rubber banded six tube cluster using BT20 and then BT50 for a core. Stick some 1/8" balsa scrap between the fins and see what kind of spacing you get. Whatever core tube gives you the best fit is what you will need to go with. If the core tube is just a hair too small and the next size up is too big, you can glue paper wrap around the smaller core tube to fill out to the correct diameter.

If you say you don't have 7 pieces of BT20/ST7, what kind of builder are you anyway?
Use whatever stock you have on hand...full length tubes, motor tubes, scrap tubes, tubes from unbuilt kits, etc. The small difference in OD between Centuri and Estes spec won't be an issue in the mockup. If you don't have enough, go ahead and place an order with all the stuff you think you will need. Even if you decide not to build this rocket, you will eventually use it all up on something else.

__________________
I love sanding.

OK. I did a mock up last night of the tube cluster at the bottom. I started with an 18mm motor mount as a the central tube. I put five of the same size tubes around it. I was left with enough gap between each tube that I could actually mount the five Balsa wood fins (3/32) to the central tube wall before actually installing the surrounding tubes. So it looks like to me that this may be the best central tube size.

Time to go shopping.

David

__________________
I used to have super powers, but then one day, my Therapist took them away from me.

NAR #96285

SoAR #503

My Low Power Rocket Fleet

Level 1 (2-22-2014) GRITS Winternationals
Level 2 TBD
Level 3 TBD